Abstract
AbstractThis research investigated the rheology of submicron silica and nano silver suspensions, focusing on the relationship between viscosity and concentration, shear rate and particle size. In the diluted solution[ ], due to the large distance between two neighboring particles, the interaction of particles can be ignored. Thus the fluid exhibits the Newtonian behavior and its viscosity is a constant,irrelevant to the particle size and shear rate. In the high concentrated suspension, the interaction between particles cannot be ignored. The fluid shows the shear thinning behavior and the viscosity decreases with increasing the shear rate. For 200nm and 300nm silica suspension without surfactant, increasing the volume fraction of concentrated silica suspension will increase the viscosity quickly. Fitting the Quemada’s expression we can get the maximum packing fraction =0.4949 and =0.4856 for 200nm and 300nm, respectively. Although, there is a some difference from the ideal case =0.71.Because, aggregation is always encountered at high concentrated silica suspension. Thus adding cationic surfactant C12TAB into the silica suspension to enhance the steric hindering force could prevent aggregation and decrease the viscosity. The C12TAB will adsorb onto the surface of silica particles due to the electrostatic force. Therefore, the fluid behavior change from non-Newtonian fluid to Newtonian, and for 300nm silica suspension at high concentration containing C12TAB one can get the maximum packing fraction =0.582 by the Quemada’s expression.For the nano silver suspension, the protecting agent PVP is only 5wt % which is not enough to prevent aggregation under shear. Thus the silver particles aggregate due to the Van der Waals force, viscosity increases rapidly and the maximum packing fraction is only 0.076.