| 1. |
- 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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| 2. |
- Dedinaite, A, et al.
(författare)
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Interactions between surfaces coated with cationic hydrophobically modified polyelectrolyte in the presence and the absence of oppositely charged surfactant
- 2000
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Ingår i: Progress in Colloid and Polymer Science. - 0340-255X .- 1437-8027. ; 116, s. 84-94
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Tidskriftsartikel (refereegranskat)abstract
- (1) Department of Chemistry Surface Chemistry Royal Institute of Technology 100 44 Stockholm and Institute for Surface Chemistry, Box 5607, 114 86 Stockholm Sweden (2) Laboratoire de Physico-Chimie Macromoleculaire, UMR-7615, ESPCI CNRS, Universite Pierre et Marie Curie ESPCI, 10 Rue Vauquelin, 75231 Paris Cedex 5, France The association between a cationic hydrophobically modified polyelectrolyte and an anionic surfactant was investigated in bulk solution and at a negatively charged solid surface. The bulk association was followed by measurements of turbidity and electrophoretic mobility. The maximum turbidity of the solution was found to closely coincide with the point of zero electrophoretic mobility of the aggregates. The forces acting between negatively charged mica surfaces across a dilute aqueous solution of the hydrophobically modified polyelectrolyte were monitored using surface force measurements. The presence of hydrophobic side chains on the polyelectrolyte leads to adsorption in an inner rather compact layer and an outer extended layer. After dilution only the inner layer remains adsorbed to the surface. In the next step, sodium dodecyl sulphate (SDS) was added. It was found that the anionic surfactant is incorporated in the adsorbed layer even at very low bulk concentrations. As the surfactant concentration is increased stepwise the layer first swells and relaxes very slowly during compression. At higher SDS concentrations, desorption occurs. The interfacial properties of the hydrophobically modified polyelectrolyte alone and in mixtures with SDS are in many ways strikingly different to those of non-hydrophobically modified polyelectrolytes having a similar linear charge density. This is due to the importance of hydrophobic interactions between the hydrophobic side chains of the polyelectrolyte and between these groups and the nonpolar part of the surfactant
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| 3. |
- Dedinaite, A, et al.
(författare)
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Polyelectrolyte-surfactant layers: Adsorption of preformed aggregates versus adsorption of surfactant to preadsorbed polyelectrolyte
- 2000
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 16, s. 5257-5266
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Matsson, MK, et al.
(författare)
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Adsorption of alkyl polyglucosides on the solid/water interface: Equilibrium effects of alkyl chain length and head group polymerization
- 2004
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 20, s. 4051-4058
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Tidskriftsartikel (refereegranskat)abstract
- The equilibrium adsorption behavior of two n-alkyl-b-D-glucosides (octyl, C8G1 and decyl, C10G1) and four n-alkyl-β-D-maltosides (octyl, C8G2, decyl, C10G2, dodecyl, C12G2 and tetradecyl, C14G2) from aqueous solution on a titania surface, as measured by ellipsometry, has been investigated. The main focus has been on the effect of changes in the alkyl chain length and head group polymerization, but a comparison with their adsorption on the silica/water and air/water interface is also presented. Some comparison with the corresponding adsorption of ethylene oxide surfactants, in particular C10E6 and C12E6 is given as well. For all alkyl polyglucosides, the maximum adsorbed amount on titania is reached slightly below cmc where it levels off to a plateau and the amount adsorbed corresponds roughly to a bilayer. However, there is no evidence that this is the actual conformation of the surfactant assemblies on the surface, but the surfactants could also be arranged in a micellar network. On hydrophilic silica, the adsorbed amount is a magnitude lower than on titania, corresponding roughly to a layer of surfactants lying flat on the surface. A change in the alkyl chain length does not result in any change in the plateau molar adsorbed amount at equilibrium, however the isotherm slope for the alkyl maltosides increases with increasing chain length. Head group polymerization on the other hand affects the adsorbed amount. The alkyl glucosides start adsorbing at lower bulk concentrations than the maltosides and equilibrate at higher adsorbed amounts above cmc. When compared with the ethylene oxide surfactants, it is confirmed that the EO-surfactants hardly adsorb on titania, since the measured changes in the ellipsometric angles are within the noise level. They do, however, adsorb strongly on silica
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| 5. |
- Persson, CM, et al.
