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  • 1.
    Dédinaité, Andra
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Thormann, Esben
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Olanya, Geoffrey
    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.
    Nystrom, Bo
    Kjoniksen, Anna-Lena
    Zhu, Kaizheng
    Friction in aqueous media tuned by temperature-responsive polymer layers2010In: SOFT MATTER, ISSN 1744-683X, Vol. 6, no 11, p. 2489-2498Article in journal (Refereed)
    Abstract [en]

    An atomic force microscope colloidal probe technique has been employed to probe normal and friction forces between silica surfaces coated with adsorbed layers of a diblock copolymer of the composition poly(N-isopropylacrylamide)(48)-block-poly(3-acrylamidopropyl)trimethyla mmonium chloride)(20), abbreviated PNIPAAM(48)-b-PAMPTMA(+)(20). The interactions between the PNIPAAM(48)-b-PAMPTMA(+)(20)-coated surfaces across a 0.1 mM NaCl (pH 6) solution at 25 degrees C are purely repulsive, due to a combination of steric and electrostatic double-layer forces. However, when the temperature is increased to 35 degrees C, and subsequently to 45 degrees C, an attractive force develops at short separations due to the unfavourable PNIPAAM-water interaction at these temperatures. The temperature-dependent polymer-water interaction has implications for the friction force between the layers. At 25 degrees C a frictional force that increases linearly with increasing load is observed once the surfaces are brought into close contact. At higher temperatures significantly higher friction forces appear as a consequence of attractive segment-segment interactions. Further, a clearly expressed hysteresis between friction forces encountered on loading and unloading is detected. Our results demonstrate that both normal and friction forces between surfaces can be controlled by temperature changes when temperature-responsive polymers are employed, and friction forces can be adjusted as required from low to high.

  • 2.
    Iruthayaraj, Joseph
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Olanya, Geoffrey
    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.
    Viscoelastic properties of adsorbed bottle-brush polymer layers studied by quartz crystal microbalance: Dissipation measurements2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 38, p. 15028-15036Article in journal (Refereed)
    Abstract [en]

    Adsorbed layers of a series of bottle-brush polyelectrolytes with 45 units long poly(ethylene oxide) [PEO], side chains have been investigated by the quartz crystal microbalance technique with dissipation monitoring. The data have been evaluated with three different models, the Sauerbrey model, the Johannsmann model, and the Voigt model. It is found that all three models predict the same trend in the variations of sensed mass and hydrodynamic layer thickness with polymer architecture, that is, with the backbone charge to side chain density ratio. However, the simple Sauerbrey model underestimates the sensed mass by a factor of 1.15-1.45 compared to the more accurate Voigt model. By following the evolution of the layer dissipation, elasticity, and viscosity with increasing surface coverage it was concluded that the layers formed by brush polymers with intermediate charge densities undergo a structural change as the coverage is increased. Initially, the polymers are anchored to the surface via the PEO side chains. However, as the adsorption proceeds a structural change that brings the backbone to the surface and forces the side chains to extend from it is observed. The layer elasticity and viscosity as a function of surface coverage go through a maximum in this transition region.

  • 3.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Olanya, Geoffrey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Makuska, Ricardas
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Desorption of bottle-brush polyelectrolytes from silica by addition of linear polyelectrolytes studied by QCM-D and reflectometry2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 323, no 2, p. 223-228Article in journal (Refereed)
    Abstract [en]

    The possibility of exchanging adsorbed layers of PEO(45)MEMA:METAC-X brush polyelectrolytes (with two different charge densities, 10 and 75 mol%, denoted by X), with poly(MAPTAC), a highly charged linear polyelectrolyte, was investigated by quartz crystal microbalance with dissipation and reflectometry. The studies were conducted on a silica substrate at pH 10, conditions under which only electrostatic interactions are effective in the adsorption process. Based on the results, it was concluded that PEO(45)MEMA:METAC-10 forms an inhomogeneous layer at the interface through which poly(MAPTAC) chains can easily diffuse to reach the surface. On the other hand, the PEO(45)MEMA:METAC-75 layer was not affected when exposed to a poly(MAPTAC) solution. We argue that the observed effect for PEO(45)MEMA: METAC-75 is due to the formation of a homogeneous protective brush layer, in combination with the small difference in surface affinity between the bottle-brush polyelectrolyte and poly(MAPTAC), together with the difficulty of displacing highly charged polyelectrolyte chains once they are adsorbed on the oppositely charged surface. We also use the combination of QCM-D and reflectometry data to calculate the Water content and layer thickness of the adsorbed layers. (c) 2008 Elsevier Inc. All rights reserved.

