Invited) Volume Phase Transition of NIPA Gels and Its Relation to the Inhomogeneity Caused by Extremely Multifunctional Crosslinker

Crosslinkers play essential role in determining physical properties of gels. Using cray substance, Laponite (Rockwood Additive Ltd, USA), as the crosslinker, we made N-isopropylacrylamide(NIPA) gels. We found, if we count one Laponite crystal as one crosslinker, that NIPA gels crosslinked with Laponite gelled at much lower fraction (1/2000) of crosslinker than the gel crosslinked with popular N,N'-methylenebisacrylamide(BIS). This result indicates that Laponite is extremely multifunctional crosslinker. Though the volume changes of the NIPA-Laponite gels were continuous one, the volume change itself was much larger than that of the NIPA-Bis gels, and we observed the hysteresis loop as well as the miner loops just like magnetic system. We will discuss about the possible mechanism of such hysteresis loops.