Predictions of the change in extinction coefficient for prolate particles under shear

The following study investigates the microstructural changes induced by she ar in dilute suspensions of colloidal Fe2O3 rods (aspect ratio = 8.4) using rheo-optic techniques. The large extinction coefficient for the hematite s ystem at the wavelength used (lambda (max) = 392 nm) enables rheo-optic exp eriments on truly dilute suspensions to be undertaken. Optical absorbance s pectra have been measured over a range of shear rates for unpolarized light and for light polarized relative to the shear direction. The measured abso rbance changes may be attributed to the shear-induced anisotropy in the sus pension. Numerical methods are used to obtain solutions of the convective-d iffusion equation, which are used to predict the measured change in extinct ion coefficient with shear for colloidal hematite rods measured using optic al rheometry. (C) 2001 American Institute of Physics.