Brownian motion in binary colloidal suspensions

Self-diffusion in two-dimensional binary colloidal hard-sphere fluids

We present a systematic experimental study of the dynamic behavior of monodisperse and bidisperse two-dimensional colloidal hard-sphere fluids. We consider the diffusive behavior of the two types of particles for systems with a variety of compositions and total area fractions. In particular, we measure the short- and long-time diffusion coefficients for both species independently. We find that the short-time self-diffusion coefficients show an approximately linear dependence on the area fraction and that the long-time self-diffusion coefficients are well described by an expression dependent upon only the area fraction and contact value of the radial distribution function. Finally, we consider the effect of composition change and find some variation in the long-time self-diffusion coefficients, which we ascribe to the complex packing effects exhibited by binary systems.

Stochastic description of the light scattered by a polydisperse colloidal suspension: simulation and experiment

In this work, the stochastic properties of the detected signal in dynamic light scattering experiments are examined in light of Doob's theorem. For Markovian observations of the Brownian particle position, we prove from this theorem that the electric field scattered by a polydisperse suspension can be accounted for by a linear combination of Ornstein-Uhlenbeck processes. A new algorithm for generating the fluctuating field scattered by a polydisperse system is proposed from this alternative formalism. The statistics of our synthetic data is compared satisfactorily with that resulting from the experimental signal scattered by a binary suspension of polystyrene microspheres.