Kinetic study of the swelling process of the polypeptide gel

The polymer gels are well known for the high absorbency and applied to various commodities. They are also utilized as the functional material with dramatic volume change in water absorption. The polypeptide gel is mentioned as one of such the materials. It is well known that a certain polypeptide gel film is accompanied by the helix-coil transition in water absorption and swelling, simultaneously with the transition molecular rigidity, volume, specific gravity, etc. greatly change, and large difference appears in the mechanical characteristic. However, only few attempts have so far been made to explore the in-situ structural change during the swelling process. The purpose of this research is to observe the change by the scattering technique. The time-resolved small-angle X-ray scattering (SAXS) and the wide-angle X-ray scattering (WAXS) techniques were employed to investigate the structural change, using synchrotron radiation. The specimen used was the crosslinked poly (N-hydroxyethyl L-glutamine) (PHEG) films. The result tells that they composed of the helices with the average distance of 13.1A, and cylindrically aggregated with its radius of ca. 18A and its height of ca. 160A, at dry condition. Both the distance between helices and the cylindrical aggregation gradually became larger. The time dependence of the distances was in good agreement with that of the swelling ratio in its early stage, which means that the micro and the macro structures swelled similarly. (author)