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  • 51.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Dedinaite, A
    YKI – Ytkemiska institutet.
    Bergenståhl, B
    YKI – Ytkemiska institutet.
    Campbell, B
    Christenson, H
    Interactions between hydrophilic mica surfaces in triolein: Triolein surface orientation, solvation forces, and capillary condensation1997In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, p. 1682-1688Article in journal (Refereed)
    Abstract [en]

    Results obtained from surface force measurements using hydrophilic mica surfaces in triolein are presented. The forces were determined for different water activities in the triglyceride sample. With anhydrous triolein two oscillations in the force curve are observed. They appear at a separation of 60-50 Å and 30-20 Å. An interfacial ordering of triolein, allowing two molecular layers between the surfaces at the position of the outer oscillation and one molecular layer at the inner one is proposed. This structure at the interface is different from the triglyceride conformation suggested for the bulk system. A dramatic effect of water content on the structural forces is observed. The number and amplitude of the oscillations are dependent on the water content. The oscillations completely disappear when the triolein sample is satured with water, and the force becomes purely attractive. These data are interpreted in terms of preferential adsorption of water molecules onto the hydrophilic mica surface and in terms of a changing water adsorption with surface separation. The adhesion force between the surfaces is strongly increased when the water content is close to its saturation value. The strong adhesion is attributes to the presence of a water capillary around the contact position.

  • 52.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Malmsten, M
    YKI – Ytkemiska institutet.
    Lindman, B
    Forces between hydrophobic surfaces coated with ethyl(hydroxyethyl)cellulose in the presence of an ionic surfactant1991In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 7, p. 1441-1446Article in journal (Refereed)
    Abstract [en]

    The forces between hydrophobic surfaces across an aqueous solution containing 0.25% ethyl(hydroxyethyl)cellulose (EHEC) and 4 mM SDS have been studied and compared with the situation in the absence of SDS. A long-range repulsive force (measurable at distances smaller than 1200 Å) is present already after an adsorption time of 30 minutes. The range of the repulsive force increases with time indicating that the adsorption process is rather slow. After 20 hours equilibration, the repulsion was measurable at separations smaller than 2500 Å. The force is rather insensitive to temperature and decays at large separations essentially exponentially, with a decay-length of approximately 300 Å. The force measured on compression is always slightly larger than the one observed on decompression. Hence, the forces are not measured in a true equilibrium situation. The system behaves strikingly different in the absence of SDS (Malmsten and Claesson, Langmuir, in press). Without any surfactant in the EHEC solution less long-range and completely reversible forces are observed. Hence, SDS causes the polymer conformation to be more extended, and is responsible for the non-equilibrium effects observed (e.g. by decreasing the polymer-surface affinity). The adsorbed amount in the presence of SDS was found to be about 1.7 mg/m2 at adsorption equilibrium, independent of temperature (20°-35°C). This is considerably less than in the absence of surfactants (5 mg/m2 at 20°C, 15 mg/m2 at 37°C).

  • 53.
    Claesson, PM
    et al.
    YKI – Ytkemiska institutet.
    Ninham, BW
    pH-dependent interactions between adsorbed chitosan layers1992In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 8, p. 1406-1412Article in journal (Refereed)
    Abstract [en]

    Chitosan is a cationic polyelectrolyte obtained after N-deacetylation of chitin by alkaline treatment. The adsorption of chitosan and the interaction between chitosan layers have been investigated using a surface force technique. Negatively charged mica surfaces were immersed in a 0.01 wt % acetic acid solution containing 0.01 wt % chitosan. The adsorption of chitosan results in a flat adsorbed layer and a reversal of the sign of the surface charge. The adsorption is essentially irreversible with respect to subsequent dilution. After dilution, the pH dependence of the forces acting between the adsorbed chitosan layers was investigated. The chitosan-mica system is uncharged around pH 6.2 (the pKa of chitosan is around 6.5) At this pH there is a weak attractive interaction between the chitosan-coated surfaces. The minimum in the force vs distance curve is located at a separation of about 20-25 Å. A steric repulsion is observed at smaller separations. At lower and higher pH values the long-range interaction is dominated by a repulsive double-layer force originating from charges on chitosan and on the mica surface, respectively. The information obtained from surface force measurements allows us to suggest a structure of the irreversibly adsorbed layer at various pH values. The pH dependence of the layer structure is rationalized in terms of changes in segment-segment and segment-surface interactions.

  • 54.
    Corkery, RW
    et al.
    YKI – Ytkemiska institutet.
    Fogden, A
    On the formation and structure of nanometric polyhedral foams: Toward the dry limit2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, p. 10443-10452Article 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.

  • 55.
    Corkery, RW
    et al.
    YKI – Ytkemiska institutet.
    Rousseau, D
    Smith, P
    YKI – Ytkemiska institutet.
    Pink, DA
    Hanna, CB
    A case for discotic liquid crystals in molten triglycerides2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, p. 7241-7246Article 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.

  • 56. Cranston, ED
    et al.
    Gray, DG
    Rutland, MW
    YKI – Ytkemiska institutet.
    Direct surface force measurements of polyelectrolyte multilayer films containing nanocrystalline cellulose2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 22, p. 17190-17197Article 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 are 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 AFM 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 betweenasilica probe and an NCC-capped multilayer film were monotonically repulsiveatpH 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 doublelayer attraction at low pH, and electrostatic double-layer repulsion at high pH, were observed. Finally, the effect of 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.

  • 57. Cárdenas, M
    et al.
    Valle-Delgado, JJ
    KTH Royal Institute of Technology, Sweden.
    Hamit, J
    Rutland, MW
    YKI – Ytkemiska institutet. KTH Royal Institute of Technology, Sweden.
    Arnebrant, T
    Interactions of hydroxyapatite surfaces: Conditioning films of human whole saliva2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 14, p. 7262-7268Article 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.

  • 58.
    Dahlgren, MAG
    YKI – Ytkemiska institutet.
    Effect of counterion valency and ionic strength on polyelectrolyte adsorption1994In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 10, p. 1580-1583Article in journal (Refereed)
    Abstract [en]

    The adsorption of cationic polyelectrolytes onto negatively charged mica from solutions of variable ionic strength was studied using the interferometric surface force technique. The results show that the structure of the adsorbed layer of polyelectrolyte is strongly dependent on the ionic strength of the solution from which the initial adsorption takes place, rather than the valency of the counter-ion. Within the time for one experiment (1 week) it was not feasible to achieve the same layer structure by a stepwise increase of the ionic strength, as was obtained when the adsorption of the polyelectrolyte was carried out directly from the solution of the higher ionic strength. A mechanism for attraction due to counter-ion-bridges when large, flexible counter-ions are present in the solution is suggested.

  • 59.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Hollenberg, HCM
    Claesson, PM
    YKI – Ytkemiska institutet.
    The order of adding polyelectrolyte and salt affects surface forces and layer structures1995In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, p. 4480-4485Article in journal (Refereed)
    Abstract [en]

    The order in which salt and polyelectrolyte is added to a solution influences the structure of adsorbed layers on surfaces in contact with the solution and the interactions between surfaces across such solutions. By performing surface force measurements, it is shown that the strong attraction observed between polyelectrolyte coated surfaces in low ionic strength solutions is changed into a long ranged repulsion at solution of high ionic strength. This repulsion is more long ranged and larger in magnitude when the salt is added before the polyelectrolyte than when additions are done in the reverse order. When increasing the ionic strength in steps, the layer thickness and short range repulsion increases. We suggest that this is due to an increased adsorption of the polyelectrolyte. Mean field calculations (Scheutjens-Fleer model) were used to rationalize experimental findings. The results show that the adsorbed layer is much more extended in high ionic strength solutions. Furthermore, we show that the adsorption of polyelectrolyte is increased with ionic strength when the non-electrostatic interaction between polymer segments and the solvent is unfavourable.

