Sub-THz complex dielectric constants of smectite clay thin samples with Na+/Ca++ ions

Abstract

We implement a technique to characterize the electromagnetic properties at frequencies 100 to 165 GHz (3 cm-1 to 4.95 cm-1) of oriented smectite samples using an open cavity resonator connected to a submillimeter wave VNA (Vector Network Analyzer). We measured dielectric constants perpendicular to the bedding plane on oriented Na+ ion and Ca++ ion stabilized smectite samples deposited on a glass slide at ambient laboratory conditions (room temperature and room light). The clay layer is much thinner (30 μm) than the glass substrate (2.18 mm). The real part of dielectric constant, ε re, is essentially constant over this frequency range but is larger in Na+ ion than in Ca++ ion infused clay. The total electrical conductivity (associated with the imaginary part of dielectric constant, ε im) of both samples increases monotonically at lower frequencies (<110 GHz) but shows rapid increase for Na+ ions in the regime > 110 GHz. The dispersion of the samples display a dependence on the ionic strength in the clay interlayers, i.e., ζ potential in the Stern layers. Key Points The pore scale electrical environment of clays The connections between EM parameters and components of surface chemistry We measure the dispersion of the dielectic permittivity up to 160 GHz