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  • 1. Abraham, T.
    et al.
    Kumpulainen, A.
    Xu, Z.
    Rutland, Mark W
    KTH, Superseded Departments, Chemistry.
    Claesson, Per M.
    KTH, Superseded Departments, Chemistry.
    Masliyah, J.
    Polyelectrolyte-mediated interaction between similarly charged surfaces: Role of divalent counter ions in tuning surface forces2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 26, 8321-8327 p.Article in journal (Refereed)
    Abstract [en]

    The effects of divalent salts (CaCl2, MgCl2 and BaCl2) in promoting the adsorption of weakly charged polyelectrolyte (polyacrylic acid), PAA, Mw similar to 250000 g/mol) on mica surfaces and their role in tuning the nature of interactions between such adsorbed polyelectrolyte layers were studied using the interferometric surface forces apparatus. With mica surfaces in 3 mM MgCl2 solutions at pH similar to8.0-9.0, the addition of 10 ppm PAA resulted in a long-range attractive bridging force and a short-range repulsive steric force. This force profile indicates a low surface coverage and weak adsorption. The range of the force can be related to the characteristic length scale R-G of polyelectrolyte chains using a scaling description. An increase of the PAA concentration to 50 ppm changed the attractive force profile to a monotonic, long-range repulsive interaction extending up to 600 Angstrom due to the increased surface coverage of polyelectrolyte chains on the mica surfaces. Comparison of the measured forces with a scaling mean field model suggests that the adsorbed polyelectrolyte chains are stretched, which eventually give rise to the polyelectrolyte brush like structure. When the mica surfaces were preincubated in 3 mM CaCl2 at pH similar to8.0-9.0, in contrast to the case of 3 MM MgCl2, the addition of 10 ppm PAA resulted in a more complex force profile: long-range repulsive forces extending up to 800 Angstrom followed by an attractive force regime and a second repulsive force regime at shorter separations. The long-range electrosteric forces can be attributed to strong adsorption of polyelectrolyte chains on mica surfaces (high surface coverage) which is facilitated by the presence of Ca2+ ions, while the intermediate range attractive forces can be ascribed to Ca2+ assisted bridging between adsorbed polyelectrolyte chains. Also interesting is to note various relaxation processes present in this system. In contrast to both MgCl2 and CaCl2 systems, with mica surfaces in 3 mM BaCl2 solution at pH similar to8.0-9.0, the addition of 10 ppm PAA resulted in precipitation of polyelectrolyte chains on mica surfaces, resulting in an extremely long-range monotonic repulsive force profile. In summary, our study showed that divalent counterions (Mg2+, Ca2+, and Ba2+) exhibit significantly different behavior in promoting PAA adsorption on mica surfaces, modifying and controlling various surface interactions.

  • 2. Al-Bataineh, Sameer A.
    et al.
    Luginbuehl, Reto
    Textor, Marcus
    Yan, Mingdi
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Covalent Immobilization of Antibacterial Furanones via Photochemical Activation of Perfluorophenylazide2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 13, 7432-7437 p.Article in journal (Refereed)
    Abstract [en]

    N-(3-Trimethoxysilylpropyl)-4-azido-2,3,5,6-tetrafluorobenzamide (PFPA-silane) was used as a photoactive crosslinker to immobilize antibacterial furanone molecules on silicon oxide surfaces. This immobilization strategy is useful, especially for substrates and molecules that lack reactive functional groups. To this end, cleaned wafers were initially incubated in solutions of different concentrations of PFPA-silane to form a monolayer presenting azido groups on the surface. The functionalized surfaces were then treated with a furanone solution followed by illumination with UV light and extensive rinsing with ethanol to remove noncovalently adhered molecules, In the presented study, we demonstrate the ability to control the surface density of the immobilized furanone molecules by adjusting the concentration of PFPA-silane solution used for surface functionalization using complementary surface analytical techniques. The fluorine in PFPA-silane and the bromine in furanone molecules were convenient markers for the XPS study. The ellipsometric layer thickness of the immobilized furanone molecules on the surface decreased with decreasing PFPA-silane concentration, which correlated with a decline of water contact angle as a sign of film collapse. The intensity of characteristic azide vibration in the MTR IR spectra was monitored as a function of PFPA-silane concentration, and the peak disappeared completely after furanone application followed by UV irradiation. As a complementary technique to XPS, TOF-SIMS provided valuable information on the chemical and molecular structure of the modified surfaces and spatial distribution of the immobilized furanone molecules. Finally, this report presents a convenient, reproducible, and robust strategy to design antibacterial coating based on furanone compounds for applications in human health care.

  • 3. Allouche, Joachim
    et al.
    Tyrode, Eric
    Laboratorio FIRP, Ingeniería Química, Universidad de Los Andes, Avenida Don Tulio Febres, Mérida .
    Sadtler, Veronique
    Choplin, Lionel
    Salager, Jean-Louis
    Simultaneous Conductivity and Viscosity Measurements as a Technique To Track Emulsion Inversion by the Phase-Inversion-Temperature Method2004In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, no 6, 2134-2140 p.Article in journal (Refereed)
    Abstract [en]

    Two kinds of transitions can occur when an emulsified water-oil-ethoxylated nonionic surfactant system is cooled under const. stirring. At a water-oil ratio close to unity, a transitional inversion takes place from a water-in-oil (W/O) to an oil-in-water (O/W) morphol. according to the so-called phase-inversion-temp. method. At a high water content, a multiple W/O/W emulsion changes to a simple O/W emulsion. The continuous monitoring of both the emulsion cond. and viscosity allows the identification of several phenomena that take place during the temp. decrease. In all cases, a viscosity max. is found on each side of the three-phase behavior temp. interval and correlates with the attainment of extremely fine emulsions, where the best compromise between a low-tension and a not-too-unstable emulsion is reached. The studied system contains Polysorbate 85, a light alkane cut oil, and a sodium chloride brine. All transitions are interpreted in the framework of the formulation-compn. bidimensional map.

  • 4.
    An, Junxue
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Dèdinaitè, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Winnik, Francoise M.
    Qiu, Xing-Ping
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Temperature-Dependent Adsorption and Adsorption Hysteresis of a Thermoresponsive Diblock Copolymer2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 15, 4333-4341 p.Article in journal (Refereed)
    Abstract [en]

    A nonionic-cationic diblock copolymer, poly(2-isopropyl-2-oxazoline)(60)-b-poly((3-acrylamidopropyl)- trimethylammonium chloride)(17), (PIPOZ(60)-b-PAMPTMA(17)), was utilized to electrostatically tether temperature-responsive PIPOZ chains to silica surfaces by physisorption. The effects of polymer concentration, pH, and temperature on adsorption were investigated using quartz crystal microbalance with dissipation monitoring and ellipsometry. The combination of these two techniques allows thorough characterization of the adsorbed layer in terms of surface excess, thickness, and water content. The high affinity of the cationic PAMPTMA(17) block to the negatively charged silica surface gives rise to a high affinity adsorption isotherm, leading to (nearly) irreversible adsorption with respect to dilution. An increase in solution pH lowers the affinity of PIPOZ to silica but enhances the adsorption of the cationic block due to increasing silica surface charge density, which leads to higher adsorption of the cationic diblock copolymer. Higher surface excess is also achieved at higher temperatures due to the worsening of the solvent quality of water for the PIPOZ block. Interestingly, a large hysteresis in adsorbed mass and other layer properties was observed when the temperature was cycled from 25 to 45 degrees C and then back to 25 degrees C. Possible causes for this temperature hysteresis are discussed.

  • 5.
    An, Junxue
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Jin, Chunsheng
    Dedinaite, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
    Holgersson, Jan
    Karlsson, Niclas G.
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden.
    Influence of Glycosylation on Interfacial Properties of Recombinant Mucins: Adsorption, Surface Forces, and Friction2017In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, no 18, 4386-4395 p.Article in journal (Refereed)
    Abstract [en]

    Interfacial properties of two brush-with-anchor mucins, C-P55 and C-PSLex, have been investigated at the aqueous solution/poly(methyl methacrylate) (PMMA) interface. Both are recombinant mucin-type fusion proteins, produced by fusing the glycosylated mucin part of P-selectin glycoprotein ligand-1 (PSLG-1) to the Fc part of a mouse immunoglobulin in two different cells. They are mainly expressed as dimers upon production. Analysis of the O-glycans shows that the C-PSLex mucin has the longer and more branched side chains, but C-P55 has slightly higher sialic acid content. The adsorption of the mucins to PMMA surfaces was studied by quartz crystal microbalance with dissipation. The sensed mass, including the adsorbed mucin and water trapped in the layer, was found to be similar for these two mucin layers. Atomic force microscopy with colloidal probe was employed to study surface and friction forces between mucin-coated PMMA surfaces. Purely repulsive forces of steric origin were observed between mucin layers on compression, whereas a small adhesion was detected between both mucin layers on decompression. This was attributed to chain entanglement. The friction force between C-PSLex-coated PMMA is lower than that between C-P55-coated PMMA. at low loads, but vice versa at high loads. We discuss our results in terms of the differences in the glycosylation composition of these two mucins.

