Confocal microscopy of colloidal dispersions in shear flow using a counter-rotatingcone–plate shear cell

Abstract

We report on novel possibilities for studying colloidal suspensions in a steady shear field inreal space. Fluorescence confocal microscopy is combined with the use of a counter-rotatingcone–plate shear cell. This allows imaging of individual particles in the bulk of a shearedsuspension in a stationary plane. Moreover, this plane of zero velocity can be moved in thevelocity gradient direction while keeping the shear rate constant. The colloidalsystem under study consists of rhodamine labelled PMMA spheres in a nearlydensity and refractive index matched mixture of cyclohexylbromide and cis-decalin.We show measured flow profiles in both the fluid and the crystalline phase andfind indications for shear banding in the case of a sheared crystal. Furthermore,we show that, thanks to the counter-rotating principle of the cone–plate shearcell, a layer of particles in the bulk of a sheared crystalline suspension can beimaged for a prolonged time, with the result that their positions can be tracked.