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  • 1. Ata, S.
    et al.
    Pugh, Robert
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Jameson, G. J.
    The influence of interfacial ageing and temperature on the coalescence of oil droplets in water2011In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 374, no 1-3, p. 96-101Article in journal (Refereed)
    Abstract [en]

    Understanding the coalescence behaviour of two single droplets of industrial kerosene oil is an important precursor for predicting the stability of a concentrated kerosene emulsion system. In taking such an approach, distinct differences in the dynamic coalescence of fresh and aged binary droplets of analytical and technical grade kerosene was observed which we believe to be important with regard to the stability of concentrated systems. It was shown from induction time measurements (the time from first contact to rupture of the thin film separating the droplets) that the analytical grade kerosene binary droplets are considerable more stable than the technical grade at higher temperature (up to 65 degrees C) but the analytical grade shows a gradual decrease in stability up to 65 degrees C. At 75 degrees C, both grades of kerosene droplets remained stable to coalescence. After this initial rupture, coalescence proceeded as a series of dynamic oscillations and further insight into the fusion behaviour could be obtained by analysis of the change in the surface area of the aggregated droplets as a function of time. The longer induction times correlated with the more vigorous post rupture oscillations (less damping resulting from an increase in interfacial elasticity) which were recorded during the drop fusion. These experiments reveal preliminary steps in the coalescence of oil droplets where measurements from first contact to final damped equilibrium are quantified. This aspect of coalescence has not been well represented in the earlier literature. (C) 2010 Elsevier B.V. All rights reserved.

  • 2.
    Bergström, Lars Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Influence of bending energetics on the size, shapeand polydispersity of droplet microemulsions2008In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 316, p. 15-26Article in journal (Refereed)
    Abstract [en]

    A theory for ellipsoidal shape fluctuating droplet microemulsions in the presence of excess discrete phase (Winsor I and II) is expounded that combines bending energetics of the amphiphilic monolayer at the droplet interface with thermodynamics of self-assembling solute and amphiphilic molecules. The theory relates the three bending elasticity constants spontaneous curvature (H0), bending rigidity (kc) and saddle-splay constant () with interfacial tension, average size and shape and polydispersity of microemulsion droplets. It is demonstrated that the well-known conventional relations become modified as the entropy of self-assembling amphiphilic as well as solute molecules are taken into account, in particular at low values of the effective bending constant . As a result, the average droplet radius 〈R〉 as well as the droplet polydispersity σR/〈R〉 behave consistently in the limit whereas the conventional expressions are recovered in the limit . It is demonstrated that association entropy effects may be quantified by a parameter kS with same dimension and order of magnitude as kc and . kS is found to be always negative and tends to decrease 〈R〉 and to increase σR/〈R〉. Moreover, the average axial ratio of an oblate/prolate fluctuating droplet is found to be a strong function of the bending rigidity (the droplets become increasingly non-spherical with decreasing kc) but is independent of , in contrast to previous investigations where association entropy effects were neglected.

  • 3.
    Blute, Irena
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Pugh, Robert J.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    van de Pas, John
    Callaghan, Ian
    Industrial manufactured silica nanoparticle sols. 2: Surface tension, particle concentration, foam generation and stability2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 337, no 1-3, p. 127-135Article in journal (Refereed)
    Abstract [en]

    Several earlier papers have revealed that several key parameters, such as hydrophobicity (contact angle), size, shape and degree of agglomeration, have an important influence on the behavior of particles at the air/water interface. However, the origin of foaming with particles is still not clear. In this article, we have tentatively related surface tension measurements and particle concentrations to the generation and stability of foam produced from industrial manufactured silica nanoparticle sols. Surprisingly, only slight reductions in surface tension were observed and the differences between the hydrophophilic and partially modified hydrophobic sols were small. However, in the case of the partially modified hydrophobic sol, the surface tension/concentration gradient was found to be pH and concentration responsive. Also, the greatest reduction in Surface tension was found to occur at low pH (in the region of the pH(pzc)) and could be related to the highest foamability (foam generation) as determined in our earlier publication [1. Blute, R.J. Pugh, J. van de Pas, I. Callaghan, Silica nanoparticle sols. 1. Surface chemical characterization and evaluation of the foam generation (foamability), J. Colloid Interface Sci. 313 (2007) 645-655]. Also, after centrifugation of the moderately hydrophobic modified concentrated sols, foaming tests carried out on the supernatant indicated that the particle concentration had a dominant influence on foamability and foam stability. Since only transient foams, with relatively short lifetimes, could be produced with these modified silica nanoparticles then (a) further surface modification or the reduction of pH to increase the Surface activity or (b) the addition of a cosurfactant Would be needed to increase the foamability and achieve foams with extended lifetimes.

  • 4.
    Bodvik, Rasmus
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Dédinaité, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Karlson, Leif
    Bergström, Lars Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Baverback, Petra
    Pedersen, Jan Skov
    Edward, Katarina
    Karlsson, Göran
    Varga, Imre
    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 and network formation of aqueous methylcellulose and hydroxypropylmethylcellulose solutions2010In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 354, no 1-3, p. 162-171Article in journal (Refereed)
    Abstract [en]

    Solution properties of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) have been investigated as a function of temperature and concentration using a broad range of experimental techniques. Novelties include the extensive comparison between MC and HPMC solutions as well as the combination of techniques, and the use of Cryo transmission electron microscopy (Cryo-TEM). The correlation between rheology and light scattering results clearly demonstrates the relation between viscosity change and aggregation. Cryo-TEM images show the network structures formed. Viscosity measurements show that for both MC and HPMC solutions sudden changes in viscosity occur as the temperature is increased. The onset temperature for these changes depends on polymer concentration and heating rate. For both MC and HPMC solutions the viscosity on cooling is very different compared to on heating, demonstrating the slow equilibration time. The viscosity changes in MC and HPMC solutions are dramatically different; for MC solutions the viscosity increases by several orders of magnitude when a critical temperature is reached, whereas for HPMC solutions the viscosity decreases abruptly at a given temperature, followed by an increase upon further heating. Light and (SAXS) small-angle X-ray scattering shows that the increase in viscosity, for MC as well as for HPMC solutions, is due to extensive aggregation of the polymers. Light scattering also provides information on aggregation kinetics. The SAXS measurements allow us to correlate aggregation hysteresis to the viscosity hysteresis, as well as to extract some structural information. Cryo-TEM images give novel information that a fibrillar network is formed in MC solutions, and the strong viscosity increase occurs when this network spans the whole solution volume. For HPMC solutions the behaviour is more complex. The decrease in viscosity can be related to the formation of compact objects, and the subsequent increase to formation of fibrillar structures, which are more linear and less entangled than for MC.

