Deformation of ‘crystal-like’ structure of a monodisperse polystyrene sphere under shear rate as studied by the transmitted-light spectrum method

Abstract

Transmitted-light spectrum measurements are used to observe the ordered structure in aqueous suspensions of monodisperse polystyrene latex spheres using a thin optical flow cell. The face-centred cubic (f.c.c.) and body-centred cubic (b.c.c.) lattice structures coexist under flow, although the lattices are more or less deformed, and melt at high shear rate. Compression of the Bragg spacing between parallel layers of the lattices occurs with increasing shear rate at relatively low concentrations. At intermediate concentrations the spacing is highly sensitive to the shear rate, i.e. a sharp increase and/or decrease in the Bragg spacing occurs. At higher concentrations the spacing simply increases with the shear rate. The deformation of the electrical double layer from a spherical shape is deduced at dilute latex concentrations under shear flow, and the sliding-layer model is supported at high latex concentrations.