  • 4.
    Olanya, Geoffrey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Adsorption behaviour of bottle-brush and block copolymers at solid-liquid interfaces2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis was spurred on by needs of current scientific and technological developments in the area of surface modification by use of adsorbed polymer layers. The importance of surface properties of polymer layers can be imparted in a broad spectrum of interfacial-related applications like lubrication, colloidal stability, detergency, and protein resistant surfaces, to just mention a few. Irrespective of all areas of application an underlying factor in all is the deep implication and footprint the molecular architecture has on the interfacial properties of polymer layers. In this context this thesis has the intention of raising awareness of the importance of the polymer architecture on interfacial behavior and the stability of layers formed by bottle-brush polymers and by temperature responsive block copolymers under different conditions. The first part of this thesis work was largely devoted to the surface properties of a series of cationic bottle-brush polymers, consisting of a main chain carrying charges and poly(ethylene oxide) (PEO) side chains close to randomly distributed along the backbone. Here particular attention was devoted to varying the molecular architecture by changing the charge/PEO ratio along the backbone. The studies demonstrated that the surface excess of the polymers went through a maximum as the number of backbone charges increased. Furthermore, the bottle-brush adlayers revealed sensitivity to changes in both ionic strength and pH when the numbers of backbone charges were relatively low. Layer properties were comprehensively elucidated by determining not only the adsorbed mass, but also layer thickness, water content and layer viscoelasticity. The change in these properties during formation of the adsorption layer was found to be complex, demonstrating significant conformational changes in the layer. The studies aimed at creating surface coatings with good resistance against species of high surface affinity, with a central interest in proteins, elucidated the optimal balance of the bottle-brush structure. The results revealed two scenarios, depending on both the type of protein and the areal density (grafting density) of the PEO side chains at the silica surface, where either protein adsorption was suppressed or enhanced by the presence of adlayers of the bottle-brush polymers. Low protein adsorption was achieved when the polymers have enough electrostatic attachment points to ensure a strong binding to the surface and at the same time a sufficient amount of PEO side chains that screen the protein-surface interactions. In the second part of the thesis a combination of QCM-D, AFM and reflectometry techniques was employed to probe the interfacial characteristics of temperature responsive cationic diblock copolymers, poly(N-ivisopropylacrylamide)m-block-poly(3-acrylamidopropyl)trimethyl ammonium chloride)n. The adsorption of these polymers to silica was of a high affinity, with no dramatic structural changes occurring during the layer build-up. The temperature dependent behavior of the adlayers demonstrated that the polymer interfacial conformation could be reversibly altered merely by cycling temperature above and below the lower critical solution temperature (LCST). This was found to have significant effects on both surface forces and boundary lubrication.

  • 5.
    Olanya, Geoffrey
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Iruthayaraj, Joseph
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Poptoshev, Evgeni
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Makuška, Ričardas
    Department of Polymer Chemistry, Vilnius University.
    Vareikis, Aušvydas
    Department of Polymer Chemistry, Vilnius University.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Adsorption characteristics of bottle-brush polymers on silica: Effect of side chain and charge density2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 10, p. 5341-5349Article in journal (Refereed)
    Abstract [en]

    The adsorption behavior of bottle-brush polymers with different charge/PEO ratio on silica was studied using optical reflectometry and QCM-D. The results obtained under different solution conditions clearly demonstrate the existence of two distinct adsorption mechanisms depending on the ratio of charge/PEO. In the case of low-charge density brush polymers (0- 10 mol %), the adsorption occurs predominantly through the PEO side chains. However, the presence of a small amount of charge along the backbone (as low as 2 mol %) increases the adsorption significantly above that of the uncharged bottle-brush polymer in pure water. As the charge density of the brush polymers is increased to 25 mol % or larger the adsorption occurs predominantly through electrostatic interactions. The adsorbed layer structure was studied by measuring the layer dissipation using QCM-D. The adsorbed layer formed by the uncharged brush polymer dissipates only a small amount of energy that indicates that the brush lie along the surface, the scenario in which the maximum number of PEO side chains interact with the surface. The adsorbed layers formed by the low-charge density brush polymers (2- 10 mol %) in water are more extended, which results in large energy dissipation, whereas those formed by the high-charge density brush polymers (50- 100 mol _%) have their backbone relatively flat on the surface and the energy dissipation is again low.

