Flow and pattern formation in a binary mixture of rotating granular materials

In a horizontally rotating cylinder, size segregation, pattern formation, a nd its time development are studied for a binary mixture of rodlike and dis klike materials at various rotational frequencies. The rodlike particles fo rmed a network that influenced their mobility and the shape of the avalanch ing surface. Windows installed on the cylinder enabled us to examine and co ntrol the distribution of the components of the mixture throughout the bulk . This has allowed us to study the evolution of naturally occurring and art ificially created patterns. All observed patterns had a degree of asymmetry and were unstable. The stability of a band pattern is shown to depend on i ts symmetry. Qualitatively, the time for the transition from one set of ban ds to another was inversely related to the degree of asymmetry of the patte rn. In addition, we propose that the parameter Did (diameter of the cylinde r over the diameter of the grains) plays a significant role in the function al dependence of the avalanching surface current on the dynamical angle of repose, and in the segregation process itself.