Ordered aggregates of particles in shear flow

A theoretical and experimental investigation was made into the behaviour of ordered aggregates of rigid spheres, disks and rods in plane Couette flow. Chains of spheres formed in an electric field behaved like rigid rods, a result which was predicted theoretically on the basis of the creeping motion equations and lubrication theory. However, such chains broke at high velocity gradients possibly from cavitation of the liquid between the spheres. For chains with non-zero gap width between spheres it was shown theoretically that one would expect periodic stretching and progressive bending. This periodic stretching was observed experimentally. Chains of spheres held together by liquid menisci behaved like flexible threads and formed disordered aggregates at high gradients. Aggregates of disks (rouleaux) behaved like deformable rods and were easily broken as the disks slid apart. Symmetrical but non-linear aggregates of spheres rotated like single spheres at low velocity gradients. The particle aggregates considered in this paper provide interesting physical models of threads, rouleaux of red blood cells and other flexible particles.