(författare)
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Interfacial behavior of n-Octylß-D-glucopyranoside compared to that of a technical mixture consisting of octyl glucosides
- 2000
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 16, s. 10227-10235
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Tidskriftsartikel (refereegranskat)abstract
- The difference in interfacial behavior between a technical mixture consisting of n-octyl glucopyranosides, having between 1 and 7 glucose units in the polar headgroup, and n-octylß-D-glucopyranoside was investigated using a range of methods. The forces acting between two hydrophobic solid surfaces across surfactant solutions were determined with a surface force apparatus. It was found that adsorption of the technical mixture generated a long-range repulsive force of electrostatic nature. At shorter separations a local minimum in the force curve (located on the repulsive side) was observed. Further in a steric repulsion dominated the interaction. In contrast, adsorption of pure n-octylß-D-glucopyranoside did not generate any long-range electrostatic double-layer force and an attractive force was present between the monolayer-coated surfaces close to contact. Wetting experiments showed that the technical mixture was a better wetting agent of hydrophobic surfaces (lower contact angle and higher wetting tension). The adsorption to air-liquid interfaces was also investigated by surface tension measurements and by measuring the forces acting across single foam films. The latter measurements were carried out using a thin film balance employing the porous frit technique. The technical mixture was more efficient in generating long-range electrostatic forces whereas the pure n-octylß-D-glucopyranoside was more efficient in generating stable Newton black films. Pyrene fluorescence measurements revealed that the micelles formed by the technical mixture continuously change its average composition with concentration toward structures with a more hydrophobic micellar core
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| 6. |
- Poptoshev, E, et al.
(författare)
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Comparison of model surfaces for cellulose interactions; elevated pH
- 2000
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Ingår i: Progress in Colloid and Polymer Science. - 0340-255X .- 1437-8027. ; 116, s. 79-83
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Tidskriftsartikel (refereegranskat)abstract
- Two different substrates have been used to measure interaction forces between cellulose and between cellulose and glass at normal and high pH. Forces between microspheres of cellulose (r=20-30 µm) have been measured using the colloidal probe atomic force microscopy technique. Interactions between Langmuir-Blodgett cellulose films on a hydrophobised mica substrate and a glass sphere have been determined with the noninterferometric surface force apparatus. Also, the interaction between two identical Langmuir-Blodgett cellulose films determined with the interferometric surface force apparatus is given for comparison. At low pH (5.5-6) the interaction at large separations in both systems is characterised by a double-layer repulsion with an electrosteric contribution dominating the shorter-range regime. At pH 10, the Langmuir-Blodgett cellulose film swells considerably, which generates a long-range steric repulsion. In many cases several inward steps have been observed in the force-distance curves. We attribute this to a sudden partial collapse of the swollen cellulose film. After initial compression of the steric layer (upon consecutive force runs) the long-range interaction is again dominated by a double-layer force. In contrast, measurements between two cellulose spheres have shown no excessive swelling. Only a limited increase (from about 10 nm to about 20 nm per surface) of the range of the electrosteric repulsion has been found at pH 10. The force at longer distances is in good agreement with the Poisson-Boltzmann theory, with the surface potential increasing with pH as expected.
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| 7. |
- Poptoshev, E, et al.
