Polysaccharides at interfaces 1. Adsorption of cholesteryl-pullulan derivatives at the solution-air interface. Kinetic study by surface tension measurements |
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Authors: | Bruno Deme Veronique Rosilio Adam Baszkin |
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Institution: | Physico-Chimie des Surfaces, URA CNRS 1218, Universite´Paris-Sud, 5 rue Jean-Baptiste Cle´ment, 92296 Cha?tenay-Malabry Cedex, France. |
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Abstract: | The surface properties of a series of cholesteryl-pullulan (CHP) derivatives have been assessed by surface tension measurements at the solution-air interface. The results reveal that these properties are related to the nature of the hydrophobic cholesteryl group substituted in pullulan, and that the unsubstituted polysaccharide does not display any surface activity. The adsorption kinetics of such an amphiphilic macromolecule has been shown to be diffusion controlled, obeying the Ward and Tordai¨diffusional model only at low solution concentrations. In the 2 × 10?7–5 × 10?6 mol l?1 concentration range for which this model is verified, the calculated diffusion coefficients are concentration dependent. The non-ideality of the system at higher concentrations may be explained both by the presence of solute/solute interactions in solution and in adsorbed monolayers, and by the existence of an adsorbed layer, even at time t0, which prevents the process of adsorption from being governed only by diffusion. |
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Keywords: | Adsorption Cholesterol Cholesteryl-pullulan Diffusion Monolayers Surface tension |
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