Figure 2. The change in microstructure of a colloidal dispersionexplains the transitions to shear thinning and shear thickening.In equilibrium, random collisions among particles makethem naturally resistant to flow. But as the shear stress (or,equivalently, the shear rate) increases, particles become organizedin the flow, which lowers their viscosity. At yet highershear rates, hydrodynamic interactions between particles dominateover stochastic ones, a change that spawns hydroclusters(red)—transient fluctuations in particle concentration. The difficultyof particles flowing around each other in a strong flowleads to a higher rate of energy dissipation and an abrupt increasein viscosity.
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