Determination of thermodynamic properties of polysulfone/PEG membrane solutions based on Flory-Huggins model

Flory-Huggins (F-H) model was used to study thermodynamic properties of polysulfone-based membrane solution that consists of water, dimethylacetamide (DMAC), polysulfone (PSf), and polyethylene glycol (PEG400). The thermodynamic properties of membrane solution were examined based on equilibrium composition in a ternary diagram of the membrane system, which known as binodal curve. The binary interaction parameters of each component in F-H model were predicted based on cloud point experiment at various PSf and PEG400 concentrations and used to calculate the binodal curve in ternary diagram. It was obtained that the binary interaction parameters in the membrane solution are: X₁₃ (water–PSf) = 6.76, g₁₄ (water–PEG400) = 0.51, g₂₃ (DMAc–PSf) = 0.46, g₂₄ (DMAc–PEG400) = 0.46, and g₃₄ (PSf–PEG400) = −0.53. Based on the thermodynamic analysis in the ternary diagram, low solubility of membrane solution was achieved when 20 wt% of PSf was blended with a high concentration of PEG400 (20–30%). It means that the membrane solution can be easily separated by the presence of a low water concentration. Consequently, the formation of membrane structure become faster and finger-like structure was formed, which was proved by SEM photograph. Above 20% PSf and 35%wt PEG400 concentration, the membrane solution became turbid indicating that the membrane solution has crossed the equilibrium boundary before casting.