Polycation charge and conformation of aqueous poly(acrylamide-co-diallyldimethylammonium chloride): Effect of salinity and temperature

Abstract

A comprehensive study on the polycation charge and conformation poly(acrylamide-co-dimethyldiallylammonium chloride) with a moar mass of 250 kDa (comprising of 45 mass% of dimethyldiallylammonium chloride) has been performed in aqueous media without and with an electrolyte as a function of temperature. Use has been made of a model of polyelectrolyte conductivity developed by Colby et al. [10] to analyze the electrical conductance-concentration data. The results indicated that the charge on each polycation reduced from a value of ∼ 450 in the maximally perturbed chain to ∼ 100 in an unperturbed chain at 298.15 K when the copolymer concentration was ∼ 0.06 monomol·L−1 (the highest concentration investigated). The intrinsic persistence length of the polycation (7.2 A0) estimated from viscosity measurements using the worm-like coil model of polymer was found to be smaller than the average length of each repeating unit, indicating inherent flexibility of this copolymer. It is observed that in salt-free solutions polycations adopt a slightly less flexible and extended conformation (upto around 4 repeating units) because of intra-chain electrostatic repulsions at 298.15 K when the copolymer concentration was ∼ 0.002 monomol·L−1 (the lowest concentration investigated). The variation of the coefficient of friction of the monomer with polymer concentration is found to be governed by the effect of chain charges over and above that of the chain stiffness; in the unperturbed state, however, the effect of chain charges is playing the pivotal role. This study sheds lights on the dependence of polycation charge and conformation with the concentration of copolymer, temperature, and salinity of the medium.