Polysulfone (PSF)/TiO₂ hybrid ultrafiltration (UF) membranes with different nano-sized TiO₂ content were prepared by sol-gel method. The effects of TiO₂ concentration on the rheological and thermodynamic properties of PSF casting solution were studied firstly. A new method used to calculate apparent diffusion coefficient (D_a) in membrane formation process was founded subsequently. After calculating D_a under different conditions, the effects of the rheological and thermodynamic properties on the kinetics of membrane formation were examined and the relationships of D_a, membrane structure and UF performance were evaluated through the methods of SEM observation, porosity test and UF experiments finally. The results showed that the rheological properties of casting solution were changed from Newtonian viscous behavior to non- Newtonian viscous behavior, and the viscosities of casting solution were increased by the addition of TiO₂. The addition of TiO₂ also reduced the miscibility of PSF solution with non-solvent, leading to thermodynamic enhancement for phase inversion. The diffusion behavior of solvent and non-solvent in membrane formation was strongly influenced by the complex correlation between thermodynamic enhancement and rheological hindrance due to TiO₂ addition. D_a increased with the increase of temperature. However, it increased firstly and then decreased with the increase of TiO₂ concentration. Moreover D_a had an accordant pertinence with membrane structure and properties, and could describe the entire membrane for-mation intuitively.

Key words: polysulphone, TiO₂, organic-inorganic hybrid membrane, rheological and thermodynamic properties, apparent diffusion coefficient