Molecular Thermodynamic Analysis for the Swelling Behavior of Thermo-Sensitive Nanoparticle Gels

Abstract

We studied the calculation and analysis for the swelling behavior of thermo-sensitive nanoparticle gels using molecular thermodynamic models. In chapter 1, a new non-solvent pair (PEG and alcohol) that enhances the miscibility of PMMA is reported. Some factors that affect the miscibility of PMMA, such as temperature, molecular weight of the polymer, chemical and structural characteristics of alcohols, are investigated. . A new version of lattice model, called the modified double-lattice associating fluid (MDL-AF), is introduced to consider specific interactions more systematically. Guggenheim’s approach for the frequency of occupation provides a basis for the MDL-AF model to consider the probability of specific interactions between segments. Required interaction parameters are obtained from each binary system, and they are directly applied both to the ternary and swelling calculation. The proposed method is applied to PMMA solutions containing PEG200, PEG400, and a wide range of aliphatic alcohols. In chapter 2, novel UCST- (upper critical solution temperature) type doubly-thermo-sensitive core-shell nanoparticle gels were prepared in order to investigate swelling behaviors. The core-shell nanoparticle gels are synthesized via precipitation polymerization, and are composed of a chemically cross-linked PMMA core and a poly(2-hydroxyethyl methacrylate) (PHEMA) shell. Photon correlation spectroscopy (PCS) measurements indicate that the large UCST gap between the shell- and core-forming polymers gives rise to a clear two-step swelling process upon heating. For theoretical analysis, a corrected modified-double-lattice (MDL) model with a new type of interaction parameter, called the MDL-T model, is introduced to represent the optimized thermal behavior of the interchange energy. Required model parameters are obtained from the experimental swelling data of homo-polymer nanoparticle gel solutions, and are directly applied to core-shell swelling calculations.