6.  Aggregation in Aqueous Solutions of Some Cationic Amphiphilic Polyelectrolytes

Authors: M.C. Stanciu, M. Nichifor and B.C. Simionescu


Abstract:

Aqueous solutions of amphiphilic polyelectrolytes, based on polysaccharides having N-(2-hydroxypropyl)-N, N-dimethyl-N-alkyl ammonium chloride as pendant groups are used for the discrimination between intra- and intermolecular hydrophobic interactions as a function of polymer physico-chemical characteristics, with a special attention paid to molecular weight and polysaccharide backbone. The aggregates characteristics are determined by steady-state fluorescence (critical aggregation concentration - CAC and micropolarity), fluorescence anisotropy (microviscosity) and capillary viscometry (macroviscosity) measurements. The results highlight the dependence of aggregate characteristics on degree of substitution with hydrophobic pendant groups, the length of alkyl substituent R, molecular weight and type of polysaccharides. CAC values decrease with the increase of the R length. The molecular weight and the nature of the polysaccharide have a reduced influence on CAC values. Higher anisotropy values are obtained for higher molecular weight and lower values of the degree of substitution. Up-level values of the reduced viscosity, at high polymer concentration, are characteristic for polymers with low DS and high Mw or backbone’s flexibility.


Keywords: amphiphilic polyelectrolytes, self-aggregation, fluorescence, capillary viscometry

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