  • 60.
    Dahlgren, MAG
    et al.
    YKI – Ytkemiska institutet.
    Leermakers, FAM
    Depletion zones in polyelectrolyte systems: polydispersity effects and colloidal stability1995In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, p. 2996-3006Article in journal (Refereed)
    Abstract [en]

    We have used the Scheutjens-Fleer theory for polymers at interfaces to study depletion zone effects in polyelectrolyte systems. The segment density profiles of depletion regions are independent of the chain length, $N$, and the depletion interaction is often fully repulsive. In polyelectrolyte systems, a depletion zone develops both at adsorbing and at non-adsorbing interfaces, especially at low ionic strengths. Interactions which are repulsive at some surface separations and attractive at others can also be found, e. g. for intermediate ionic strength conditions or for very low charge density in the chain. At very high ionic strength or very low charge density, the classical neutral polymer depletion layers develop, causing attraction between particles in solution. Effects of polydispersity of the polyelectrolytes on the segment density profiles are small. There is a minor effect on the depletion region at low ionic strengths, provided that there is not a large fraction of very short chainspresent. Only depletion zones near adsorbing surfaces tend to be preferentially populated by low molecular weight polymer. Under these conditions, long chains are still depleted from this filled-up depletion region, which has immediate implications for the equilibration of the adsorbed layer: The diffusion of long chains through this region to the surface is slow. At an adsorbing surface, preferential adsorption of the longer polyelectrolytes over the shorter ones results in a fractionation of the chains at the adsorbing interface, if equilibrium can be reached.

  • 61.
    de Kort, Daan W
    et al.
    Wageningen University, The Netherlands; TI-COAST, The Netherlands.
    Schuster, Erich
    RISE - Research Institutes of Sweden, Bioscience and Materials, Agrifood and Bioscience.
    Hoeben, Freek J M
    TI-COAST, The Netherlands; SyMO-Chem B.V, The Netherlands.
    Barnes, Ryan
    University of California, USA.
    Emondts, Meike
    University of California, USA.
    Janssen, Henk M
    TI-COAST, The Netherlands; SyMO-Chem B.V, The Netherlands.
    Loren, Niklas
    RISE - Research Institutes of Sweden, Bioscience and Materials, Agrifood and Bioscience.
    Han, Songi
    University of California, USA.
    Van As, Henk
    Wageningen University, The Netherlands; TI-COAST, The Netherlands.
    van Duynhoven, John P M
    Wageningen University, The Netherlands; TI-COAST, The Netherlands ; Unilever R&D, The Netherlands.
    Heterogeneity of Network Structures and Water Dynamics in κ-Carrageenan Gels Probed by Nanoparticle Diffusometry.2018In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 34, no 37Article in journal (Refereed)
    Abstract [en]

    A set of functionalized nanoparticles (PEGylated dendrimers, d = 2.8-11 nm) was used to probe the structural heterogeneity in Na+/K+ induced κ-carrageenan gels. The self-diffusion behavior of these nanoparticles as observed by 1H pulsed-field gradient NMR, fluorescence recovery after photobleaching, and raster image correlation spectroscopy revealed a fast and a slow component, pointing toward microstructural heterogeneity in the gel network. The self-diffusion behavior of the faster nanoparticles could be modeled with obstruction by a coarse network (average mesh size <100 nm), while the slower-diffusing nanoparticles are trapped in a dense network (lower mesh size limit of 4.6 nm). Overhauser dynamic nuclear polarization-enhanced NMR relaxometry revealed a reduced local solvent water diffusivity near 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-labeled nanoparticles trapped in the dense network, showing that heterogeneity in the physical network is also reflected in heterogeneous self-diffusivity of water. The observed heterogeneity in mesh sizes and in water self-diffusivity is of interest for understanding and modeling of transport through and release of solutes from heterogeneous biopolymer gels.

  • 62.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Bastardo, L
    Interactions between mucin and surfactants at solid-liquid interfaces2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, p. 9383-9392Article 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-dodecylß -D-maltopyranoside (C12-mal). All three surfactants were found to be potent in removing mucin from hydrophobic surfaces. On the other hand, C12-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

  • 63.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Campbell, B
    Interactions between mica surfaces across triglyceride solution containing phospholipid and polyglycerol polyricinoleate2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 2248-2253Article 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 PE/PGPR mixture are presented. It was shown that PE adsorbed on mica >from anhydrous triolein and thus rendered the surface non-polar. 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 Å. 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 non-polar 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.

  • 64.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Interfacial properties of aggregates formed by cationic polyelectrolyte and anionic surfactant2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 1951-1959Article in journal (Refereed)
    Abstract [en]

    Interactions between mica surfaces across aqueous solutions containing mixtures of a highly positively charged polyelectrolyte and an anionic surfactant were studied using a surface force apparatus. The investigation was carried out using a constant polyelectrolyte concentration (20 ppm) and a wide range of surfactant concentrations (0 - 1 cmc). The chemical composition of the adsorbed polyelectrolyte-surfactant layers was analysed by XPS. The properties of polyelectrolyte-surfactant aggregates formed in bulk were studied by measurements of turbidity and electrophoretic mobility. The aggregates formed at low surfactant concentrations (<0.04 cmc) were positively charged, whereas at higher surfactant concentrations the aggregates carried a net negative charge. It was shown that polyelectrolyte-surfactant aggregates rapidly adsorb on negatively charged mica surfaces regardless of the sign of their charge. At surfactant concentrations up to 0.01 cmc, the polyelectrolytes adsorb on mica surfaces with loops and tails stretching out into solution and repulsive steric forces are generated. The thickness of the layer decreases with time and we suggest that this conformational change is accompanied by some expulsion of surfactant >from the adsorbed layers. Thick adsorbed layers were formed in the surfactant concentration range 0.02 - 0.1 cmc. In this concentration regime the measurement of equilibrium forces was inaccessible due to a very slow layer relaxation. During compression the forces were repulsive and during separation an attraction developed. We attribute this to formation of interlayer surfactant bridges. Finally, at high surfactant concentrations (≥ 0.4 cmc) highly negatively charged aggregates adsorb on the surfaces in rather thin layers, resulting in purely repulsive forces of mixed electrostatic and steric origin.

  • 65.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Campbell, B
    Mays, H
    Interactions between modified mica surfaces in triglyceride media1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 5546-5554Article in journal (Refereed)
    Abstract [en]

    Results obtained from surface force measurements using modified nonpolar mica surfaces immersed in triolein are presented. The force vs distance curves were determined for different water activities in the interaction medium. Two oscillations with a periodicity of 20 Å were observed in the force curve measured across anhydrous triolein. The force barriers appear at separations of 45-40 and 20-30 Å. It is suggested that triolein has no clear preferential orientation of the oleic acid chains outside a nonpolar surface. This is different from outside a polar mica surface where triolein adopts conformations with the three oleic acid residues directed toward the bulk. At high water contents the triolein molecules outside nonpolar surfaces suddenly change their orientation when a high compressive force is applied. The forces acting between mica surfaces were measured in triolein solutions containing phospholipids at different water activities. It was shown that the phospholipid self-assembled onto the mica surfaces and rendered them nonpolar. The forces between such surfaces in anhydrous triolein are similar to those observed between mica hydrophobized using the Langmuir-Blodgett technique. In addition, at high water activities a weak long range repulsive force was observed. This force was interpreted as being due to weakly adsorbed phospholipid aggregates. We discuss the implications of the results for the stability and physical properties of colloidal particle dispersions in nonpolar media. Adsorption isotherms for the phospholipid from refined vegetable oil at low water activity on mica and sucrose crystals are presented. They show that the phospholipid adsorbs in a monolayer on mica. On sucrose more than monolayer coverage is observed, which we interpret in terms of a phase separation of phospholipid into crevices and cracks.

  • 66.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Bergström, M
    YKI – Ytkemiska institutet.
    Polyelectrolyte-surfactant layers: Adsorption of preformed aggregates versus adsorption of surfactant to preadsorbed polyelectrolyte2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 5257-5266Article in journal (Refereed)
    Abstract [en]

    The character of adsorbed layers containing both polyelectrolyte and surfactant depends on the type of polyelectrolyte used and the surfactant concentrations, as demonstrated by several recent studies. However, the layer properties also depend on the experimental pathway. This shows that the adsorbed layers can be trapped in quasi-equilibrium states, and that the true equilibrium state is only reached over experimentally inaccessible time scales. This has to be kept in mind when comparing different results reported in the literature. The present article highlights these effects using a system consisting of a highly charged cationic polyelectrolyte and an anionic surfactant. The adsorbed layer properties were determined using mainly surface force measurements and AFM imaging. We also present some new small angle neutron scattering data for bulk complexes formed between the polyelectrolyte and the surfactant, which demonstrates the presence of a characteristic correlation length of about 37-39 Å. A similar characteristic length-scale is also observed in some of the adsorbed layers, both employing the AFM and the surface force apparatus.

