Kinetics of Exchange of the Water Absorbed in Poly (Acrylic Acid) Hydrogel with Ethanol

Isothermal kinetics of exchange of absorbed water with ethanol in poly(acrylic acid) hydrogel was investigated at different temperatures: 295 K, 303 K and 313 K. By applying isoconversional and model-fitting methods it was found that the exchange of absorbed water with ethanol is an elementary (single step) kinetic process which can be mathematically described with the kinetic model of Jander three-dimensional diffusion (3D). The values of kinetics parameters (rate constants (kM), energy of activation Ea = 18.8 kJ mol–1, pre-exponential factor ln[A/min–1] = 4.93) and thermodynamics parameters of activated complex formation (∆H* = 16.5 kJ mol–1, ∆S* = -177 J K-1 mol–1, ∆G* = 68.73-71.92 kJ mol–1) of exchange were calculated. It was found that the value of ∆H* corresponds to the energy of rearrangements of bound water around hydrophilic groups of polymeric network.