The slow relaxation mode: From solutions to gel networks

Abstract

In the past, many laser light-scattering experimental results revealed that besides the fast relaxation mode, there existed an additional slow mode in semidilute solutions. This slow mode has been assigned to a variety of origins, but there has been no clear and well-accepted explanation. As the polymer concentration increases, the slow relaxation mode persists in the concentrated region, in melts and in gels in which polymer chains are crosslinked instead of entangled. The slow relaxation mode has also been reported for charged macromolecules in aqueous and nonaqueous solutions. However, it is generally thought to be different in nature from that observed in semidilute neutral polymer solution. In recent years, armed with novel solution preparation methods and some specially designed polymers, we have reexamined the dynamics of polymer chains, especially the slow mode, in semidilute neutral polymer solutions, dilute polyelectrolyte solutions and gels, which are reviewed here. Our results suggest that the slow mode can be qualitatively considered as hindered motions of interacting chains even though the nature of interaction can be very different; namely, from the weak segment-segment interaction in a less good solvent to strong electrostatic interaction among polyelectrolyte chains, and even to chemical crosslinking inside gel networks. © The Society of Polymer Science, Japan (SPSJ).