Synthesis, equilibrium swelling, kinetics, permeability and applications of environmentally responsive gels

This article is a review of the research on environmentally responsive polymer gels done by Stevin H. Gehrke's research group at the University of Cincinnati. This group has studied a wide variety of responsive gels, including crosslinked cellulose ethers, poly(N-isopropylacrylamide), and radiation-crosslinked poly(vinyl methyl ether). Equilibrium swelling has been studied both experimentally and theoretically, with the general goal of learning how to control the nature of the volume transition. Conditions under which transition-inducing stimuli affect the rate of volume change have been identified and a diffusion analysis is shown to be broadly useful for correlating the kinetics. Polymer scaling theory provides a qualitative basis for understanding how polymer composition and stimulus interval influence the magnitude of the network diffusion coefficient. The response rate of gels can be several orders of magnitude greater than this if they are microporous and can absorb and expel solvent by a convective process. Diffusion coefficients of solutes in gels decline as the gel shrinks, in generally good agreement with free volume theories. Hydrophobic interactions between gels and drugs are often quite strong, especially in deswollen gels. The ability of these gels to dewater coal slurries has also been established.