  • 67.
    Dedinaite, A
    et al.
    YKI – Ytkemiska institutet.
    Lundin, M
    Macakova, L
    YKI – Ytkemiska institutet.
    Auletta, A
    Mucin-chitosan complexes at the solid-liquid interface: Multilayer formation and stability in surfactant solutions2005In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 21, p. 9502-9509Article in journal (Refereed)
    Abstract [en]

    The adsorption of a biologically important glycoprotein, mucin, and mucin-chitosan complex layer formation on negatively charged surfaces, silica and mica, have been investigated employing ellipsometry, the interferometric surface apparatus, and atomic force microscopy techniques. Particular attention has been paid to the effect of an anionic surfactant sodium, dodecyl sulfate (SDS), with respect to the stability of the adsorption layers. It has been shown that mucin adsorbs on negatively charged surfaces to form highly hydrated layers. Such mucin layers readily associate with surfactants and are easily removed from the surfaces by rinsing with solutions of SDS at concentrations ≥0.2 cmc (1 cmc SDS in 30 mM NaCl is equal to 3.3 mM). The mucin adsorption layer is negatively charged, and we show how a positively charged polyelectrolyte, chitosan, associates with the preadsorbed mucin to form mucin-chitosan complexes that resist desorption by SDS even at SDS concentrations as high as 1 cmc. Thus, a method of mucin layer protection against removal by surfactants is offered. Further, we show how mucin-chitosan multilayers can be formed.

  • 68.
    Dedinaite, Andra
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Polymer och fiber.
    Claesson, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Kinetic and equilibrium aspects of adsorption and desorption of class II hydrophobins HFBI and HFBII at silicon oxynitride/water and air/water interfaces2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 8, p. 2683-2691Article in journal (Refereed)
  • 69.
    Dedinaite, Andra
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Polymer och fiber.
    Claesson, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Nanostructured composite layers of mussel adhesive protein and ceria nanoparticles2013In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 30, p. 9551-9561Article in journal (Refereed)
  • 70.
    Dedinaite, Andra
    et al.
    RISE, SP – Sveriges Tekniska Forskningsinstitut, SP Kemi Material och Ytor, Polymer och fiber.
    Claesson, Per
    RISE, SP – Sveriges Tekniska Forskningsinstitut.
    Temperature-dependent adsorption and adsorption hysteresis of a thermoresponsive diblock copolymer2014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 15, p. 4333-4341Article in journal (Refereed)
  • 71. Djuve, J
    et al.
    Grant, LM
    Sjöblom, J
    Goloub, TP
    Pugh, RJ
    YKI – Ytkemiska institutet.
    Templating of ethyl(hydroxyethyl) cellulose on graphite by surfactant-polymer interactions2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, p. 2673-2677Article in journal (Refereed)
    Abstract [en]

    Ordered, templated, thin films of ethyl(hydroxyethyl)cellulose (EHEC) were produced on a freshly cleaved crystalline graphite surface by exploiting the nature of sodium dodecyl sulfate adsorption (SDS) and its interaction with EHEC. The films were prepared by exposing the graphite surface to a dilute aqueous solution containing EHEC-SDS mixtures, followed by rinsing to remove the SDS and drying. The structure of the remaining EHEC film at the graphite-air interface was investigated by atomic force microscopy and compared with images of SDS and EHEC polymer on adsorbed graphite obtained in separate experiments. The results showed that polymer networks were formed from the EHEC-SDS mixture (after rinsing out the SDS), which were predominately aligned in one of three preferential directions separated by 60°, presumably as a result of templating by coadsorbed SDS. In addition, the alignment of the EHEC polymer and spacing between the polymer strands was found to be a function of surfactant concentration. Films formed from a solution containing EHEC (10 ppm) and SDS solution (5 mM) after removal of the SDS by washing formed "tight", highly aligned networks. At the same EHEC concentration and 20 mM SDS, a more "open" structure was formed. The results provide valuable insights into the interaction and organization of SDS and EHEC at a crystalline hydrophobic surface.

  • 72.
    Dobryden, Illia
    et al.
    KTH Royal Institute of Technology, Sweden.
    Cortes Ruiz, Maria
    City College of New York, US.
    Zhang, Xuwei
    University of Montreal, Canada.
    Dedinaite, Andra
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Wieland, Floria
    Institute for Materials Research, Germany.
    Winnik, Francoise
    University of Helsinki, Finland.
    Claesson, Per M
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Thermoresponsive Pentablock Copolymer on Silica: Temperature Effects on Adsorption, Surface Forces, and Friction2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 3, p. 653-661Article in journal (Refereed)
    Abstract [en]

    The adsorption of hydrophilic or amphiphilic multiblock copolymers provides a powerful means to produce well-defined "smart" surfaces, especially if one or several blocks are sensitive to external stimuli. We focus here on an A-B-A-B-A copolymer, where A is a cationic poly((3-acrylamido-propyl)-trimethylammonium chloride) (PAMPTMA) block containing 15 (end blocks) or 30 (middle block) repeat units and B is a neutral thermosensitive water-soluble poly(2-isopropyl-2-oxazoline) (PIPOZ) block with 50 repeat units. X-ray reflectivity and quartz crystal microbalance with dissipation monitoring were employed to study the adsorption of PAMPTMA15-PIPOZ50-PAMPTMA30-PIPOZ50-PAMPTMA15 on silica surfaces. The latter technique was employed at different temperatures up to 50 °C. Surface forces and friction between the two silica surfaces across aqueous pentablock copolymer solutions at different temperatures were determined with the atomic force microscopy colloidal probe force and friction measurements. The cationic pentablock copolymer was found to have a high affinity to the negatively charged silica surface, leading to a thin (2 nm) and rigid adsorbed layer. A steric force was encountered at a separation of around 3 nm from hard wall contact. A capillary condensation of a polymer-rich phase was observed at the cloud point of the solution. The friction forces were evaluated using Amontons' rule modified with an adhesion term.

  • 73.
    Dobryden, Illia
    et al.
    KTH Royal Institute of Technology, Sweden.
    Steponaviciu Te, Medeina
    Vilnius University, Lithuania.
    Klimkevicius, Vaidas
    Vilnius University, Lithuania.
    Makuska, Ričardas
    Vilnius University, Lithuania.
    Dedinaite, Andra
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Liu, Xiaoyan
    Shaanxi Normal University, China.
    Corkery, Robert W
    KTH Royal Institute of Technology, Sweden.
    Claesson, Per Martin
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Bioinspired Adhesion Polymers: Wear Resistance of Adsorption Layers.2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 48, p. 15515-15525Article in journal (Refereed)
    Abstract [en]

    Mussel adhesive polymers owe their ability to strongly bind to a large variety of surfaces under water to their high content of 3,4-dihydroxy-l-phenylalanine (DOPA) groups and high positive charge. In this work, we use a set of statistical copolymers that contain medium-length poly(ethylene oxide) side chains that are anchored to the surface in three different ways: by means of (i) electrostatic forces, (ii) catechol groups (as in DOPA), and (iii) the combination of electrostatic forces and catechol groups. A nanotribological scanning probe method was utilized to evaluate the wear resistance of the formed layers as a function of normal load. It was found that the combined measurement of surface topography and stiffness provided an accurate assessment of the wear resistance of such thin layers. In particular, surface stiffness maps allowed us to identify the initiation of wear before a clear topographical wear scar was developed. Our data demonstrate that the molecular and abrasive wear resistance on silica surfaces depends on the anchoring mode and follows the order catechol groups combined with electrostatic forces > catechol groups alone > electrostatic forces alone. The devised methodology should be generally applicable for evaluating wear resistance or "robustness" of thin adsorbed layers on a variety of surfaces.

