Rheology of Aqueous Dispersions of Hydrogenated Castor Oil

Three major hydrogenated castor oil crystal morphologies have been observed: fiber, rosette and irregular crystal. Due to the difficulty in obtaining samples with a single crystal morphology, rheological studies of suspensions containing mixtures of the three morphologies in an aqueous solution have been undertaken. The viscometry of dilute suspensions has shown that the magnitude of intrinsic viscosity is dominated by the fraction of a crystal morphology type, i.e. fiber > rosette > irregular crystal. A modified Farris model was fitted to the rheology data for mixtures of crystal morphology with interacting particles. A yield stress exists for concentrated suspensions followed by a shear thinning behavior with the increase of shear rate. A power-law relation has been found between yield stress and total particle volume fraction, and a constant exponent of 1.5 has been obtained regardless of crystal morphology.