(författare)
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Weakly charged polyelectrolyte adsorption to glass and cellulose studied by surface force technique
- 2002
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 18, s. 1184-1189
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Tidskriftsartikel (refereegranskat)abstract
- Interaction forces were measured between glass surfaces and between one glass and one cellulose surface in the presence of a 10% charged, random copolymer of acrylamide and cationic [(3-(2-methylpropionamide) propyl] trimethylammonium chloride (AM-MAPTAC-10), using a non interferometric surface force technique (MASIF). Adsorption to glass from 1 ppm solution leads to neutralization of the substrate negative surface charge. When the bulk polymer concentration is increased to 50 ppm, a weak charge reversal occurs as indicated by the reappearance of the double-layer force. Throughout the concentration range studied here (1-50 ppm), the forces measured on approach between two glass surfaces could be adequately described by the DLVO theory. The interactions between one glass and one model cellulose surface under the same conditions follow a different pattern. AM-MAPTAC-10 adopts an extended conformation upon adsorption to cellulose and steric repulsion is generated when the thick adsorbed layer is compressed. The different structure of the adsorbed layers on cellulose is explained in terms of its lower surface charge density compared to glass. This leads to fewer attachment spots on the solid surface and an increased amount of polymer loops and tails proturding into solution, i.e. thicker adsorbed layers are formed and the resulting system is sterically stabilised.
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| 8. |
- Rippner Blomqvist, B, et al.
(författare)
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Disruption of visco-elastic β-lactoglobulin surface layers at the air-water interface by non-Ionic polymeric surfactants
- 2004
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Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 20, s. 10150-10158
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Tidskriftsartikel (refereegranskat)abstract
- Non-equilibrium interfacial layers formed by competitive adsorption of β-lactoglobulin and the non-ionic triblock co-polymer PEO99-PPO65-PEO99 (F127) to the air-water interface were investigated in order to explain the influence of polymeric surfactants on protein film surface rheology and foam stability. Surface dilatational and shear rheological methods, surface tension measurements, dynamic thin-film measurements, diffusion measurements (from fluorescence recovery after photo bleaching) and determinations of foam stability were used as methods. The high surface visco-elasticity, both the shear and dilatational, of the protein films was significantly reduced by co-adsorption of polymeric surfactant. The drainage rate of single thin films, in presence of β-lactoglobulin, increased with the amount of added F127, but equilibrium F127 films were found to be thicker than β-lactoglobulin films, even at low concentration of the polymeric surfactant. It is concluded that the effect of the non-ionic triblock copolymer on the interfacial rheology of £]-lactoglobulin layers is similar to that of low molecular weight surfactants. They differ however in that F127 increase the thickness of thin liquid films. In addition, the significant destabilising effect of low molecular weight surfactants on protein foams is not found in the investigated system. This is explained as due to that long-range steric forces start to stabilise the foam films at low concentrations of F127.
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| 9. |
- Stålgren, J, et al.
(författare)
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Adsorption of liposomes and emulsions studied with a quartz crystal microbalance
- 2001
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Ingår i: Advances in Colloid and Interface Science. - 0001-8686 .- 1873-3727. ; 89, s. 383-394
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Tidskriftsartikel (refereegranskat)abstract
- The QCM (Quartz Crystal Microbalance) is an ultra sensitive weighing device based on the piezoelectric, electromechanical oscillator principle. It consists of a thin single-crystal quartz disk, with one metal electrode deposited on each side. When the electrodes are connected to an electric oscillator, the crystal can be made to oscillate in a very stable manner at its resonance frequency, f. When a mass is adsorbed on one or both of the electrodes, then this leads to a change in the resonance frequency of the quartz crystal. If the adsorbed mass is small compared to the mass of the quartz crystal and there is no slip or deformation due to the oscillatory motion, then the resonance frequency decreases proportionally to the mass of the adsorbed film. It is possible to determine very small changes of the resonance frequency and hence very small mass changes, since the QCM generally has very stable oscillations. However, there are situations where the change in resonance frequency is not linearly related to the change in deposited mass, for example, when the mass is not rigid, slipping on the surface, or not deposited evenly over the electrode(s). There are also other things besides an applied mass that can influence the resonant frequency of a QCM including electrical effects, pressure, and temperature. In this diploma work the interaction between hydrophilic potassium mica surface and hydrogen mica surface and airs of different humidities have been investigated. The resulting adsorption isotherms show how much water that is adsorbed on the two surfaces.
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| 10. |
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