Neutron scattering from dense colloidal dispersions at high shear rates: The deformation of the structure factor in the shear plane

A parallel-plate shear cell was used in small-angle neutron scattering experiments with the D11 diffractometer at the ILL. This cell allows the study of the deformation of the structure factor in a large part of the velocity-gradient plane (the shear plane) as well as the more commonly studied velocity-vorticity plane. The gap between the plates in a vertical plane and can be rotated about a vertical axis such that the horizontally incident neutron beam makes an arbitrary angle with the axis of rotation of the moving plate. The scattering in the flow-gradient plane is reconstructed from a series of scattering patterns sharing a common vorticity direction but different sectors of the velocity-gradient plane. Concentrated hardsphere dispersions were subjected to high-shear flow. It is found that an increase of the Peclet number from Pe=1 to Pe=10 does lead to a significant change in the micro-structure of the dispersion, whereas a further increase to Pe=20 or higher does not induce a further change. If the volume fraction of the particles is lower than φ=0.50, the qualitative deformation of the structure factor is independent of concentration. However, if the concentration is above φ=0.50, then a different structure is observed in the flow-gradient plane. These findings are consistent with previous light scattering experiments on the same hard-sphere dispersions and support the proposal of a “non-equilibrium phase” diagram.