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 t he binodal. The spinodal is determined from an extrapolation of the di ffusion coefficient as measured in the one-phase region, where it is e ssential to take the hydrodynamic interactions into account. The dista nce between the binodal and spinodal is small in the entire region so that it is difficult to locate the critical point accurately. The corr elation length, measured with static light scattering, increases drast ically on approaching the binodal. From these measurements the spinoda l could be determined as well. For not yet understood reasons, there i s a considerable discrepancy between the location of the spinodal as f ound from extrapolated dynamic and static light scattering data.