  • 5.
    Cozzolino, Carlo A.
    et al.
    University of Sassari.
    Blomfeldt, Thomas
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Nilsson, Fritjof
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Piga, Antonio
    University of Sassari.
    Piergiovanni, Luciano
    Farris, Stefano
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
    Dye release behavior from polyvinyl alcohol films in a hydro-alcoholic medium: Influence of physicochemical heterogeneity2012In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 403, p. 45-53Article in journal (Refereed)
    Abstract [en]

    In this paper we investigated the release kinetics of a model drug-like compound (Coomassie brilliant blue) from polyvinyl alcohol (PVOH) films into a hydro-alcoholic solution as a function of the physicochemical properties of the polymer matrix. After 33 days of monitoring, the total amount released ranged from 10% for the high hydrolysis degree/low molecular weight PVOH films to 60% for the low hydrolysis degree/low molecular weight films. Mathematical modeling allowed for an estimation of the two diffusion coefficients (D 1 and D 2) that characterized the release profile of the dye from the films. The degree of hydrolysis dramatically affected both the morphology and the physical structure of the polymer network. A high hydroxyl group content was also associated with the shifting of second order and first order transitions toward higher temperatures, with a concurrent increase in crystallinity. Moreover, the higher the degree of hydrolysis, the higher the affinity of the polymer to the negatively charged molecule dye. Selection of the polymer matrix based on physicochemical criteria may help in achieving different release patterns, thereby representing the first step for the production of polymer systems with modulated release properties.

  • 6. Dutta, Joydeep
    et al.
    Hofmann, H.
    Houriet, R.
    Hofmeister, H.
    Hollenstein, C.
    Growth, microstructure and sintering behavior of nanosized silicon powders1997In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 127, no 1-3, p. 263-272Article in journal (Refereed)
  • 7.
    Enarsson, Lars-Erik
    et al.
    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.
    Carlén, Joakim
    Eka Chemicals AB.
    Ottosson, Niklas
    VTC Elastoteknik AB.
    Tailoring the chemistry of polyelectrolytes to control their adsorption on cellulosic surfaces2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 340, no 1-3, p. 135-142Article in journal (Refereed)
    Abstract [en]

    The adsorption of two types of cationic polyacrylamides in the presence of a background electrolyte was studied on substrates including silicon oxide, kraft pulp fibres and thin films of regenerated cellulose. One of the polyelectrolytes was a conventional cationic polyacrylamide (MeCPAM) and the other was a benzyl-containing derivative of cationic polyacrylamide (BzCPAM). It was found that the aromatic substituents of BzCPAM strongly enhanced the adsorption on substrates of hydrophobically modified silicon oxide when a background electrolyte was present. A similar effect was also seen in the case of BzCPAM adsorption on unbleached pulp fibres, but in this case MeCPAM also exhibited a strong adsorption at high background electrolyte concentrations. On bleached pulp fibres, BzCPAM maintained a high adsorption up to a concentration of 100 mM NaCl whereas MeCPAM adsorption showed a significant decrease at this salt concentration. On model cellulose films, the adsorption of BzCPAM was similar to that of MeCPAM and the non-ionic interactions with cellulose appeared weak, since there was no adsorption of either polyelectrolyte in 300 mM NaCl.

  • 8. Engqvist, C.
    et al.
    Forsberg, S.
    Norgren, Magnus
    Edlund, H.
    Andreasson, B.
    Karlsson, O.
    Interactions between single latex particles and silica surfaces studied with AFM2007In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 302, no 03-jan, p. 197-203Article in journal (Refereed)
    Abstract [en]

    The spreading of single styrene-acrylic latex particles on silicon oxide C surfaces was studied using atomic force microscopy (AFM). Three latexes with different glass transition temperature (Tg) were used and the effects of temperature, time and preparation method were investigated. Particle sizes and shape were measured with AFM and the contact angles were calculated. The observed rate for the spreading of latex particles was low and it took several days before the particles reached steady state, even at temperatures well above their T-g. The experimental particle spreading results deviated with two orders of magnitude from predictions Using the WLF equation for polymer diffusion. The deviation could be attributed to polymer-surface interactions that slowed down the particle spreading. The work of adhesion was calculated using two models. The results from using the regular Young-Dupre equation and a modified version of this equation that also included the mechanical properties (E-modulus and Poisson's ratio) of the latexes, were compared. For soft latex particles the results from the two models agreed well and were of the order of 75 J/m(2), but for glassy latexes the Young-Dupre equation underestimated the work of adhesion.

  • 9. Eriksson, Jan Christer
    et al.
    Henriksson, Ulf
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Kumpulainen, Atte
    Hydrophobic attraction forces in asymmetric aqueous films between hydrophobized mica/bare mica surfaces2006In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 282, p. 79-83Article in journal (Refereed)
    Abstract [en]

    The water-structure-based, quasi-thermodynamic theory published several years ago of hydrophobic interaction forces in symmetric aqueous films [J.C. Eriksson, S. Ljunggren, P.M. Claesson, J. Chem. Sec., Faraday Trans. 2 (85) (1989) 1631 has been generalized to encompass asymmetric films between, e.g. a hydrophobized mica surface and a bare mica surface. The interaction pressures derived on this basis are in good agreement with the experimental data recorded by Claesson et al. [P.M. Claesson, P.C. Herder. C.E. Blom, B.W. Ninham. J. Colloid Interface Sci. 118 (1987) 68]. Hence, additional support is gathered for the original claim that the hydrophobic attraction is related with hydrogen-bond-dependent cluster formation processes in water contacted with a hydrophobic solid Surface.

