PARTIAL SCATTERED INTENSITIES FROM A BINARY SUSPENSION OF POLYSTYRENE AND SILICA

The paper reports SANS (small angle neutron scattering) experiments on aqueous binary suspension mixtures of charged polystyrene latex and silica particles, characterized by the size ratio, gamma=sigma(si)/sigma(ps)similar to 0.72, with a nominal polystyrene diameter, sigma(ps)=91 nm. The scattered intensities are reported over the wave vector (Q) range 0.025 < Q/nm(-1) < 0.4. Partial scattered intensities were obtained by contrast matching the constituents with an appropriate D2O/H2O solvent. Results are presented for mixtures at a volume fraction phi(T)=0.1 as a function of the number ratio, n=N-ps/N-si; n=2/1, 1/1, 1/2, and 1/4. The partial scattered intensity of polystyrene differs significantly from that of silica at a given value of n, and the partial scattered intensity of a component in a mixture suspension can differ markedly from the equivalent scattered intensity of the component in a pure suspension. The variation of the intensity with Q for silica in a 1/1 mixture suggests long range silica order at low Q. There is some evidence that the larger component, polystyrene, may form a polycrystalline fee phase, in agreement with the density functional theory. The effect of multiple scattering on the data is discussed.