  • 74. Ederth, T
    et al.
    Claesson, P
    YKI – Ytkemiska institutet.
    Liedberg, B
    Self-assembled monolayers of alkanethiolates on thin gold films as substrates for surface force measurements. Long-range hydrophobic interactions and electrostatic double-layer interactions1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 4782-4789Article in journal (Refereed)
    Abstract [en]

    Surfaces prepared by self-assembly of alkanethiolates onto thin (10 nm) gold films supported on glass have been used as substrates for surface force measurements between macroscopic surfaces. Surface roughness, the order in the monomolecular film, wetting properties and their stability in aqueous electrolyte solutions have been investigated using atomic force microscopy, infrared absorption spectroscopy, and contact angle measurements. Direct force measurements have been performed with a non-interferometric bimorph surface force apparatus, using surfaces with differently functionalised thiolates; measurements were made in air, water and aqueous electrolyte solutions. Results from force measurements between hydrophobic and neutral hydrophilic surfaces in air and water are presented and discussed, as well as some results from measurements with surfaces exposing carboxylic groups in various aqueous electrolyte solutions. It is demonstrated that alkanethiol monolayers self-assembled onto thin gold films on macroscopic surfaces are well suited as substrates for direct measurements of long-range surface forces. The utility of these surfaces as substrates for investigations of short-range phenomena is limited until the effect of the roughness on the adhesion between the surfaces has been properly quantified, and the contribution of the van der Waals force to the total interaction has been calculated. The latter is difficult to assess due to the large number of layers in the system, and the presence of conducting surfaces.

  • 75.
    Ederth, T
    et al.
    YKI – Ytkemiska institutet.
    Liedber, g B
    Influence of wetting properties on the long-range "hydrophobic" interaction between self-assembled alkylthiolate monolayers2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 2177-2184Article in journal (Refereed)
    Abstract [en]

    The effect of solid-liquid interfacial energy on the long-range attraction between self-assembled thiolate monolayers in water has been studied by direct force measurements. The solid-liquid interfacial energy was tuned by changing the properties of the solid surface: the thiolate monolayers were prepared by self-assembly of mixtures of methyl- and hydroxyl- functionalized alkylthiols onto thin gold films. The wetting properties were examined by contact angle measurements with the Wilhelmy plate method. Our results show that the shape of the long-ranged attractive force is sensitive to the advancing solid-liquid contact angle: whenever it exceeds 90° the force profiles are discontinuous and contains steps, whereas no attraction beyond the van der Waals force is observed for contact angles lower than 90°. We attribute the steps in the long-range attraction between hydrophobic surfaces to bridging of microscopic bubbles residing on the surfaces, and we conclude that the stability of these bubbles are related to macroscopic contact angles.

  • 76. Ericsson, C
    et al.
    Söderman, O
    Garamus, VM
    Bergström, M
    YKI – Ytkemiska institutet.
    Ulvenlund, S
    Effects of temperature, salt, and deuterium oxide on the self-aggregation of alkylglycosides in dilute solution. 1. n-Nonyl-β-D-Glucoside2004In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, p. 1401-1408Article in journal (Refereed)
    Abstract [en]

    The influence of salt, temperature, and deuterium oxide on the self-aggregation of n-nonyl--D-glucoside (-C9G1) in dilute solution has been investigated by static and dynamic light scattering, neutron scattering, and tensiometry. Scattering data show that the micelles can be described as relatively stiff, elongated structures with a circular cross section. With a decrease of temperature, the micelles grow in one dimension, which makes it surprising that the critical micelle concentration (cmc) shows a concomitant increase. On the other hand, substitution of D2O for H2O causes a large increase in micelle size at low temperatures, without any appreciable effect on cmc. With increasing temperature, the deuterium effect on the micelle size diminishes. The effects of salt on the micelle size and cmc were found to follow the Hofmeister series. Thus, at constant salt concentration, the micelle size decreased according to the sequence SO42- > Cl- > Br- > NO3- > I- > SCN-, whereas the effect on cmc displays the opposite trend. Here, I- and SCN- are salting-in anions. Similarly, the effects of cations decrease with increasing polarizability in the sequence Li+ > Na+ > K+ > Cs+. At high ionic strength, the systems separate into two micellar phases. The results imply that the size of -C9G1 micelles is extremely sensitive to changes in the headgroup size. More specifically, temperature and salt effects on effective headgroup size, including intermolecular interactions and water of hydration, are suggested to be more decisive for the micelle morphology than the corresponding effects on unimer solubility.

  • 77. Eriksson, J
    et al.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Zhmud, B
    YKI – Ytkemiska institutet.
    Wetting effects due to surfactant carryover through the three-phase contact line2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, p. 7274-7279Article in journal (Refereed)
    Abstract [en]

    Surfactant transport through the three-phase contact line is studied in relation to the wetting-enhancing effect of surfactants. A specially designed experimental setup is used to simultaneously monitor interfacial adsorption and wetting tension during forced immersion of a hydrophobic or hydrophilic plate into aqueous surfactant solutions. The adsorption at the liquid/solid interface has been measured by ellipsometry, the wetting tension has been determined according to the Wilhelmy plate method, and the adsorption to the liquid/vapor interface has been evaluated from surface tension measurements. The relative importance of different adsorption modes could thereby be grasped. For hydrophobic substrates, the dynamic wetting behavior is strongly affected by surfactant carryover through the advancing three-phase contact line, which appears to be the dominant mode of surfactant transport to the solid/liquid interface. Conversely, for hydrophilic substrates, three-phase contact line carryover of surfactant does not appear to be so important; the predominant transport mode being bulk diffusion.

  • 78.
    Eriksson, Mimmi
    et al.
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Claesson, Per Martin
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation. KTH Royal Institute of Technology, Sweden.
    Järn, Mikael
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Tuominen, Mikko
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Wallqvist, Viveca
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Schoelkopf, Joachim
    Omya International AG, Switzerland.
    Gane, Patrick A C
    Aalto University, Finland.
    Swerin, Agne
    KTH Royal Institute of Technology, Sweden.
    Wetting Transition on Liquid-Repellent Surfaces Probed by Surface Force Measurements and Confocal Imaging.2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 41, p. 13275-13285Article in journal (Refereed)
    Abstract [en]

    Superhydrophobic surfaces in the Cassie-Baxter wetting state retain an air layer at the surface which prevents liquid water from reaching into the porous surface structure. In this work we explore how addition of ethanol, which reduces the surface tension, influences the wetting properties of superhydrophobic and smooth hydrophobic surfaces. Wetting properties are measured by dynamic contact angles, and the air layer at the superhydrophobic surface is visualized by laser scanning confocal microscopy. Colloidal probe atomic force microscopy measurements between a hydrophobic microsphere and the macroscopic surfaces showed that the presence of ethanol strongly affects the interaction forces. When the macroscopic surface is superhydrophobic, attractive forces extending up to a few micrometers are observed on retraction in water and in 20 vol % ethanol, signifying the presence of a large and growing gas capillary. Submicrometer attractive forces are observed between the probe particle and a smooth hydrophobic surface, and in this case a smaller gas capillary is formed. Addition of ethanol results in markedly different effects between superhydrophobic and hydrophobic surfaces. In particular, we show that the receding contact angle on the superhydrophobic surface is of paramount importance for describing the interaction forces.

  • 79.
    Eskilsson, K
    et al.
    YKI – Ytkemiska institutet.
    Grant, LM
    Hansson, P
    Tiberg, F
    YKI – Ytkemiska institutet.
    Self-aggregation of triblock copolymers at the solid silica-water interface1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, p. 5150-5157Article in journal (Refereed)
    Abstract [en]

    We report on the adsorption and surface aggregation behavior of triblock copoly(ethylene oxide-tetrahydrofuran-ethylene oxide) copolymers, EOn/2THFmEOn/2, at the silica-water interface. In this work, we have used both time-resolved fluorescence spectroscopy and atomic force microscopy to study the morphology of the adsorbed layers. We confirm previous suggestions that the copolymers self-assemble at the silica surface to form discrete micelle-like structures. The surface aggregation, however, starts at a much lower copolymer concentration than the corresponding micellization process in solution. The time-resolved fluorescence measurements reveal that the copolymer aggregates are smaller at the surface than those in bulk solution. The AFM measurements that were performed clearly confirm the existence of discrete micelle-like copolymer aggregates at the silica surface. An interesting result seen in the AFM surface topography images is that, for the high molecular weight copolymer, we observe no surface aggregates at some parts of surface. We believe this is related to the polydispersity of the copolymer. Single high molecular weight copolymers may effectively compete for surface area with surface aggregates formed by a copolymer fraction of lower molecular weight.