  • 6.
    An, Junxue
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Liu, Xiaoyan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Linse, Per
    Dedinaite, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry. SP Technical Research Institute of Sweden, Sweden .
    Winnik, Francoise M.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Tethered Poly(2-isopropyl-2-oxazoline) Chains: Temperature Effects on Layer Structure and Interactions Probed by AFM Experiments and Modeling2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 10, 3039-3048 p.Article in journal (Refereed)
    Abstract [en]

    Thermoresponsive polymer layers on silica surfaces have been obtained by utilizing electrostatically driven adsorption of a cationic-nonionic diblock copolymer. The cationic block provides strong anchoring to the surface for the nonionic block of poly(2-isopropyl-2-oxazoline), referred to as PIPOZ. The PIPOZ chain interacts favorably with water at low temperatures, but above 46 degrees C aqueous solutions of PIPOZ phase separate as water becomes a poor solvent for the polymer. We explore how a change in solvent condition affects interactions between such adsorbed layers and report temperature effects on both normal forces and friction forces. To gain further insight, we utilize self-consistent lattice mean-field theory to follow how changes in temperature affect the polymer segment density distributions and to calculate surface force curves. We find that with worsening of the solvent condition an attraction develops between the adsorbed PIPOZ layers, and this observation is in good agreement with predictions of the mean-field theory. The modeling also demonstrates that the segment density profile and the degree of chain interpenetration under a given load between two PIPOZ-coated surfaces rise significantly with increasing temperature.

  • 7.
    Andersson, Nina
    et al.
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Kronberg, Bengt
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Corkery, Robert W.
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Alberius, Peter
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Combined Emulsion and Solvent Evaporation (ESE) Synthesis Route to Well-Ordered Mesoporous Materials2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 3, 1459-1464 p.Article in journal (Refereed)
    Abstract [en]

    Control over morphol. and internal mesostructure of surfactant templated silicas remains a challenge, esp. when considering scaling lab. syntheses up to industrial vols. Here we report a method combining emulsification with the evapn.-induced self-assembly (EISA) method for prepg. spherical, mesoporous silica particles. This emulsion and solvent evapn. (ESE) method has several potential advantages over classic pptn. routes: it is easily scaled while providing superior control over stoichiometric homogeneity of templating surfactants and inorg. precursors, and particle sizes and distributions are detd. by principles developed for manipulating droplet sizes within water-in-oil emulsions. To demonstrate the method, triblock copolymer P104 is used as a templating amphiphile, generating unusually well-ordered 2D hexagonal (P6mm) mesoporous silica, while particle sizes and morphologies were controlled by varying the type of emulsifier and the method for emulsification. [on SciFinder(R)]

  • 8. Arleth, L.
    et al.
    Bergström, Lars Magnus
    KTH, Superseded Departments, Chemistry.
    Pedersen, J. S.
    Small-angle neutron scattering study of the growth behavior, flexibility, and intermicellar interactions of wormlike SDS micelles in NaBr aqueous solutions2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 14, 5343-5353 p.Article in journal (Refereed)
    Abstract [en]

    SDS wormlike micelles in water with NaBr are studied using small-angle neutron scattering. SDS concentrations ranging from 0.08 to 8.6 % vol in NaBr aqueous solutions at salinities from 0.6 to 1.0 M are covered. The scattering data are analyzed using a novel approach based on polymer theory and the results of Monte Carlo simulations. The method makes it possible to give a full interpretation of the scattering data, even for the entangled micellar solutions occurring at high concentrations and high salinities. Analysis of the scattering data at zero scattering angle demonstrates that the length of the micelles increases according to a power law as a function of concentration in the studied interval. The analysis furthermore shows that the length of the micelles increases exponentially with increasing salinity. The scattering data in the full range of scattering angles are analyzed using a model for polydisperse wormlike micelles where excluded volume effects are taken into account via an expression based on the polymer reference interaction site model (PRISM). This part of the analysis show that the micelles become more flexible as the salinity increases, which is due to an increased screening of the ionic micelles.

  • 9.
    Asencio, Rubén Alvarez
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Cranston, Emily D.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Atkin, Rob
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Ionic Liquid Nanotribology: Stiction Suppression and Surface Induced Shear Thinning2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 26, 9967-9976 p.Article in journal (Refereed)
    Abstract [en]

    The friction and adhesion between pairs of materials (silica, alumina, and polytetrafluoroethylene) have been studied and interpreted in terms of the long-ranged interactions present. In ambient laboratory air, the interactions are dominated by van der Waals attraction and strong adhesion leading to significant frictional forces. In the presence of the ionic liquid (IL) ethylammonium nitrate (EAN) the van der Waals interaction is suppressed and the attractive/adhesive interactions which lead to "stiction" are removed, resulting in an at least a 10-fold reduction in the friction force at large applied loads. The friction coefficient for each system was determined; coefficients obtained in air were significantly larger than those obtained in the presence of EAN (which ranged between 0.1 and 0.25), and variation in the friction coefficients between systems was correlated with changes in surface roughness. As the viscosity of ILs can be relatively high, which has implications for the lubricating properties, the hydrodynamic forces between the surfaces have therefore also been studied. The linear increase in repulsive force with speed, expected from hydrodynamic interactions, is clearly observed, and these forces further inhibit the potential for stiction. Remarkably, the viscosity extracted from the data is dramatically reduced compared to the bulk value, indicative of a surface ordering effect which significantly reduces viscous losses.

  • 10.
    Aulin, Christian
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Josefsson, Peter
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Nanoscale Cellulose Films with Different Crystallinities and Mesostructures: Their Surface Properties and Interaction with Water2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 13, 7675-7685 p.Article in journal (Refereed)
    Abstract [en]

    A systematic study of the degree of molecular ordering and swelling of different nanocellulose model films has been conducted. Crystalline cellulose II surfaces were prepared by spin-coating of the precursor cellulose solutions onto oxidized silicon wafers before regeneration in water or by using the Langmuir-Schaefer (LS) technique. Amorphous cellulose films were also prepared by spin-coating of a precursor cellulose solution onto oxidized silicon wafers. Crystalline cellulose I surfaces were prepared by spin-coating wafers with aqueous suspensions of sulfate-stabilized cellulose nanocrystals and low-charged microfibrillated cellulose (LC-MFC). In addition, a dispersion of high-charged MFC was used for the buildup of polyelectrolyte multilayers with polyetheyleneimine on silica with the aid of the layer-by-layer (LbL) technique. These preparation methods produced smooth thin films on the nanometer scale Suitable for X-ray diffraction and swelling measurements. The surface morphology and thickness of the cellulose films were characterized in detail by atomic force microscopy (AFM) and ellipsometry measurements, respectively. To determine the surface energy of the cellulose surfaces, that Is, their ability to engage in different interactions with different materials, they were characterized through contact angle measurements against water, glycerol, and methylene iodide. Small incidence angle X-ray diffraction revealed that the nanocrystal and MFC films exhibited a cellulose I crystal structure and that the films prepared from N-methylmorpholine-N-oxide (NMMO), LiCl/DMAc solutions, using the LS technique, possessed a cellulose II structure. The degree of crystalline ordering was highest in the nanocrystal films (similar to 87%), whereas the MFC, NMMO, and LS films exhibited a degree of crystallinity of about 60%. The N,N-dimethylacetamide(DMAc)/LiCl film possessed very low crystalline ordering (<15%). It was also established that the films ha different mesostructures, that is, structures around 10 nm, depending on the preparation conditions. The LS and LiCl/DMAc films are smooth without any clear mesostructure, whereas the other films have a clear mesostructure in which the dimensions are dependent oil the size of the nanocrystals, fibrillar cellulose, and electrostatic charge of the MFC. The swelling of the films was studied using a quartz crystal microbalance with dissipation. To understand the swelling properties of the films, it was necessary to consider both the difference in crystalline ordering and the difference in mesostructure of the films.

  • 11.
    Aulin, Christian
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Varga, Imre
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Claesson, Per
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Lindström, Tom
    STFI-Packforsk AB.
    Buildup of Polyelectrolyte Multilayers of Polyethyleneimine and Microfibrillated Cellulose Studied by in situ Dual Polarization Interferometry and Quartz Crystal Microbalance with Dissipation2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 6, 2509-2518 p.Article in journal (Refereed)
    Abstract [en]

    Polyethyleneimine (PEI) and Microfibrillated cellulose (MFC) have been used to buildup polyelectrolyte multilayers (PEM) on silicone oxide and silicone oxynitride surfaces at different pH values and with different electrolyte and polyelectrolyte/colloid concns. of the components.  Consecutive adsorption on these surfaces was studied by in situ dual-polarization interferometry (DPI) and quartz crystal microbalance measurements.  The adsorption data obtained from both the techniques showed a steady buildup of multilayers.  High pH and electrolyte concn. of the PEI soln. was found to be beneficial for achieving a high adsorbed amt. of PEI, and hence of MFC, during the buildup of the multilayer.  On the other hand, an increase in the electrolyte concn. of the MFC dispersion was found to inhibit the adsorption of MFC onto PEI.  The adsorbed amt. of MFC was independent of the bulk MFC concn. in the investigated concn. range (15-250 mg/L).  At. force microscopy measurements were used to image a MFC-treated silicone oxynitride chip from DPI measurements.  The surface was found to be almost fully covered by randomly oriented microfibrils after the adsorption of only one bilayer of PEI/MFC.  The surface roughness expressed as the rms-roughness over 1 μm2 was calcd. to be 4.6 nm (1 bilayer).  The adsorbed amt. of PEI and MFC and the amt. of water entrapped by the individual layers in the multilayer structures were estd. by combining results from the two anal. techniques using the de Feijter formula.  These results indicate a total water content of ca. 41% in the PEM.

