Pretransitional phenomena of a colloid polymer mixture studied with static and dynamic light scattering

A mixture of hard-sphere colloidal silica particles (radius 48 nm) and a nonadsorbing polymer (poly(dimethylsiloxane), radius of gyration 23 nm) is studied by means of static and dynamic light scattering near the binodal. The spinodal is determined from an extrapolation of the diffusion coefficient as measured in the one-phase region, where it is essential to take the hydrodynamic interactions into account. The distance between the binodal and spinodal is small in the entire region so that it is difficult to locate the critical point accurately. The correlation length, measured with static light scattering, increases drastically on approaching the binodal. From these measurements the spinodal could be determined as well. For not yet understood reasons, there is a considerable discrepancy between the location of the spinodal as found from extrapolated dynamic and static light scattering data.