THE RELATIONSHIP BETWEEN INTERPARTICLE FORCES AND THE BULK RHEOLOGY OF SUSPENSIONS

Forces between block and graft copolymers adsorbed to mica surfaces have been measured in both aqueous and non-aqueous media. The forces are long range (commencing at 20-60 nm, depending on the molecular weight of the polymer) and repulsive, decaying approximately exponentially with increasing surface separation. The results agree with current theories and with previous experiments. Subsequently, the same copolymers have been adsorbed onto or incorporated into stable colloidal particles. The rheological properties or suspensions of these particles have been determined, in particular the high-frequency limit of storage modulus, G'-infinity. Previous workers have derived an expression to relate this parameter to the forces between the colloidal particles. Although these forces cannot be measured directly, they can be calculated from those measured between the mica surfaces. It has therefore been possible to test the derived expression. It has been found that although this expression gives a good qualitative prediction of G'-infinity, it tends to underestimate it by about 1 to 2 decimal orders of magnitude.