Flow-induced anisotropic sals in silica-filled pdms liquids

Anisotropic butterfly-type patterns have been observed during shear flow in polydimethylsiloxane liquids (M_n = 8700 to 67,000) filled with colloidal silica (radius = 50 nm) using small-angle light scattering. These anisotropic patterns indicate the formation of particle or agglomerate fluctuations organized parallel to the shear direction. The shear-induced fluctuations appear to be due to deformation and alignment of large flocs or agglomerates formed in these systems by polymer bridging. Unsheared agglomerate structures were examined using static light scattering, transmission electron, and optical microscopy, and agglomerates subjected to shear flow were examined using light scattering and optical microscopy. The shear-induced ordering was found to increase with shear rate and the volume fraction of agglomerates.