Confining effects in dielectric relaxations of water aggregates in rock samples from a lithological contact at two different locations (Northeastern Venezuela)

Abstract

Thermal stimulated depolarization currents (TSDC), natural remanent magnetization (NRM) and scanning electron microscopy (SEM) measurements have been used here to study the confining effects of water aggregates of porous samples from a lithological contact at two sedimentary sequences from Cretaceous Northeastern Venezuela. The contact was dielectrically characterized by the TSDC technique. Two different locations were studied and the magnetic and dielectric results were correlated. Drying and rehydration treatments performed on these samples indicate that these peaks could be associated with physisorbed moisture. The dielectric relaxation peaks, located from 200 to 320 K, were related to water clusters confined In the pores. The direct signal analysis (DSA method) was applied to find the mean overlapping processes and the characteristic relaxations parameters. The pore dimension was determined from SEM microphotographs. Above the contact, a confining effect is observed and the peaks move towards lower temperatures as the pore size diminishes. Below the contact, as the pore sizes increase, adsorption effects mainly control these relaxations. The interaction between the clusters and the pore surface is mainly due to hydrogen bonding via terminal OH groups. Due to the change in the environment seen by the adsorbed water molecules, a variation in the mean reorientation energy is observed as the contact is approached, in the same lithological zone where NRM anomalies have been reported.