  • 12. Bacalum, Mihaela
    et al.
    Wang, Lina
    Boodts, Stijn
    Yuan, Peijia
    Leen, Volker
    Smisdom, Nick
    Fron, Eduard
    Knippenberg, Stefan
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fabre, Gabin
    Trouillas, Patrick
    Beljonne, David
    Dehaen, Wim
    Boens, Noel
    Ameloot, Marcel
    A Blue-Light-Emitting BODIPY Probe for Lipid Membranes2016In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 32, no 14, 3495-3505 p.Article in journal (Refereed)
    Abstract [en]

    Here we describe a new BODIPY-based membrane probe (1) that provides an alternative to dialkylcarbocyanine dyes, such as DiI-C,8, that can be excited in the blue spectral region. Compound 1 has unbranched octadecyl chains at the 3,5 -positions and a meso-amino function. In organic solvents, the absorption and emission maxima of 1 are determined mainly by solvent acidity and dipolarity. The fluorescence quantum yield is high and reaches 0.93 in 2-propanol. The fluorescence decays are well fitted with a single -exponential in pure solvents and in small and giant unilamellar vesicles (GUV) with a lifetime of ca. 4 ns. Probe 1 partitions in the same lipid phase as DiI-C-18(5) for lipid mixtures containing sphingomyelin and for binary mixtures of dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC). The lipid phase has no effect on the fluorescence lifetime but influences the fluorescence anisotropy. The translational diffusion coefficients of 1 in GUVs and OLN-93 cells are of the same order as those reported for DiI-C-18. The directions of the absorption and transition dipole moments of 1 are calculated to be parallel. This is reflected in the high steady-state fluorescence anisotropy of 1 in high ordered lipid phases. Molecular dynamic simulations of 1 in a model of the DOPC bilayer indicate that the average angle of the transition moments with respect to membrane normal is ca. 70 degrees, which is comparable with the value reported for al DiI-C-18.

  • 13.
    Badal Tejedor, Maria
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. RISE Research Institutes of Sweden, Sweden.
    Nordgren, Niklas
    Schuleit, Michael
    Millqvist-Fureby, Anna
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    AFM Colloidal Probe Measurements Implicate Capillary Condensation in Punch-Particle Surface Interactions during Tableting2017In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, no 46, 13180-13188 p.Article in journal (Refereed)
    Abstract [en]

    Adhesion of the powders to the punches is a common issue during tableting. This phenomenon is known as sticking and affects the quality of the manufactured tablets. Defective tablets increase the cost of the manufacturing process. Thus, the ability to predict the tableting performance of the formulation blend before the process is scaled-up is important. The adhesive propensity of the powder to the tableting tools is mostly governed by the surface surface adhesive interactions. Atomic force microscopy (AFM) colloidal probe is a surface characterization technique that allows the measurement of the adhesive interactions between two materials of interest. In this study, AFM steel colloidal probe measurements were performed on ibuprofen, MCC (microcrystalline cellulose), alpha-lactose monohydrate, and spray-dried lactose particles as an approach to modeling the punch particle surface interactions during tableting. The excipients (lactose and MCC) showed constant, small, attractive, and adhesive forces toward the steel surface after a repeated number of contacts. In comparison, ibuprofen displayed a much larger attractive and adhesive interaction increasing over time both in magnitude and in jump-in/jump-out separation distance. The type of interaction acting on the excipient steel interface can be related to a van der Waals force, which is relatively weak and short-ranged. By contrast, the ibuprofen steel interaction is described by a capillary force profile. Even though ibuprofen is not highly hydrophilic, the relatively smooth surfaces of the crystals allow "contact flooding" upon contact with the steel probe. Capillary forces increase because of the "harvesting" of moisture due to the fast condensation kinetics leaving a residual condensate that contributes to increase the interaction force after each consecutive contact. Local asperity contacts on the more hydrophilic surface of the excipients prevent the flooding of the contact zone, and there is no such adhesive effect under the same ambient conditions. The markedly different behavior detected by force measurements clearly shows the sticky and nonsticky propensity of the materials and allows a mechanistic description.

  • 14. Bahadur, Jitendra
    et al.
    Sen, Debasis
    Mazumder, S.
    Santoro, Gonzalo
    Yu, Shun
    Deutsches Elektronen-Synchrotron, Germany.
    Roth, S.V.
    Melnichenko, Yuri
    Evaporation Assisted Transition of Interaction Between Colloids: In-situ Small-angle X-ray Scattering Investigation2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 16, 4612-4618 p.Article in journal (Refereed)
    Abstract [en]

    In-situ scanning small-angle X-ray scattering (SAXS) experiments have been performed to probe the,drying of a single suspended droplet of silica colloids. It has been demonstrated that the formation of a nanoparticle shell during drying can be confirmed just by measuring the temporal evolution of the spatial transmission profile across the drying droplet. The shrinkage of the droplet stops once the shell is formed. The temporal dependence Of the shell thickness and droplet radius has been estimated by quautitative analysis of the functionality of the transmission profiles. It is' revealed that the position of the correlation peak originating from interactions between silica nanoparticles evolves linearly during the initial stage of drying and exhibits sigmoidal growth behavior in later stages. The interaction between colloidal particles, in different drying stages has been investigated We provide,experimental confirmation of the transition from repulsive interaction to a capillary driven short-range,attraction,during shell formation. The present work demonstrates that in situ scanning SAXS on,a suspended droplet is an invaluable technique for monitoring the dynamic self organization of colloids as it probes the drying of complex,fluids without the interference of a substrate.

  • 15. Barroso da Silva, Fernando Luis
    et al.
    Boström, Mathias
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Effect of Charge Regulation and Ion-Dipole Interactions on the Selectivity of Protein-Nanoparticle Binding2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 14, 4078-4083 p.Article in journal (Refereed)
    Abstract [en]

    We investigate the role of different mesoscopic interactions (Coulomb, charge regulation, and ion-dipole "surface patch" effects) on the binding of bovine serum albumin (BSA) and beta-lactoglobulin (BLG) to a cationic gold nanoparticle (TTMA+). The results demonstrate that the charge-regulation mechanism plays a vital role for selectivity of protein-nanoparticle complexation at low salt concentration. At slightly higher ionic strengths, charge-dipole effects are the dominating driving force. Thus, very small variations in salt concentration strongly influence the origin of complexation.

  • 16.
    Bastardo Zambrano, Luis Alejandro
    et al.
    KTH, Superseded Departments, Chemistry.
    Claesson, Per Martin
    KTH, Superseded Departments, Chemistry.
    Brown, W.
    Department of Physical Chemistry, University of Uppsala,.
    Interactions between mucin and alkyl sodium sulfates in solution: a light scattering study2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 10, 3848-3853 p.Article in journal (Refereed)
    Abstract [en]

    The properties of negatively charged mucin in aqueous solutions and its interaction with anionic sodium alkyl sulfates with different hydrocarbon chain lengths were studied by means of dynamic light scattering. It was observed that mucin forms aggregates in aqueous solutions with a hydrodynamic radius above 500 nm. These aggregates dissolve when sodium dodecyl sulfate or sodium decyl sulfate is present at sufficiently high concentration, above about 0.2 cmc (critical micellar concentration). On the other hand, sodium octyl sulfate is not very effective in dissolving the mucin aggregates. The hydrodynamic radius of the dissolved mucin, decorated with some associated surfactant, is found to be in the range of 40-90 nm. The observation that the dissolving power of the sodium alkyl sulfates decreases with decreasing surfactant chain length suggests that the association between the surfactant and mucin is hydrophobically driven. The kinetics of the dissolution process depends on the surfactant concentration, a higher surfactant concentration giving rise to a more rapid dissolution of the aggregates. It was also observed that when the ionic strength is increased, the surfactant concentration needed to dissolve the mucin aggregates decreases. This can be explained by reduction of repulsive electrostatic forces by the salt.

  • 17.
    Bastardo Zambrano, Luis Alejandro
    et al.
    KTH, Superseded Departments, Chemistry.
    Dedinaite, A.
    Unilever Res. Dvmt. Port Sunlight, Quarry Road East, Bebington, Wirral.
    Interactions between Mucin and Surfactants at Solid-Liquid Interfaces2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 24, 9383-9392 p.Article in journal (Refereed)
    Abstract [en]

    The association between mucin and surfactants at the solid-liquid interface has been investigated employing reflectometry. The study is particularly aimed at understanding the removal of preadsorbed mucin layers by surfactant addition. To this end we investigated the effect of three different surfactants, one anionic surfactant, sodium dodecylsulfate (SDS), and two nonionic ones, penta(oxy ethylene) dodecyl ether (C12E5) and n-dodecyl beta-D-maltopyranoside (C-12-mal), All three surfactants were found to be potent in removing mucin from hydrophobic surfaces. On the otherhand, C-12-mal was found to have a very limited effect on mucin adsorbed to hydrophilic negatively charged surfaces, whereas the mucin layer was removed by SDS and C12E5. The association between mucin and the three different surfactants was also investigated by means of dynamic light scattering and surface tension measurements. It was concluded that SDS associates readily with mucin above a critical surfactant concentration, about 0.2 cmc, whereas the nonionic surfactants associate with mucin to a very limited degree. The results obtained with the different techniques allow us to propose that C12E5 removes mucin from silica surfaces by competitive adsorption, whereas the removal of mucin by SDS is due to formation of mucin/SDS complexes that have reduced surface affinity and increased water solubility compared to mucin alone.