  • 80.
    Eskilsson, K
    et al.
    YKI – Ytkemiska institutet.
    Leal, C
    Lindman, B
    Miguel, M
    Nylander, T
    DNA-surfactant complexes at solid surfaces2001In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 17, p. 1666-1669Article in journal (Refereed)
    Abstract [en]

    In this work, we report on the adsorption of complexes between DNA of different molecular weight and a cationic surfactant, cetyltrimethylammonium bromide (CTAB), on hydrophobized and hydrophilic negatively charged silica surfaces as measured by ellipsometry. We will demonstrate how the adsorption is affected by the state of the DNA-surfactant complexes formed in bulk solution. High molecular weight DNA molecules, which condense (transform from coil to globule state) on addition of small amounts of cationic surfactants, do not adsorb on hydrophilic silica prior to phase separation. However, DNA-surfactant complexes formed from low molecular weight DNA were found to adsorb. For these complexes surfactants interact with DNA, without condensation of the DNA. Adsorbed DNA-surfactant complexes can easily be removed from the hydrophilic silica surface when replacing the bulk DNA-surfactant solution with pure salt solution. At the hydrophobic surface the DNA adsorbs without addition of cationic surfactant. However, with addition of a very low amount of surfactant, a rapid increase in adsorbed amount and a simultaneous decrease in adsorbed layer thickness are observed. This compaction of the adsorbed layer is to some extent reversible when replacing the bulk DNA-surfactant solution with pure salt solution.

  • 81. Eskilsson, K
    et al.
    Ninham, BW
    Tiberg, F
    YKI – Ytkemiska institutet.
    Yaminsky, VV
    Effects of adsorption of low-molecular-weight triblock copolymers on interactions between hydrophobic surfaces in water1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, p. 3242-3249Article in journal (Refereed)
    Abstract [en]

    In this work, we report on the interaction forces between hydrophobized silica surfaces immersed in polymer solutions. The polymers studied were a series of polyethylene oxide-polytetrahydrofuran-polyethylene oxide (PEO-PTHF-PEO) triblock copolymers and a polyethylene oxide homopolymer. The interaction forces were measured by the interfacial gauge technique. We show how the interactions depend on the adsorbed state of the copolymers, which in turn depends both on the copolymer concentration and the adsorption time. Above a critical surface coverage, the interaction between approaching surfaces was found to begin with a steric repulsion due to overlap of the adsorbed polymer layers. This repulsion increases as the distance between the surfaces was decreased. The energy-distance curve could, in this regime, be accounted for by the theory of grafted polymer brushes by Alexander-de Gennes. However, the interaction curves did not follow this prediction for small surface-to-surface distances. Instead, the repulsion stabilised at a more or less constant level with decreasing inter-surface separation. Finally, however, hard wall contact was established between the two surfaces. We infer that adsorbed copolymers to a large extent are expelled from the gap between the surfaces in this surface-to-surface distance range. The force needed to expel copolymers from the inter-surface gap was shown to be equal to the surface pressure at the solid-liquid interface. We also studied the influence of the rate of approach and separation of the surfaces on the energy-distance curves. The process of expelling polymers from the surface-to-surface gap was shown to depend on the velocity of the approaching surfaces and the surface coverage. For high approach rates and/or large surface coverage's, the lateral mobility of the polymers was generally observed to restrict the expulsion process of polymers from the gap. However, rapidly repeated force curves measured at constant rate in succession were found to be perfectly reproducible.

  • 82.
    Eskilsson, K
    et al.
    YKI – Ytkemiska institutet.
    Ninham, BW
    Tiberg, F
    YKI – Ytkemiska institutet.
    Yaminsky, VV
    Interaction between hydrophilic surfaces in triblock copolymer solution1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 7287-7291Article in journal (Refereed)
    Abstract [en]

    We report on the interactions between fused quarts surfaces immersed in solutions of low molecular weight nonionic homopolymers and triblock copolymers. The polymers studied were a polyethylene oxide homopolymer and a triblock copolymer of the type polyethylene oxide - polytetrahydrofuran - polyethylene oxide. The surface force measurements were done by the interfacial gauge technique. In water, a strong repulsive force was observed at short surface separations. Similar effects, previously attributed to the presence of hydration water, are due to electro-steric interactions imposed by partial stabilisation and formation of a gel layer on silica. Interestingly, this repulsive interaction was suppressed and not noticed when small amounts of polymers were adsorbed, or when water was substituted for ethanol as medium. Adsorbed polymers induce a long range steric repulsion of a quite different character. However, in solutions of PEO homo polymers, when the distance between the surfaces decreases, the repulsive interaction levels off. It remains more or less constant with decreasing surface-to-surface distance in this region. In this depletion range polymers are partly expelled from the gap between the surfaces. When the surfaces were separated after compression, an adhesive force was observed. This indicates that some adsorbed macromolecules remained in the gap after compression. For the PEO homopolymer the interaction both on approach and separation, showed a weak dependence on polymer concentration over a wide range. For the block copolymers, however, a stronger concentration dependence was observed. For instance, close to the surface aggregation concentration we observed an attractive interaction at some distances. This attraction is caused by bridging of surface micelles. It does not shows up at higher copolymer concentrations where the surface are fully covered by polymers. At low copolymer concentrations the copolymer aggregates are expelled to some extent from the gap between the surfaces at small surface-to surface distances. This depletion leads to a weak distance indifferent region with a small constant repulsion. At higher concentrations the interaction is purely repulsive at all surface-to surface distances, at both approach and separation. We studied also the role of solvent on interaction between surfaces in copolymer solutions. Adsorption of copolymers to silica from ethanol did not show long range interaction patterns but was sufficient to induce adhesion between the surfaces.

  • 83. Feiler, A
    et al.
    Plunkett, MA
    YKI – Ytkemiska institutet.
    Rutland, MW
    YKI – Ytkemiska institutet.
    Atomic force microscopy measurements of adsorbed polyelectrolyte layers 1: Dynamics of forces and friction2003In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 19, p. 4173-4179Article in journal (Refereed)
    Abstract [en]

    The measurement of surface forces and friction between silica substrates bearing adsorbed layers acrylamide-1% [3-(2-methylpropionamide)propyl]trimethylammonium chloride (AM-MAPTAC) was examined using atomic force microscopy. The cationic polymer had a large molecular weight (900 000) and a very low charge density (1% MAPTAC units). The force curves in the presence of adsorbed polyelectrolyte showed a very long range repulsive interaction and large deformation on compression typical of electrosteric interactions and consistent with the expected adsorption profile. There was also a strong dependence on the scan rate with increased repulsion during approach and increased attraction during separation as the scan rate increased. The hysteresis was attributed entirely to a hydrodynamic interaction induced by the polyelectrolyte. At slow enough scan rates, the hysteresis between approach and retract curves was absent. The friction force measurements were sensitive to both applied load and scan rate. With increasing applied load, a critical load was apparent, above which the friction force increased. Upon decrease of the load, the friction force remained higher than that before the yield point, suggesting a metastable deformation of the polymer layer. In addition, the friction coefficient increased with increasing scan rate. At low scan rates the friction coefficient was lower than the bare surfaces, whereas at high scan rates the friction coefficient was significantly larger that obtained than for the bare surfaces. Subsequent force curves taken after friction measurements confirm that a permanent change in the polyelectrolyte layer had occurred. The magnitude of the repulsive interaction was reduced to about half of its original force

  • 84.
    Feiler, A
    et al.
    YKI – Ytkemiska institutet.
    Stiernstedt, J
    YKI – Ytkemiska institutet.
    Theander, K
    YKI – Ytkemiska institutet.
    Jenkins, P
    Rutland, M
    YKI – Ytkemiska institutet.
    Effect of capillary condensation on friction force and adhesion2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 2, p. 517-522Article in journal (Refereed)
    Abstract [en]

    Friction force measurements have been conducted with a colloid probe on mica and silica (both hydrophilic and hydrophobised) after long (24 hour) exposure to high humidity air. Adhesion and friction measurements have also been performed on cellulose substrates. The long exposure to high humidity led to a large hysteresis between loading and unloading in the friction measurements with separation occurring at large negative applied loads. The large hysteresis in the friction-load relationship is attributed to a contact area hysteresis of the capillary condensate which built up during loading and did not evaporate during the unloading regime. The magnitude of the friction force varied dramatically between substrates and was lowest on the mica substrate and highest on the hydrophilic silica substrate with the hydrophobised silica and cellulose being intermediate. The adhesion due to capillary forces on cellulose was small compared to that on the other substrates, due to the greater roughness of these surfaces.

