| 1. |
- Alexandrova, L, et al.
(författare)
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Confirmation of the heterocoagulation theory of flotation
- 1999
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 15, s. 7464-7471
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Tidskriftsartikel (refereegranskat)abstract
- To model the flotation process, we have used the microscopic method developed by Scheludko to study the stability of an aqueous thin film containing tetradecyltrimethylammonium bromide ( C14TAB ) between an air bubble and a silica substrate. Experiments were performed at a range of C14TAB concentrations and pH values. Spontaneous rupture of the thin aqueous film was interpretated in terms of heterocoagulation resulting from the preferential adsorption of relatively low surfactant concentrations at the vapour/solution interface causing a net positive charge while the solution/silica interface remained negatively charged. In addition, during the the three-phase-contact (TPC) expansion or de-wetting step following film rupture, the movement of TPC across the silica substrate leads to transfer of amine from the vapour/solution interface to the vapour/silica. This process resembles a Langmuir-Blodgett deposition process and emphasized the importance of the solution/vapour interface in the de-wetting process.
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| 2. |
- Barauskas, Justas, et al.
(författare)
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Cubic phase nanoparticles (Cubosome): Principles for controlling size, structure, and stability
- 2005
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 21:6, s. 2569-2577
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Tidskriftsartikel (refereegranskat)abstract
- Methods and compositions for producing lipid-based cubic phase nanoparticles were first discovered in the 1990s. Since then a number of studies have been presented, but little is known about how to control key properties such as particle size, morphology, and stability of cubic phase dispersions. In the present work we give examples of how these properties can be tuned by composition and processing conditions. Importantly we show that stable particle dispersions with consistent size and structure can be produced by a simple processing scheme comprising a homogenization and heat treatment step.
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| 3. |
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| 4. |
- Bogdanovic, G., et al.
(författare)
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Sliding friction between cellulose and silica surfaces
- 2001
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:19, s. 5911-5916
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Tidskriftsartikel (refereegranskat)abstract
- An atomic force microscope was used to measure kinetic friction forces between a colloidal cellulose sphere and different planar surfaces in air. The planar surfaces were bare silica, silica modified with a monolayer of alkyl ketene dimer (AKD), a common additive used for paper sizing, and silica with surface grafted terminal methyl groups. Friction was measured as a function of the effective load resulting from adhesive interactions between the cellulose sphere and the planar surface. Friction in the regime of low effective loads was shown to be a linear function of the load, and the friction coefficients determined from the slope of these curves were 0.26, 0.07, and 0.021 for the cellulose-silica, cellulose-AKD, and cellulose-methylated silica systems, respectively. The ratio between friction coefficients for the two first systems agrees well with that reported for paper in the presence and absence of AKD sizing agents, respectively. In the high effective load regime, deviations from linearity between measured friction and load were observed. This is an indication that we have single asperity contact, at least at high loads. These results were analyzed in terms of a contact mechanics transition equation, By making assumptions on the moduli of the materials, the interfacial shear strength tau and the contact radius ao were calculated. The results obtained through this analysis provide an important insight into the relationship between friction and chemical surface properties.
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| 5. |
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| 6. |
- Brinck, J, et al.
(författare)
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Influence of long-chain alcohols on the adsorption of nonionic surfactants to silica
- 1999
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 15, s. 7719-7724
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of surfactant-alcohol mixtures at the silica-water interface was studied by means of ellipsometry. The results show that addition of even small amounts of alcohol can have large effects on the characteristics of the adsorbed layer. For example, a 20% replacement of the octa(ethylene glycol) dodecyl (C12E8) surfactants by dodecanol results in an increase in the total surface excess of 80%. The thickness of the adsorbed layer, on the other hand, is virtually unaffected by the alcohol being added. Hence, as the alcohol content increases, the adsorbed surfactant aggregates at the silica-water interface mainly grow in the surface plane. A surfactant such as C12E5, which forms relatively large surface aggregates from the start, can only solubilize a small fraction of the long-chain alcohols before the system phase separates. This fraction was found not to result in any major structural changes in the surface layer. These findings are discussed in terms of surfactant packing and in relation to observations in bulk solutions reported earlier. Our study also includes measurements of adsorption and desorption kinetics for both the surfactant and the surfactant-alcohol systems. The main finding is that the effect of alcohol is most obvious in the desorption kinetics. We conclude that the effects observed are due to differences between the surfactant and the alcohol in monomer solubility.
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| 7. |
- Brinck, J, et al.
