Effect of titanium oxide nanoparticles on the dielectric properties and ionic conductivity of a new smectic bis-imidazolium salt with dodecyl sulfate anion and cyanobiphenyl mesogenic groups

Abstract

A new bis-imidazolium salt with two cyanobiphenyl groups and dodecyl sulfate counterion (BIC) was prepared by the metathesis reaction of the bromide salt with sodium dodecyl sulfate. The ILC shows at room-temperature a stable smectic A phase, confirmed by differential scanning calorimetry, polarized optical microscopy, and powder X-ray diffraction investigations. The ILC was doped with TiO2 nanoparticles, having a high specific area, in concentrations of 0.1%, 0.2%, 1% and 2%.Broadband Dielectric Spectroscopy spectra have been registered in the (10−1–107) Hz frequency range, and (250–330) K temperature domain.The study shows that at constant frequency, the conductivity increases with the temperature and dopant concentration. The characteristic times of the observed relaxation processes showed a temperature variation according to the Vogel-Fulcher-Tammann law. Higher values of characteristic times were calculated at the increase of the thickness of the sample. On the other hand, the increase of the concentration of TiO2 nanoparticles leads to a decrease of the characteristic relaxation times.In order to detect whether the obtained high permittivity increase is due to the Maxwell-Wagner or Electrode Polarization (EP) type phenomena, studies were made on samples of the same concentration, but different thicknesses, and EP was assigned as the main cause of this dielectric constant variation.