  • 85.
    Feiler, AA
    et al.
    YKI – Ytkemiska institutet.
    Bergström, L
    YKI – Ytkemiska institutet.
    Rutland, MW
    YKI – Ytkemiska institutet.
    Superlubricity using repulsive van der Waals forces2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 6, p. 2274-2276Article in journal (Refereed)
    Abstract [en]

    Using colloid probe atomic force microscopy, we show that if repulsive van der Waals forces exist between two surfaces prior to their contact then friction is essentially precluded and supersliding is achieved. The friction measurements presented here are of the same order as the lowest ever recorded friction coefficients in liquid, though they are achieved by a completely different approach. A gold sphere attached to an AFM cantilever is forced to interact with a smooth Teflon surface (templated on mica). In cyclohexane, a repulsive van der Waals force is observed that diverges at short separations. The friction coefficient associated with this system is on the order of 0.0003. When the refractive index of the liquid is changed, the force can be tuned from repulsive to attractive and adhesive. The friction coefficient increases as the Hamaker constant becomes more positive and the divergent repulsive force, which prevents solid-solid contact, gets switched off

  • 86. Feldötö, Z
    et al.
    Pettersson, T
    Dedinaite, A
    YKI – Ytkemiska institutet.
    Mucin – electrolyte interactions at the solid/liquid interface probed by QCM-D2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, p. 3348-3357Article in journal (Refereed)
    Abstract [en]

    he interaction between mucin and ions has been investigated by employing the quartz crystal microbalance technique with measurement of energy dissipation. The study was partially aimed at understanding the adsorption of mucin on surfaces with different chemistry, and for this purpose, surfaces exposing COOH, OH, and CH3 groups were prepared. Mucin adsorbed to all three types of functionalized gold surfaces. Adsorption to the hydrophobic surface and to the charged hydrophilic surface (COOH) occured with high affinity despite the fact that in the latter case both mucin and the surface were negatively charged. On the uncharged hydrophilic surface exposing OH groups, the adsorption of mucin was very low. Another aim was to elucidate conformational changes induced by electrolytes on mucin layers adsorbed on hydrophobic surfaces from 30 mM NaNO3. To this end, we investigated the effect of three electrolytes with increasing cation valance: NaCl, CaCl2 and LaCl3. At low NaCl concentrations, the preadsorbed layer expands, whereas at higher concentrations of NaCl the layer becomes more compact. This swelling/compacting of the mucin layer is fully reversible for NaCl. When the mucin layer instead is exposed to CaCl2 or LaCl3, compaction is observed at 1 mM. For CaCl2, this process is only partially reversible, and for LaCl3, the changes are irreversible within the time frame of the experiment. Finally, mucin interaction with the DTAB cationic surfactant in an aqueous solution of different electrolytes was evaluated with turbidimetry measurements. It is concluded that the electrolytes used in this work screen the association between mucin and DTAB and that the effect increases with increasing cation valency.

  • 87. Feldötö, Zsombor
    et al.
    Varga, Imre
    Blomberg, Eva
    YKI – Ytkemiska institutet.
    Influence of salt and rinsing protocol on the structure of PAH/PSS polyelectrolyte multilayers2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 22, p. 17048-17057Article in journal (Refereed)
    Abstract [en]

    A quartz crystal microbalance (QCM) and dual polarization interferometry (DPI) have been utilized to study how the structure of poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) multilayers is affected by the rinsing method (i.e., the termination of polyelectrolyte adsorption). The effect of the type of counterions used in the deposition solution was also investigated, and the polyelectrolyte multilayers were formed in a 0.5 M electrolyte solution (NaCl and KBr). From the measurements, it was observed that thicker layers were obtained when using KBr in the deposition solution than when using NaCl. Three different rinsing protocols have been studied: (i) the same electrolyte solution as used during multilayer formation, (ii) purewater, and (iii) first a salt solution (0.5M) and then purewater.When the multilayerwith PAH as the outermost layer was exposed to pure water, an interesting phenomenon was discovered: a large change in the energy dissipationwas measured with theQCM.This could be attributed to the swelling of the layer, and from bothQCMandDPI it is obvious that only the outermost PAH layer swells (to a thickness of 25-30 nm) because of a decrease in ionic strength and hence an increase in intra- and interchain repulsion, whereas the underlying layers retain a very rigid and compact structure with a low water content. Interestingly, the outermost PAH layer seems to obtain very similar thicknesses in water independent of the electrolyte used for the multilayer buildup. Another interesting aspect was that the measured thickness with the DPI evaluated by a single-layer model did not correlate with the estimated thickness from the model calculations performed on theQCM-Ddata. Thus,we applied a two-layermodel to evaluate theDPI data and the resultswere in excellent agreement with the QCM-D results. To our knowledge, this evaluation of DPI data has not been done previously.

  • 88. Fielden, ML
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Schillén, K
    Investigation of a 31% charged cationic polyelectrolyte interacting with sodium dodecyl sulfate in bulk solution and as a preadsorbed layer on mica. Low ionic strength1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 5366-5375Article in journal (Refereed)
    Abstract [en]

    The behavior of mixtures of a cationic polyelectrolyte of intermediate charge density (31%) and anionic surfactant both in bulk and at a negatively charged solid surface has been investigated. The polyelectrolyte employed was a random copolymer of the neutral acrylamide and cationic [3-(2-methylpropionamido)propyl]trimethylammonium chloride, and the surfactant was sodium dodecyl sulfate (SDS). Measurements of flocculation and electrophoretic mobility in bulk solution clearly showed a phase separation with a maximum in turbidity corresponding roughly to charge neutralization of the polyelectrolyte/surfactant complex. Conductivity measured at low SDS concentrations showed a strong uptake of ions by the polyelectrolyte at a critical SDS concentration. The interferometric surface force apparatus was used to measure forces between muscovite mica surfaces onto which the polyelectrolyte was adsorbed from a 20 ppm, 10-4 M KBr solution. After the polymer solution was replaced with polymer-free 10-4 M KBr solution, a weak long range double-layer repulsion was observed between approaching surfaces, with a bridging attraction dominating at smaller separations. A weak adhesion was observed upon separating the surfaces. Addition of 4.2 ? 10-4 M SDS caused a large swelling of the preadsorbed polymer layer due to formation of an associative complex between the polymer and surfactant. Further increasing the SDS concentration decreased the force and layer thickness due to screening of the electrostatic repulsion within the layers and some desorption of polymer molecules. That a slight desorption did occur was supported by electron spectroscopy for chemical analysis measurements. The results broaden the understanding of the effect of polyelectrolyte charge density on the interaction of preadsorbed polyelectrolyte layers with oppositely charged surfactants.

