A new hydrogel system undergoing a volume phase transition upon heating

A new hydrogel system capable of a thermotropic collapse at about 47 degree s C is the complex poly(diallyldimethylammonium chloride)/sodium dodecyl su lfate (PDADMA-Cl/SDS). It was found that the stoichiometric complex of PDAD MA-Cl/SDS being highly ordered in the collapsed state is capable of swellin g strongly in the presence of excess SDS. Upon swelling the gel loses its o rdered structure and becomes transparent. The hydrogel shrinks upon heating approaching its initial volume. However, in the newly achieved collapsed s tate the gel has no ordered structure and the volume phase transition is as sociated with drastic changes in the heat capacity typical of co-operative conformational and phase transitions. It is reasonable to suggest that this hydrogel system is only an example of a wide group of thermosensitive poly mer systems which may undergo conformational and phase transitions.