Small-angle neutron scattering of sheared concentrated dispersions: Microstructure along principal flow axes

Abstract

Using a novel parallel-plate flow cell, the shear-induced distortion of the structure factor S(k) for concentrated hard-sphere dispersions by small-angle neutron scattering is examined. The flow cell is vertically mounted, and the angle of incidence of the neutrons can be varied by rotating the flow cell as a whole. Thus data can be collected in many planes including those containing the principal flow axes. Dispersions containing sterically stabilized silica spheres of 40 nm radius, with volume fractions from 0.03 to 0.45, are studied. The Peclet number is varied between 0 and 1.0, and measured scattering patterns for wave vectors 0<k<0.3 nm−1 are measured. Contour plots for S(k) in part of the shear plane are presented for the first time. Based on the shear-induced distortion of S(k), it is proposed that particle density increases along the compressional and vorticity axes, but decreases along the extensional axis.