  • 89. Fielden, ML
    et al.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Verrall, E
    Investigating the adsorption of the gemini surfactant "12-2-12" onto mica using atomic force microscopy and surface force apparatus measurements1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, p. 3924-3934Article in journal (Refereed)
    Abstract [en]

    The adsorption of the cationic gemini surfactant 1,2-bis(n-dodecyldimethylammonium)ethane dibromide on mica was followed by measuring forces between mica surfaces and by atomic force microscopy (AFM) imaging. The surface charge was found to be neutralized at total surfactant concentrations between 8 ? 10-7 and 5 ? 10-6 M, depending on equilibration time, as judged by the elimination of the repulsive electrostatic double-layer force. At around this concentration, monolayer aggregates of the surfactant started to form on the surface, varying in size between 8 and 130 nm across and between 0.5 and 0.6 nm high. The coverage rapidly increased with a small increase in surfactant concentration, as seen by AFM images. In the concentration range (5 ? 10-6)-(1 ? 10-4) M the surfactant continued to adsorb steadily as judged by the increase in the double-layer repulsion between surfaces. The hydrophobicity of the surfaces was confirmed by the magnitude of the force required to separate the surfaces, which increased from 20 mN/m in pure water to 120 mN/m at 4.6 ? 10-6 M, up to 270 mN/m at 9.0 ? 10-6 M; it then stayed virtually constant. AFM imaging showed that, in this range, a significant amount of the surfactant adsorbed on top of the monolayer, although neither technique suggested that the adsorbing material aggregated into bilayer patches. At 1.8 ? 10-4 M, a full bilayer formed on each surface, causing an increase in the compressed layer thickness from 1 to 4 nm, and a reduction in pull-off force to 5-10 mN/m. In this concentration range, the nucleation and growth of the complete bilayer was directly observed with AFM. It appeared to occur as isotactic growth of patches, which were initially around 70 nm in size and evenly distributed. These patches grew and joined together to form a flat bilayer over a time scale of around 2 h. Between 1.8 ? 10-4 and 7.6 ? 10-4 M, a non-DLVO (Derjaguin-Landau-Verwey-Overbeek) force was observed between 12 and 7 nm, followed by an attractive force which pulled the surfaces into bilayer-bilayer contact. The extra repulsive force, which has not been observed previously with cationic surfactant bilayers, was probably due to additional surfactant adsorbed outside the bilayer. AFM imaging confirmed that an extra layer was present above the critical micellar concentration (cmc), as indicated by a significant increase in surface roughness from 0.5 nm to 7-8 nm.

  • 90.
    Folmer, B
    et al.
    YKI – Ytkemiska institutet.
    Holmberg, K
    YKI – Ytkemiska institutet.
    Svensson, M
    Interaction of Rhizomucor miehei lipase with an amphoteria surfactant at different pH values1997In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, p. 5864-5869Article in journal (Refereed)
    Abstract [en]

    The interactions of surfactants with the enzyme Rhizomucor miehei lipase have been studied. From earlier studies, it is known that the enzyme binds to cationic surfactants but not to nonionic and anionic surfactants. The influence of the charge of the surfactant has been studied using surface tension, ellipsometry and micro calorimetry techniques. The study has included several anionic, nonionic and cationic surfactants, but the major part of teh work has been concerned with a zwitterionic surfactant (N-(2-hydroxy) dodecyl sarcosine sodium salt) The zwitterionic surfactant changes its charge from anionic at high pH to cationic at low pH values. It has been confirmed that when the headgroup is positively charged, the surfactant binds to teh enzyme. However, the number of surfactants that bind to the enzyme is dependent on the structure of the surfactant. An interaction model has been proposed. Negatively charged sites on the enzyme are available for binding cationic surfactant headgroups. Furthermore, a hydrophobic group is available close to the anionic site, which makes a hydrophobic attraction possible between the tail of the cationic surfactant and the enzyme.

  • 91.
    Folmer, B
    et al.
    YKI – Ytkemiska institutet.
    Kronberg, B
    YKI – Ytkemiska institutet.
    The effect of surfactant-polymer association on the stabilities of foams and thin films: sodium dodecyl sulfate and poly(vinyl pyrrolidone)2000In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 16, p. 5987-5992Article in journal (Refereed)
    Abstract [en]

    The foaming behaviour of the anionic surfactant Sodium Dodecyl Sulphate (SDS) has been studied in the presence and in the absence of the nonionic polymer Poly Vinyl Pyrrolidone (PVP). A current model of surfactant - polymer aggregation in bulk and at the air-water interface is related to the foam and thin film stability. Tensiometry, foaming tests and a thin film balance are used to obtain this relationship. It is found that at very low surfactant concentrations, where the surfactants are present as unimers in the bulk solution, there is association between surfactants and polymer at the liquid/air surface, giving an increased foam and thin film stability as compared to the same surfactant concentration but without polymer. As the surfactants and polymers associate in the bulk solution there is desorption of surfactants and polymers from the surface rendering a decrease in foam and thin film stability. At higher surfactant concentrations the bulk viscosity is significantly increased due to the presence of both micelles and saturated micelle-polymer complexes. Also the surfactant surface coverage at the liquid/air surface has reached its maximum value and is similar to the SDS solution above the CMC when no polymer is present. Both the increased surface viscosity and the increased bulk viscosity contribute to the observed foam and film stability. In the thin film studies several stratification steps are observed probably due to micelles, which are being pushed out of the film.

  • 92.
    Friberg, S
    et al.
    YKI – Ytkemiska institutet.
    Blute, I
    Kunieda, H
    Stenius, P
    YKI – Ytkemiska institutet.
    Stability of hydrophobic foams1986In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 2, p. 659-664Article in journal (Refereed)
  • 93.
    Friberg, SE
    et al.
    YKI – Ytkemiska institutet.
    Claesson, P
    YKI – Ytkemiska institutet.
    Hydrolysis and condensation of alkylmethoxysilanes. Studied by means of the Langmuir-Blodgett technique and electron spectroscopy for chemical analysis1995In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 11, p. 2652-2660Article in journal (Refereed)
    Abstract [en]

    Hydrolysis and condensation reactions of octadecyltrimethoxysilane (C18TMS) and octadecyldimethylmethoxysilane (C1sDMMS) have been studiedby means ofthe Langmuir-Blodgetttechnique and electron spectroscopy for chemical analysis (ESCA). C18TMS can form linear two-dimensional polymers, while C1eDMMS forms only dimers. The polymerization/dimerization rate seems to increase in the sequence pH 5.6—11—1. At pH 11 the spread monolayer contracts when electrolyte is added and becomes less compressible. This indicates decreased electrostatic repulsion within the ionized monolayer and/or a higher level of polymerization/dimerization of the film molecules. C18DMMS could be compressed at pH 1 to a surface area of ~18 Å2, before the film enters a condensed phase. Constant surface pressure-area relaxation experiments indicate that a nucleation process takes place in the C18DMMS film at pH 1 for sr = 20 mN m-l. In contrast, the C1sTMS film at pH 1 was stable for more than 12 h at 40 mN m-l. When two subsequent compression steps are applied with a delay of 16 h the C18TMS films (pH 5.6 and 11) reproduced the condensed pH 1 film, with molecular areas of ~20 Å2, while the C18DMMS film (pH 5.6 and 11) was still in an expanded state. A condensed state in the two-dimensional film indicates good packing and strong cohesion forces between the hydrocarbon chains. The dimer-forming C1sDMMS will not achieve the same strong cohesion that we find in the fully polymerized C18TMS films. For the C1aTMS film at pH 11 a lowering of the barrier speed increased the polymerization rate, as observed by decreasing compressibility and decreasing areas per molecule for a given surface pressure. Langmuir-Blodgett films analyzed by ESCA confirmed these results.

  • 94. Fröberg, JC
    et al.
    Arnebrant, T
    McGuire, J
    Claesson, PM
    YKI – Ytkemiska institutet.
    Effect of structural stability on the characteristics of adsorbed layers of T41998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 456-462Article in journal (Refereed)
    Abstract [en]

    The interferometric surface force technique has been employed to determine how the structural stability of globular proteins affects their adsorption and the interactions between adsorbed protein layers. The system consisted of positively charged bacteriophage T4 lysozyme and negatively charged mica surfaces. The wild type and one synthetic mutant of the protein, Ile3->Trp, differing in structural stability while the total charge and tertiary structure are the same, were studied. The adsorption leads to a nearly complete neutralization of the negative surface charge of mica, reducing the long-range electrostatic double-layer interaction acting between mica surfaces. The thickness of the adsorbed layer is for the wild type consistent with the dimensions of the protein, while the Ile3->Trp mutant gives a layer with a thickness smaller than any of its native dimensions. Another consequence of the difference in structural stability is that the short range attraction between one protein layer and one bare mica surface is an order of magnitude larger for the Ile3->Trp mutant than for the wild type. The results demonstrate that the less stable mutant loses its tertiary structure upon adsorption, whereas the wild type retains its globular shape. These differences provide an understanding for the differences in adsorbed amount and complements the information about changes in secondary structure upon adsorption observed with other methods.

