Static inhomogeneities in thermoreversible gels

The effect of cross-linking on static inhomogeneities in a thermoreversible polymer gel was investigated by light scattering. Speckle patterns of poly(vinyl alcohol)Congo Red ion complexes in an aqueous solution were measured at a temperature range between 20 and 60 degrees C. The system changed from the gel state to the sol state in the vicinity of 45 degrees C. An interesting feature was disclosed; the formation of gel leads to a remarkable increase in the spatial fluctuations of scattered intensity (I(q)). By comparing these results with those for a chemically cross-linked gel, it was concluded that the increase in I(q) is solely due to the restricted ergodicity of gels as a result of introducing cross-links to the system.