DENSITY AND CONCENTRATION FLUCTUATIONS IN PLASTICIZED POLY(CYCLOHEXYL METHACRYLATE) AS STUDIED BY X-RAY-DIFFRACTION

Small-angle X-ray scattering (SAXS) and pressure-volume-temperature (PVT) measurements are employed in bulk and plasticized poly(cyclohexyl methacrylate) (PCHMA) in the temperature range 252-448 K and provide a way of separating the density from the concentration fluctuations. We show that the density fluctuations are suppressed in the mixtures and that the concentration fluctuations increase with plasticizer content. Rayleigh-Brillouin scattering was also employed on the same mixtures, and the contribution of propagating density fluctuations (phonons) to the total fluctuations was evaluated at T above and below the glass transition temperature T(g). The excess intensities in the light scattering (LS) and SAXS studies of bulk PCHMA make necessary the introduction of two additional Landau-Placzek ratios, not treated by conventional theories of the liquid state.