MICROSTRUCTURE-DEPENDENT VISCOSITY IN CONCENTRATED SUSPENSIONS OF SOFT SPHERES

Monodisperse colloidal suspensions of polymethylmethacrylate spheres s wollen in benzyl alcohol have been theologically examined under applie d steady and oscillatory shear while simultaneously monitoring microst ructure via light scattering, In concentrated samples, long-lived none quilibrium microstructures can be induced, corresponding to random hex agonal-close-packed planes (hcp) stacked in the direction of the shear gradient. The direction of closest packing within each hcp plane fan be oriented along either the vorticity or direction of flow. Creep and creep recovery measurements have been examined for each of these two orientations as a function of particle concentration and stress. Resul ts indicate a strain-dependent dissipative profess correlated with cha nges sample microstructure, while dynamic measurements of the storage modulus show no significant difference between microstructures. We arg ue that instantaneous viscosities can be measured and show how they ar e correlated with changes in particle microstructure. The observed ela stic response in these suspensions will be shown to be due to local mi crostructure and particle deformation.