Visco-Elastic Behavior and Small Angle Scattering of Complex Fluids

Abstract

In this contribution we investigate whether the structure of concentrated shear-ordered dispersions as determined by small angle synchrotron x-ray or neutron scattering can be rationalized in terms of viscoelastic flow behavior as in rheological investigations. Although so far scattering experiments have contributed little to the understanding of rheological systems we are convinced that rheological investigations will profit considerably from a better knowledge of the micro-structure of the dispersions. Sheared dispersions are usually ordered in layers. There are two kinds of ordering of interest: (a) The structure in a layer (b) The structure between the layers. One interesting point of mesogenic systems is their viscoelastic nature. There is strong evidence that the structure in a layer (a) can be treated as elastic or solid-like, whereas the structure (b) between the layers seems to be fluid-like. With scattering experiments one is in the excellent position that two experiments exist with which the two effects can be investigated separately: The solid-like microstructure (a) can be determined at perpendicular incidence. The fluid-like microstructure (b) is given by the scattering intensity along certain Bragg rods (3n±1-rods). In particular this second micro-structure may change in time by aging.