  • 10. Gernandt, Renate
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gärdlund, L.inda
    Dautzenberg, Herbert
    Polyelectrolyte complexes for surface modification of wood fibres - I. Preparation and characterisation of complexes for dry and wet strength improvement of paper2003In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 213, no 1, p. 15-25Article in journal (Refereed)
    Abstract [en]

    Polyelectrolyte complexes (PEC) were formed between a cationic polyamideamine epichlorohydrine condensate (PAE) and an anionic carboxymethylcellulose (CMC) at different ratios between the polymers, orders of mixing, salt concentrations and polymer concentrations. Initially the polymers were characterised by polyelectrolyte titration (charge), static light scattering (molecular weight, radius of gyration) and measurements with a scanning interferometric refractometer (refractive index). The complexes were characterised by ocular inspection and static light scattering in combination with a special evaluation algorithm allowing an estimation of the geometric form of the complexes. The results show that the initial complexes have a spherical form and that the size is fairly constant over a large range of charge ratios between the polymers, provided the complexes are formed in deionised water. When the charge mixing ratio exceeded neutrality a secondary agglomeration of the initially formed complexes occurred. The presence of salt during PEC formation caused a dependence of the level of aggregation on the mixing ratio, whereby small amounts of NaCl drastically lowered the particle mass at lower mixing ratios. Subsequent addition of salt to PECs formed in water led to a strong swelling of the complex particles and at a critical salt concentration to dissolution.

  • 11. Glomm, Wilhelm R.
    et al.
    Ese, Marit-Helen Glomm
    Volden, Sondre
    Pitois, Claire
    Hult, Anders
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Sjoblom, Johan
    Europium(III)-cored fluorinated dendrimers at the air-water surface2007In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 299, no 03-jan, p. 186-197Article in journal (Refereed)
    Abstract [en]

    A series of lanthanide (Eu3+) cored fluorinated dendrimers of generations I through 4 (G1-G4) have been studied with respect to their film-forming properties at the air-water surface. All dendrimers studied here formed stable films at the air-water surface. At the air-water surface, the dendrimers are likely to adopt asymmetric funnel-like conformations wherein the lanthanide core is directed towards the water surface and the fluorinated phenyl groups are directed away from the bulk phase. This hypothesis was further tested by addition of an electrolyte (0.01 M MgSO4) to the subphase. The added electrolyte was found to (i) advance the onset of network formation, as well as completion of monolayers, and (ii) increase the collapse pressure. Both features support the asymmetric conformation hypothesis, in that addition of an electrolyte promotes further conformational changes and shields electrostatic repulsion between lanthanide cores, thus allowing for closer packing of the molecules.

  • 12.
    Gustafsson, Emil
    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.
    Larsson, Per A.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    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.
    Treatment of cellulose fibres with polyelectrolytes and wax colloids to create tailored highly hydrophobic fibrous networks2012In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 414, p. 415-421Article in journal (Refereed)
    Abstract [en]

    Paper is a versatile material with obvious advantages in being both inexpensive and environment friendly. However, a major drawback compared with many other materials, such as plastics, is that it is sensitive to both liquid water and moist air. Traditionally paper is protected from liquid water by sizing. The present work presents a new way to make paper water resistant by combining the layer-by-layer (LbL) technique with the adsorption of a colloidal wax onto the multilayer structure. After the adsorption of five layers of poly(allylamine hydrochloride) and poly(acrylic acid) followed by the adsorption of 8. mg paraffin wax per gram fibre, the contact angle measured 60. s after a drop of water was applied to the sheet was about 138°. If the sheets were cured for 30. min at 160. °C after sheet making, the contact angle was ca. 150°. The heat treatment of sheets prepared from LbL-modified fibres without the addition of wax gave a contact angle of about 113°. To decouple structural effects from changes in surface energy upon heat treatment of PAH/PAA LbL films, model experiments were carried out where LbL assemblies were prepared on silicon oxide and cellulose model surfaces. The contact angle increased when these films were heat treated but it did not exceed 90°. The reason for this is due to the lack of structure of the model surfaces on a micrometre scale. The adsorption of wax impaired the mechanical properties of paper sheets made from modified fibres compared to sheets from the LbL-modified fibres. However, at an adsorption of 8. mg paraffin wax per gram fibre there was still an increase by 37 ± 1% in tensile strength index compared to the untreated reference pulp (33.8 ± 0.7 and 24.7 ± 0.6. kNm/kg respectively).

  • 13. Gärdlund, Linda
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Gernandt, Renate
    Polyelectrolyte complexes for surface modification of wood fibres II. Influence of complexes on wet and dry strength of paper2003In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 218, no 1-3, p. 137-149Article in journal (Refereed)
    Abstract [en]

    The current paper presents a way of enhancing paper strength by the use of polyelectrolyte complexes (PEC) of cationic poly(amideamine) epichlorohydrin condensate (PAE) and anionic carboxymethylcellulose (CMC). In this study the complexes were pre-formed in different mixing ratios, but with an overall anionic charge. The complexes were characterized by means of size, charge, and adsorption properties both to fibres and to model silica surfaces. Finally the PECs were applied as strength additive in paper sheet preparation. The main findings are that by changing polymer weight-ratios when preparing the complexes the charge and the amount adsorbed could be altered. Addition of the complexes to the fibres before sheet preparation led to a significant increase in strength of the paper, compared to sheets prepared with only the PAE. The strength improvement depended upon the mixing ratio and a maximum in dry strength was found for complexes where the anionic charge of the CMC had been neutralized to 60%.

  • 14.
    Johansson, Erik
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    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.
    Tailoring the mechanical properties of starch-containing layer-by-layer films2012In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 394, p. 14-22Article in journal (Refereed)
    Abstract [en]

    The Young's modulus of layer-by-layer (LbL) films containing starch was determined using the recently developed SIEBIMM (strain-induced elastic buckling instability for mechanical measurements) technique. By using cationic starch (CS) in combination with anionic starch (AS), silica nanoparticles (SNP), and nanofibrillated cellulose (NFC), the mechanical properties of these sub-micrometer starch-containing LbL films could be tailored. At 50% relative humidity (RH), the Young's modulus of CS/AS, CS/SNP, and CS/NFC was 0.6 GPa, 0.9 GPa, and 1.8 GPa, respectively, in the 25-85-nm thickness range. As expected for these hygroscopic starch-containing LbL films, the mechanical properties depended on RH. At 0% RH, the Young's modulus was 2-4.5 times higher than at 50% RH. The LbL buildup on polydimethylsiloxane (PDMS) was studied in situ using quartz crystal microgravimetry with dissipation (QCM-D), and atomic force microscopy (AFM) was used to characterize the surface morphology and thickness of the films.

