  Depletion interactions between colloidal particles dispersed in a fluid
medium are effective interactions induced by the presence of other types of
colloid. They are not instantaneous but build up in time. We show by means
Brownian dynamics simulations that the fluctuations in the depletion force
between two guest particles in a host dispersion of differently sized colloids
do not decay exponentially with time, but show a power-law dependence. A simple
scaling theory accurately describes the dependence of the magnitude of these
fluctuations on time, on the inter-particle distance and on the size ratio of
guest and host particles. The consequences in particular for the dynamics of
colloidal mixtures are discussed.