  • 18. Baverback, Petra
    et al.
    Oliveira, Cristiano L. P.
    Garamus, Vasil M.
    Varga, Imre
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Pedersen, Jan Skov
    Structural Properties of beta-Dodecylmaltoside and C12E6 Mixed Micelles2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 13, 7296-7303 p.Article in journal (Refereed)
    Abstract [en]

    Mixed micelles formed in aqueous solutions of nonionic surfactants n-dodecyl-hexaethylene-glycol (C12E6) and n-dodecyl-beta-D-maltoside (C(12)G(2)) have been studied using small-angle neutron and X-ray scattering (SANS and SAXS) and static light scattering (SLS). Apparent micelle molar masses obtained with SLS were analyzed with a model taking into account both micelle growth and interference effects. The analysis shows that pure C(12)G(2) forms small globular micelles whereas C12E6 and the mixtures form elongated micelles of much higher molar mass. The elongated micelles grow with increased concentration according to mean-field theory, and the masses are larger for increasing amounts of C12E6. To describe the SANS and SAXS data for C12E6 and the mixtures, it: was necessary to employ a model with coexisting spherical and spherocylindrical micelles. The SANS and SAXS data were fitted simultaneously using this model with core-shell particles and molecular constraints. All mixtures, as well as pure C12E6, can be described by this model, demonstrating the coexistence of spherical and cylindrical micelles. The spherical micelles are the same size in all samples, whereas the cylindrical micelles grow in length with the fraction of C12E6 in the samples, as well as with concentration, in agreement with the SLS analysis. The mass fraction of surfactant in cylindrical aggregates also increases with the fraction of C12E6 and with overall concentration. The analysis of the SAXS and SANS data for pure C(12)G(2) shows that the micelles are disk-shaped. The presence of elongated micelles in pure C12E6 and in the mixtures demonstrates that the behavior of the mixtures is dominated by C12E6.

  • 19.
    Belonoshko, A. B.
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Rosengren, Anders
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Ab Initio Study of Water Interaction with a Cu Surface2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 21, 16267-16270 p.Article in journal (Refereed)
    Abstract [en]

    We have performed a first principles investigation of water interaction with a Cu surface. The calculated surface energy of a Cu(100) slab is in reasonable agreement with experimental data. The energy of water dissociation is in agreement with experiment. The results of the ab initio calculations are compared to experimental data on hydrogen partial pressure. It is concluded that Cu(OH)(ads) is formed due to a reaction between Cu and anoxic water. The energy of the Cu(100) slab with OH and H adsorbed is lower than the energy of the same slab with an adsorbed water molecule.

  • 20.
    Benselfelt, Tobias
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Pettersson, Torbjörn
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Influence of Surface Charge Density and Morphology on the Formation of Polyelectrolyte Multilayers on Smooth Charged Cellulose Surfaces2017In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, no 4, 968-979 p.Article in journal (Refereed)
    Abstract [en]

    To clarify the importance of the surface charge for the formation of polyelectrolyte multilayers, layer-by-layer (LbL) assemblies of polydiallyldimethylammonium chloride (pDADMAC) and polystyrenesulfonate (PSS) have been investigated on cellulose films with different carboxylic acid contents (20, 350, 870, and 1200 μmol/g) regenerated from oxidized cellulose. The wet cellulose films were thoroughly characterized prior to multilayer deposition using quantitative nanomechanical mapping (QNM), which showed that the mechanical properties were greatly affected by the degree of oxidation of the cellulose. Atomic force microscopy (AFM) force measurements were used to determine the surface potential of the cellulose films by fitting the force data to the DLVO theory. With the exception of the 1200 μmol/g film, the force measurements showed a second-order polynomial increase in surface potential with increasing degree of oxidation. The low surface potential for the 1200 μmol/g film was attributed to the low degree of regeneration of the cellulose film in aqueous media due to increasing solubility with increasing charge. The multilayer formation was characterized using a quartz crystal microbalance with dissipation (QCM-D) and stagnation-point adsorption reflectometry (SPAR). Extensive deswelling was observed for the charged films when pDADMAC was adsorbed due to the reduced osmotic pressure when ions inside the film were released, and the 1:1 charge compensation showed that all the charges in the films were reached by the pDADMAC. The multilayer formation was not significantly affected by the charge density above 350 μmol/g due to interlayer repulsions, but it was strongly affected by the salt concentration during the layer build-up.

  • 21.
    Bergenstråhle, Malin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Thormann, Esben
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Nordgren, Niklas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Berglund, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Force Pulling of Single Cellulose Chains at the Crystalline Cellulose-Liquid Interface: A Molecular Dynamics Study2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 8, 4635-4642 p.Article in journal (Refereed)
    Abstract [en]

    Pulling single cellulose molecules from a crystalline cellulose surface has been modeled by molecular dynamics (MD) simulations of the experimental procedure used in atomic force microscopy (AFM). Specifically, the aim of the study was to investigate cellulose interactions at desorption. Simulations were performed in both water and the organic solvent cyclohexane. Moreover, the effects of initial octamer conformation and orientation with respect to the surface chains were studied. A strong effect from the solvent was observed. In cyclohexane, normal forces of 200-500 pN and energies of 43.5 +/- 6.0 kJ/mol glucose unit were required to pull off the octamer. The normal forces in water were substantially lower, around 58 pN, and the energies were 18.2 +/- 3.6 kJ/mol glucose unit. In addition, the lateral components of the pull-off force were shown to provide information on initial conformation and orientation. Hydrogen bonds between the octamer and surface were analyzed and found to be an important factor in the pull-off behavior. Altogether, it was shown that MD provides detailed information on the desorption processes that may be useful for the interpretation of AFM experiments.

  • 22.
    Bergström, L. Magnus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Garamus, Vasil M.
    Geometrical Shape of Micelles Formed by Cationic Dimeric Surfactants Determined with Small-Angle Neutron Scattering2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 25, 9311-9321 p.Article in journal (Refereed)
    Abstract [en]

    The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C12H25N(CH3)(2)(CH2)(5)N(CH3)(2)C12H25 (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 124-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 <= s <= 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 <= s <= 12.

  • 23.
    Bergström, L. Magnus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Skoglund, Sara
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Edwards, K.
    Eriksson, J.
    Grillo, I.
    Self-assembly in mixtures of an anionic and a cationic surfactant: A comparison between small-angle neutron scattering and cryo-transmission electron microscopy2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 38, 11834-11848 p.Article in journal (Refereed)
    Abstract [en]

    The self-assembly in SOS-rich mixtures of the anionic surfactant sodium octyl sulfate (SOS) and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) has been investigated with the complementary techniques small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). Both techniques confirm the simultaneous presence of open and closed bilayer structures in highly diluted samples as well as the existence of small globular and large elongated micelles at higher concentrations. However, the two techniques sometimes differ with respect to which type of aggregates is present in a particular sample. In particular, globular or wormlike micelles are sometimes observed with cryo-TEM in the vicinity of the micelle-to-bilayer transition, although only bilayers are present according to SANS and the samples appear bluish to the eye. A similar discrepancy has previously been reported but could not be satisfactorily rationalized. On the basis of our comparison between in situ (SANS) and ex situ (cryo-TEM) experimental techniques, we suggest that this discrepancy appears mainly as a result of the non-negligible amount of surfactant adsorbed at interfaces of the thin sample film created during the cryo-TEM specimen preparation. Moreover, from our detailed SANS data analysis, we are able to observe the unusually high amount of free surfactant monomers present in SOS-rich mixtures of SOS and CTAB, and the experimental results give excellent agreement with model calculations based on the Poisson-Boltzmann mean field theory. Our careful comparison between model calculations and experiments has enabled us to rationalize the dramatic microstructural transformations frequently observed upon simply diluting mixtures of an anionic and a cationic surfactant.

  • 24.
    Bergström, L. Magnus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Skoglund, Sara
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Edwards, Katarina
    Eriksson, Jonny
    Grillo, Isabelle
    Spontaneous Transformations between Surfactant Bilayers of Different Topologies Observed in Mixtures of Sodium Octyl Sulfate and Hexadecyltrimethylammonium Bromide2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 14, 3928-3938 p.Article in journal (Refereed)
    Abstract [en]

    The influence of adding salt on the self-assembly in sodium octyl sulfate (SOS)-rich mixtures of the anionic surfactant SOS and the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) have been investigated with the two complementary techniques, small-angle neutron scattering (SANS) and cryo-transmission electron microscopy. We are able to conclude that addition of a substantial amount of inert salt, NaBr, mainly has three effects on the structural behaviors: (i) the micelles become much larger at the transition from micelles to bilayers, (ii) the fraction of bilayer disks increases at the expense of vesicles, and (iii) bilayer aggregates perforated with holes are formed in the most diluted samples. A novel form factor valid for perforated bilayer vesicles and disks is introduced for the first time and, as a result, we are able to directly observe the presence of perforated bilayers by means of fitting SANS data with an appropriate model. Moreover, we are able to conclude that the morphology of bilayer aggregates changes according to the following sequence of different bilayer topologies, vesicles --> disks --> perforated bilayers, as the electrolyte concentration is increased and surfactant mole fraction in the bilayer aggregates approaches equimolarity. We are able to rationalize this sequence of transitions as a result of a monotonous increase of the bilayer saddle-splay constant ((k) over bar (bi)(c)) with decreasing influence from electrostatics, in agreement with theoretical predictions as deduced from the Poisson-Boltzmann theory.

