Thermal response of double network hydrogels with varied composition

The series of double network (DN) hydrogels, based on poly(N,N & PRIME;-diethylacrylamide) (PDEAAm), polyacrylamide (PAAm), or poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) were synthesized with various mass ratios of components and their thermal response was investigated. The formation of DN structure in studied hydrogels results in significant increase in Young's modulus. PDEAAm/PAMPS hydrogels exhibited rather high swelling ratio and consequently their temperature sensitivity was not detected. DN hydrogels PDEAAm/PAAm and PDEAAm/PDEAAm displayed thermo-responsive behavior, and the dependence of transition parameters on the feed molar concentration of acrylamide and N,N & PRIME;-diethylacrylamide monomers, respectively, was determined through deswelling, NMR, and Differential scanning calorimetry (DSC) experiments. A two-state process model was employed to describe the phase transition of hydrogels. By utilizing a modified van't Hoff equation with data from deswelling, NMR, and DSC experiments, we were able to obtain thermodynamic parameters of the transition and determine the size of the cooperative domains consisting of polymer units and water molecules.