  • 15.
    Khan, Abdullah
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Redelius, Per
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Kringos, Nicole
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Toward a new experimental method for measuring coalescence in bitumen emulsions: A study of two bitumen droplets2016In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 494, p. 228-240Article in journal (Refereed)
    Abstract [en]

    Cold mix asphalt (CMA) emulsion technology could become an attractive alternative for the road industry due to low startup and equipment installation costs, diminished energy consumption and reduced environmental impact. The performance of cold asphalt mixtures produced from emulsions is strongly influenced by a good control of the breaking and coalescence process. The wetting of bitumen on the surface of the aggregates is hereby of major importance for the performance of the asphalt. Premature coalescence of the bitumen emulsions away from the surface, could lead to poor adhesion and decreased mechanical strength of the asphalt. Today, the breaking and coalescence mechanisms of bitumen emulsions are still not fully understood due to their complexities and the lack of fundamental experimental methods and existing models. However, in the past years efforts have been made in defining relationships for understanding the bitumen emulsions. In this paper, a new experimental method is presented to study coalescence of bitumen by using shape relaxation of bitumen droplets in an emulsion environment. The coalescence of spherical droplets of different bitumen have been correlated with neck growth, densification and surface area change during the coalescence process. The test protocol was designed in a controlled climate chamber, to study the coalescence process with varying environmental conditions. The kinetics of the relaxation process was influenced by the temperature as well as other parameters. The research showed that the developed test procedure is repeatable and able to study the coalescence process on a larger scale. However, the relationship between the measured parametric relationships at the larger scale and the bitumen emulsion scale still needs further investigation.

  • 16.
    Koivula, Hanna
    et al.
    Åbo Akademi University.
    Kamal Alm, Hajer
    Innventia AB, Sweden.
    Toivakka, Martti
    Åbo Akademi University.
    Temperature and moisture effects on wetting of calcite surfaces by offset ink constituents2011In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 390, p. 105-111Article in journal (Refereed)
    Abstract [en]

    Offset printability is influenced by interactions between ink constituents: linseed oil, mineral oil and water (fountain solution), with the mineral surfaces of paper coatings. To exclude complications of the porous structure effects, the influence of temperature and moisture on wetting by offset ink model liquids were studied on cleaved optical calcite surfaces with and without sodium polyacrylate dispersant. Contact angle measurement was chosen as the method of analysis. The results show that a moderate temperature increase from 25 °C to 60 °C, which might occur in the process, does not affect the wetting of these surfaces by mineral oil. Water and linseed oil are affected by the transport of moisture at the surfaces as an indirect consequence of temperature increase. The linseed oil behavior was found to be sensitive to polarity changes of the surfaces.

  • 17.
    Li, Xin
    et al.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Jiang, Li
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Zhan, Q. Q.
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Qian, Junling
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    He, Sailing
    KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Localized surface plasmon resonance (LSPR) of polyelectrolyte-functionalized gold-nanoparticles for bio-sensing2009In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 332, no 2-3, p. 172-179Article in journal (Refereed)
    Abstract [en]

    Gold-nanoparticles can be used as a robust tool for bio-sensing based on localized surface plasmon resonance (LSPR). Both local refractive index change and self-assembly of the nanoparticles can lead to some spectral shifts of the LSPR extinction peak. Using different mechanisms of LSPR peak shifts, two types of transducers are set up to detect the streptavidin concentration through the specific recognition with biotin moleculars, which are conjugated to gold-nanoparticles. One is based on the self-assembly of gold-nanoparticles in Solution, and the other is based on the increase of the local refractive index near the surface of the immobilized gold-nanoparticles after streptavidin-biotin binding. The sensitivity and efficiency of the two transducers are compared. Gold-nano particles are functionalized with polyelectrolyte, which can improve significantly the stability of the nanoparticles and reduce the unspecific binding of streptavidin. Polyelectrolyte functionalization also provides a simple way to conjugate gold-nanoparticles with charged molecules such as biotin and BSA-biotin.

  • 18.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Permeability and expansibility of sodium bentonite in dilute solutions2010In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 358, no 1-3, p. 68-78Article in journal (Refereed)
    Abstract [en]

    In developing the dynamic force balance model for colloidal expansion, it was acknowledged that accurate description of the viscous drag force, or equivalently the permeability, is very important to describe the swelling process of compacted bentonite as it expands and eventually turns from a gel into a sol in low ionic strength waters. We therefore developed a Kozeny-Carman-like equation to quantify the permeability of the purified and fully Na-exchanged bentonite in dilute homoionic solutions, based on a set of permeability measurements. The force balance model, together with a friction model derived from the permeability, is then validated against accurate observations of the expansion process of the Na-exchanged bentonite in a water filled vertical test tube. The expansion is followed in detail over a month, by use of the magnetic resonance imaging technique with a spatial resolution of 0.2 mm. as an initially compacted tablet of Na-bentonite expands in water. The model accurately predicts not only the expansion rate and the general features of the expansion but also the basic behaviour at the expanding gel/sol interface. In addition, the use of the developed Kozeny-Carman-like equation substantiates that the expansion rate depends strongly on the friction of the particles against the water.

  • 19.
    Liu, Longcheng
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Prediction of swelling pressures of different types of bentonite in dilute solutions2013In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 434, p. 303-318Article in journal (Refereed)
    Abstract [en]

    A mechanistic model is developed to predict the swelling pressure of fully saturated, bentonite-based materials in distilled water or dilute saline solutions over a large range of final dry densities of bentonite. It applies a thermodynamic relationship between swelling pressure and suction to describe the contribution of crystalline swelling, while using a diffuse double-layer model to explain the behavior of osmotic swelling. In addition, it accounts for the demixing of exchangeable cations and the disintegration of the montmorillonite particles into small stacks of unit layers upon water uptake.Comparison of the model predictions with a great number of experimental results of swelling pressures of different types of bentonites and bentonite-aggregate mixtures in both distilled water and saline solutions suggests that the model works excellently in the cases tested. It is found that the water chemistry, the montmorillonite content, the type and amount of exchangeable cations in the interlayers are important in determining the extent to which the montmorillonite particles are delaminated and hence the swelling behavior of saturated, bentonite-based materials.On the other hand, the applicability of the model in predicting the water retention curves of unsaturated bentonites is also tested. The results show that the predicted curves are in good agreement with the measured data and that the montmorillonite particles are more difficult to disintegrate into small pieces in the case of unsaturated bentonites than would otherwise be possible.

