Resumen de Polymer inverse temperature-dependent solubility: a visual demonstration of the importance of TAS in the Gibbs equation
David E. Bergbreiter, Alexander J. Mijalis, Hui Fu
Reversible polymer dehydration and precipitation from water due to the unfavorable entropy of hydration is examined using a melting-point apparatus. The thermoresponsive lower critical solution temperature (LCST) behavior of poly(N-isopropylacrylamide) (PNIPAM) is responsible for these effects. An experiment is described that allows students to test the effects of different salts at various concentrations on PNIPAM's LCST. These studies demonstrate the Hofmeister effect of salts on macromolecule hydration. The use of readily available melting-point equipment and sealed capillary tube samples of aqueous solutions of PNIPAM in various salts provides an economical and simple way to study these phenomena.
