| 1. |
- Stenius, P, et al.
(författare)
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Nonionic hydrophilic surfaces: adsorption and interactions
- 1990
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Ingår i: Croatica Chemica Acta. - 0011-1643 .- 1334-417X. ; 63, s. 501-516
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Tidskriftsartikel (refereegranskat)abstract
- An overview is given of recent studies of nonionic, hydrophilic surfaces formed by the adsorption surfactants or surface active polymers. Hydrophobic surfaces can be easily hydrophilized by the adsorption of nonionic surfactants or block copolymers containing hydrophobic chain segements; the cooperative interaction between the hydrocarbon moieties contributes more to the free energy of adsorption than the interaction with the hydrophobic surface. Hydrophilic layers are also readily formed on hydrophilic surfaces provided specific interaction between the hydrophilic end groups and the surface creates a sufficiently hydrophobic surface so that a second layer can bed formed through cooperative interaction. The temperature dependence of the interaction forces between layers of surfactants can be closely correlated with their phase equilibria with water. In order to prevent protein adsorption the surface should be neither charged nor hydrophobic; it is shown that, accordingly, protein adsorption is extremely low on poly ethylene oxide-covered surfaces.
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| 2. |
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| 3. |
- Touroude, R, et al.
(författare)
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Preparation of colloidal platinum/palladium alloy particles from nonionic microemulsions: Characterization and catalytic behaviour
- 1992
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Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 67, s. 9-19
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Tidskriftsartikel (refereegranskat)abstract
- Bimetallic particles of platinum and palladium have been prepared by reduction with hydrazine at ambient temperature of H2PtCl6 and PdCl2 dissolved in microemulsions consisting of water, hexadecane and pentaetyleneglycol dodecyl ether. The particles were deposited onto Al2O3.. Examination by STEM and EXAFS of particles with atomic ratio Pt:Pd = 35:65 showed that the particles are true Pt/Pd alloys. Indirect evidence was also obtained that particles containing only 4% Pd are alloys. The diameter of the particles ranges from 10-100 nm; there is evidence that they are formed by aggregation of particles in the diameter range 2-5 nm. The catalytic properties of the Pt/Pd/Al2O3 catalysts prepared from microemulsions were similar to those of catalysts prepared by conventional impregnation. Catalysts with low Pd content had the same selectivity in the isomerization of 2-methylpentane and hydrogenolysis of methylcyclopentane as a highly dispersed Pt catalyst (or a pure Pd catalyst). The catalytic cracking of 2-methylpentane indicates that the particle surfaces behave as Pt surfaces up to a Pd concentration of 60% in the particles. Isomerization of hexanes is dominated by the cyclic mechanism already at Pd concentrations as low as 4%; for these very low Pd concentrations hydrogenolysis of methylcyclopentane is the same as observed for very small Pt particles. It is concluded that Pd is enriched in the particle surfaces in such way that they consist of Pd and some highly dispersed Pt, even at bulk Pd concentrations as low as 4%.
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| 4. |
- Eriksson, L, et al.
(författare)
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Formation and structure of polystyrene latex aggregates obtained by flocculation with cationic polyelectrolytes. I. Adsorption and optimum flocculation concentrations
- 1993
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Ingår i: Colloids and Surfaces A. - 0927-7757 .- 1873-4359. ; 70, s. 47-60
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of modified polyacrylamide polyelectrolytes and their effect on the flocculation of negatively charged polystyrene latex was investigated. Conditions were chosen so that the adsorbed polymers approached equilibrium configuration before the occurrence of appreciable flocculation. Polymers with very low charge density ( a few % charged monomers) form loops and tails at the latex surface and flocculate the latex by bridging. Polymers with higher charge adsorb in a flat configuration and flocculate the latex by net charge neutralization, possibly leading to long-range attraction between positively and negatively charged domains on different particles. Minima in the ratio of the total polymer charge adsorbed at the plateau level to the total charge on the latex occur at intermediate polymer charge densities. At these densities the mean distance between charge groups on the polymers matches the mean distance between charged groups on the latex. At maximum adsorption of highly charged polymers the latex particles acquire a high positive charge. The reason for this is that the mean distance between positive charges on the polymer is smaller than the distance between charges on the latex, so that ion binding of the polymer to the ionized latex surface groups cannot take place without simultaneous attachment of an excess of positive charge to the latex surface.
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| 5. |
- Johansson, K, et al.