  • 20.
    Liu, Longcheng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Neretnieks, Ivars
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Chemical Engineering.
    Homo-interaction between parallel plates at constant charge2008In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 317, no 1-3, p. 636-642Article in journal (Refereed)
    Abstract [en]

    Various approximate solutions to the Poisson-Boltzmann (PB) equation have been derived to describe the interaction of electric diffuse double layers adjacent to charged surfaces. However, all these expressions are case-specific and accurate only in limited ranges of particle separations. None can cover the entire range of plate separations and/or surface charge densities generally found in real systems. In this paper, we derive an approximate expression for the force between two parallel similar plates with constant surface charge densities in a symmetrical electrolyte solution, which agrees well with the rather complex exact analytical solution over a wide range of plate separations. The method used is based on the so-called "compression" approach developed previously for the case of low surface charge densities. The results are also in good agreement with "exact" numerical solutions over a wide range where no restriction is actually required on the magnitudes of the surface charge densities, surface potentials or the distance between the plates. Furthermore, an expression for the derivative of the force is also given, which is fairly simple and is very useful in modelling, e.g. colloidal transport problems based on a force balance on particles in a colloidal system. In such cases it is very impractical to use either the exact analytical or numerical solution to the PB,equation.

  • 21.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Bergström, Lars Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Dedinaite, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Trapped non-equilibrium states in aqueous solutions of oppositelycharged polyelectrolytes and surfactants: effects of mixing protocoland salt concentration2005In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 253, no 1-3, p. 83-93Article in journal (Refereed)
    Abstract [en]

    The very slow equilibration time in oppositely charged systems makes it necessary to control not only the concentration of the species but also the details of the mixing process. This has been demonstrated for processes occurring at interfaces where order of addition effects can be of great importance. In this investigation we set out to study the bulk properties of aqueous mixtures of a highly charged cationic polyelectrolyte mixed with an anionic surfactant with the aim to learn if long-lived non-equilibrium states were formed also in this case, and thus if the details of the mixing procedure would affect the structure of the aggregates formed. For simplicity we chose two mixing protocols, denoted “PTS” and “STP”. In the PTS-method the polyelectrolyte is added to the surfactant solution whereas in the STP-method the surfactant is added into the polyelectrolyte solution. The properties of the mixtures in aqueous solutions, with different NaCl concentrations and as a function of time, were followed by conducting turbidity, electrophoretic mobility and dynamic light scattering measurements. The results demonstrate that the mixing protocol indeed has a great impact on the size of the aggregates initially formed and that this size difference persists for long times. Hence, trapped non-equilibrium states do play an important role also in the bulk solution. We found that in excess surfactant solutions the smaller aggregates formed by the STP-method are more resistant than the larger ones formed by the PTS-method to colloidal instability induced by electrolytes (NaCl). Based on our results we suggest that for producing small and stable polyelectrolyte–surfactant aggregates in systems with excess surfactant, the surfactant should be added last, while the opposite should be applied for systems with excess polyelectrolyte.

  • 22. Norgren, Magnus
    et al.
    Edlund, H.
    Stabilisation of kraft lignin solutions by surfactant additions2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 194, no 03-jan, p. 239-248Article in journal (Refereed)
    Abstract [en]

    The colloidal stability of kraft lignin (KL) and some various KL-surfactant mixtures in aqueous alkaline solutions, pH 10.0-11.50, was tuned and investigated at high ionic strengths, 0.5-1.1 M, and elevated temperatures, 70 and 150 degreesC. The main techniques used were Quasi-Elastic Light-Scattering (QELS) and turbidity measurements, together with sample inspection by the naked eye. Samples without surfactant additions and samples containing various alkyl sulfonates showed a comparably low colloidal stability, whereas in mixtures containing sodium salts of bile acids, the stability was found greatly improved. The efficiency of different bile salts was investigated and it was found that the overall best solution stability is obtained in mixtures of KL and sodium taurodeoxycholate (STDC). STDC showed a relatively good stabilising effect also at very high temperatures (150 degreesC). Furthermore, in already aggregated KL solutions, additions of STDC were found to cause 'de-aggregation' and the number of formed aggregates was dramatically decreased. From the outcome of the investigation, it can be concluded that by introducing surfactants, and maybe other designed additives too, new possibilities in controlling the colloidal stability of KL at rough solution conditions are given.

  • 23. Norgren, Magnus
    et al.
    Edlund, H.
    Wågberg, Lars
    Lindström, B.
    Annergren, G.
    Aggregation of kraft lignin derivatives under conditions relevant to the process, part I: phase behaviour2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 194, no 03-jan, p. 85-96Article in journal (Refereed)
    Abstract [en]

    Aggregation of a commercial, polydisperse softwood kraft lignin (Indulin AT) in diluted aqueous alkaline solutions was investigated experimentally, by means of turbidity measurements. The influence of temperature, salt concentration and pOH and the role of a divalent counterion on the aggregation behaviour were studied. When the temperature was increased, an increased tendency of aggregation in samples containing high concentrations of sodium chloride was found. Phase separation could be detected even at pOH = 2 at 175 degreesC and the effect was pronounced when the concentration of hydroxide ions decreased. The phase transition from soluble to precipitated lignin was found to be irreversible concerning temperature change. Small amounts of calcium ions were seen to induce dramatic effects on the system stability, even at relatively high hydroxide concentrations (pOH 1-2). At a given temperature and pOH, the coagulation was found to appear at a certain critical coagulation concentration (CCC) of the added electrolyte. Furthermore, calculations were carried out to compare with the outcome of the experimental observations. A theoretical model, based on the DLVO theory, was found to predict the kraft lignin solution behaviour well.

