Polysulfone-Aerosil composite membranes - Part 1. The influence of the addition of Aerosil on the formation process and membrane morphology

Presented organo-mineral membranes are the result of the addition of Aerosi l 200 spheres to a solution of polysulfone (PSf) in N-methylpyrrolidone (NM P). They are prepared using the wet phase inversion process by casting the suspension on a glass plate and immersing it in water. For the first time, transparent suspensions are used to investigate the effect of the filler on the membrane formation process. It allows the transport of nonsolvent into the membrane to be followed by light microscopy. The results prove that an increase of the filler concentration slows down the indiffusion rate. Clou d point measurements indicate that the addition of fillers changes the ther modynamic behavior of the polymer/solvent/nonsolvent system in such a way t hat demixing occurs at a lower concentration of nonsolvent. A special exper imental 'slide'-setup is designed and presented here to follow the instanta neous demixing process of the filled polymer solutions as a function of tim e. These experiments prove that the presence of a small amount of filler in creases the demixing rate in the initial stage of membrane formation. A fur ther increase of the amount of filler decreases the demixing rate of the in stantaneous demixing process due to viscosity effects, (C) 2000 Elsevier Sc ience B.V. All rights reserved.