(402h) Hindered Diffusion of Soft Spheres Under Geometrical Confinement

We have investigated the Brownian diffusion of fluorescent colloidal particles under geometric confinement via particle tracking video microscopy. The presence of confinement hinders the Brownian diffusion due to hydrodynamic coupling between particles and the confining walls. Hard spheres (polystyrene particle) and soft spheres (polystyrene/hydrogel core/shell particle) were used to compare the effect of softness on hindered diffusion of colloidal particles between parallel walls for a wide range of wall spacings. While the hindered diffusion for hard spheres shows excellent agreement with available model predictions, the hindrance experienced by soft spheres is much less than can be explained with current models: soft spheres in our study exhibit significant diffusion even when the spacing between walls is smaller than the unperturbed diameter of these particles. This anomalous diffusion is most likely due to the deformability and compressibility of the hydrogel particles.