Polyacrylamide volume phase transition

Fluorescence studies of volume phase transition of polyacrylamide (PAAM) in mixed acetone/ water solvent, with incorporated dansyl group and pyrenyl probe were reported by Hu and co-workers [70, 71]. They observed an increase in the fluorescence lifetime of the probe with increase of acetone content in the solvent. They reported that gradual increase of fluorescence lifetime accompanies the volume phase transition of the PAAM gels from the swollen to collapsed state with increasing hydrophobicity of the microenvironment. 

Tanaka observed that ionized (polyacrylamide) (PAA) gels, immersed in a 50% acetone and 50% water mixture, collapsed and physically shrunk, by measured loss of volume, in the presence of an electric field. When the electric field was removed, the collapsed gel swelled to its initial proportions [28]. Tanaka observed phase transitions of cross-linked partially hydrolyzed PAA gels as a function of temperature, solvent, ionic concentration, pH, and electric field [28-40]. Very small changes in electric potential across partially hydrolyzed PAA gels produced significant volume changes [39, 40]. 

Fig. C9.7 (a) A cartoon showing how free energy profile changes with the change of environment, and how phase transition occurs when the barrier between states becomes very low. (b) The volume of a polyacrylamide network in a mixture of acetone and water, as a function of the percentage of acetone. (Vb is the volume that the network had when just prepared.) The figure is courtesy of T. Tanaka.

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