| 1. |
- Bastardo, LA, et al.
(författare)
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Deuterium isotope effects on the interaction between hyperbranched polyethylene imine and an anionic surfactant
- 2005
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Ingår i: Journal of Physical Chemistry B. - 1520-6106 .- 1520-5207. ; 109, s. 16196-16202
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Tidskriftsartikel (refereegranskat)abstract
- Solvent isotope effects on the interaction between the hyperbranched cationic polyelectrolyte, polyethylene imine (PEI), and the anionic surfactant sodium dodecyl sulfate (SDS) were investigated using potentiometric titration and eletrophoretic mobility measurements. In the basic pH range a significantly higher fraction of the amine groups was found to be protonated when the PEI was dissolved in D2O compared to H2O at the same pH/pD. The difference in polymer charge in the two solvents gradually decreases with decreasing pH and it completely diminishes at around pH=4. Electrophoretic mobility measurements of PEI/SDS complexes at different pH values correlated very well with these observations. At pH/pD≈9 a much higher mobility of the PEI/SDS complexes was found at low surfactant concentrations in D2O than in H2O, and the charge neutralization point shifted to a considerably larger surfactant concentration in heavy water. These results can be explained by the significantly higher charge density of the PEI in D2O compared to H2O. On the other hand, at the natural pH/pD as well as at pH=4 and pD=4 conditions the PEI molecules have roughly equal charge density which results in very similar charged characteristics (mobilities) of the PEI/SDS complexes as well as the same charge neutralization SDS concentration. It can be concluded, that extreme care must be taken in the general analysis of those experiments where weak polyelectrolyte/surfactant aggregates are investigated in heavy water and then these observations are correlated with structures of the same system in water.
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| 2. |
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| 3. |
- Berg, JM, et al.
(författare)
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Forces between surfaces coated with a polymerizable surfactant before and after polymerization
- 1994
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 163, s. 289-298
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Tidskriftsartikel (refereegranskat)abstract
- The forces between layers of a cationic polymerizable surfactant, cetyl p-vinylbenzyl dimethyl ammonium chloride (CVDAC), adsorbed onto muscovite mica have been measured with a surface force technique. The forces were measured both prior to and after partial W polymerization of the adsorbed layers, and the stability of adsorbed bilayers after dilution of the adsorption solution was studied for these two cases. Due to their large headgroup, CVDAC molecules do not pack efficiently into monolayers and bilayers. This can be observed by, for instance, the lower surface potential of adsorbed bilayers and the lower pull-off force from monolayer contact, compared to what is found for simpler surfactants like CTAB. It was also found that surface aggregates build up on top of the bilayer, due to the partly hydrophobic headgroup. When the bilayer structure, including the surface aggregates, is polymerized, it is stabilized both with respect to mechanical forces and with respect to dilution of the surrounding solution
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| 4. |
- Berg, JM, et al.
(författare)
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Interactions between mica surfaces in sodium polyacrylate solutions containing calcium ions
- 1993
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 161, s. 182-189
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Tidskriftsartikel (refereegranskat)abstract
- The forces acting between negatively charged muscovite mica surfaces immersed in solutions containing sodium polyacrylate (NaPAA) have been studied. No evidence for PAA adsorption in the absence of calcium ions in the solution was found. However, at a CaCl2 concentration of about 3x10-3 M a layer of PAA adsorbed on each surface. At large separations, the forces between the PAA-coated surfaces were dominated by repulsive double-layer forces. At separations below 50-80 Å, depending on the solution conditions, an attractive force in excess of the van der Waals attraction was observed. The adhesion force between the layers was 7-8 mN/m at pH 6 and increased somewhat with increasing pH to about 9 mN/m at pH 10. We argue that both the long-range attraction and the adhesion force primarily are due to COO- - Ca2+ --OOC bridges between the opposing surfaces and possibly charge correlation effects. It was found that calcium ions bind to the PAA and to the mica surface, whereby the electrostatic repulsion between the polyelectrolyte and the surface is lowered. We suggest that this is the main re ason why Calcium ions promote the adsorption of PAA onto negatively charged minerals. However, it also seems likely that calcium ions increase the attractive interactions between the surface and the PAA segments.
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| 5. |
- Berg, JM, et al.
(författare)
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Three-component Langmuir-Blodgett films with a controllable degree of polarity
- 1994
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 10, s. 1225-1234
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Tidskriftsartikel (refereegranskat)abstract
- Two different series of mixed Langmuir-Blodgett (LB) films with a controllable degree of polarity, deposited on mica, have been studied by wetting and surface force techniques. Both series contain of 50% eicosylamine (EA). Films of one series consist of EA, arachidic acid and docosanedioic acid, while those of the other consist of EA, 1-eicosanol and 1,22-docosanediol. Carboxylic acid groups give lower contact angles than hydroxy groups. Concerning the stability of the LB films in aqueous solutions, repeated exposure to a three-phase line and high salt solutions were found to cause breakdown. Surface force measurements on carboxylic acid-containing films show that films with a 0% (contact angle = 113°) and 25% (contact angle ≈ 90°) content of diacid interact with a long-range (hydrophobic) attraction across water. No similar long-range attraction is observed for the 50% case (contact angle ≈ 65°). Surface force measurements also detected instabilities and imperfections of the films.
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| 6. |
- Bergeron, V, et al.
