Depletion and cluster formation in soft colloid-polymer mixtures

The dynamics of colloidal star-linear homopolymer mixtures is investigated by photon correlation spectroscopy. In dilute star solutions, osmotic forces due to the added polymers lead initially to a shrinkage of the stars and eventually, at higher polymer concentrations, to stable star clusters. Furthermore, concentrated glassy star solutions melt upon addition of small amounts of linear polymers, as manifested by the remarkable speed-up of the star self-diffusion. Quantitative description of the experimental findings is provided by calculations of the effective star-star pair potential.