CHANGE IN MICRO-ENVIRONMENTS IN POLY(ACRYLAMIDE) GEL WITH PYRENYL PROBE DUE TO ITS VOLUME PHASE-TRANSITION INDUCED BY PH CHANGE

Changes in the micro-environments and interactions among the side groups during pH-induced volume phase transition of poly(acrylamide) gels having pyrenyl group as a fluorescent probe in acetone water (9:11) mixed solvent were studied with fluorescence spectra and lifetime measurements. The results are as follows: (a) The volume phase transition is caused by hydrophobic interaction of polymer main chains and charge repulsive force of carboxylate anion at polymer side chains inside the gel, indicated by change in fluorescence intensity ratio I1/I3 of the pyrenyl probe and the shifts in fluorescence wavelength. (b) In the collapsed state, the gel consists of two phases: one is the portion of polymer main chain aggregate, and the other is the portion of polar side group assembly, which results from a competitive interaction between the hydrophobic interaction of polymer main chains and the charge repulsive force of carboxylate anion in the coexisting two phase regime.