The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

Abstract

Conductive nanoparticles, especially elongated ones such as carbon nanotubes, dramatically modify the electrical behavior of liquid crystal cells. These nanoparticles are known to reorient with liquid crystals in electric fields, causing significant variations of conductivity at minute concentrations of tens or hundreds ppm. The above notwithstanding, impedance spectroscopy of doped cells in the frequency range customarily employed by liquid crystal devices, 100 Hz-10kHz, shows a relatively simple resistor/capacitor response where the components of the cell can be univocally assigned to single components of the electrical equivalent circuit. However, widening the frequency range up to 1 MHz or beyond reveals a complex behavior that cannot be explained with the same simple EEC. Moreover, the system impedance varies with the application of electric fields, their effect remaining after removing the field. Carbon nanotubes are reoriented together with liquid crystal reorientation when applying voltage, but barely reoriented back upon liquid crystal relaxation once the voltage is removed. Results demonstrate a remarkable variation in the impedance of the dielectric blend formed by liquid crystal and carbon nanotubes, the irreversible orientation of the carbon nanotubes and possible permanent contacts between electrodes.

Reorientation of single-wall carbon nanotubes in negative anisotropy liquid crystals by an electric field

“…In a previous paper [ 18 ] we determined the electrical behavior of positive LC cells doped with CNTs, and the results were in accordance with a reorientation of the nanotubes due to the electrical field, as well as the irreversible condition of this orientation in some cases. But since a positive liquid crystal and the CNTs reorient in the same manner under an electrical field, it was not possible to separate the switching of the CNTs caused by the interaction with the field and with the LC molecules in this study.…”

Absence of giant dielectric permittivity in graphene oxide materials

“…Several models for GO-based LCs have been reported in the literature. They vary in complexity but were found in most cases suitable to explain experimental measurements in a certain frequency range [50].…”

Nano-Objects and Ions in Liquid Crystals: Ion Trapping Effect and Related Phenomena

“…Table 2 provides a short summary of the reported effects. As can be seen, both decrease [118,119,[121][122][123][124][125][126][127][143][144][145][146][147][148][149][150][151][152] and increase [105,120,[128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][150][151][152][153] in the electrical conductivity of liquid crystals doped with carbon-based nanomaterials were reported.…”

“…The electrical properties of liquid crystals doped with carbon nanotubes (CNT) were explored in numerous papers [105,116,. The majority of these manuscripts [105,116,117,[128][129][130][131][132][133][134][135][136][137][138][139][140][141][142] report the enhancement of the electrical conductivity  of liquid crystals doped with carbon nanotubes. The increase in  is associated with the percolation phenomenon and high intrinsic electrical conductivity of carbon nanotubes: a sharp transition from the ionic conductivity to the dominating charge hopping conductivity occurs at a certain concentration called the percolation concentration [105,116].…”