(författare)
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Kinetics of nonionic surfactant adsorption and desorption at the silica-water interface: Binary systems
- 1998
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 14, s. 5863-5876
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Tidskriftsartikel (refereegranskat)abstract
- This paper is the second of two dealing with the adsorption and desorption kinetics of nonionic surfactants at a solid-liquid interface. The first paper described a model of the kinetics of single nonionic surfactant adsorption.1 This work is now being completed by extending the theoretical model to cover binary surfactant systems. The evolution of the total surface excess during the adsorption and desorption has been modeled and compared with experimental results obtained by in situ null ellipsometry. In this comparison, the surface behavior of the two nonionic surfactant pairs C14E6-C10E6 and C12E5-C12E8 at a planar silica-water interface was studied. These binary systems represent two different types of polydispersity: different lengths of the hydrocarbon chains and unequal numbers of ethylene oxide groups in the hydrophilic headgroups. The critical micelle concentrations (cmcs) of the surfactants in the former pair therefore differ a great deal, whereas those of the surfactants in the latter pair are similar. A comparison between experiments and simulations showed good agreement. In an attempt to further analyze the experimental results, individual amounts adsorbed and concentration profiles were calculated. The results of these simulations showed that each surfactant in a given pair has a characteristic adsorption and desorption path. According to the model, this path is determined mainly by the mutual relationship between their cmcs.
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| 8. |
- Brinck, J, et al.
(författare)
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Kinetics of nonionic surfactant adsorption and desorption at the silica-water interface: One component
- 1998
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 14, s. 1058-1071
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we present a theoretical model which describes the kinetics of adsorption and desorption from a micellar solution of nonionic surfactants at a silica surface. Numerical calculations based on this model have been compared with experimental results of CnEm surfactant adsorption, obtained by ellipsometry, and show good agreement. The aim of this work was to develop a model for adsorption through a stagnant layer onto a solid, hydrophilic surface. The surface is considered to be planar and homogeneous. Outside the surface there is a micellar solution of a pure nonionic surfactant. Both monomers and micelles are considered to be able to adsorb. To facilitate the evaluation of the model, a computer program was written which solves the mathematical equations numerically. The course of adsorption and desorption of a number of short-chain CnEm surfactants has been simulated with this program. The results obtained, in terms of amounts adsorbed as a function of time, were compared with experimental data determined by time-resolved null ellipsometry. The same program was used to calculate concentration profiles outside the silica surface. Not only has this model made it possible for us to explain and better understand experimental results, but it has also allowed us to gain an understanding of how the course of adsorption and desorption is affected by parameters which are difficult to vary experimentally in a controlled way. Two examples of this, which will be discussed in this paper, are the effects of stagnant layer thickness and the relation between critical surface aggregation concentration (csac) and critical micelle concentration (cmc).
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| 9. |
- Brink, C, et al.
(författare)
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Using poly(ethylene imine) to graft poly(ethylene glycol) or polysaccharide to polystyrene
- 1992
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Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 66, s. 149-156
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Tidskriftsartikel (refereegranskat)abstract
- A novel method of grafting poly(ethylene glycol) (PEG) or polysaccharide to polystyrene has been developed. The non-charged hydrophilic polymer is firstly grafted to poly(ethylene imine). After prior oxidation of the solid surface, the graft copolymer is subsequently adsorbed. Analysis by electron spectroscopy for chemical analysis and ellipsometry indicates a trains-and-loops arrangement of the copolymer on the surface with densely packed PEG or polysaccharide chains oriented towards the bulk water phase. Ellipsometry also shows that whereas the PEG grafting is fast, the polysaccharide grafting is more sluggish. Attachment of both graft copolymers is completely irreversible, as seen also by ellipsometry. The surfaces obtained are highly protein repellent, as shown by enzyme-linked immunosorbent assay using fibrinogen and immunoglobulin G as model proteins.
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| 10. |
- Eriksson, J, et al.
(författare)
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Model cellulose films exposed to H. insolens glucoside hydrolase family 45 endo-cellulase—the effect of the carbohydrate-binding module
- 2005
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 285, s. 94-99
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Tidskriftsartikel (refereegranskat)abstract
- The effects of enzyme structure and activity on the degradation of model cellulose substrates were investigated by ellipsometry for the cellulase Humicola insolens GH45. The inactive variant D10N was found to adsorb at the cellulose surface but also to be incorporated into the cellulose films to an extent that depended on pH. For the native protein, the initial adsorption monitored for the inactive variant D10N was followed by enzyme-mediated degradation of the cellulose films. Again, a dependence on pH was found, such that higher pH resulted in slower enzymatic degradation. Removing the carbohydrate-binding module eliminated this pH dependence but also resulted in a decreased adsorption to the cellulose surface, and in a decreased net catalytic effect
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