The Interaction of Linear and Network Poly(diallyldimethylammonium chloride) with Water. Thermodynamic Experiment and Modeling

Comprehensive thermodynamic analysis of mixing of poly(diallyldimethylammonium chloride) (PDADMAC) with water at 25°C has been performed. Isotherms of water sorption with linear and network poly(diallyldimethylammonium chloride) have been measured by means of interval sorption. Enthalpy of dilution of solutions of linear poly(diallyldimethylammonium chloride) and enthalpy of swelling of network poly(diallyldimethylammonium chloride) have been measured over the entire composition range by means of isothermal calorimetry. Concentration dependences of the Gibbs energy of mixing and enthalpy of mixing of poly(diallyldimethylammonium chloride) with water have been computed. It has been shown that these thermodynamic functions are negative over the entire range of composition of the solution and swollen hydrogel. The experimental data have been used in thermodynamic modeling of the interaction process, accounting for different contribution to the thermodynamic functions of mixing of poly(diallyldimethylammonium chloride) with water. It has been shown that the thermodynamic of mixing is predominantly affected, on one hand, by the molecular interaction described in the scope of the Flory–Huggins theory and, on the other hand, by the nonequilibrium disruption of glass structure of the polymer during formation of the solution and swelling of the gel. The modeling has given the values of the Flory–Huggins parameter: –0.05 ± 0.02 for aqueous solution of linear poly(diallyldimethylammonium chloride) and 0.20 ± 0.01 for hydrogel of network poly(diallyldimethylammonium chloride). Basing on the model parameters, individual contributions into the enthalpy, Gibbs energy, and entropy of mixing of poly(diallyldimethylammonium chloride) with water have been calculated.