Effect of Crosslinking on Thermodynamics Interactions and Network Parameters of Terpolymeric Hydrogels

Abstract

The physiochemical and thermodynamic interactions of N-isopropylacrylamide (NIPAM) based thermoresponsive hydrogels are influenced by their crosslinking density. In the current contribution a detailed study of the effect of crosslinking ratio on the swelling kinetics, network parameters, thermodynamic interactions and mechanical strength of Poly (N-isopropylacrylamide-co-N-tertiarybutylacrylamide-co-hydroxyethylacrylamide) (Poly-NIPAM-co-NTBA-co-HEAAm) hydrogels are discussed. The Poly (NIPAM-co-NTBA-co-HEAAm) hydrogels were prepared using methylenebisacrylamide (MBA) as a crosslinking agent in various stoichiometric proportions and characterized in terms of Fourier transform infrared spectroscopy (FTIR), swelling and mechanical properties. The results from the swelling experiments, exploiting the Flory–Rehner theory, and compression measurements showed a significant crosslinker content-dependent behavior. Our studies of the effect of temperature on swelling percentage, diffusion characteristics, interaction parameter and thermodynamic interactions, such as partial molar enthalpy and partial molar entropy, shed light on the thermodynamic and physical behavior of thermoresponsive hydrogels. Overall, our study demonstrated that by varying the amount of crosslinking agent (MBA), the structure and physiochemical properties of the poly (NIPAM-co-NTBA-co-HEAAm) hydrogels could be controlled effectively. Also, this study represents, we believe, the first step toward a correlation between their network structure and their thermodynamic properties, which is a key requirement for specific future applications and/or industrial scale-up.