The research of rheology and thermodynamics of organic–inorganic hybrid membrane during the membrane formation

Abstract

To clarify the mechanism of organic–inorganic hybrid membrane formation by phase-inversion method, the thermodynamical and rheological properties of PSF/TiO 2 casting solution were investigated by the viscosity measurement and the triangle phase diagram, respectively. TiO 2 introduction decreased the non-solvent tolerance of casting solution with non-solvent 20% ethanol aqueous solution, which caused thermodynamic enhancement of phase separation, and also resulted in the change of rheological properties from Newtonian fluid to non-Newtonian fluid and the viscosity increase of casting solution, which induced rheological hindrance in demixing process. On the basis of the relationship between wet membrane thickness and coagulation time, a novel method used to calculate kinetics parameter ( D a) of membrane formation was founded and an equation of D a = d 2/ t was established. With the increase of TiO 2 concentration, it was revealed that D a increased firstly and then decreased with a maximum value of 0.002204 mm 2/s at certain temperature (20 °C). With the increase of coagulation bath temperature, D a increased and the viscosity decreased continuously when the composition of casting solution was constant. D a was mainly influenced by the porosity of membrane and the thermodynamic, rheological properties of casting solution. In addition, D a also had a main influence on membrane structure by SEM observation, a higher D a was apt to form a more open membrane, as consequence, it was feasible using D a as a parameter to evaluate PSF/TiO 2 hybrid membrane structure.