E0005

Small-angle Neutron Scattering and Dynamic Light Scattering Studies of the Sol-gel Transition in Polymer Gels. Mitsuhiro Shibayama¹ and Fumiyoshi Ikkai², ¹Neutron Scattering Laboratory, Institute for Solid State Physics, The University of Tokyo, Tokai, Ibaraki 319-1106, Japan, ²Department of Polymer Science, Kyoto Institute of Technology, Matsugasaki, Kyoto 606-8585, Japan, e-mail sibayama@issp.u-tokyo.ac.jp.

Structural characterization of the sol-gel transition in polymer gels is a sophisticated process because of the presence of heterogeneities introduced during the cross-linking reaction. One aspect of this complexity is the emergence of strong excess scattering observed at low angles in small-angle X-ray and neutron scattering as compared with the scattering from the corresponding polymer solutions. Currently, this phenomenon is interpreted as the scattering from frozen heterogeneities superimposed on that from thermal fluctuations.^1,2

The heterogeneities are observed as speckles when a gel is irradiated by a laser light. This is due to non-zero-sum cancellation of thermal fluctuations by the introduction of cross-links. We developed a method known as ensemble-average dynamic light scattering, which allows a decomposition of the static and thermal components in the scattered intensity. ³By applying this method to a chemical system undergoing gelation, the gelation threshold was uniquely determined. The appearance of heterogeneities can also be detected by small-angle X-ray or neutron scattering. Fitting functions, such as a combination of Gaussian and Lorentzian functions, allow one to evaluate the structural parameters of gels.⁴ Here, we focus on the analysis of the sol-gel transition in Poly(vinyl-alcohol)-Congo Red aqueous solutions, and the nature of the sol-gel transition is discussed^4-6 in relation to site-bond percolation theory.

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