VISCOELASTICITY-CONCENTRATION RELATIONSHIPS FOR NONAQUEOUS CONCENTRATED DISPERSIONS

The viscoelastic properties of a concentrated 0. 6 mu m diameter polymethyl methacrylate (pMMA) dispersion, sterically stabilised with a pMMA-polyhydroxystearic acid (pHS) graft copolymer in a hydrocarbon medium, have been measured as a function of concentration at a single fixed frequency (10 Hz) and temperature (23 degree C). The measurements were made with a novel viscoelastometer, where the properties of a large (150 g) sample are measured under conditions of minimal disturbance (shear strain and strain rate). The results demonstrate that, in the system measured, small but distinct elastic effects are measurable at concentrations (phase volume fraction) values, where the average particle core separation is considerably in excess of twice the average stabiliser barrier thickness. This finding supports the author's argument that elasticity can arise from forces, such as hydrodynamic, other than those colloid forces produced by the interaction of the stabiliser barriers of neighbouring particles of the dispersion.