Work on hyper-rigid membrane materials aimed at producing molecular sieving environments for gas separations is becoming an important topic in our group. This work relies upon homogeneous flat films for sorption and steady state permeation studies. We have followed three approaches to this goal:

• Chemically modifying standard materials
• Thermally modifying semi-exotic materials (e.g. polyimides) at moderate temperatures
• Formation of exotic new materials that require only moderate treatment to transform to molecular sieving properties

Ongoing work also seeks to bridge the gap between efforts in new materials and in membrane formation. The influence of pyrolysis atmosphere and temperatures on final carbon molecular sieve transport properties is dependent upon the precursor morphology being used. This work seeks to understand how effects of quenched-in symmetry in hollow fiber skins and substrates are "remembered" during subsequent thermal transformation to form molecular sieve structures. Polymer properties and characterization, therefore, are important even in this work related to carbon membranes. Moreover, while the molecular sieve membranes are largely comprised of carbon, our studies suggest that 1-5% oxygen and traces of nitrogen typically remain in optimum structures. The detailed morphologies and chemical natures of these complex materials are not yet well-understood, but under controlled conditions, reproducible separation properties can be produced.

• Formation and application of polymeric, ceramic, and carbon membranes
• Penetrant history and temperature-dependent phenomena