COLLOIDAL GLASSES UNDER SHEAR STRAIN

We have studied the effects of oscillatory shear strain on the structu re of a colloidal hard-sphere glass. By light scattering, we measure t he kinetic development of ordered structures induced by shearing betwe en parallel plates. Diffusing wave spectroscopy ''echo'' experiments s how that for peak to peak oscillatory strain below around 30% the coll oidal glass strains approximately reversibly. At higher strains a part ly ordered structure develops, the kinetics of the ordering being stro ngly dependent on strain. Kinetic measurements demonstrate an ''induct ion'' time for crystallization with a divergentlike behavior as strain decreases toward similar to 25-30 %. We compare the behavior of glass y samples with that of samples at lower volume fraction, where in equi librium without shear the sample is fully (poly)crystalline. At the lo wer volume fraction, irreversible yielding is observed at lower strain s. There appears some tendency for very high volume fraction glass sam ples to ''fracture.'' Similar evidence of fracture is not observed at the lower volume fractions. [S1063-651X(98)01010-1].