Effect of electric double layer on viscoelastic behavior of highly concentrated suspension

Experimental results on rheological behaviors of highly concentrated suspensions are presented. Suspensions of acryl-styrene copolymer particles with radius 45 nm dispersed in water were used as samples. Rheological properties were measured at particle volume fractions phi ranging from 0.177 to 0476. The rheological data were rescaled using the effective volume fraction phi (eff) calculated from the effective radius estimated as a sum of the Debye length and the particle radius. In the range of phi (eff) lower than the random close packing volume fraction(0.63), rheological behaviors of suspensions gave good agreement with those of ideal suspensions of rigid spheres. This shows that the Brownian contribution is the origin of the linear viscoelastic behavior in lower phi (eff) range. In the range of phi (eff) higher than 0.63, the longest relaxation time and the activation energy rapidly increased with an increase in phi (eff) and the vertical shift factor diverged from estimated values of ideal suspensions. These results suggest that restraint of neighboring particles affects the Brownian motion, and furthermore, repulsive force induced by overlapping of electric double layers affects the viscoelastic behavior.