Surface properties of polymeric membranes are of fundamental importance in many branches of industrial applications (e.g. separation of gases, liquid mixtures, filtration, water treatment, desalination, medicine etc.). Hence, it is natural that much attention has been paid to the membrane surface modification. Review of the patents that have appeared since the year 2000 concerning the surface modification of the polymeric and other synthetic membranes was made in this article by classifying them according to the modification method. The surface modification of synthetic membranes can be performed; i) by blending or adding some other component(s) into the host polymeric material, ii) by coating the surface of the membrane with some other polymer including grafting and in situ polymerization, iii) by altering the membrane surface via chemical reaction iv) by radiation via high energy particles, and, v) by other methods. It should be noted that most of surface modification was done for the membranes used in water treatment and liquid filtration to reduce fouling and to enhance membrane performance. In contrast, very few are found in the field of gas separation. This is because surface modification is thought to have stronger impact on the performance of water treatment membranes such as RO/NF/UF/MF membranes. On the other hand, in gas treatment membranes the role of membrane surface in gas transport is less emphasized. This, however, will change as the membrane scientists and engineers will recognize the role of surface flow in the gas and vapour transport and attempt to utilize these phenomena in practical separation processes. This is already happening in the field of molecular sieve and carbon nano-tube membranes. As well, the surface phenomena will play a pivotal role in reducing the aging phenomena of gas separation membrane. The surface modification technique will also be used in other separation processes such as vapour separation and membrane distillation in the future, as shown by some examples.
Synthetic polymeric membranes, filtration, microfiltration, ultrafiltration, nanofiltration, gas separation, nano-fiber material
Industrial Membrane Research Laboratory, Chemical and Biological Engineering Department, University of Ottawa, Ottawa, K1N 6N5, Canada.