Effect of carbon nanotube on physical properties of the nematic liquid crystal N-(4`-methoxybenzylidene) - 4-nbutylaniline (MBBA

In this work the nematic liquid crystal (NLC) N-(4`-methoxybenzylidene)-4-n-butylaniline (MBBA) with transition temperature range between (22oC - 42℃) was prepared and identified using FTIR and 1H NMR spectroscopy. The liquid crystalline behavior was examined by means of hot-stage polarizing microscopy to determine the phase transition temperatures and the type of mesophases. The prepared compound MBBA was doped with different concentrations of multi wall carbon nanotube in order to study the electric
properties of (LC-CNTs) cell in comparing with that of pure MBBA. The capacitance- voltage (C-V) relationship for (LC-CNTs) cell doped with different concentrations was studied after it applied 1 KHz
voltage. It was found that, the capacitance for doped cell with concentration ≤ 0 .0 5 wt. % is less t han that of pure liquid crystal. As the concentration increased more than 0.05wt. %, the capacitance of (LC-CNTs) cell becomes higher than that of pure LC cell. The dielectric permittivity is determined as a function of applied frequency; it is found that a concentration increase of CNTs led to increase in the real parts and decrease in imaginary parts of the dielectric constants for doped cell (0.1 wt.%) compared with the pure liquid crystal. Also the effect of different concentrations of carbon nanotubes for the conductivity of (LC-CNT) cell was studied. It found that the conductivity was increased with increasing concentration more than 0.05 wt.%. Theoretical study for stable geometries of a nematic liquid crystal molecule assembled on the carbon nanotubes wall was carried out by using semi-empirical molecular quantum calculations within the PM3 method as implemented in HyperChem package. The result showed that the interaction influence of π,π-stacking between MBBA molecule on the CNT wall may led to formation of the local short range orientation order by LC molecules on the surface of the CNT. The binding energy of the LC molecule on the CNT wall was within the typical van der Waals interaction. This binding was originated from the electrostatic energy by a significant amount of charge transfer from the LC molecule to the CNT. Further calculations of the permanent dipole moment of the CNT could explain the dynamical motion of CNTs under various external fields.