Optical detection of shear induced structure changes in concentrated suspensions

Several concentrated aqueous suspensions with kaolin, alumina or limestone as disperse phase show a particular non-Newtonian time dependent flow behavior. The apparent viscosity oscillates with time at constant shear rate. The oscillation period can range between a few minutes and 2 h. This behavior is assumed to be caused by shear induced structure changes. In order to detect these structure changes we have applied a fiber optical system for measuring the intensity of laser light reflected from a small part of the sheared suspension. We have found a correlation between the optical signal and the viscosity oscillations.