  • 24.
    Oko, Asaf
    et al.
    SP Technical Research Institute of Sweden - Chemistry, Materials and Surfaces, Sweden .
    Swerin, Agne
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden - Chemistry, Materials and Surfaces, Sweden .
    Brandner, Birgit D.
    Bugner, Douglas
    Cook, Wayne
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden - Chemistry, Materials and Surfaces, Sweden .
    Aggregation of inkjet ink components by Ca and Mg ions in relation to colorant pigment distribution in paper2014In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 456, p. 92-99Article in journal (Refereed)
    Abstract [en]

    Papers coated with salts containing divalent cations exhibit superior inkjet print quality, which has been suggested to be due to fast aggregation of the colorant pigments close to, or even on, the surface of the paper. In this work we show the pivotal role of the carboxylic acid containing dispersing polymer. We report a series of aggregation and sedimentation experiments with commercial inks, generic ink formulations and specific ingredients comprising these formulations, and find differences in their response to the presence of MgCl2 or CaCl2. In particular, flocs and sediments formed in the presence of MgCl2 are denser than those formed in the presence of CaCl2. These differences are not predicted by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. We suggest that ion specific interactions occurring between Mg2+ or Ca2+, and charged carboxylate groups residing on the dispersing polymers, provoke the observed behavior.

  • 25.
    Persson, Clas Marcus
    et al.
    KTH, Superseded Departments, Chemistry.
    Kumpulainen, Atte J.
    KTH, Superseded Departments, Chemistry.
    Surface forces measured in sugar surfactant solutions between two hydrophobic thiolated silica spheres2004In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 233, no 1-3, p. 43-49Article in journal (Refereed)
    Abstract [en]

    The force acting between two hydrophobic surfaces (hexadecyl-thiolated gold surfaces) across two different non-ionic sugar surfactant solutions above cmc was investigated. The two surfactants studied were n-decyl-beta-D-glucopyranoside (Glu) and n-decyl-beta-D-maltopyranoside (Mal). No long-range double-layer force was detected between the surfactant covered surfaces showing that they are non-ionic as expected. At distances from 20 nm down to a separation of 3 nm the ever-present van der Waals force creates a net attraction between the surfaces. At 3 nm the surfaces are in monolayer-monolayer contact and the system has a secondary force minimum. At shorter separations the surfactant monolayer starts to interact and a steric force develops counteracting the depletion of surfactants from the gap. As the compressive load reaches FIR approximate to 1.5 mN/m the surfaces are in hydrophobic-hydrophobic contact, where the system has its primary energy minimum. The nature of the pressure-induced depletion of surfactants from the contact zone showed a strong dependence on the approach velocity. This reveals that the time scale of the surfactants to reach their equilibrium situation under external compression is of several seconds. The surfactant with the glucoside head group offered a greater resistance against being forced out (15% higher). This was attributed to the larger adsorbed amount of Gin at the hydrophobic solid-liquid interface. It was further concluded that the forces generated from the surfactants were enough to prevent the system from coagulating but that flocculation will occur in the secondary force minimum (primary energy minimum). The hydrodynamic force was studied by changing the approach velocity of the surfaces. The position of the slipping plane coincided with the layer thickness of the adsorbed monolayer of surfactant at moderate approach velocities. The adhesion force increased with the time the surfaces were in contact and no limiting value was reached. This was attributed to surfactants remaining in the gap slowly being removed from the contact zone, thereby, increasing its hydrophobic character.

  • 26. Poptoshev, Evgeni
    et al.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Adsorption of dimethyldodecylamine-N-oxide at the mica-solution interface studied by ellipsometry2006In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 291, no 03-jan, p. 45-50Article in journal (Refereed)
    Abstract [en]

    The surface excess of dimethyldodecylamine-N-oxide (DDAO) surfactant at the mica-water interface has been determined using phase modulated ellipsometry. Surface excess versus bulk surfactant concentration isotherms were constructed at different pH values. The plateau adsorbed amount reaches a maximum in the pH range 6-7.5, which includes the native pH of DDAO solutions at the cmc (pH 7.5). At low pH values, where the surfactant is essentially cationic, the surface excess is reduced due to decrease of the mica surface charge, and due to that electrostatic repulsion between charged headgroups prevents formation of tightly packed surfactant bilayers. Adsorption from solutions at pH 9 also renders a lower plateau surface excess than that obtained at neutral pH. In this case the surfactant-substrate affinity is greatly reduced due to complete deprotonation of the headgroup of the surfactant in bulk solution. The results suggest that the degree of protonation of DDAO in the adsorbed layer differs from its bulk value. Close to the negatively charged mica surface the protonation of the headgroup is increased in order to adjust its charge to that of the surface, whereas the uncharged form is expected to be enriched in the outer part of the bilayer.

  • 27. Reverdy, C.
    et al.
    Belgacem, N.
    Moghaddam, M. S.
    Sundin, M.
    Swerin, Agne
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology. RISE Research Institutes of Sweden – Bioscience and Materials, Box 5607, Stockholm, Sweden.
    Bras, J.
    One-step superhydrophobic coating using hydrophobized cellulose nanofibrils2018In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 544, p. 152-158Article in journal (Refereed)
    Abstract [en]

    Superhydrophobic surfaces have high potential in self-cleaning and anti-fouling applications. We developed a one-step superhydrophobic coating formulation containing sodium oleate (NaOl), hydrophobized precipitated calcium carbonate and biobased cellulose nanofibrils (CNFs) hydrophobized with either alkyl ketene dimer (AKD) or amino propyl trimethoxy silane (APMS) as a binder to fix and distribute the particles. Coatings were made on paperboard and the wetting behavior of the surface was assessed. Static, advancing and receding contact angles with water as well as roll-off and water shedding angle were compared to coatings made with styrene butadiene latex as binder instead of CNFs. Modifications with alkyl ketene dimer showed most promising results for a viable process in achieving superhydrophobic paperboard but required reformulation of the coating with optimized and reduced amount of NaOl to avoid surfactant-induced wetting via excess NaOl. A static water contact angle of 150° was reached for the CNF-AKD. The use of CNFs enables the improvement of coating quality avoiding cracking with the use of nanocellulose as a renewable binder.

