摘要

This work examines the rheological behavior of exfoliated dispersions of organically modified montmorillonite clay in p-xylene. The clay loadings in these dispersions range from 0.5 wt% to 4 wt%, and they have been studied under oscillatory shear, steady shear, and double-step shear stress flows. The dispersions exhibit a storage modulus plateau whose magnitude varies over three orders of magnitude, depending upon clay loading, which is consistent with a solid-like, percolated clay network. All samples also exhibit a yield stress whose magnitude also increases with clay loading. Like many yield stress fluids, these dispersions also show a shear stress vs. shear rate hysteresis, suggesting that once the clay network has been disrupted, flow can prevent it from reforming even at shear stresses somewhat less than the yield stress. Within the hysteresis regime, the viscosity shows time-periodic behavior, raising the possibility that the balance between flow and network reformation is unstable at those shear stresses. Finally, preliminary data demonstrate that the time scale for network reformation depends strongly upon the initial shear stress. We intend to use these results to further clarify the physics of the percolated clay network.