Light scattering from gels, theory

Tanaka, Hocker, and Benedek first realized this essential nature of gds and developed a theory of the dynamics of gel networks [16]. According to their theory the quasi-elastic light scattering from gel networks became one of the standard methods of studying polymer gels. Here we briefly outline the theory of the dynamics of gels. 

The authors attempted to measure the intensities of light scattered from a NIPA gel during the phase separation induced by a change in temperature [23]. In this study, we examined the applicability of Cahn s linearized theory [24] to the spinodal decomposition of the geL... 

Dynamical study of the phase transition of the gels in spinodal regimes was described. The evolution of intensity of light scattered from the gels indicated the applicability of Cahn s linearized theory to the phase transition. Our work offers a basis for the determination of diffusion coefficient of gels in their spinodal regimes. 

The use of photon correlation spectroscopy to study the dynamics of concentration fluctuations in polymer solutions and gels is now well established. In bulk polymers near the glass transition there will be slowly relaxing fluctuations in density and optical anisotropy which can also be studied by this technique. In this article we review the development of the field of photon correlation spectroscopy from bulk polymers. The theory of dynamic light scattering from pure liquids is presented and applied to polymers. The important experimented considerations involved in the collection and analysis of this type of data are discussed. Most of the article focuses on the dynamics of fluctuations near the glass transition in polymers. All the published work in this area is reviewed and the results are critically discussed. The current state of the field is summarized and many suggestions for further work are presented. 

Current theories for the dynamic fluctuations and kinetics of polymeric gel swelling are reviewed. The cooperative diffusion constant can be determined either from quasi-elastic light scattering experiments or from the swelling kinetics of spherical or cylindrical gels. The influence of the structure and ionization degree of the network on the cooperative diffusion constant is discussed. 

The dilute solution methods have been used for characterising polymers since day one of polymer science. Measurements of dilute solution viscosity, osmotic pressure and light scattering have been well-established in theory as well as in practice. They are described practically in every textbook and in many review articles. More than 30 years have passed since the introduction of size exclusion chromatography (or gel permeation chromatography CPC), which provides fractionation data very conveniently. This chapter is not intended to be a review of these methods. It is directed to examining how useful these methods are with respect to sensitivity, reproducibility, and reliability. Stated differently, the question is whether or not differences in processability can be explained on the basis of information available from the dilute solution methods. 

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