Quasielastic light scattering study of the formation of inhomogeneities in gels

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Abstract
The inhomogeneities in gels, in particular the mechanism of the formation of the inhomogeneities, were studied. The gels used in this report are water based poly(acrylamide) gels (AA gels) and poly(N‐isopropylacrylamide) gels (N‐IPA gels). It is known that the cross linkers in AA gels are water insoluble at low temperature and that the linear components in N‐IPA gels are water insoluble at high temperature. By changing the gelation temperature at which gels are made, we can control the formation of the inhomogeneous structure in the samples. In order to investigate the inhomogeneities in the gels, two experiments were performed by using the standard laser light scattering method. For the characterization of the degree of inhomogeneities in gels, the position dependence of scattered light intensity from homogeneous and inhomogeneous gels were measured. It was found that the position dependence was a very good indicator of gel inhomogeneities. We also observed the change of the autocorrelation function of scattered light intensity from a sample undergoing the gelation process. It was found that the profile of the correlation functions measured from pregel solution, which is going to be inhomogeneous gel, were different from the correlation functions measured from pregel solution which is going to be homogeneous gel. From the correlation function measured from the sample which will be inhomogeneous gels, two relaxation modes were observed−one is the fast decaying mode which is expected to be observed from ideal gels or ideal semidilute solutions (the cooperative diffusion) and another mode is the slow decaying mode which is not expected to be observed from ideal gels or ideal semidilute solutions. From the experimental results, we discussed the mechanism of the formation of inhomogeneities in gels.