  • 95. Fröberg, JC
    et al.
    Blomberg, E
    YKI – Ytkemiska institutet.
    Claesson, PM
    YKI – Ytkemiska institutet.
    Desorption of lysozyme layers by sodium dodecyl sulfate studied with the surface force technique1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, p. 1410-1417Article in journal (Refereed)
    Abstract [en]

    The effect of sodium dodecyl sulphate (SDS) on pre-adsorbed lysozyme layers on mica was investigated using a surface force technique and ESCA. Lysozyme was adsorbed onto mica surfaces from a 0.2 mg/ml protein solution containing 1 mM NaCl at pH 5.6 which nearly neutralizes the surface charge on the mica, and it was found that the adsorption was irreversible with respect to dilution with 1 mM NaCl solution. Addition of SDS (0.83 to 4 mM) to the bulk solution does not induce large-scale desorption of the adsorbed protein layers, the layer thickness remains the same, 4.8±0.4 nm, up to 4 mM. However, addition of SDS results in a pronounced gradual increase in the interfacial charge manifested in the long-ranged double-layer repulsion. At 6 mM the surfactant binding to the protein layer does change the layer properties. An initial surfactant induced denaturation of the adsorbed protein occurs, whereby the thickness of the layers decreases to 2.7±0.3 nm, yet the interfacial charge remains high, similar in magnitude to the charge of mica. When SDS is introduced at the cmc the protein layers are completely desorbed, we thus conclude that the desorption results from the combined effect of protein denaturation, and the increased complex charge.

  • 96. Gerdes, S
    et al.
    Cazabat, A-M
    Ström, G
    YKI – Ytkemiska institutet.
    The spreading of silicone oil droplets on a surface with parallel V-shaped grooves1997In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 13, p. 7258-7264Article in journal (Refereed)
    Abstract [en]

    In this paper we report on dynamic wetting studies on model rough surfaces. A series of well-defined model surfaces has been manufactured and the dynamic wetting of silicone oil droplets on these surfaces has been studied. The surface structures are etched parallel v-shaped grooves with varying width and spacing. Spreading has been studied in two different time regimes with two different techniques. At "short times", the liquid does not penetrate significantly inside the grooves ahead of the edge of the main drop. At "long times", the penetration of liquid inside the grooves is significant and the grooves are practically filled up at the edge of the main drop, which we consider as the "contact line". In both regimes, contact line velocity, v, and dynamic contact angle, q, are measured in the flat parts between grooves. The spreading parallel to the grooves is described by Tanner-like laws in both cases, but with different characteristics: At short times, the spreading velocity increases with the area covered by grooves. At long times no effect of the grooves are observed until the distance between the grooves are smaller than approximately 30µm. In this case, it appears that the effect is correlated with the disturbance of the contact line due to the interaction of the groove 'defects'.

  • 97. Gerdes, S
    et al.
    Cazabat, A-M
    Ström, G
    Tiberg, F
    YKI – Ytkemiska institutet.
    Effect of surface structure on the spreading of a PDMS droplet1998In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 14, p. 7052-5057Article in journal (Refereed)
    Abstract [en]

    The effect of surface structures on the dynamics of wetting was investigated through measurements of the dynamic contact angle and spreading velocity of a PDMS droplet spreading over a surface with a gridlike pattern of V-shaped surface channels. A rim of liquid was observed to spread out in the channels ahead of the dropfront after a short time of spreading (seconds). The characteristics of the rim were investigated as well, with respect to channel depth and spacing and compared to the spreading characteristics in channels with no intersections, i.e. parallel channels. The macroscopic droplet appears to be dependent on the rim for spreading, before the rim had appeared the dropfront spread stepwise between the perpendicular channels and did not advance until the channel was liquid filled. The spreading on the filled channels was correlated to the surface area covered by channels rather than the depth and width of the individual channel. The spreading of the rim follows the expected scaling with (time)1/2 and (channel depth)1/2 ..

  • 98.
    Gerdes, S
    et al.
    YKI – Ytkemiska institutet.
    Tiberg, F
    YKI – Ytkemiska institutet.
    Dynamic wetting of silica by aqueous triblock copolymer solutions -Low concentrations1999In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 15, p. 4916-4921Article in journal (Refereed)
    Abstract [en]

    We report on the wetting of silica by aqueous solutions of triblock copoly(ethylene oxide-tetrahydrofuran-ethylene oxide), PEO-PTHF-PEO. The wetting behaviour was measured by means of a Wilhelmy force balance and by direct images of the contact angle. The results show that the three-phase contact line (tcl) advances in jumps over the surface when this is immersed with constant rate into copolymer solutions. This stick-slip behaviour was studied with respect to both the concentration of copolymers in the solution and the immersion rate of the silica plate into the solution. The wetting results are compared with adsorption data obtained by ellipsometry and dynamic surface tension measurements. It is clear that the stick-slip spreading behaviour results from the same basic mechanisms as have previously been proposed to be responsible for the stick-slip spreading observed for short chain cationic surfactants. The pinning of the contact line is due to the formation (through adsorption) of an autophobic copolymer layer at the solid-vapour interface. At low copolymer concentrations, transport of copolymers to the solid-vapour interface seems to occur mainly through surface diffusion from the liquid-vapour interface to the three-phase contact line. De-pinning and slip occurs when the dynamic contact angle has increased above a critical value, which exceeds that stipulated by the Young's equation in the presence of the autophobic layer at the solid-vapour interface.

  • 99. Gestblom, B
    et al.
    Sjöblom, J
    YKI – Ytkemiska institutet.
    Dielectric properties of some microemulsion systems containing electrolytes1988In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 4, p. 360-364Article in journal (Refereed)
  • 100.
    Ghorbani, Morteza
    et al.
    KTH Royal Institute of Technology, Sweden; Sabanci University, Turkey.
    Olofsson, Karl
    KTH Royal Institute of Technology, Sweden.
    Benjamins, Jan Willem
    RISE - Research Institutes of Sweden, Bioscience and Materials, Surface, Process and Formulation.
    Loskutova, Ksenia
    KTH Royal Institute of Technology, Sweden.
    Paulraj, Thomas
    KTH Royal Institute of Technology, Sweden.
    Wiklund, Martin
    Grishenkov, Dmitry
    KTH Royal Institute of Technology, Sweden.
    Svagan, Anna
    KTH Royal Institute of Technology, Sweden.
    Unravelling the Acoustic and Thermal Responses of Perfluorocarbon Liquid Droplets Stabilized with Cellulose Nanofibers2019In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 35, no 40, p. 13090-13099Article in journal (Refereed)
    Abstract [en]

    The attractive colloidal and physicochemical properties of cellulose nanofibers (CNFs) at interfaces have recently been exploited in the facile production of a number of environmentally benign materials, e.g. foams, emulsions, and capsules. Herein, these unique properties are exploited in a new type of CNF-stabilized perfluoropentane droplets produced via a straightforward and simple mixing protocol. Droplets with a comparatively narrow size distribution (ca. 1-5 μm in diameter) were fabricated, and their potential in the acoustic droplet vaporization process was evaluated. For this, the particle-stabilized droplets were assessed in three independent experimental examinations, namely temperature, acoustic, and ultrasonic standing wave tests. During the acoustic droplet vaporization (ADV) process, droplets were converted to gas-filled microbubbles, offering enhanced visualization by ultrasound. The acoustic pressure threshold of about 0.62 MPa was identified for the cellulose-stabilized droplets. A phase transition temperature of about 22 °C was observed, at which a significant fraction of larger droplets (above ca. 3 μm in diameter) were converted into bubbles, whereas a large part of the population of smaller droplets were stable up to higher temperatures (temperatures up to 45 °C tested). Moreover, under ultrasound standing wave conditions, droplets were relocated to antinodes demonstrating the behavior associated with the negative contrast particles. The combined results make the CNF-stabilized droplets interesting in cell-droplet interaction experiments and ultrasound imaging. 

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