Membrane formation: diffusion induced demixing processes in ternary polymeric systems

In this thesis the mechanism of membrane formation by means of immersion precipitation is studied. Immersion of a concentrated polymer solution film into a nonsolvent bath induces an exchange of solvent and nonsolvent in the film by means of diffusion. This process results in an asymmetric polymer distribution and leads to metastable compositions in the immersed polymer solution film. Demixing processes occur, yielding polymer rich and polymer lean entities in the film. When the exchange of solvent and nonsolvent is completed, a solidified film with a dense toplayer and a porous sublayer is obtained. The thin toplayer determines the permselectivity and the permeability of the membrane. The objective of this study is to gain insight into diffusional mass transport and demixing phenomena occurring during the immersion precipitation process.