Molecular Thermodynamic Analysis for Assessing the Relationship Between Reentrant Swelling Behavior and Ternary Liquid-Liquid Equilibrium for Poly(N-isopropylacrylamide) Nanometer-Sized Gel Particles in a Water-Tetrahydrofuran Cosolvent System

Abstract

The influence of phase separation on swelling behavior was investigated based on the thermodynamic framework of reswelling phenomena. The cloud-point for a ternary system of water(1)-tetrahydrofuran (THF)(2)-poly(N-isopropylacrylamide)(3) was examined by thermo-optical analysis (TOA). Nanometer-sized N-isopropylacrylamide (NIPA) gel particles were prepared by precipitation polymerization, and their swelling behaviors were determined using photon correlation spectroscopy (PCS). NIPA gel particles underwent reswelling when the ratio of water to THF was varied. First, the modified double lattice model (MDL) was employed to determine ternary interaction energy parameters for the liquid-liquid equilibrium (LLE) of linear poly-NIPA in a water-THF cosolvent system. The reentrant swelling equilibria of the NIPA gel in the water-THF system were then calculated using the interaction energy parameters.