mally observed for the suspension of charged colloid, is one The viscosity of a dilute suspension of sodium montmorillonite source of the electroviscous effect; the viscosity of the suspenunder dispersed conditions was measured as a function of electrosion exceeds that of an uncharged suspension.
lyte concentration using a capillary viscometer. Analyses were fo-It is known that there are three distinctive regimes of cused on the evaluation of electroviscous effects. The absence of electroviscous effect for the solution of macroions or the particle expansion due to swelling was confirmed by the Stokes suspension of charged colloidal particles when the fluid is diameter measured by photon correlation spectroscopy (PCS). The set in motion (2). The primary effect is caused by the resisintrinsic viscosity obtained was found to increase with an increase tance of ionic atmosphere against fluid distortion of shear. of reciprocal Debye length (k 01 ) which demonstrated the evidence It can be detected as an increment of the intrinsic viscosity.
of a primary electroviscous effect. By extrapolating this relation to k 01 ร
1 nm, we obtained the intrinsic viscosity [h] free from the The secondary effect is the additional energy dissipation electroviscous effect. Using this value, the shape factor and size of genarated due to the overlapping of diffuse double layers of the montmorillonite sheet were estimated. The estimated size was colloidal particles when two charged particles are conveyed slightly smaller than that obtained from PCS. The viscosity data to a close position by an external fluid motion. This effect also suggested the importance of the multiparticle interaction is still significant even in the dilute suspension and is proporwhich appeared in accordance with an increment in double layer tional to the second power of the volume fraction of colloidal thickness. At lower electrolyte concentration, we found a larger particles. Therefore, the effect can be detected as an incre-Huggins' coefficient, which is an index of the degree of pair interacment of the Huggins' coefficient from that estimated for an tion, and we found that the multiparticle interaction appeared at uncharged colloidal dispersion. Because this effect demona lower volume fraction of clay sheets. แญง 1998 Academic Press strates shear dependency, it has been regarded as one of the