LIGHT-SCATTERING-STUDIES IN CROSS-LINKED GELS - EVIDENCE OF A MICROPHASE SEPARATION

In this paper we report experimental results from depolarized Rayleigh , Brillouin, and elastic (zero-frequency intensity) scattering, on met hyl-methacrylate (MMA) gels cross-linked with ethylene-dimethacrylate (EDMA). The study is performed by varying the cross-linking amount of the gels from 0 to 6%. The depolarized Rayleigh scattering is studied in the frequency range 0-150 cm(-1) while the Brillouin and the zero-f requency intensity data are measured at different scattering wave vect ors in the angular ranges 90 degrees-150 degrees and 10 degrees-150 de grees, respectively. The behavior of the measured quantities confirms that in these gels a microphase separation phenomenon takes place. In particular, for samples with crosslinking content higher than 3%, Bril louin data (studied in terms of the group velocity) give information a bout the existence of well-defined solidlike and liquidlike islands (h eterogeneities in the gel structure) with an extent of several hundred angstroms (as confirmed by elastic-scattering data). Increasing the c ross-link concentration in the gel seems to generate an increase in th e number of the liquidlike islands, with a reduction in their correspo nding size. Depolarized-light-scattering data show (in the same concen tration region of EDMA) a change in the freely rotating terminal group s of the MMA polymer.