Abstract
The development of asymmetric and composite membranes with very thin dense “skins” needed to achieve high fluxes enabled the commercial use of membranes for molecular level gas separations. It has been generally assumed that these thin skins, with thicknesses of the order of 100 nm, have the same permeation characteristics as films with thicknesses of 25 microns or more. Thick films are easily made in the laboratory and have been used extensively for measuring permeation characteristics to evaluate the potential of new polymers for membrane applications. There is now evidence that this assumption can be in significant error, and use of thick film data to select membrane materials or predict performance should be done with caution. This presentation will summarize the preparation of films from glassy polymers as thin as 20 nm and characterization of their behavior by gas permeation, ellipsometry and positron annihilation lifetime spectroscopy. Some of the most important polymers used commercially as gas separation membranes, i.e., Matrimid® polyimide, polysulfone (PSF) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), have been made into well-defined thin films by spin casting techniques and their properties studied using the techniques developed. These thin films densify (or physically age) much faster than thicker films, and, as result, the permeability decreases, sometimes by several-fold over weeks or months for thin films. This means that the properties of these thin films can be very different from bulk films. The techniques, interpretations and implications of these observations will be discussed. In a broader sense, gas permeation measurements can be a powerful way of developing a better understanding of the effects of polymer chain confinement and/or surface mobility on the behavior of thin films.
Biography
Donald R. Paul holds the Ernest Cockrell, Sr. Chair in Engineering at the University of Texas at Austin. He received his B.S. from North Carolina State University in 1961 and his PhD in Chemical Engineering from the University of Wisconsin in 1965. He then worked as a Research Engineer at the Chemstrand Research Center. He joined the Department of Chemical Engineering at the University of Texas at Austin in 1967, becoming Professor in 1973, and department chairman from 1977-85. Prof. Paul’s research has involved various aspects of polymer blends, membranes for separation, drug delivery, packaging, processing, and nanocomposites. He has edited numerous books on polymer blends and membranes and has published more than 600 research papers. He has received numerous awards for teaching, research, and leadership from the University of Texas, ACS, AIChE, SPE, and the Council for Chemical Research. He has been designated a distinguished graduate of North Carolina State University and of the University of Wisconsin. In 1998 he received the William H. Walker Award and in 2008 the Founders Award from AIChE. He was elected to the National Academy of Engineering in 1988 and as a Corresponding Member of the Mexican Academy of Sciences in 2000 and the Academy of Sciences of Bologna in 2011. He has served as Editor of Industrial and Engineering Chemistry Research since 1986.
Tea and coffee will be served from 15.30 in the walkway outside the lecture theatre