Rheology of suspensions of weakly attractive particles: Approach to gelation

Abstract

The flow properties of suspensions of weakly attractive particles are investigated as a function of volume fraction and strength of interparticle attraction. The suspensions are composed of uniform silica spheres with covalently bound octadecyl chains with diameters 100–125 nm suspended in decalin and tetradecane. At elevated temperatures, the particles interact like hard spheres. As the temperature is lowered, the suspensions gel. At the gel point, storage and loss moduli are power law functions of strain frequency providing evidence that cluster relaxation rates are much slower than the lowest strain frequency used. At volume fractions below the gel point (temperatures above the gel point), suspensions shear thin in much the same way as hard spheres. These studies suggest that the effect of volume fraction and attractive strength can be correlated when the normalized zero shear rate viscosity, η0/η0HS is written as a function of φ/φG, where η0HS is the high temperature (hard sphere), zero shear rate viscosity of a suspension at volume fraction φ, and φG is the volume fraction where, at the same strength of attraction, the suspensions gel. At φ/φG⩽0.95, η0/η0HS⩽5 suggesting suspension viscosities are weak function of attractions up to the gel point where relaxation times rapidly increase.