| Abstract
| - A polyacrylamide hydrogel undergoing a volume change was studied by using interferometricimaging. The method produces the radial distribution of the matrix density for the cylindrical hydrogelat different times during the volume transition caused by solvent change. When the water-swollen gelwas immersed in a water−methanol mixture, contraction of the gel matrix occurred first in the edge andpropagated to the center. The edge did not reach the equilibrium density immediately after the solventchange. The gel contracted rather evenly, although the edge maintained a higher density during thechange. After reaching the uniform density, the center of the gel contracted further whereas the edgeremained unchanged. A similar pattern was observed in the reswelling in pure water. These findingsindicate that the gel studied had a shear modulus not small compared with its bulk modulus.
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