  • 28. Rundlöf, M.
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Formation of multilayers on silica surfaces of a cationic polyelectrolyte and dissolved and colloidal substances originating from mechanical wood pulp-Adsorption and influence on adhesion2004In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 237, no 03-jan, p. 33-47Article in journal (Refereed)
    Abstract [en]

    By measuring adsorption using a stagnation point reflectometer, it was shown that multilayers consisting of cationic polymers and dissolved and colloidal material released from wood fibres into process waters are formed on an anionic silica surface. The similarity of this experiment to the papermaking process was established. It was established using the JKR-method that this multilayer adsorption had a profound effect on the adhesion, in air, of an elastic polydimethyl siloxane (PDMS) probe to these surfaces. The adhesion of PDMS to a bare silica surface showed a large hysteresis, with a much stronger adhesion measured upon the separation of the two surfaces compared with the value obtained from gradually pressing them together. It was suggested that this hysteresis was due to specific interactions (hydrogen bonding) that develop over time. The first adsorbed layer, a cationic poly(dimethyldiallylammoniumchloride) (polyDMDAAC), decreased the magnitude of the hysteresis and gave a relatively low adhesion, which may be due to the fact that these specific interactions were blocked. The subsequent build up of layers of lipophilic wood extractives in the form of colloidal particles and cationic polymer increased the adhesion. This was interpreted as being due to the build up of a soft layer on the stiff mineral surface causing additional energy dissipation upon separation, even though the molecular adhesion was still decreased compared with the bare silica. This was supported by the fact that none of the individual components of the multilayer increased the adhesion when applied in a relatively thin layer on the silica, and by the fact that a thick deposition of cast coated wood extractives gave a very high adhesion. Stearic acid was chosen as a model substance for extractives and deposited onto silica from vapour phase. This resulted in a partial coverage of the surface where the stearic acid was present as patches of different size. This gave a significant reduction of the adhesion. The solid stearic acid melted and was redistributed when confined between the PDMS and the silica. This gave a thinner and more uniform layer. The application of a monolayer of C-18-tails covalently bound to the silica by siloxane links, gave a very significant reduction of the magnitude of the adhesion hystersis. It is concluded that the distribution of the contaminants over the surface is very significant for the adhesion properties. This is relevant to practical papermaking with respect to: (i) the build up of deposits on process equipment and its effect on adhesion to these surfaces; (ii) fibre-fibre adhesion and thereby paper strength, a phenomenon that can never be studied without directly measuring the adhesion, which makes specific solutions to the practical problems possible.

  • 29. Seppanen, R.
    et al.
    Ström, Göran
    Elftonson, J.
    Heteroflocculation of kaolin pre-treated with oppositely charged polyelectrolytes2000In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 164, no 2-3, p. 131-141Article in journal (Refereed)
    Abstract [en]

    Heteroflocculation studies of kaolin particles have been carried out by mixing two kaolin suspensions; one stabilised by a cationic polymer and the other stabilised by a highly charged and low molecular weight anionic polymer. Molar mass and charge density of cationic polymer as well as the mixing ratio of oppositely charged suspensions were varied. Flee size and degradation during shearing were investigated by measuring hoc size using a light scattering/diffraction method at different flow rates. It was observed that floc size was small when subjected to a low flow rate and decreased with increasing how rate. Cationic polymers with high molar mass and low charge density produced flocs with high resistance towards flee degradation. Maximum flee size was obtained at a mixing ratio where the flocs became slightly negatively charged. Flee size and degradation were observed to be independent of primary kaolin particle size. Furthermore, floc size increased with increasing ionic strength. Scanning electron micrographs showed flocs with an open structure, which is expected to improve the optical properties of paper when using microflocs as a filler in paper production.

  • 30. Siegel, G.
    et al.
    Meyer-Rath, G.
    Ermilov, E.
    Rodriguez, M.
    Malmsten, M.
    Claesson, Per
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Saunders, R.
    Hetzer, R.
    Lindman, B.
    Flow sensing in the cardiovascular system2015In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 480, p. 318-327Article in journal (Refereed)
    Abstract [en]

    Background: This contribution deals with chemical processes at the biological membranes of endothelial cells in blood vessels. A basic observation is that the intensity of blood flow navigates the vascular width through a negative feedback circle. When the blood flow increases, the vessels become wider; when it decreases the vascular smooth muscle cells contract. The anionic polyelectrolyte heparan sulfate proteoglycan (HS-PG) reacts to the shear stress generated by the flowing blood. In the present investigation, this naturally occurring biosensor is characterized in more detail, which is crucially involved in the regulation of peripheral blood flow and organ perfusion. A dysfunction of this sensor can lead to organ insufficiency, hypertension and arteriosclerosis.

  • 31. Solberg, D.
    et al.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    Adsorption and flocculation behavior of cationic polyacrylamide and colloidal silica2003In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 219, no 03-jan, p. 161-172Article in journal (Refereed)
    Abstract [en]

    The adsorption of cationic polyacrylamide and silica nanoparticle systems onto a model surface has been compared with the adsorption and flocculation of a fiber suspension. An increase in ionic strength affects the polyelectrolyte adsorption in different ways in these two systems. With a silica surface, an increase in the ionic strength leads to a continuous increase in the adsorption. On a cellulose fiber, the adsorption increases at low ionic strength (1-10 mM NaCl) and then decreases at higher ionic strength (10-100 mM NaCl). When polyelectrolyte is added to the fiber suspension, flocculation occurs with an optimum around a polyelectrolyte addition of 0.4 mg g(-1). Above this addition level the flocculation effect is reduced and dispersion occurs when more than 1.2 mg g(-1) polyelectrolyte is added. This behavior suggests a bridging flocculation, the dispersion being explained by electrosteric stabilization of the suspension. Addition of silica nanoparticles to the fiber suspension leads to a greater degree of flocculation than in a single polyelectrolyte system. The adsorption of nanoparticles to a polyelectrolyte-covered silica surface increases both the adsorbed amount and the thickness of the adsorbed film. A more extended silica particle, giving a more extended polyelectrolyte-silica film, also results in a higher degree of fiber flocculation.

