Fluorescence studies of micro-environment and dynamic fluctuation for volume phase transition of polyacrylamide gels with pyrenyl probe at crosslinks

Abstract

The changes in micro-environments and dynamics of the network of polyacrylamide (PAAm) gels were studied by means of the fluorescence spectra, lifetimes and rotational diffusion motions of pyrenyl probe at crosslinks during the volume phase transition (VPT) of the gels induced by the change in acetone content in acetone/water mixed solvent. The results are summarized as follows. (a) The volume phase transition of the PAAm gels from the swollen to the collapsed state is accompanied by increases in the interaction of PAAm main chains and the hydrophobicity in the micro-environment, which were indicated by the decrease in the relative fluorescence intensity, I 1/ I 3, and the increase in the monomer emission lifetimes. (b) Excimer formation between the pyrenyl probes at crosslinks was noticed only in the collapsed state and only for gels with higher probe contents. (c) A marked dynamic fluctuation and divergence of rotational diffusion coefficient at VPT of the PAAm gels can be observed by using the pyrenyl probe bonded as a crosslinking reagent to the PAAm gels.