Unusual salt effects on the time-dependent behavior of charge and shape anisotropic hectorite clay gels: Role of electric double layer (EDL) repulsive force.

Salt strengthened the bond formed and quickened the bonding process of 3-5 wt. % hectorite gels during the structural rejuvenation process. This even occurred at 0.002M KCl. Microstructure showed exfoliated, flexible platelet bonding in (+)edge-(-)face configurations. The display of prominent aging time-dependent behavior is due to the structural rejuvenation process being controlled by the electric double layer (EDL) repulsive force. Salt increased the lower energy paths to bonding in the (+)edge-(-)face configurations and weakened the EDL force to form stronger bonds. The Leong model time constant data supported the faster bonding process. In shear, the gels with a weakened EDL repulsive force caused by 0.01 and 0.1M KCl treatment were unable to display EDL force-control time-dependent behavior in the stepdown shear stress response. This situation was remedied by increasing the negative charge density of platelets with adsorbed P2O74-. The amount of P2O74- needed was higher at 0.1M KCl.