Conductivity and dielectric properties of cholesteryl tridecylate with nanosized fragments of fluorinated graphene

Abstract In order to improve the performance properties of electro-optical devices based on mesogenic materials, a cholesteric liquid crystal (cholesteryl tridecylate, X-20) was doped with nanoscale fragments of multilayer fluorinated graphene (GrF). A stable dispersion of X-20 with GrF was obtained. It was shown that the addition of 0.02 wt% of the nanosized GrF slightly affects phase transition temperatures of the mesogen, insignificantly reducing the mesophase temperature range due to increasing of Cr–SmA and decreasing N*–Iso transition temperatures. The dielectric properties of the pure X-20 and X-20/GrF composition were investigated in the frequency range from 20 Hz to 5 MHz and within the temperature range from 303 to 373 K. It was established that the introduction of the dopant is accompanied by an increase of the absolute value of the dielectric permittivity of the composition. At the same time, for the X-20/GrF composition a significant increase of the specific ionic conductivity was observed in the range of all studied phases due to an increase of free charge carriers. At the low frequencies of the electric field, the main contribution to the loss of dielectric permittivity makes the ionic conductivity. For the pure X-20, with the frequency increase, the contribution of the ionic conductivity decreases rapidly. This leads to a serious decrease of the imaginary part of the dielectric permittivity values and at the frequency of around 20 kHz it becomes negligible. For the X-20/GrF composition, this effect can be observed at the frequency of approximately 500 kHz and the imaginary part of the dielectric permittivity increases almost 10 times. The obtained results show the real possibility to modify conductive and dielectric properties of cholesteric liquid crystal by doping it with carbon nanomaterials. This approach opens up new opportunities in creating and improving of microantennas, frequency filters and photonic crystals based on liquid crystals.