Universality and specificity of polymer gels viewed by scattering methods

Concentration fluctuations in polymer gels are composed of dynamic thermal fluctuations and frozen inhomogeneities. Particularly, the latter is a characteristic of gels and is due to cross-linking. The frozen inhomogeneities manifest unique properties in polymer gels. Speckle patterns are commonly observed in gels. The time-correlation function of the scattering intensity entails a power-law behavior at the sol-gel transition. The appearance of speckle patterns is related to the nonergodicity of gels, and the power-law behavior corresponds to the self-similarity of clusters at the gelation threshold. In this review, it will be demonstrated that light scattering is one of the most powerful tools for structure characterization of polymer gels. Then, the Universality and specificity of polymer gels will be examined for various types of gels, including physical gels, composite gels, and gelators.