  • 25. Bergström, Lars Magnus
    Bending elasticity of charged surfactant layers: The effect of layer thickness2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 8, 3678-3691 p.Article in journal (Refereed)
    Abstract [en]

    The bending properties of charged one-component surfactant films of finite thickness have been theoretically investigated. It is demonstrated that finite thickness effects are of crucial importance for layers formed by an ionic surfactant with a flexible hydrophobic tail, whereas the influence on layers formed by a surfactant with a rigid tail is less pronounced. As a matter of fact, in the former case, the spontaneous curvature and mean and Gaussian bending constants all become significantly modified as compared to an infinitely thin surface and assume identical values as if the surfactant layer were bent at constant layer thickness. As a result, the spontaneous curvature is found to decrease, whereas the magnitudes of the mean and Gaussian bending constants both increase with increasing layer thickness as well as with increasing hydrophobic-hydrophilic interfacial tension. All of these trends are consistent with experimental observations. In addition, it is demonstrated that separating the hydrophilic-hydrophobic interface and the surface of charge a certain distance from each other tends to increase the spontaneous curvature and the mean bending constant, whereas the Gaussian bending constant becomes increasingly negative. It is also found that the work of bending a bilayer into a geometrically closed vesicle is substantially raised to large positive values for surfactants with flexible aliphatic chains, whereas the corresponding quantity is negative for surfactants with rigid tails, indicating that stable bilayer structures may only be formed by the former surfactant. Furthermore, each of the bending elasticity constants for monolayers formed by a double-chain ionic surfactant are found to assume lower values as compared with layers formed by the corresponding single-chain surfactant.

  • 26. Bergström, Lars Magnus
    Bending elasticity of charged surfactant layers: The effect of mixing2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 16, 6796-6813 p.Article in journal (Refereed)
    Abstract [en]

    Expressions have been derived from which the spontaneous curvature (H-0), bending rigidity (k(c)), and saddle-splay constant ((k) over bar (c)) of mixed monolayers and bilayers may be calculated from molecular and solution properties as well as experimentally available quantities such as the macroscopic hydrophobic-hydrophilic interfacial tension. Three different cases of binary surfactant mixtures have been treated in detail: (i) mixtures of an ionic and a nonionic surfactant, (ii) mixtures of two oppositely charged surfactants, and (iii) mixtures of two ionic surfactants with identical headgroups but different tail volumes. It is demonstrated that k(c)H(0), k(c), and (k) over bar

  • 27.
    Bergström, Lars Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Bending Elasticity of Nonionic Surfactant Layers2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 4, 1949-1960 p.Article in journal (Refereed)
    Abstract [en]

    A novel approach to evaluate the bending elasticity of monolayers formed by nonionic surfactants with a rigid head group is introduced by means of considering head group repulsion as derived from the free energy of mixing rigid hydrophilic head groups with surrounding solvent molecules as well as contributions related to the hydrophobic tails. Explicit expressions for the spontaneous curvature (H-0), bending rigidity (k(c)) and saddle-splay constant ((k) over bar (c)) have been derived for the constraint of constant chemical potential of free surfactant (thermodynamically open layers) as well as the constraint of constant aggregation number (thermodynamically closed layers). Most interestingly, it is demonstrated that k(c) for thermodynamically open layers formed by a nonionic surfactant with rigid tail and head group always must be zero. However, k(c) for surfactants with a flexible tail as a function of the head group-to-tail volume ratio is found to go through a maximum at some large, positive value of k(c) and H-0 approximate to 0. Eventually, k(c) falls below zero as the head group volume increases above a certain value. Hence, we may conclude that nonionic surfactants with a rigid head group may form thermodynamically stable fluid layers or aggregates only insofar the hydrophobic part is flexible with respect to chain conformational. degrees of freedom and the head group is not too voluminous. It is found that the head group repulsion contribution to k(c)H(0) is always positive whereas the corresponding contribution to (k) over bar

  • 28.
    Bergström, Lars Magnus
    KTH, Superseded Departments, Chemistry.
    Molecular interpretation of the mean bending constant for a thermodynamically open vesicle bilayer2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 24, 7675-7686 p.Article in journal (Refereed)
    Abstract [en]

    Expressions for the various molecular contributions to the mean bending constant k(c) of a thermodynamically open vesicle bilayer have been derived, from which k(c) maybe calculated from an appropriate molecular-thermodynamic model as a function of the structure of the surfactants making up the aggregates as well as the solution state. It is demonstrated that k(c) determines the shape of a vesicle bilayer insofar as spherical vesicles form when k(c) is large and positive! whereas nonspherical. vesicles predominate at values of k(c) close to or below zero. It is found that contributions due to electrostatics and residual headgroup effects, which are present for one-component as well as mixed aggregates, mainly give rise to a positive value of k(c) whereas geometrical packing constraints are less important. However, the mixing of two or more surfactants can significantly reduce k(c) to values where nonspherical vesicles may begin to form. The magnitude of the reduction of k(c) due to mixing increases with increasing asymmetry with respect to headgroup cross-section area, charge number, and hydrocarbon tail volume between two surfactants in a binary surfactant mixture. The asymmetry is most pronounced for a binary mixture where the surfactant that carries the charge has the larger headgroup and the smaller tail. The reduction of k(c) due to mixing is, however, expected to be less than the corresponding effect for the bilayer bending constant of a spherical vesicle as a result of an additional positive contribution in the expression for the compositional contribution to k(c).

  • 29.
    Bergström, Lars Magnus
    KTH, Superseded Departments, Chemistry.
    Synergistic effects in mixtures of an anionic and a cationic surfactant2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 4, 993-998 p.Article in journal (Refereed)
    Abstract [en]

    Synergistic effects in mixtures of an anionic and a cationic surfactant have been theoretically investigated. We derive an explicit expression far the critical micelle concentration (cmc) as a function of the aggregate composition from the Poisson-Boltzmann mean field theory and, thus, demonstrate that the conspicuously large synergistic effects that have been experimentally observed can be rationalized without the need of invoking any specific interactions between the surfactant headgroups. The simple relation beta = -4 epsilon (el/kTelNzT) is derived, i.e.,the interaction parameter beta is directly related to the electrostatic free energy contribution epsilon (el) for the pure surfactant, implying, among other things, that the magnitude of beta decreases vith increasing cmc for the pure surfactant in agreement with experimental observations. We furthermore demonstrate that the aggregate composition is close to equimolar composition (x(1) = 0.5) at cmc in almost the entire regime of overall surfactant compositions and that the free monomer concentration of the surfactant in excess is generally much larger than the corresponding quantity for the surfactant in deficit.

  • 30.
    Bergström, Lars Magnus
    et al.
    KTH, Superseded Departments, Chemistry.
    Eriksson, J. C.
    A theoretical analysis of synergistic effects in mixed surfactant systems2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, no 18, 7173-7181 p.Article in journal (Refereed)
    Abstract [en]

    Synergistic effects in mixed binary surfactant systems have been investigated by analyzing the main contributions to the free energy of forming a mixed surfactant aggregate. We show that a nonlinear behavior of the critical micelle concentration (cmc) with respect to the surfactant composition of the aggregates is determined by a nonlinear behavior of the free energy per aggregated surfactant. It appears that synergistic effects are due mainly to entropic free energy contributions related with the surfactant headgroups. For a mixture of a monovalent ionic and a nonionic surfactant in the absence of added salt we obtain, entirely because of electrostatic reasons, a negative deviation from ideal behavior of the cmc vs the aggregate composition corresponding to an interaction parameter beta approximate to -1, whereas beta values on the order of -5 or even less can arise for mixtures of two ionic surfactants with the same charge number but with different hydrocarbon moieties. Moreover, we introduce a novel expression for the free energy of mixing aggregated surfactant headgroups with surrounding solvent molecules. Accordingly, synergistic effects arise as a result of different headgroup cross-section areas in mixtures of two nonionic surfactants with rigid headgroups. These effects are found to be rather small, with 0 > beta > -1, when the difference in headgroup size is modest but can become more significant when the size difference is larger. In mixtures of an ionic and a nonionic surfactant with different headgroup cross-section areas the two contributions to synergistic effects always enhance one another and, hence, beta values below -1 are obtained. Generally, the synergistic effects tend to increase with increasing asymmetry between the two surfactants.

  • 31.
    Bergström, Lars Magnus
    et al.
    KTH, Superseded Departments, Chemistry.
    Jonsson, P.
    Persson, M.
    Eriksson, J. C.
    A model-independent evaluation of experimental data, and comparison with theory, of synergistic effects in mixtures of an ionic and a nonionic surfactant2003In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, no 26, 10719-10725 p.Article in journal (Refereed)
    Abstract [en]

    Critical micelle concentrations for mixtures of an anionic (sodium dodecyl sulfate) and a nonionic (decyl beta-glucoside) surfactant was obtained from surface tension measurements at different concentrations of added NaCl. The observed synergistic effects were analyzed by means of introducing a novel model-independent synergy parameter. The model-independent evaluation has enabled the comparison of experimental results with a theoretical model based on the Poisson-Boltzmann (PB) mean field theory for spherical, cylindrical, and planar geometries, respectively. We found that best agreement with experimental data was obtained for largely curved structures (spherical and cylindrical micelles) at all [NaCl], which is consistent with the fact that rather small micelles, as a rule, form at the critical micelle concentration. Moreover, the PB theory was found to better describe synergistic behavior of the experimental data than the more conventional regular mixture theory, in particular at low electrolyte concentrations. The magnitude of the observed synergistic effects was found to increase as a small amount of NaCl was added and reach a maximum at [NaCl] = 10 mM, in agreement with the PB theory. As expected, synergism was observed to decrease in magnitude upon further addition of NaCl.

