Steady Flow Viscosity and Rigidity of Colloidal Spheres in Deionized Suspensions

Abstract

AbstractSteady‐flow viscosities of colloidal spheres, i.e., colloidal silica (8–45 nm in diameter) and monodisperse polystyrene latices (diam. 85 to 780 nm), are measured in deionized suspensions and in the presence of a small amount of NaCl. The plots of shear stress (S) of the crystal‐like structure of the colloids against shear rate (q) show the following features: (1) at very small values of q (smaller than 0.1 s−1), S increases very sharply with increasing q. The S – q curve is S‐shaped, and the rigidity (G) of the colloidal crystal is evaluated from the plots of S against qt/2 (shear strain), where t is time. The G‐values are between 20 and 3000 Pa, which are consistent with those reported hitherto, and increase as the sphere's concentration increases. (2) The sharp increase in S ceases above the critical q value, from which the yield stress of the crystal‐like structure is evaluated to be between 0.1 to 2 Pa. (3) The log (viscosity, η) vs. log q plots shows non‐Newtonian flows: η increases as q decreases and then η reachs a constant value. Furthermore, log η begins to increase linearly as log q decreases with a slope of −1, which supports the crystal‐like nature of the suspensions.