Shear induced order of hard sphere suspensions

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Abstract
Hard spheres serve as one of the basic models in classical equilibrium statistical mechanics, as well as, in fluid mechanics. Sterically stabilized polymethylmethacrylate (PMMA) spheres suspended in certain organic solvents have interparticle interactions which approximate the hard sphere interaction. Thus the equilibrium properties of PMMA particle suspensions should correlate with theoretical and computer simulation results of pure hard sphere systems. However, non-equilibrium properties must be compared with theories which include the hydrodynamic effects of the suspending medium. Experimental results are presented which suggest hard sphere behaviour: a solid-liquid phase transition, equilibrium crystal structure, liquid and crystal sedimentation velocities. Non-equilibrium microstructure in steady and oscillatory shear flows is then examined using light scattering from samples where the solvent index of refraction matches that of the particles. Oscillatory shear flows of the proper strain amplitude can shake crystal-like order into an equilibrium liquid-like sample. These results may be understood in terms of a simple hard sphere model.

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