| Colloidal particles exhibit Brownian motion, while granular particles do not. Associated with their thermal motion, colloidal particles exhibit thermally driven rearrangements that lead to relaxation and aging in dense suspensions. We investigate the effect of such relaxations on slow suspension flows. Based on three-dimensional particle trajectories determined with confocal microscopy (colloids) and laser sheet imaging (granulates), I will show that thermally induced relaxations have a substantial effect on spatio-temporal correlations of particle displacements. For granular particles, the lack of relaxation and aging leads to strong directional correlations. Because the structure does not 'heal', local flow creates more flow, leading to a distinct, localized flow pattern over long times. |
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