Prediction of rheological properties in polymer colloids

The rheological properties of concentrated suspensions, containing sterically stabilized polymer colloids, are reviewed. It is shown that the various rheological characteristics are strongly interrelated in such systems. They deviate from Brownian hard sphere behaviour, but these deviations are closely related to the interparticle potential and other colloidal characteristics like particle diffusivity. As a result the rheological properties can be predicted from the colloidal characteristics and vice versa. This is demonstrated by means of available data on well characterized model dispersions. In the experiments volume fraction, particle size, suspending medium and temperature have been changed. Data reduction schemes and scaling laws for these parameters are discussed.     

The nonlinear change in conformation of polyelectrolyte macromolecules in saltless water-organic solvent

High molecular weight polyelectrolyte: poly(dimethylaminoethyl methacrylate) [PDMAEMA] with molecular weights M_W = 28.0×10⁶, 20.0×10⁶, 15.0×10⁶ was investigated in dilute solution by light scattering, flow birefringence and viscometry (at different rate gradients) in a water-acetone system by varying the weight fraction of acetone r in the mixture. At r=0.76 the polymer undergoes a reversible coil-globule transition accompanied by a drastic decrease in intrinsic viscosity [n], mean-square radius of gyration R²_z^1/2 and second virial coefficient A₂, with no change in molecular weight. The coil asymmetry parameter p (p=2.5 at r=0.50) decreases with increasing r and attains unity (completely symmetrical particle) at the transition point (r=0.76). The anomalous behavior of the viscosity of PDMAEMA-water-acetone solutions, detected near the transition point (r=0.6+0.7), is interpreted by formation of local knots of compactization on the molecular chain under the influence of a hydrodynamic field.