Complex dielectric permittivity of organically modified bentonite suspensions (0.2–1.3 GHz)

Abstract

To quantify the impact of organic carbon on the complex dielectric permittivity of organoclays, nine organically modified clays were synthesized with controlled organic carbon structure and density of loading. Resonance polarization responses were observed for six of the organoclays at resonant frequencies from 0.74 to 1.37 GHz; however, organoclays synthesized with the smallest organic cations did not exhibit resonant frequency. A structural model of water molecules near the surface of organoclay and in the diffuse layer was proposed, which consists of a surface-bound water layer, an organic cation-interactive zone, and bulk water. The Cole–Cole equation was used to fit the resonance response. Increasing the density of loading (30% to 100% of the cation exchange capacity of the base clay) on the clay surface led to a reduction in the resonance time of the clay, while increasing the size of the organic cation led to a longer dielectric resonance time for the clay, which indicates that altering the structure and density of the organic carbon phase changed the degree of constraint of water molecules within the clay’s interlayer. However, the impact of organic carbon content on real permittivity was not significant. Water content had no obvious effect on the resonant frequency of the organoclays at high water content (porosity ranging from 0.7 to 1.0) in this study. In addition, it was shown that a linear approximation was sufficient in relating real permittivity of organoclay suspensions to porosity, and the effective conductivity decreased linearly proportional to porosity. That is, the real permittivity and effective conductivity were dominated by that of the aqueous phase until the inception of resonance polarization.