The phase separation behaviour and the viscoelastic properties of particles with non-adsorbing polymers: Part I - Experimental study

A series of well characterised cis-polyisoprene polymers have been added to dispersions of PHS coated PMMA particles in dodecane. At a molecular weigh t of 8000 g mol(-1) and above, these systems showed phase separation at low particle volume fractions and above a critical polymer concentration. The rate of separation has been shown to be influenced by the viscosity of the polymer. At high polymer and particle volume fractions long lived metastabl e phases occurred. Above a critical concentration these were viscoelastic i ndicating an appreciable change in diffusion dynamics with two relaxation p rocesses present. A significant Bingham yield stress was also observed. The Asakura Oosawa potential was not able to describe the observed rheological properties. At a molecular weight of 1000 g mol(-1) no phase separation wa s observed. At high particle concentrations the yield stress was found to r educe with the addition of polymer. This was due to the polymer acting as a 'solvent' and penetrating the stabilising layer on the particles. (C) 2000 Elsevier Science B.V. All rights reserved.