| 1. |
- Berg, JM, et al.
(author)
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Forces between surfaces coated with a polymerizable surfactant before and after polymerization
- 1994
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 163, s. 289-298
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Journal article (peer-reviewed)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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| 2. |
- Berg, JM, et al.
(author)
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Interactions between mica surfaces in sodium polyacrylate solutions containing calcium ions
- 1993
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 161, s. 182-189
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Journal article (peer-reviewed)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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| 3. |
- Berg, JM, et al.
(author)
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Three-component Langmuir-Blodgett films with a controllable degree of polarity
- 1994
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In: Langmuir. - 0743-7463 .- 1520-5827. ; 10, s. 1225-1234
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Journal article (peer-reviewed)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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| 4. |
- Blomberg, E, et al.
(author)
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Adsorbed layers of human serum albumin investigated by the surface force technique
- 1991
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In: Journal of Dispersion Science and Technology. - 0193-2691 .- 1532-2351. ; 12, s. 179-200
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Journal article (peer-reviewed)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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| 5. |
- Blomberg, E, et al.
(author)
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Elastohydrodynamic effects with adsorbed layers in surface force measurements
- 1990
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 138, s. 291-293
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Journal article (peer-reviewed)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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| 6. |
- Blomberg, E, et al.
(author)
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Interaction between adsorbed layers of lysozyme studied with the surface force technique
- 1994
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In: Langmuir. - 0743-7463 .- 1520-5827. ; 10, s. 2325-2334
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Journal article (peer-reviewed)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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| 7. |
- Blomberg, E, et al.
(author)
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Short-range interaction between adsorbed layers of human serum albumin
- 1994
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In: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 166, s. 427-436
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Journal article (peer-reviewed)abstract
- The adsorption of human serum albumin (HSA) onto muscovite mica has been investigated by means of surface force and ESCA measurements. The range of protein concentration explored was 0.001-1.0 mg/ml in 10-3 M NaCl at pH 5.6. It was found that negatively charged albumin adsorbs onto negatively charged mica. Co-adsorption of small ions into the adsorbed protein layer was also inferred. Small structural changes are induced by the adsorption, and further structural changes can be induced by applying an external compressive force. The structure of the adsorbed layer depends on the surface density. As surfaces with a low adsorption density of HSA are brought together, the protein molecules are able to diffuse along the surface, facilitating the merging of the two HSA layers into one single HSA layer in the gap between the surfaces. At high surface density crowding effects impede the rearrangement of the HSA layers and two separate layers of HSA remain in the gap between the surfaces. An adhesion force is present at low packing but not at high packing densities. It was found that the short-range interaction between one HSA-coated surface and one bare mica surface was strongly attractive, demonstrating that the adhesion forces likely are induced by HSA molecules bridging between two surfaces and not by attractive interactions between the proteins themselves.
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| 8. |
- Cho, DL, et al.
(author)
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Structure and surface properties of plasma polymerized acrylic acid layers
- 1990
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In: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 41, s. 1373-1390
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Journal article (peer-reviewed)abstract
- Thin plasma polymerized layers of acrylic acid (PPAA) were deposited onto polyethylene and muscovite mica surfaces. Structure and surface properties of the deposited layer depend on the polymerization conditions. The content of carboxylic groups in the layer decreases, whereas the degree of crosslinking or branching increases, with increasing discharge power. A soft, sticky layer with a low contact angle against water is obtained when a low discharge power (5 W) is used. In contrast, a hard film with a rather high water contact angle is obtained when the discharge power is high (50 W). A surface force apparatus was employed to study some film properties including adhesion force, crack formation, and capillary condensation. The adhesion force between plasma polymerized acrylic acid layers prepared at a low discharge power is high in dry air. It decreases remarkably in humid air and no adhesion is observed in water. In dry air, the adhesion force between PPAA layers decreases as the discharge power increases.
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| 9. |
- Claesson, PM, et al.
(author)
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Amine functionalized surfactants - pH effects on adsorption and interaction
- 1992
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In: Progress in Colloid and Polymer Science. - 0340-255X .- 1437-8027. ; 88, s. 64-73
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Journal article (peer-reviewed)abstract
- The interactions between layers of two hydrolyzable surfactants, dodecylamine (DA) and tetraoxyethylene dodecylamine (TEDA), adsorbed on negatively charged muscovite mica have been investigated. It was found that the variation of the interaction and adsorption as a function of pH was similar, but not identical, for the two kinds of surfactants. At a concentration of 10-4 M at low pH (below 8) both types of surfactants adsorb electrostatically to form a monolayer. The resulting surfaces have a hydrophobic character, particularly in the case of dodecylamine. A series of events takes place as the pH is increased. For DA the first event is that uncharged molecules adsorb within the monolayer. This does not occur to any significant degree for TEDA due to steric hindrance within the adsorbed layer. In the next step a bilayer builds up on the surface. The binding of the outer layer is stronger for DA than for TEDA. The DA bilayer becomes uncharged at pH 10.3, and liquid dodecylamine droplets, which phase separate from the bulk solution at this pH-value, precipitate on the surface. At pH-values above 11-12 the affinity between both types of surfactants and the surface decreases significantly, resulting in a less ordered first layer. In addition a strong surface charge develops that prevents multilayer build-up.
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| 10. |
- Claesson, PM, et al.
(author)
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Forces between hydrophobic surfaces coated with ethyl(hydroxyethyl)cellulose in the presence of an ionic surfactant
- 1991
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In: Langmuir. - 0743-7463 .- 1520-5827. ; 7, s. 1441-1446
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Journal article (peer-reviewed)abstract
- 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).
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