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

To clarify the mechanism of organic-inorganic hybrid membrane formation by phase-inversion method, the thermodynamical and theological properties of PSF/TiO2 casting solution were investigated by the viscosity measurement and the triangle phase diagram, respectively. TiO2 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 theological 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 TiO2 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 degrees 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, theological 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/TiO2 hybrid membrane structure. (C) 2007 Elsevier B.V. All rights reserved.