  • 32.
    Bergström, Lennart Magnus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Tehrani-Bagha, A.
    Nagy, G.
    Growth behavior, geometrical shape, and second CMC of micelles formed by cationic gemini esterquat surfactants2015In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 31, no 16, 4644-4653 p.Article in journal (Refereed)
    Abstract [en]

    Micelles formed by novel gemini esterquat surfactants have been investigated with small-angle neutron scattering (SANS). The growth behavior of the micelles is found to differ conspicuously depending on the length of the gemini surfactant spacer group. The gemini surfactant with a long spacer form rather small triaxial ellipsoidal tablet-shaped micelles that grow weakly with surfactant concentration in the entire range of measured concentrations. Geminis with a short spacer, on the other hand, form weakly growing oblates or tablets at low concentrations that start to grow much more strongly into polydisperse rodlike or wormlike micelles at higher concentrations. The latter behavior is consistent with the presence of a second CMC that marks the transition from the weakly to the strongly growing regime. It is found that the growth behavior in terms of aggregation number as a function of surfactant concentration always appear concave in weakly growing regimes, while switching to convex behavior in strongly growing regimes. As a result, we are able to determine the second CMC of the geminis with short spacer by means of suggesting a rather precise definition of it, located at the point of inflection of the growth curve that corresponds to the transition from concave to convex growth behavior. Our SANS results are rationalized by comparison with the recently developed general micelle model. In particular, this theory is able to explain and reproduce the characteristic appearances of the experimental growth curves, including the presence of a second CMC and the convex strongly growing regime beyond. By means of optimizing the agreement between predictions from the general micelle model and results from SANS experiments, we are able to determine the three bending elasticity constants spontaneous curvature, bending rigidity, and saddle-splay constant for each surfactant.

  • 33.
    Blomberg, Eva
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
    Konradsson, Peter
    Department of Physics, Chemistry and Biology, Linköping University.
    Liedberg, Bo
    Department of Physics, Chemistry and Biology, Linköping University.
    Globotriose- and oligo(ethylene glycol)-terminated self-assembled monolayers: Surface forces, wetting, and surfactant adsorption2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 24, 10038-10046 p.Article in journal (Refereed)
    Abstract [en]

    A set of oligo( ethylene glycol)-terminated and globotriose-terminated self-assembled monolayers (SAMs) has been prepared on gold substrates. Such model surfaces are well defined and have good stability due to the strong binding of thiols and disulfides to the gold substrate. They are thus very suitable for addressing questions related to effects of surface composition on wetting properties, surface interactions, and surfactant adsorption. These issues are addressed in this report. Accurate wetting tension measurements have been performed as a function of temperature using the Wilhelmy plate technique. The results show that the nonpolar character of oligo( ethylene glycol)-terminated SAMs increases slightly but significantly with temperature in the range 20-55 degrees C. On the other hand, globotriose-terminated SAMs are fully wetted by water at room temperature. Surface forces measurements have been performed and demonstrated that the interactions between oligo( ethylene glycol)-terminated SAMs are purely repulsive and similar to those determined between adsorbed surfactant layers with the same terminal headgroup. On the other hand, the interactions between globotriose-terminated SAMs include a short-range attractive force component that is strongly affected by the packing density in the layer. In some cases it is found that the attractive force component increases with contact time. Both these observations are rationalized by an orientation- and conformation-dependent interaction between globotriose headgroups, and it is suggested that hydrogen-bond formation, directly or via bridging water molecules, is the molecular origin of these effects.

  • 34.
    Blomberg, Eva
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
    Kumpulainen, Atte
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
    David, C.
    Laboratoire de Recherche sur les Polymères, CNRS, Thiais, France.
    Amiel, C.
    Laboratoire de Recherche sur les Polymères, CNRS, Thiais, France.
    Polymer bilayer formation due to specific interactions between beta-cyclodextrin and adamantane: A surface force study2004In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, no 24, 10449-10454 p.Article in journal (Refereed)
    Abstract [en]

    The purposes of this study are to utilize the interactions between an adamantane end-capped poly(ethylene oxide) (PEO) and a cationic polymer of beta-cyclodextrin to build polymer bilayers on negatively charged surfaces, and to investigate the interactions between such layers. The association of this system in solution has been studied by rheology, light scattering, and fluorescence measurements. It was found that the adamantane-terminated PEO (PEC-Ad) mixed with the beta-cyclodextrin polymer gives complexes where the interpolymer links are formed by specific inclusion of the adamantane groups in the beta-cyclodextrin cavities. This results in a higher viscosity of the solution and growth of intermolecular clusters. The interactions between surfaces coated with a cationized beta-cyclodextrin polymer across a water solution containing PEO-Ad polymers were studied by employing the interferometric surface force apparatus (SFA). In the first step, the interaction between mica surfaces coated with the cationized beta-cyclodextrin polymer in pure water was investigated. It was found that the beta-cyclodextrin polymer adsorbs onto mica and almost neutralizes the surface charge. The adsorbed layers of the beta-cyclodextrin polymer are rather compact, with a layer thickness of about 60 Angstrom (30 Angstrom per surface). Upon separation, a very weak attractive force is observed. The beta-cyclodextrin solution was then diluted by pure water by a factor of 3000 and a PEO-Ad polymer was introduced into the solution. Two different architectures of the PEO-Ad polymer were investigated: a four-arm structure and a linear structure. After the adsorption of the PEO polymer onto the beta-cyclodextrin layer reached equilibrium, the forces were measured again. It was found that the weak repulsive long-range force had disappeared and an attractive force caused the surfaces to jump into contact, and that the compressed layer thickness had increased. The attractive force is interpreted as being due to a specific recognition between the hydrophobic adamantane groups on the PEO-Ad polymer and the hydrophobic cavity in the beta-cyclodextrin molecules. Furthermore, the attractive force observed on separation has increased significantly, which is a further indication of a specific interaction between the beta-cyclodextrin polymer and the adamantane groups.

  • 35.
    Blomberg, Eva
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Poptoshev, Evgeni
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Caruso, F.
    Centre for Nanoscience and Nanotechnology, Department of Chemical and Biomolecular Engineering, University of Melbourne, Victoria, Australia.
    Surface interactions during polyelectrolyte multilayer build-up. 2. The effect of ionic strength on the structure of preformed multilayers2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 9, 4153-4157 p.Article in journal (Refereed)
    Abstract [en]

    Interactions between surfaces bearing multilayer films of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate sodium salt) (PSS) were investigated across a range of aqueous KBr solutions. Three layer films (PAH/PSS/PAH) were preassembled on mica surfaces, and the resulting interactions were measured with the interferometric surface force apparatus (SFA). Increasing the ionic strength of the medium resulted in a progressive swelling of the multilayer films. Interactions in solutions containing more than 10(-3) M KBr were dominated by a long-ranged steric repulsion originating from compression of polyelectrolyte segments extending into solution. In 10(-1) M KBr, repeated measurements at the same contact position showed a considerable reduction of the range and the strength of the steric force, indicating a flattening of the film during initial approach. Furthermore, this flattening was irreversible on the time scale of the experiments, and measurements performed up to 72 h after the initial compression showed no signs of relaxation. These studies aid in understanding the dominant interactions between polyelectrolyte multilayers, including polyelectrolyte films deposited on colloidal particles, which is important for the preparation of colloidally stable nanoengineered particles.

  • 36.
    Blomberg, Eva
    et al.
    KTH, Superseded Departments, Chemistry.
    Poptoshev, Evgeni
    KTH, Superseded Departments, Chemistry.
    Claesson, Per M.
    KTH, Superseded Departments, Chemistry.
    Caruso, F.
    Centre for Nanoscience and Nanotechnology, Department of Chemical and Biomolecular Engineering, The University of Melbourne, Victoria, Australia.
    Surface interactions during polyelectrolyte multilayer buildup. 1. Interactions and layer structure in dilute electrolyte solutions2004In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, no 13, 5432-5438 p.Article in journal (Refereed)
    Abstract [en]

    We report the investigation of surface forces between polyelectrolyte multilayers of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate sodium salt) (PSS) assembled on mica surfaces during film buildup using a surface force apparatus. Up to four polyelectrolyte layers were prepared on each surface ex situ, and the surface interactions were measured in 10(-4) M KBr solutions. The film thickness under high compressive loads (above 2000 muN/m) increased linearly with the number of deposited layers. In all cases, the interaction between identical surfaces at large separations (> 100 Angstrom from contact) was dominated by electrostatic double-layer repulsion. By fitting DLVO theory to the experimental force curves, the apparent double-layer potential of the interacting surfaces was calculated. At shorter separations, an additional non-DLVO repulsion was present due to polyelectrolyte chains extending some distance from the surface into solution, thus generating an electrosteric type of repulsion. Forces between dissimilar multilayers (i.e., one of the multilayers terminated with PSS and the other with PAH) were attractive at large separations (30-400 Angstrom) owing to a combination of electrostatic attraction and polyelectrolyte bridging.

  • 37.
    Blomberg, Eva
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
    Verrall, Ronald
    Department of Chemistry, University of Saskatchewan, Saskatoon, Canada.
    Claesson, Per M
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry (closed 20081231).
    Interactions between adsorbed layers of cationic gemini surfactants2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 4, 1133-1140 p.Article in journal (Refereed)
    Abstract [en]

    The forces acting between glass and between mica surfaces in the presence of two cationic gemini surfactants, 1,4 diDDAB (1,4-butyl-bis(dimethyldodecylammonium bromide)) and 1,12 diDDAB (1,12-dodecyl-bis(dimethyldodecylammonium bromide)), have been investigated below the critical micelle concentration (cmc) of the surfactants using two different surface force techniques. In both cases, it was found that a recharging of the surfaces occurred at a surfactant concentration of about 0.1 x cmc, and at all surfactant concentrations investigated repulsive double-layer forces dominated the interaction at large separations. At smaller separations, attractive forces, or regions of separation with (close to) constant force, were observed. This was interpreted as being due to desorption and rearrangement in the adsorbed layer induced by the proximity of a second surface. Analysis of the decay length of the repulsive double-layer force showed that the majority of the gemini surfactants were fully dissociated. However, the degree of ion pair formation, between a gemini surfactant and a bromide counterion, increased with increasing surfactant concentration and was larger for the gemini surfactant with a shorter spacer length.

