Enhanced solvation effect of re-collapsing behavior for cross-linked PMMA particle gel in aqueous alcohol solutions

The phase behaviors of poly(methyl methacrylate) (PMMA) and cross-linked PMMA gel in the mixtures of water and alcohol (ethanol, 2-propanol, and t-butanol) were investigated at three different temperatures. Phase separation temperature was determined through thermo-optical analysis (TOA) and the swelling transition of PMMA gel was measured by a photon correlation spectroscopy (PCS) technique. All the studied systems exhibited the cosolvency effect, i.e. enhanced PMMA compatibility within definite ranges of composition in water/alcohol mixture, and a possible mechanism for cosolvency is discussed. The effects produced by the different alcohol were qualitatively compared, considering aspects related to their chemical and structural nature. The relationship between the cosolvency of PMMA and the re-collapsing swelling transition of PMMA gel was studied. These behaviors were quantitatively described by molecular thermodynamic models: the modified double lattice (MDL) model for mixing term and the Flory-Rehner (FR) chain model for elasticity term. A new parameter ( ε ˜ co ) was introduced to consider cosolvency effect.