Small-angle neutron scattering from viscoelastic polymer-clay solutions

The influence of shear on viscoelastic polymer-clay solutions was investigated by means of small-angle neutron scattering (SANS) under shear. SANS was used to measure the shear-induced orientation of polymer and platelets. With increasing shear rate an anisotropic scattering pattern developed. At higher shear rates, the scattering anisotropy increased due to the enhanced orientation of the clay platelets in the shear field. The clay platelets aligned by the flow in an unusual direction, with the surface normal parallel to the vorticity direction. SANS on regular samples (contrast between D2O and solution components) measured the shear-induced orientation of polymer and platelets. However, with contrast matching the orientation of the polymer alone could be detected. With increasing shear rate, clay particles oriented first (SANS on regular samples) and then polymer chains started to stretch (SANS on contrast matched samples). Cessation of shear led to fast recovery, demonstrating the system to be highly elastic.