  • 38.
    Bodvik, Rasmus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Karlson, Leif
    Edwards, Katarina
    Eriksson, Jonny
    Thormann, Esben
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Aggregation of Modified Celluloses in Aqueous Solution: Transition from Methylcellulose to Hydroxypropylmethylcellulose Solution Properties Induced by a Low-Molecular-Weight Oxyethylene Additive2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 38, 13562-13569 p.Article in journal (Refereed)
    Abstract [en]

    Temperature effects on the viscosity and aggregation behavior of aqueous solutions of three different cellulose ethers-methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), and ethyl(hydroxyethyl)cellulose (EHEC)-were investigated using viscosity and dynamic light scattering measurements as well as cryo-TEM. In all cases, increasing temperature reduces the solvent quality of water, which induces aggregation. It was found that the aggregation rate followed the order EHEC > HPMC > MC, suggesting that cellulose ethers containing some bulky and partially hydrophilic substituents assemble into large aggregates more readly than methylcellulose. This finding is discussed in terms of the organization of the structures formed by the different cellulose ethers. The temperature-dependent association behavior of cellulose ethers was also investigated in a novel way by adding diethyleneglycolmonobutylether (BDG) to methylcellulose aqueous solutions. When the concentration of BDG was at and above 5 wt %, methylcellulose adopted HPMC-like solution behavior. In particular, a transition temperature where the viscosity was decreasing, prior to increasing at higher temperatures, appeared, and the aggregation rate increased. This observation is rationalized by the ability of amphiphilic BDG to accumulate at nonpolar interfaces and thus also to associate with hydrophobic regions of methylcellulose. In effect, BDG is suggested to act as a physisorbed hydrophilic and bulky substituent inducing constraints on aggregation similar to those of the chemically attached hydroxypropyl groups in HPMC and oligo(ethyleneoxide) chains in EHEC.

  • 39.
    Bodvik, Rasmus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Macakova, Lubica
    Karlson, Leif
    Thormann, Esben
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Temperature-Dependent Competition between Adsorption and Aggregation of a Cellulose Ether-Simultaneous Use of Optical and Acoustical Techniques for Investigating Surface Properties2012In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, no 25, 9515-9525 p.Article in journal (Refereed)
    Abstract [en]

    Adsorption of the temperature-responsive polymer hydroxypropylmethylcellulose (HPMC) from an aqueous solution onto hydrophobized silica was followed well above the bulk instability temperature (T-2) in temperature cycle experiments. Two complementary techniques, QCM-D and ellipsometry, were utilized simultaneously to probe the same substrate immersed in polymer solution. The interfacial processes were correlated with changes in polymer aggregation and viscosity of polymer solutions, as monitored by light scattering and rheological measurements. The simultaneous use of ellipsometry and QCM-D, and the possibility to follow layer properties up to 80 degrees C, well above the T-2 temperature, are both novel developments. A moderate increase in adsorbed amount with temperature was found below T-2, whereas a significant increase in the adsorbed mass and changes in layer properties were observed around the T-2 temperature where the bulk viscosity increases significantly. Thus, there is a clear correlation between transition temperatures in the adsorbed layer and in bulk solution, and we discuss this in relation to a newly proposed model that considers competition between aggregation and adsorption/deposition. A much larger temperature response above the T-2 temperature was found for adsorbed layers of HPMC than for layers of methyl cellulose. Possible reasons for this are discussed.

  • 40. Bogdanovic, G.
    et al.
    Tiberg, F.
    Rutland, Mark W
    KTH, Superseded Departments, Chemistry.
    Sliding friction between cellulose and silica surfaces2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, no 19, 5911-5916 p.Article in journal (Refereed)
    Abstract [en]

    An atomic force microscope was used to measure kinetic friction forces between a colloidal cellulose sphere and different planar surfaces in air. The planar surfaces were bare silica, silica modified with a monolayer of alkyl ketene dimer (AKD), a common additive used for paper sizing, and silica with surface grafted terminal methyl groups. Friction was measured as a function of the effective load resulting from adhesive interactions between the cellulose sphere and the planar surface. Friction in the regime of low effective loads was shown to be a linear function of the load, and the friction coefficients determined from the slope of these curves were 0.26, 0.07, and 0.021 for the cellulose-silica, cellulose-AKD, and cellulose-methylated silica systems, respectively. The ratio between friction coefficients for the two first systems agrees well with that reported for paper in the presence and absence of AKD sizing agents, respectively. In the high effective load regime, deviations from linearity between measured friction and load were observed. This is an indication that we have single asperity contact, at least at high loads. These results were analyzed in terms of a contact mechanics transition equation, By making assumptions on the moduli of the materials, the interfacial shear strength tau and the contact radius ao were calculated. The results obtained through this analysis provide an important insight into the relationship between friction and chemical surface properties.

  • 41.
    Bäbler, Matthäus
    et al.
    Swiss Fed Inst Technol, Inst Proc Engn.
    Moussa, Amgad S.
    Soos, Miroslav
    Morbidelli, Massimo
    Structure and Kinetics of Shear Aggregation in Turbulent Flows: I. Early Stage of Aggregation2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 16, 13142-13152 p.Article in journal (Refereed)
    Abstract [en]

    Aggregation of rigid colloidal particles leads to fractal-like structures that are characterized by a fractal dimension d(f) which is a key parameter for describing aggregation processes. This is particularly true in shear aggregation where d(f) strongly influences aggregation kinetics. Direct measurement of d(f) in the early stages of shear aggregation is however difficult, as the aggregates are small and few in number. An alternative method for determining d(f) is to use an aggregation model that when fitted to the time evolution of the cluster mass distribution allows for estimating d(f). Here, we explore three such models, two of which are based on an effective collision sphere and one which directly incorporates the permeable structure of the aggregates, and we apply them for interpreting the initial aggregate growth measured experimentally in a turbulent stirred tank reactor. For the latter, three polystyrene latexes were used that differed only in the size of the primary particles (d(p) = 420, 600, and 810 nm). It was found that all three models describe initial aggregation kinetics reasonably well using, however, substantially different values for 4 To discriminate among the models, we therefore also studied the regrowth of preformed aggregates where d(f) was experimentally accessible. It was found that only the model that directly incorporates the permeable structure of the aggregates is able to predict correctly this second type of experiments. Applying this model to the initial aggregation kinetics, we conclude that the actual initial fractal dimension is d(f) = 2.07 +/- 0.04 as found from this model.

  • 42. Cardenas, Marite
    et al.
    Valle-Delgado, Juan Jose
    Hamit, Jildiz
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Arnebrant, Thomas
    Interactions of hydroxyapatite surfaces: Conditioning films of human whole saliva2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 14, 7262-7268 p.Article in journal (Refereed)
    Abstract [en]

    Hydroxyapatite is a very interesting material given that it is the main component in tooth enamel and because of its uses in bone implant applications. Therefore, not only the characterization of its surface is of high relevance but also designing reliable methods to study the interfacial properties of films adsorbed onto it. In this paper we apply the colloidal probe atomic force microscopy method to investigate the surface properties of commercially available hydroxyapatite surfaces (both microscopic particles and macroscopic discs) in terms of interfacial and frictional forces. In this way, we find that hydroxyapatite surfaces at physiological relevant conditions are slightly negatively charged. The surfaces were then exposed to human whole saliva, and the surface properties were re-evaluated. A thick film was formed that was very resistant to mechanical stress. The frictional measurements demonstrated that the film was indeed highly lubricating, supporting the argument that this system may prove to be a relevant model for evaluating dental and implant systems.

  • 43.
    Carlborg, Carl Fredrik
    et al.
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    van der Wijngaart, Wouter
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Sustained Superhydrophobic Friction Reduction at High Liquid Pressures and Large Flows2011In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 1, 487-493 p.Article in journal (Refereed)
    Abstract [en]

    This Article introduces and experimentally explores a novel self-regulating method for reducing the friction losses in large microchannels at high liquid pressures and large liquid flows, overcoming previous limitations with regard to sustainable liquid pressure on a superhydrophobic surface. Our design of the superhydrophobic channel automatically adjusts the gas pressure in the lubricating air layer to the local liquid pressure in the channel. This is achieved by pneumatically connecting the liquid in the microchannel to the gas-pockets trapped at the channel wall through a pressure feedback channel. When liquid enters the feedback channel, it compresses the air and increases the pressure in the gas-pocket. This reduces the pressure drop over the gas liquid interface and increases the maximum sustainable liquid pressure. We define a dimensionless figure of merit for superhydropbic flows, W-F = PLD/gamma cos(theta(c)), which expresses the fluidic energy carrying capacity of a superhydrophobic microchannel. We experimentally verify that our geometry can sustain three times higher liquid pressure before collapsing, and we measured better friction-reducing properties at higher W-F values than in previous works. The design is ultimately limited in time by the gas-exchange over the gas-liquid interface at pressures exceeding the Laplace pressure. This method could be applicable for reducing near-wall laminar friction in both micro and macro scale flows.

  • 44. Carravetta, Vincenzo
    et al.
    Monti, Susanna
    Li, Cui
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical Simulations of Structure and X-ray Photoelectron Spectra of Glycine and Diglycine Adsorbed on Cu(110)2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 32, 10194-10204 p.Article in journal (Refereed)
    Abstract [en]

    The study of adsorption of glycine and glycylglycine (or diglycine) on a copper surface is an important step for the comprehension of mechanisms that determine the stability of biological functionalizers on metal substrates. These two molecules can be considered as prototypes and essential models to investigate, theoretically and experimentally, the adaptability of flexible short peptide chains to a definite interface. In this work, we have improved and updated earlier molecular dynamics simulations by including reactivity of the various species and the comparison of ab initio calculated C, N, and O core photoelectron chemical shifts with the ones found in previous studies. New diglycine-copper bonding is predicted, and the results of the chemical shift analysis are, in all cases, fully compatible with structural information obtained through experimental measurements. Moreover, we have found that the process of proton transfer, which is fundamental in the dynamics of amino acids and peptides, occurs mainly by intermolecular interaction between the first and second layer of the adsorbate.

