Large-scale bundle ordering in sterically stabilized latices

Time-resolved small-angle light scattering and linear conservative dichrois m measurements are presented for concentrated, sterically stabilized, aqueo us latices under simple shear flow. At low stress levels, how causes a mild distortion of the liquid-like structure in colloidally stable dispersions, which is quite well understood, In this paper how-induced structures are i nvestigated in concentrated dispersions when the system is brought far from equilibrium by means of hydrodynamic forces. At high stress levels various structural changes have been predicted by numerical simulation, among othe rs string phases oriented in the flow direction, Here, experimental results are reported on a bundle-like ordering in very dense systems, which involv es a length scale much larger than that of a single string of particles, Tw o latices, with different particle sizes and different thicknesses of the s tabilizing layer, are compared. The occurrence of the bundle-like ordering is related to the rheological behavior: it causes a significant decrease in viscosity. It is shown that the presence of this phase results in a struct ural hysteresis, which explains a thixotropic behavior that is encountered in some stable colloidal suspensions, Also the relaxation behavior of the b undle-like phases has been studied, Interparticle forces are found to have a very strong effect on the relaxation time scales. (C) 1999 Academic Press .