Flow-small angle neutron scattering measurements of colloidal dispersion microstructure evolution through the shear thickening transition

The shear induced microstructure for electrostatic and Brownian suspensions are compared using in situ small angle neutron scattering (SANS). The dispersions consist of 75 nm Stober silica coated with 3-(trimethoxysilyl) propyl methacrylate (TPM) and have a zeta potential of -42.6+/-4.7 mV. Neutralizing the surface charge with 0.066 (M) under bar nitric acid yields stable hard-sphere dispersions. SANS is conducted over a range of shear rates on the charge-stabilized and Brownian suspensions to test the order-disorder transition and hydrocluster mechanisms for shear thickening, and demonstrate the influence of stabilizing forces on the shear induced microstructure evolution. Through treatment of the colloidal micromechanics, shear induced changes in the microstructure are correlated to the hydrodynamic component of the shear stress and the thermodynamic component of the normal stress, i.e., the method of Rheo-SANS is developed. The results demonstrate that hydrocluster formation accompanies the shear thickening transition. (C) 2002 American Institute of Physics.