Environmentally Responsive Hydrogels

Abstract

A hydrogel experimental module was designed for an undergraduate upper-level laboratory course. Cross-linked poly(N-isopropylacrylamide) (PIPAM) is a thermo-sensitive hydrogel; it undergoes a volume collapse driven by hydrophobic interactions in pure water as the temperature increases to 32 °C. The extent and temperature of the volume transition are two critical parameters in its applications ranging from pharmaceutics to biotechnology and they can be controlled by incorporating ionic components in the PIPAM system. In this experiment, linear PIPAM, cross-linked neutral PIPAM gel, and cross-linked ionic PIPAM gel were prepared by radical polymerization. Viscosity, molecular weight, and thermal transition (cloud point) of linear PIPAM were determined. Volume collapses of the neutral and ionic PIPAM gels as a function of temperature were examined and compared. In this module, students were exposed to original literature and contemporary chemical research in polymer chemistry and they learned to integrate concepts from different disciplines of chemistry into a unified experimental approach to problem solving. This module could also be used for polymer chemistry or physical chemistry laboratory courses.