Abstract

Brownian particles in an aqueous suspension diffuse freely in regions far from the walls of a cuvette. However, close to the solid-liquid interface, a hydrodynamic interaction called the Stokes drag force drastically suppresses their motion. This is referred to as the wall-drag effect. Such the spatial-nonstationary Brownian dynamics always occurs near the interface between different phases, for example liquid and solid, liquid and gas, and so on. The theory behind this phenomenon was investigated by Brenner and his coworkers in the 1960s [1,2]. The difficulty in obtaining experimental confirmation lies in measuring the dynamics of Brownian particles in a region near the interface whose thickness is restricted to a few particle radii. In addition, the non-stationary spatial dependence of the diffusion coefficient on the scattering position should be measured simultaneously and seamlessly under the same conditions at each position. To realize such the one-shot measurement, we have developed a spectral-domain low-coherence dynamic light scattering (LC-DLS) technique and have investigated the wall-drag effects in the present study.

© 2013 Japan Society of Applied Physics, Optical Society of America