(författare)
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Disjoining pressure measurements for foam films stabilized by a nonionic sugar-based surfactant
- 1996
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 12, s. 1336-1342
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Tidskriftsartikel (refereegranskat)abstract
- Disjoining pressure isotherms for foam films made from a nonionic surfactant, octyl b-glucoside, are measured at different surfactant concentrations, ionic strengths and solution pH values. Below the cmc an electrostatic double-layer repulsion is present and dominates the long-range interaction. The decay length of the forces agrees with the expected Debye length and the measured long-range interactions are consistent with solutions to the non-linear Poisson-Boltzmann equation using constant charge conditions. The deduced surface charge densities increase with pH and ionic strength but decrease with increasing surfactant concentration. At, or just above, the cmc, surfactant covers the interface and suppresses the charge sufficiently to induce a transition from a common black film to a Newton black film. Ultimately, the film stability is determined by both surface forces and elasticity. Combining both, via an overall film tension, leads to a general expression for the film elasticity.
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| 7. |
- Bergström, M, et al.
(författare)
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Small-angle neutron scattering study of mixtures of cationic polyelectrolyte and anionic surfactant: Effect of polyelectrolyte charge density Polyelectrolyte and Anionic Surfactant: Effect of Polyelectrolyte Charge
- 2004
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Ingår i: Journal of Physical Chemistry B. - 1520-6106 .- 1520-5207. ; 108, s. 1874-1881
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Tidskriftsartikel (refereegranskat)abstract
- We have studied mixtures of an anionic surfactant (deuterated sodium dodecyl sulfate, SDS-d) and cationic polyelectrolytes with different charge densities (10%, 30%, 60%, and 100%) using small-angle neutron scattering (SANS). Near compositions corresponding to charge neutralization, the solutions phase separate into a complex phase (precipitate) consisting of, in the cases of 30%, 60%, and 100% charge density, a two-dimensional (2D) hexagonal lattice of close-packed cylindrical micelles and a clear liquid. When either polyelectrolyte with charge density less than 100% or SDS-d is present in sufficient excess, the solution becomes clear and isotropic, and from the scattering data we may conclude that prolate or rod-shaped micelles are present. The micelles are seen to grow in length with increasing SDS-d concentration and polyelectrolyte charge density from about 80 Å to 550 Å, whereas the cross-sectional radius is 15 Å and approximately constant. The number of micelles per polyelectrolyte chain is found to be slightly larger than unity (1-6). In some of the (turbid) samples rod-shaped micelles are found to coexist with larger polyelectrolyte-surfactant complexes. Solutions consisting of 10% charged polyelectrolyte and SDS-d are very viscous and gellike, and the complex phase is much less defined with a much larger distance between adjacent aggregates in the complex phase.
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| 8. |
- Blomberg, E, et al.
(författare)
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Adsorbed layers of human serum albumin investigated by the surface force technique
- 1991
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Ingår i: Journal of Dispersion Science and Technology. - 0193-2691 .- 1532-2351. ; 12, s. 179-200
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between human serum albumin (HSA) layers adsorbed from solution onto muscovite mica have been investigated by means of surface force measurements. The effects of varying the ionic strength and the serum albumin concentration have been studied at pH=5.5. The negatively charged protein cannot be desorbed from the negatively charged mica surface by dilution with water. The thickness of the (compressed) adsorbed layer is small compared to the dimension of HSA, except at the highest concentration used (1mg/ml). Hence, under a compressive load at low packing densities the protein conformation on the surface is different from that in bulk solution. No adhesion was observed when the amount adsorbed was large. However, an attractive
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| 9. |
- Blomberg, E, et al.
(författare)
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Elastohydrodynamic effects with adsorbed layers in surface force measurements
- 1990
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 138, s. 291-293
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Tidskriftsartikel (refereegranskat)abstract
- When two elastic surfaces carrying adsorbed layers are forced together under high loads, as in measurement with the surface forces apparatus, a bell-shaped deformation develops in the flattened contact zone. This behavior is due to the elastohydrodynamic "lubrication" of the adsorbed layer. Compression of molecules thus trapped between the surfaces may under some cicumstances, e.g., in the cases of surfaces carrying weakly adsorbed proteins, lead to irreversible changes in the adsorbed layer and consequently in the surface interaction.
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| 10. |
- Blomberg, E, et al.
(författare)
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Interaction between adsorbed layers of lysozyme studied with the surface force technique
- 1994
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 10, s. 2325-2334
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Tidskriftsartikel (refereegranskat)abstract
- The surface force technique was employed to investigate the adsorption of positively charged lysozyme onto negatively charged mica surfaces in 10-3 M NaCl at pH 5.6 at lysozyme concentrations ranging from 0.002 to 0.2 mg/ml. At equilibrium the adsorbed lysozyme nearly neutralizes the surface charge of the mica at all bulk lysozyme concentrations investigated. Prior to charge neutralization the decay length of the longrange force is consistent with the electrostatic double-layer force predicted by the DLVO theory. At low concentration, 0.002 mg/ml, a densely packed side-on oriented layer adsorbs on the mica surface. Above 0.02 mg lysozyme/ml, a rather thick layer is adsorbed onto the surface. It consists of an inner, strongly bound layer of both side-on and end-on adsorbed proteins and outer, weakly adsorbed proteins. An adhesion force is established upon contact of the adsorbed protein layers. The force measured between one lysozyme coated surface and one bare mica surface is attractive at short separations. It was demonstrated that at a concentration of 0.02 mg/ml, lysozyme adsorbs "irreversibly" with respect to dilution with 10-3 M NaCl.
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