The Microrheology of Colloidal Dispersions. III. Concentrated Emulsions

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Abstract
The flow behavior of 50 and 70 vol% transparent 2-.mu.m emulsions of amyl acetate in aqueous glycerol is described. The systems exhibited shear thinning behavior and large normal stress differences, the latter an order of magnitude greater than the tangential shear stresses. Particle motions were studied in 100-.mu.m tubes at mean flow rates from 40-1500 .mu.m s-1 using 2-.mu.m resin tracer spheres. The velocity profiles were blunted at all flow rates and at both concentrations with a region of apparent plug flow in the tube center whose radius Rc decreased with increasing flow rate and decreasing concentration. Large radial displacements of tracer spheres were observed at R [radial distance] > Rc, and even when R < Rc small displacements were detected. The distribution of tracer particles across the median plane of the tube was non-uniform with a markedly higher concentration in the plug; this effect increased with distance downstream from the tube entrance and with decreasing flow rate.

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