Swelling behaviors of poly(methyl methacrylate) nano-sized gels in PEG/alcohol solutions

• We investigate the phase behavior behavior of PMMA in PEG/alcohol cosolvent system.
• Some factors that affect the miscibility of PMMA are investigated.
• We introduce a new type of swelling behavior, called re-collapsing behavior.
• We introduce a new lattice model (MDL-AF) incorporating the oriented interaction.
• A possible cosolvency mechanism is discussed using experimental and simulation data.

A new non-solvent pair (PEG and alcohol) that enhances the miscibility of poly(methyl methacrylate) (PMMA) is reported. A possible mechanism for the enhanced solvation effect (cosolvency) is discussed based on experimental and simulation data. Some factors that affect the miscibility of PMMA, such as temperature, molecular weight of the polymer, chemical and structural characteristics of alcohols, are investigated. The close relationship between the cosolvency of PMMA and the re-collapsing swelling behavior of PMMA particle gels is studied within the framework of molecular thermodynamics. 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. The Helmholtz free energy of mixing is calculated by the MDL-AF model, and the Flory–Rehner (F–R) chain model is employed for the free energy of elasticity. 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. The calculation results well represent the experimental cosolvency and re-collapsing data, and exhibited a noticeable improvement compared to other models.

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