The rheological behavior of a latex dispersion including a non-ionic polymer

Abstract

The rheological behavior of polystyrene latex dispersion stabilized sterically by hydroxypropyl cellulose (HPC) with a lower critical solution temperature was investigated. It was revealed that adsorbed HPC layers cannot completely shield electrostatic effects arising from the surface charge on the bare particles, and that adsorbed layers of high molecular weight HPC are “soft”, whereas those of low molecular weight are hard so that the behavior can best be expressed by an equation for dispersion of hard spheres. As for systems including free (non-adsorbing) HPC, relative viscosities under a low shear rate show a peak against the concentration change of free HPC, which is influenced by the molecular weight of added HPC. These experimental results indicate that, after saturated adsorption, the free HPC molecules induce the dispersion to flocculate in spite of the dense adsorbing layer of HPC on the particles which would tend to give rise to a steric stabilization. This behavior is interpreted to be a result of the depletion effect.