  • 45.
    Carrick, Christopher
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Lindström, Stefan B.
    Larsson, Per Tomas
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Lightweight, Highly Compressible, Noncrystalline Cellulose Capsules2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 26, 7635-7644 p.Article in journal (Refereed)
    Abstract [en]

    We demonstrate how to prepare extraordinarily deformable, gas-filled, spherical capsules from nonmodified cellulose. These capsules have a low nominal density, ranging from 7.6 to 14.2 kg/m(3), and can be deformed elastically to 70% deformation at 50% relative humidity. No compressive strain-at-break could be detected for these dry cellulose capsules, since they did not rupture even when compressed into a disk with pockets of highly compressed air. A quantitative constitutive model for the large deformation compression of these capsules is derived, including their high-frequency mechanical response and their low-frequency force relaxation, where the latter is governed by the gas barrier properties of the dry capsule. Mechanical testing corroborated these models with good accuracy. Force relaxation measurements at a constant compression rendered an estimate for the gas permeability of air through the capsule wall, calculated to 0.4 mL mu m/m(2) days kPa at 50% relative humidity. These properties taken together open up a large application area for the capsules, and they could most likely be used for applications in compressible, lightweight materials and also constitute excellent model materials for adsorption and adhesion studies.

  • 46.
    Corkery, Robert W
    et al.
    Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University.
    Fogden, Andrew
    Physical Chemistry 1, Center for Chemistry and Chemical Engineering, Lund University.
    On the formation and structure of nanometric polyhedral foams: toward the dry limit2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 18, 10443-10452 p.Article in journal (Refereed)
    Abstract [en]

    High surface area, high porosity, nanometric polygonal silica foams with hierarchically connected and uniformly sized pore systems are reported here. We observe a remarkable increase in foam cell sizes from mesoscopic to macroscopic dimensions upon swelling the self-assembled template with oil. The resultant structures resemble classical macroscopic soap foams and display, among other features, Plateau borders and volume fractions approaching the dry limit of 100%. In well-developed foams of this kind, dimensionally isometric polyhedral cells are connected by relatively short, flat cylindrical mesopores through polyhedral faces and micropores through the walls. For one sample, with approximately 75 nm diameter primary foam cells, we infer three separate sets of cell-connecting mesopores puncturing tetragonal, pentagonal, and hexagonal faces of the component polyhedra. A multiple step model of foam formation is discussed where an organic silica precursor progressively hydrolyzes and condenses as a growing flexible shell from the core-corona interface of oil-swollen triblock copolymer micelles or microemulsion droplets, inducing a clouding phenomena in the otherwise stabilizing poly(ethylene oxide) chains, leading to aggregation, deformation, and jamming to high volume fractions.

  • 47.
    Corkery, Robert W.
    et al.
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Rousseau, Derick
    chool of Nutrition, Ryerson University, Toronto, Ontario, Canada.
    Smith, Paul
    YKI, Institute for Surface Chemistry, Stockholm, Sweden.
    Pink, David A.
    Department of Physics, St. Francis Xavier University, Antigonish, Nova Scotia, Canada.
    Hanna, Charles B.
    Canada, and Department of Physics, Boise State University, Boise, Idaho, USA.
    A case for discotic liquid crystals in molten triglycerides2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 13, 7241-7246 p.Article in journal (Refereed)
    Abstract [en]

    To date, essentially only two structural models have been proposed and debated in detail for explaining the liquid state order of triglycerides, and both invoke a form of thermotropic liquid crystalline order in triglyceride melts. These are the paralamellar model of Larsson et al. (J. Am. Oil Chem. Soc. 1992, 69, 835) and the nematic model of Cebula et al. (J. Am. Oil Chem Soc. 1992, 69, 130). An alternative discotic model is proposed here that adequately accounts for the broad small-angle X-ray diffraction peak often observed in the liquid state of fats and oils. In this alternative model, triglyceride molecules exist in the liquid state with fully splayed chains, approximating "Y"-shapes (Y-conformers). These are loosely bound within discs that stack into flexible, relatively short cylindrical rods of colloidal dimension, which in turn assemble into rod-packings with short-range order akin to disordered versions of thermotropic discotic liquid crystalline phases in other lipidic systems.

  • 48.
    Cranston, Emily D.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Gray, Derek G.
    Rutland, Mark W.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Direct Surface Force Measurements of Polyelectrolyte Multi layer Films Containing Nanocrystalline Cellulose2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 22, 17190-17197 p.Article in journal (Refereed)
    Abstract [en]

    Polyelectrolyte multilayer films containing nanocrystalline cellulose (NCC) and poly(allylamine hydrochloride) (PAH) make up a new class of nanostructured composite with applications ranging from coatings to biomedical devices. Moreover, these materials arc amenable to surface force studies using colloid-probe atomic force microscopy (CP-AFM). For electrostatically assembled films with either NCC or PAH as the outermost layer, surface morphology was investigated by A FM and wettability was examined by contact angle measurements. By varying the surrounding ionic strength and pH, the relative contributions from electrostatic, van der Waals, steric. and polymer bridging interactions were evaluated. The ionic cross-linking in these films rendered them stable under all solution conditions studied although swelling at low pH and high ionic strength was inferred. The underlying polymer layer in the multilayered film was found to dictate the dominant surface forces when polymer migration and chain extension were facilitated. The precontact normal forces between a silica probe and an NCC-capped multilayer film were monotonically repulsive at pH values where the material surfaces were similarly and fully charged. In contrast, at pH 3.5, the anionic surfaces were weakly charged but the underlying layer of cationic PAH was fully charged and attractive forces dominated due to polymer bridging from extended PAH chains. The interaction with an anionic carboxylic acid probe showed similar behavior to the silica probe; however, for a cationic amine probe with an anionic NCC-capped Film, electrostatic double-layer attraction at low pH, and electrostatic double-layer repulsion at high pH, Were observed. Finally, the effect or the capping layer was studied with an anionic probe, which indicated that NCC-capped films exhibited purely repulsive forces which were larger in magnitude than the combination of electrostatic double-layer attraction and steric repulsion. measured for PAH-capped films. Wherever possible, DLVO theory was used to fit the measured surface forces and apparent surface potentials and surface charge densities were calculated.

  • 49.
    Cunha, Gisera
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. INRA, Biopolymeres Interact & Assemblages, France.
    Mougel, Jean-Bruno
    Cathala, Bernard
    Berglund, Lars A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Capron, Isabelle
    Preparation of Double Pickering Emulsions Stabilized by Chemically Tailored Nanocelluloses2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 31, 9327-9335 p.Article in journal (Refereed)
    Abstract [en]

    Nanocelluloses are bio-based nanoparticles of interest as stabilizers for oil-in-water (o/w) Pickering emulsions. In this work, the surface chemistry of nanocelluloses of different length, nanofibrillated cellulose (NFC, long) and cellulose nanocrystals (CNC, short), was successfully tailored by chemical modification with lauroyl chloride (C12). The resulting nanofibers were less hydrophilic than the original and able to stabilize water-in-oil (w/o) emulsions. The combination of the two types of nanocelluloses (C12-modified and native) led to new surfactant-free oil-in-water-in-oil (o/w/o) double emulsions stabilized by nanocellulose at both interfaces. Characterization was performed with respect to droplet size distribution, droplet stability over time, and stability after centrifugation. Nanocellulose-based Pickering emulsions can be designed with a substantial degree of control, as demonstrated by the stability of the chemically tailored NFC double emulsions. Furthermore, it was demonstrated that increased nanofiber length leads to increased stability.

  • 50.
    Dedinaite, Andra
    et al.
    KTH, Superseded Departments, Chemistry.
    Campbell, B.
    Interactions between mica surfaces across triglyceride solution containing phospholipid and polyglycerol polyricinoleate2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, no 5, 2248-2253 p.Article in journal (Refereed)
    Abstract [en]

    Results obtained by direct measurements of the forces acting between polar mica surfaces interacting across solutions of triolein containing phosphatidylethanolamine (PE), polyglycerol polyricinoleate (PGPR), and a PE/PGPR mixture are presented. It was shown that PE adsorbed on mica from anhydrous triolein and thus rendered the surface nonpolar. The change in ordering of the liquid triolein molecules induced by bringing two such surfaces together gives rise to a structural force with two force barriers. In contrast, the adsorption of PGPR from anhydrous triolein resulted in a steric force barrier with a range of 120 Angstrom. It was also found that from the mixture of PE and PGPR in triolein both additives adsorbed as a complex on mica surfaces. The presence of these aggregates on the surfaces gave rise to a very long-range strong repulsive force. We discuss the implication of the measured forces to colloidal stability of particle dispersion in nonpolar media and compare the efficiency of additives as dispersion stabilizers. We also show that the presence of water has an effect on the adsorbed layer structures. When PE is used as a dispersing agent, water induces formation of aggregates, which would provide strong repulsive barriers between the particles. In contrast, when PGPR is used as additive, water preferentially adsorbs on the polar mica surface and at water saturation gives rise to a capillary formation around the surface contact position. Finally, when a mixture of PE and PGPR is used, water is found to result in formation of a viscous, sticky, adsorbed layer that would flocculate the particles.

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