EXPERIMENTAL-STUDY OF THE INDUCED FLOW BIREFRINGENCE OF A SUSPENSION OF RIGID PARTICLES AT THE TRANSITION FROM COUETTE-FLOW TO TAYLOR VORTEX FLOW

The flow birefringence induced in solutions of rigid particles is studied experimentally in the region of the axisymmetrical Taylor vortex flow which arises once the velocity gradient G in the annular gap of a conventional Couette cell reaches a critical value G(c). The measurements are performed for several values of G > G(c) and for 10 radial observation points in the annular gap. Solutions of two types of rigid particles are investigated: the first is a suspension of flattened clay particles like bentonite, while the second contains rod-like particles of tobacco mosaic virus (TMV). The variations of the birefringence intensity DELTA-n and of the extinction angle chi-measured in the domain of the axisymmetrical flow show a different behavior according to the shape of the particle in solution. This fact is confirmed theoretically with a good agreement for the measurements performed with solutions of flat particles.