  • 32.
    Swerin, Agne
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden-Chemistry, Materials and Surfaces, Sweden.
    Sundin, Mikael
    Wåhlander, Martin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
    One-pot waterborne superhydrophobic pigment coatings at high solids with improved scratch and water resistance2016In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 495, p. 79-86Article in journal (Refereed)
    Abstract [en]

    A pigment coating was developed to achieve superhydrophobicity in one step from a waterborne formulation containing aragonite calcium carbonate, hydrophobized using sodium oleate, latex binder and cross -linker. Coatings formulated <= 50 mass% and applied to polyethylene coated paperboard substrates displayed typical superhydrophobic features: water contact angles >= 150 degrees, low roll-off angle and low stain sizes, but poor scratch and water resistance as well as foaming issues during preparation. Reformulation at higher solids content significantly improved scratch and water resistance properties. Water rinsing of the dried coatings further increased the water barrier capacity due to reduced surfactant-assisted wetting; findings were corroborated by detailed surface chemistry analyses showing the removal of surface-active components after water rinsing of the dried coatings. A plausible cause for the improved durability is the fact that capillary forces increase exponentially with increasing pigment volume fraction (power law exponent of 2.2) leading to efficient binder coverage during the early stage of pigment coating consolidation.

  • 33.
    Thiyam, Priyadarshini
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway .
    Parsons, D. F.
    Huang, Dan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. College of Physical Science and Technology, China .
    Buhmann, S. Y.
    Bostrom, M.
    Trends of CO2 adsorption on cellulose due to van der Waals forces2015In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 470, p. 316-321Article in journal (Refereed)
    Abstract [en]

    The non-retarded van der Waals and Casimir-Polder forces on a CO2 molecule in water near a single surface and between surfaces are explored. We observe preferential adsorption and desorption of CO2 molecules depending on the material of the surfaces. We also find a potential mechanism of capture and storage of CO2 molecules in a geometry consisting of a cellulose surface coated by a thin film of water and then by air.

  • 34.
    Thormann, Esben
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Bodvik, Rasmus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Karlson, Leif
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Surface forces and friction between non-polar surfaces coated by temperature-responsive methylcellulose2014In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 441, p. 701-708Article in journal (Refereed)
    Abstract [en]

    Methylcellulose is a heterogeneous polymer that exposes both methyl groups and -OH-groups to the solution, and the solvent quality of water for methylcellulose deceases with increasing temperature. In bulk solution this leads to aggregation into fibrils at high temperatures. In this report we address how temperature affects adsorbed layers of methylcellulose on hydrophobized silica surfaces in contact with an aqueous methylcellulose solution. The layers were imaged using PeakForce tapping mode atomic force microscopy, in order to determine how the additional adsorption that occurs with increasing temperature affects the layer structure. Surface force and friction measurements were carried out using the AFM colloidal probe method. The data demonstrate that the normal surface forces were rather insensitive to temperature, whereas the friction forces changed significantly with increasing temperature. At low loads the friction increases with increasing temperature, whereas at high loads the reverse is observed. These findings are discussed in terms of how the worsening of the solvent condition affects the aggregation state in the adsorbed layer, and the polymer-surface affinity.

  • 35. Wallqvist, Viveca
    et al.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Swerin, Agne.
    Schoelkopf, J.
    Gane, P. A. C.
    Interaction forces between talc and hydrophobic particles probed by AFM2006In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 277, no 03-jan, p. 183-190Article in journal (Refereed)
    Abstract [en]

    The interaction between cleaved talc surfaces and hydrophobic probe particles, silanized silica and thiolized gold, has been investigated employing the atomic force microscopy (AFM) colloidal probe technique. These model systems have hydrophobicities similar to some of the talc-pitch combinations present during pulp and paper manufacture. The talc surfaces used in this study, in the [0 0 1] plane, show a micro-roughness with sharp peaks of up to 3 nm in height. The force profiles obtained demonstrate the predominance of a long-range attractive force. However, the range and magnitude of the attractive force show large variability. The variability of the attractive force, and the frequent observations of clear steps in the force curve demonstrate that it is caused by gas/vapor cavities bridging the Surfaces once the surfaces are brought sufficiently close together. The results suggest that the same mechanism is of importance in applications where talc is used as a collector for pitch.

  • 36.
    Yushmanov, Pavel V.
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Furó, Istvan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Stilbs, Peter
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
    Stopped-flow F-19 NMR studies of surfactant precipitation2006In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 291, no 1-3, p. 59-62Article in journal (Refereed)
    Abstract [en]

    The kinetics of the phase change in surfactant solutions is studied by F-19 stopped-flow NMR. In the aqueous solution of sodium perfluooctanoate, we observe precipitation and crystal growth induced by the addition of NaCl solution to the system. The time dependences of the NMR signal intensity and chemical shift, evaluated in the framework of a single model, narrow the range of possible scenarios, the most plausible of which is monomer incorporation into the growing crystals. In accordance to existing models of crystallization, both the nucleation rates and the crystal growth rates are strongly dependent on the magnitude of supersaturation.

  • 37. Zhang, Jinhong
    et al.
    Yoon, Roe-Hoan
    Eriksson, Jan Christer
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    AFM surface force measurements conducted with silica in C(n)TACl solutions: Effect of chain length on hydrophobic force2007In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 300, no 3, p. 335-345Article in journal (Refereed)
    Abstract [en]

    Surface forces were measured using an AFM with silica surfaces immersed in C(n)TACl (n = 12-18) solutions in the absence of added salt. The results showed long-range attractive forces that cannot be explained by the DLVO theory. The long-range attractions increased with increasing surfactant concentration, reaching a maximum at the point of charge neutralization (p.c.n.) and then decreased. The long-range forces decayed exponentially, with the decay lengths increasing from 3 to 32 run as the chain length of the surfactants increased from C-12 to C-18. The measured forces can be fitted to the charged-patch model of Miklavic et al. [S.J. Miklavic, D.Y.C. Chan, L.R. White, T.W. Healy, J. Phys. Chem. 98 (1994) 9022-9032] by assuming patch sizes that are much larger than the values reported in the literature. It was found that the decay length decreases linearly with the effective concentration of the CH2/CH3 groups of the C(n)TACl homologues raised to the power of -1/2, which is in line with the Eriksson et al.'s hydrophobic force model derived using a mean-field approach. It appears, therefore, that the long-range attractions observed in the present work are hydrophobic forces originating from changes in water structure across the thin surfactant solution film between the silica surfaces. It is conceivable that hydrocarbon chains in solution disrupt the surface-induced water structure and cause a decrease in hydrophobic force. This observation may also provide an explanation for the very long-range forces observed with silylated, LB-deposited, and thiol-coated surfaces.

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