Bulletin Spring‧Summer Autumn‧Winter 1999

polyelectrolyte gels in a more cost-effective way. Specifically, the research w i l l t ry to determine the kinetics of the swelling and shrinkage, in other words, the course of time development when external conditions are changed. Upon shrinkage, water has to come out from the inside of the entangled cross- linked web; upon swelling, water has to burrow deep into the inside. This occurs through a relatively slow process of diffusion, and may be a crucial step that determines the course of time development ; so the diffusion process wi ll be investigated. The gel structure w i l l also be examined, both for gel ne two rk as a who l e, and for the individual chains in the gel. It is hoped that the relationship between the structure and the dynamics can be revealed. The method is simple. One simply looks' at the sample. More precisely, one probes the sample by shining light on it. The scattered light, monitored by modern optical techniques such as miniature interferometry, laser light scattering, differential refractometry, holographic relaxation spectroscopy and time-resolved small-angle x-ray scattering, w i l l reveal detailed information about the sample. This is then analysed to obtain information about the gel, both statically and also as it undergoes volume changes. Model Gels and Results Two model systems have been studied in detail. The first is simply gelatin, which has been used extensively in the food/feed and pharmaceutical industries as an important stabilizer and gelling ingredient. The second is poly(N-isopropylacrylamide). This is a model gel system wi th a transition temperature of 31 °C. Macromolecules exist i n a range of molecular weights — just as people may be heavier or thinner. The first step was to synthesize a set of samples w i t h narrow distributions of molecular weights — just as focussing on groups of people in different weight ranges. The picture always becomes clearer and sharper when one looks at such segregated samples. With these samples, the research group has found that the swelling of a thin gel film can be better described by first-order kinetics. The group has also accomplished the study of the swelling and shrinking of single polymer chains. W i th abetter understanding of single chain properties they wi ll move onto the gel networks. They also intend to study both micro gel particles and thin gel films. Their ultimate goal is to find out why some polyelectrolyte gels undergo intelligent phase transitions. Dr. Wu Chi specializes in chemical physics and obtained his BS degree from the China University of Science and Technology in 1982. He undertook postgraduate studies in polymer physical chemistry at State University of New York at Stony Brook, where he earned his doctorate. Before joining this university as lecturer in c h e m i s t r y , Dr. Wu worked for BASF in West Germany for three years, first as an Alexander von Humboldt fellow and later as the chief of its laser light scattering laboratory. Research 15