Hydrodynamic properties of some cationic amphiphilic polysaccharides in dilute and semi-dilute aqueous solutions

Abstract

The dynamic properties of aqueous solutions of amphiphilic cationic polyelectrolytes based on polysaccharides with N,N-dimetyl-N-alkyl-N-(2-hydroxypropyl)ammonium chloride pendant groups were studied by capillary viscometry over a large concentration range (0.01–10 g/dL), as a function of the degree of substitution with pendant groups, length of the alkyl substituent (C 8, C 12, C 16), molar mass and nature of polysaccharide backbone. Intrinsic viscosity determined in dilute solution using Rao or Heller equations provided information on the conformation of individual polymer chains. Comparison of the specific viscosity–concentration relationships with scaling theories allowed the delimitation of concentration domains and calculation of overlap and entanglement concentrations. Semi-empirical equations (Fedors, Martin) could describe the viscosity variation with concentration only for polymers with low degree of substitution (<10 mol%). All these studies help to identify the predominant characteristic for each amphiphilic polyelectrolyte (neutral, charged or associative polymer), determined by its chemical structure, as a result of the balance between electrostatic repulsion and intra- or/and intermolecular associations. The obtained information could be very useful to tailor the cationic amphiphilic polysaccharide's chemical structure to the viscometric properties suitable to different application as flocculants, thickeners or drug delivery systems.