Particle segregation in monodisperse sheared suspensions

It has been known for a long time that many mixtures of granular materials tend to segregate when tumbled in a rotating horizontal cylinder, with the different components separating into bands of relatively pure single concen tration along the rotational axis [Mixing of Solids, Advances in Chemical E ng., edited by T. B. Drew and J. W. Hoopes (Academic Press, New York, 1952) , Vol. 2, p. 211]. Here we report a phenomenon that seems to be analogous, but in suspensions of monodisperse neutrally buoyant spherical particles in a Newtonian liquid medium being sheared in a partially filled horizontal C ouette device in which the suspension separates itself into alternating reg ions of high and low particle concentration along the length of the tube. T he experiment is mostly qualitative, the aim at this stage being primarily to provide photographic evidence of a curious and as yet unexplained phenom enon. (C) 1999 American Institute of Physics. [S1010-6631(99)00503-6].