COLL 386

The dilatational rheological properties of adsorption monolayers of cationic polysoaps on the basis of chitosan, on the one hand, and of SPECs formed between chitosan and alkylsulphates, on the other hand, at the air-water interface have been studied by the axisymmetric bubble shape analysis under dynamic (=3.10-3-10-1 Hz) and ramp type deformations as a function of different physico-chemical parameters : concentration of PE, degree of alkylation of polysoaps or compositon of SPEC, alkyl chain length, pH and ionic strength of the solutions. The gradual increase with the ageing time (at least up to 105s) of two-dimensional storage G’ and loss G’’ elastic modules have been interpreted in terms of the formation of a gel-like structure in the adsorption layers of polysoaps and SPECs. It has been found that the elastic storage module G’ increases with increasing alkyl chain content in the case of both polysoaps and SPECs, but unexpectedly, the kinetics of the adsorption and the elasticity of the SPEC adsorption layer are remarkable higher with regard to that of polysoaps. This is explained by higher diffusion mobility of alkyl groups of surfactants inside the SPEC with regard to that of polysoaps allowing the formation of more compact gel-like structure in the adsorption layers. It has been found that the conformation of the polysoap macroion and of SPEC in the bulk of solution has an impact on the kinetics of the structure formation in the adsorption layers.

References. [1] V.G.Babak, I.G. Lukina, G.A. Vikhoreva, J. Desbrières, M.Rinaudo, Colloids and Surfaces. A. Physicochem. and Eng. Aspects, 147 (1999) 139. [2] V.G.Babak, J. Desbrières, Mendeleev Communications, (2003) in press.