(författare)
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The interactions between alkyd resin binders and kaolinite
- 1991
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Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 56, s. 313-338
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between alkyd resins and kaolinte has been studied by means of adsorption measurements and spectroscopic methods such as electron spectroscopy for chemical analysis (ESCA) and diffuse reflectance infrared Fourier transform spectroscopy. The interaction is mainly governed by Lewis acid-base interactions but the molecular weight distribution and the oil length of the alkyds are of great importance. The kaolinite surface appears to be amphoteric since both acidic and basic species are adsorbed. The alkyd resins are very polydisperse. The experimental results are in agreement with the prediction of the theory of Cohen Stuart et al. (M.A Cohen Stuart, J.M.H.M. Scheutjens and G.J. Fleer, J. Polym. Sci., Polym. Phys. Ed., 18(1980) 559) for adsorption of polydisperse polymers. The alkyds are strongly adsorbed on the kaolinite, but not aluminium or hydroxxyl groups next to the aluminium. Double bonds, orginationg from the fatty acid part of the alkyd, play an active role in the adsorption process. The adsorption is only slightly affected by the temperature.
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| 6. |
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| 7. |
- Järnström, L, et al.
(författare)
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Adsorption of polyacrylate and carboxy methyl cellulose on kaolinite: Salt effects and competitive adsorption
- 1990
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Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 50, s. 47-73
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of sodium polyacrylate (NaPAA) and sodium carboxy methyl cellulose (NaCMC) on homoionic sodium and calcium kaolinite has been investigated. Adsorption is strongly dependent on Ca2+/polyelectrolyte interactions in solution , while the nature of the kaolinite is of less importance. Adsorption takes place on two types of sites where the energetically more favorable sites appear to be the edges and the other sites are the basal planes. On addition of Ca2+ to a PAA solution, a maximum binding (saturation) corresdponding to 0.306 Ca2+ /PAA segement is reached. An adsorption model has been developed in which it is assumed that while any PAA may be adsorbed on the more favoable sites, only PAA molecules that are saturated with Ca2+ adsorb on the other sites. Equilibrium calculations using apparent binding constants of Ca2+ to the PAA determined from potentiometric titration show that this model is able to predict the experimentally determined isotherms with good accuracy. Although detailed calculations have not been perfomed, the model appears to be applicable also to the adsorption of NaCMC.
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| 8. |
- Kizling, J, et al.
(författare)
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Viscoelastic properties of dodecylammonium chloride monolayers
- 1995
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 171, s. 162-167
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Tidskriftsartikel (refereegranskat)abstract
- Monolayers of dodecylammonium chloride formed at the solution-air interface at different electrolyte concentrations have been investigated by dynamic surface light scattering. Pronounced maxima in the damping of capillary waves were observed at surfactant concentrations around 0.1xCMC. These maxima occur at concentrations just above the break points in the surface tension vs. concentration curves caused by first order phase transitions from a gaseous to a liquid- expanded state. The experimental results were analysed by comparing with theoretical calculations based on the standard theory of light scattering due to capillary waves on liquid surfaces, and the molecular theory of the surface tension of ionic surfactant solutions presented earlier by Eriksson and Ljunggren. In this way it was possible to account satisfactorily for the observed concentration and salt dependencies of the central frequency and width of the spectral peak.
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| 9. |
- Laine, J, et al.
(författare)
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Surface characterization of unbleached kraft pulps by means of ESCA
- 1994
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Ingår i: Cellulose. - 0969-0239 .- 1572-882X. ; 1, s. 145-160
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Tidskriftsartikel (refereegranskat)abstract
- The effect of digestion conditions (amount of effective alkali, digestion time) on the surface compositions of unbleached softwood (Pinus sylvestris) kraft pulp has been investigated by ESCA analysis. The quantities monitored were the angular dependence of the total O/C ratio, the relative amounts of carbons in different states of oxidation and the adsorption of Al and Ca ions to the carboxyl groups in the surface. Analysis of the angular dependence of ESCA intensities shows that the concentration of alkyl carbon is high in a very thin surface layer. This enrichment becomes more marked as the lignin content (kappa number) decreases, but it is not affected by extraction of the fibres with dichloromethane. It is concluded that the observed distribution is due to re-precipitation of lignin. In pulp that has not been extracted, there is also strong enrichment of extractives in the surface. This amount increases with increasing effective alkali but is relatively independent of the time of digestion. ESCA analysis of the Al and Ca bound to the carboxyl groups shows that the amount of these depends on digestion time; the results are consistent with the notion that the reprecipitated lignin contains carboxyl groups.
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| 10. |
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