  • 6.
    Olanya, Geoffrey
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Thormann, Esben
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Varga, Imre
    Makuska, Ricardas
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Protein Interactions with Bottle-Brush Polymer Layers: Effect of Side Chain and Charge Density Ratio Probed by QCM-D and AFM2010In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 349, no 1, p. 265-274Article in journal (Refereed)
    Abstract [en]

    Silica surfaces were coated with a range of cationic bottle-brush polymers with 45 units long poly(ethylene oxide) side chains, and their efficiency in reducing protein adsorption was probed by QCM-D, reflectometry and AFM. Preadsorbed layers formed by bottle-brush polymers with different side chain to charge ratio was exposed to two proteins with different net charge, lysozyme and BSA. The reduction in protein adsorption was found to depend on both the type of protein and on the nature of the polyelectrolyte layer. The most pronounced reduction in protein adsorption was achieved when the fraction of charged backbone segments was in the range 0.25-0.5 equivalent to a fraction of poly(ethylene oxide) side chains of 0.75-0.5. It was concluded that these polymers have enough electrostatic attachment points to ensure a strong binding to the surface, and at the same time a sufficient amount of poly(ethylene oxide) side chains to counteract protein adsorption. In contrast, a layer formed by a highly charged polyelectrolyte without side chains was unable to resists protein adsorption. On such a layer the adsorption of negatively charged BSA was strongly enhanced, and positively charged lysozyme adsorbed to a similar extent as to bare silica. AFM colloidal probe force measurement between silica surfaces with preadsorbed layers of bottle-brush polymers were conducted before and after exposure to BSA and lysozyme to gain insight into how proteins were incorporated in the bottle-brush polymer layers.

  • 7. Stubenrauch, Cosima
    et al.
    Shrestha, Lok Kumar
    Varade, Dharmesh
    Johansson, Ingegard
    Olanya, Geoffrey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Aramaki, Kenji
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Aqueous foams stabilized by n-dodecyl-beta-D-maltoside, hexaethyleneglycol monododecyl ether, and their 1: 1 mixture2009In: Soft Matter, ISSN 1744-683X, Vol. 5, no 16, p. 3070-3080Article in journal (Refereed)
    Abstract [en]

    Aqueous foams stabilized by the non-ionic surfactants n-dodecyl-beta-D-maltoside (beta-C(12)G(2)) and hexaethyleneglycol monododecyl ether (C12E6) as well as by their 1 : 1 mixture were studied as a function of the total surfactant concentration from 0.1 to 10 cmc. Foamability and foam stability were measured with home-built winding equipment, the commercially available FoamScan, and a home-built foam conductivity apparatus (FCA), respectively. It was found that the foamability increases with increasing surfactant concentration for both the single and the mixed surfactant systems. On the other hand, at a fixed relative surfactant concentration (c/cmc) the foamability of beta-C(12)G(2) solutions was found to be much higher than that of C12E6 solutions, while the 1 : 1 mixture behaves like the pure C12E6. Measurements at different gas (N-2) flow rates have shown that the foamability decreases non-linearly with decreasing N-2 flow rate, which shows that foam generation and foam breakdown occur simultaneously. Regarding foam stability it was found that it also increases with increasing surfactant concentration. As was the case for the foamability, the stability of foams stabilized by beta-C(12)G(2) was much higher than that of foams stabilized by C12E6, while the foam stability of the 1 : 1 mixture was comparable to that of the pure C12E6. The foam results are discussed in the light of static surface tensions, dynamic surface tensions, and surface elasticities, which were measured for the single and the mixed surfactant systems.

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