Preparation of ultrathin polymeric membranes for gas separation by the new method of spontaneous film formation

A new method for the production of nanoscaled polymeric films with a width of 10 cm and of infinite length is presented. The principle is based on a modified water casting method where a polymer solution spreads on a water surface and is wound up by a rotating cylinder. The film thickness depends on several parameters and varies from 30 to 1000 nm. In contrast to most processes for the: production of thin polymeric films, the one described here can be driven continuously and allows a production speed of up to 10 m/min. Films were produced from Various commercially available polymers and were investigated regarding surface quality, molecular orientation and gas permeation properties. The best results concerning film formation and surface quality were obtained with polymers containing aromatic rings such as polyether imide, polycarbonate and polysulfone. A slight chain orientation was found which increases with drawing velocity. Gas permeation experiments with oxygen and nitrogen showed maximum separation factors of 4.9 (polyether imide) and 6.1 (polysulfone) which is in good agreement with values reported in the literature. It turned out that the fabrication of ultrathin polymeric films by the method of spontaneous film forming seems to be a suitable way to get gas separation membranes at low costs and almost industrial quantities. (C) 2001 Elsevier Science B.V. All rights reserved.