Diffusing-wave spectroscopy and interferometry, the extensions of dynamic light scattering to materials which exhibit a very high degree of multiple scattering, have been used to measure the early-time, short length scale motion of Brownian particles. The transition from ''ballistic'' to ''diffusive'' motion is observed. In very dilute samples, this transition is described very well by theories which explicitly account for the time-dependent hydrodynamic interaction between a Brownian particle and the surrounding fluid. For particle volume fractions exceeding a few per cent, the data deviate from the theory for dilute suspensions, but exhibit a remarkable scaling with the suspension viscosity.
Times Cited: 0 33rd Microsymposium on Macromolecules: Optics and Dynamics of Polymers/6th Meeting of European-Macromolecular-Club Jul 15-16, 1993 Prague, czech republic Int union pure & appl chem, macromolec div; acad sci czech republic; inst macromolec chem, prague; czech chem soc