Dielectric characterization of the water-matrix interaction in porous materials by thermal depolarization spectroscopy

Abstract

We investigate the dielectric behavior of sandstone, which consists of a porous matrix with a small amount of inherent humidity, by the thermal-stimulated depolarization current technique. Nine different relaxation mechanisms are detected by the thermal sampling scheme, and are characterized. The activation energy distribution and the pre-exponential factor are obtained by analyzing the signals under the constraint of a normal distribution in the activation energy. The drying of the specimen at elevated temperature under dynamic vacuum affects some of the relaxation mechanisms. The model of freely rotating dipoles may not account for all the drying-sensitive mechanisms. It is probable that water molecules are organized in a way that provide either conductive layers over the surface of the grains or for conductive inclusions inside the bulk. Longdistance charge-transport mechanisms are also affected by the removal of the humidity.

Dielectric and conductivity measurements as proxy method to monitor contamination in sandstone

“…Previous investigations on partially filled or saturated with fluid sandstone exhibit polarization phenomena, which are probably due to the electrochemical interaction of moisture with the grains surface. A dispersion, which appears in the low frequency region, has been related to the humidity that coats the solid grains and provides diffusion paths, thus, suggesting a solid-liquid interfacial phenomenon rather than an electrode effect [15,23].…”

“…Dielectric properties of porous materials, such as sandstone, have been widely investigated during the last decades, and various models have been proposed by several researchers [9][10][11][12][13][14][15]. Dielectric permittivity and conductivity prove to be extremely sensitive to ambient conditions like temperature and pressure, the chemical composition of the solid and liquid phases, the water content of the specimen and micro-structural factors like porosity [10,12,[16][17][18][19].…”

Signs of low frequency dispersions in disordered binary dielectric mixtures (fifty–fifty)

“…The dielectric responses of several selected disordered systems are presented. The dielectric permittivity values calculated were as high as in the porous solids (Nettelblad 1996, Papathanassiou and Grammatikakis 2000, Papathanassiou 2001, Capaccioli et al 2001, Shen et al 1990. Therefore, the results of two dimensional calculations are compared not only to dielectric responses of binary polymeric composites (Tuncer andGubański 2000, Tuncer and and of porous liquid-solid systems as well.…”

“…More illustrative examples in which higher dielectric constants have observed are porous materials that are saturated with conductive phases such as salts and water (Nettelblad 1996, Papathanassiou and Grammatikakis 2000, Papathanassiou 2001, Capaccioli et al 2001, Shen et al 1990). In these systems real part of the permittivity are reported to reach even 10 7 levels as in Nettelblad (1996), however in those system the liquid conductivity was responsible for the larger polarization observed in the system.…”

Molecular dynamics of the liquid crystal 6O2OCB in nanopores

“…Investigations of various physical properties of liquids in porous materials were performed recently using different experimental techniques [1][2][3][4][5][6]. The results obtained by dielectric relaxation spectroscopy [7][8][9] help us to understand the influence of the surface interactions on the dynamics of the enclosed molecules.…”