Viscosity of a Dilute Suspension of Sodium Montmorillonite in a Electrostatically Stable Condition

The viscosity of a dilute suspension of sodium montmorillonite under dispersed conditions was measured as a function of electrolyte concentration using a capillary viscometer. Analyses were focused on the evaluation of electroviscous effects. The absence of particle expansion due to swelling was confirmed by the Stokes diameter measured by photon correlation spectroscopy (PCS). The intrinsic viscosity obtained was found to increase with an increase of reciprocal Debye length (κ−1) which demonstrated the evidence of a primary electroviscous effect. By extrapolating this relation to κ−1= 1 nm, we obtained the intrinsic viscosity [η] free from the electroviscous effect. Using this value, the shape factor and size of the montmorillonite sheet were estimated. The estimated size was slightly smaller than that obtained from PCS. The viscosity data also suggested the importance of the multiparticle interaction which appeared in accordance with an increment in double layer thickness. At lower electrolyte concentration, we found a larger Huggins’ coefficient, which is an index of the degree of pair interaction, and we found that the multiparticle interaction appeared at a lower volume fraction of clay sheets.