Flat film membranes

The technology of membrane separations continues to be a growing field where the polymer membrane contributes unique separation properties based on its structure and on its chemical composition. Various manufacturing processes are used to create special structures in forms such as flat films and hollow fibers. Lonsdale [187] provides a review of the history and status of separation media and their applications, and a text [188] provides a discussion of the materials science of synthetic membranes. 

Electron microscopy has been applied to the determination of the structure of membranes for 

Transmission electron microscopy was used to study high temperature pol3rimide-based nanofoams derived from triblock copolymers for applications in microelectronics packaging, storage cells, and high temperature polymer membranes [192]. Films before and after forming were prepared for microtomy by sub- 

Process Filtration Materials retained Pore size 

Conventional filtration Coarse filters Large particles 2 (10-1000) /an 

Electron microscopy has been applied to the determination of the structure of membranes for correlation with transport properties. The SEM provides both the best overall view and detailed. 

Ultrafiltration UF membrane Macromolecules, colloids (passes salts) 0.01-0.5 pm 

Reverse osmosis Semipermeable membrane Dissolved and suspended materials (ionic) saline 1-80 nm 

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Fig. 2.2 Flat-film membrane stack design by GKSS (used with permission of GKSS).

Asymmetric polybenzimidazole membranes have been developed for RO applications, in the form of hollow fibers [154] and flat film membranes [155] for water transport. By comparison with cellulose acetate, FBI has very attractive chemical, flammability and thermal properties. There are two problems encountered in attempting the preparation of such membranes for TEM (1) deformation during drying and (2) lack of contrast. Often specific methods must be developed for each membrane type, although method development is quite time consuming. 

As a conclusion, during the preparation of precursor membranes, the process parameters involved must be optimized to form a good precursor for pyrolysis. Moreover, the choices of supported and unsupported carbon membranes depend on the application for which the carbon membranes will be used. Normally, most of today s gas separation membranes are formed into hollow fiber modules [73]. Hollow fiber membranes offer a greater area per specific module volume than flat film membranes, by a factor of 1-40 [31]. 

Table I. Summary of Test Results Obtained for Nafion Flat Film Membranes.

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