Interactions in mixtures of latex particles and polymers as revealed by turbidimetry

We report a turbidimetric study of the depletion forces between latex particles induced by a dissolved polyelectrolyte. The system consists of a polystyrene latex and potassium polystyrene sulfonate (PSS). Since turbidimetry is practically insensitive to multiple scattering the analysis of the mixtures of the colloid and the dissolved polymer could be extended up to latex concentrations of 50 g/l. The amount of dissolved PSS was varied between 0.025 and 0.2 wt.%. The scattering contribution of the polymer can be neglected in very good approximation and the change in scattering intensity upon addition of PSS can directly be related to the effective attraction of the latex spheres caused by the dissolved polymer. It is demonstrated that a potential based on the volume-exclusion mechanism can describe in good approximation the osmotic compressibility resulting from the turbidimetric analysis.