ROTATIONAL DIFFUSION OF COLLOID SPHERES IN CONCENTRATED SUSPENSIONS STUDIED BY DEUTERON NMR

We present a study of the application of deuteron-nuclear magnetic res onance spectroscopy (NMR) to the investigation of the rotational diffu sion of spherical colloidal particles. We performed NMR pulse experime nts on colloidal suspensions of polystyrene latex spheres In water-gly cerol mixtures in a wide range of particle volume fractions phi from t he dilute suspension up to phi=0.504. We have analyzed the stimulated echo NMR signal in the time domain. The full shape of the orientationa l correlation function deviates from an exponential behavior in the wh ole phi range examined. We evaluate the rotational diffusion;coefficie nt and calculate-its phi dependence up to the phi(2) term in view of t he theory proposed recently [V. Degiorgio, R. Piazza, and R. B. Jones, Phys. Rev. E 52, 2707 (1995)], which considers the effect of two- and three-body hydrodynamic interactions upon particle reorientation. We find considerable slowing down of sphere reorientation for phi greater than or equal to 0.2. The agreement between experimental results and theoretical considerations is satisfactory.