INVESTIGATION OF DIELECTRIC PROPERTIES OF MBBA-5CB NEMATIC LIQUID CRYSTAL STRUCTURES

Öz

The dielectric anisotropy (Δε') is the response of the LC molecules to an applied electric field. In this study, the dielectric properties of 4-pentyl-4'-cyanobiphenyl (5CB) and N-(4-methoxybenzylidene)-4-butylaniline (MBBA) nematic liquid crystals with positive and negative dielectric anisotropy were investigated in detail. In addition, a structure with zero dielectric anisotropy was obtained by mixing MBBA and 5CB liquid crystals in certain rate (1:0.02). The behavior of the samples under 0V and 20V voltages was investigated in detail. Dielectric measurements were made with dielectric spectroscopy technique, which is a powerful method to investigate the molecular interaction mechanisms of liquid crystal materials, at a frequency of 1 kHz-10 MHz and a voltage of 0-20 V at room temperature. Some important parameters such as dielectric anisotropy (Δε'), relaxation frequency (f_R), relaxation time (τ) were determined for the samples. When electric field is applied to nematic liquid crystals, it is seen that, depending on the voltage, the relaxation frequency decreases, and the relaxation time increases.

Anahtar Kelimeler

• Nematic liquid crystal
• 5CB; MBBA
• dielectric properties
• dielectric anisotropy.

Kaynakça

1. Takikawa, Y., Kaneko, K., Odani, S., Ikemura, T., Iwata, M. “Dielectric anisotropy in PCPB/MBBA mixtures showing the dual frequency characteristic”, Japanese Journal of Applied Physics, 59, 1-6, 2019.
2. Jain, A. K., Deshmukh, R. R., Liquid Crystals and Display Technology, London, 2020.
3. García-Sánchez, E., Mendoza-Huizar, L. H., Martínez-Ruíz, F. J., Pasilla-Díaz, J. R., Solís-Sánchez, L. O., Bañuelos-García, L. E. “Prediction of the density–pressure–temperature behavior in the isotropic–nematic phase transition of MBBA liquid crystal”, Indian Journal of Physics, 95, 7, 1357-1363, 2021.
4. Tripathi, P. Kr., Misra, A. Kr., Manohar, S., Gupta, S. Kr., Manohar, R. “Improved dielectric and electro-optical parameters of ZnO nano-particle (8% Cu2+) doped nematic liquid crystal”, Journal of Molecular Structure, 1035, 371–377, 2013.
5. Deschamps, J., Trusler, J. M., Jackson, G., “Vapor pressure and density of thermotropic liquid crystals: MBBA, 5CB, and novel fluorinated mesogens”, Journal of Physical Chemistry B, 112, 13, 3918-3926, 2008.
6. Sharma, D., Tiwari, G., Tiwari, S. N., “Electronic and electro-optical properties of 5CB and 5CT liquid crystal molecules: A comparative DFT study”, Pramana, 95, 2, 1-7, 2021.
7. Bezrodna, T., Melnyk, V., Vorobjev, V., Puchkovska, G., “Low-temperature photoluminescence of 5CB liquid crystal”, Journal of Luminescence, 130, 7, 1134-1141, 2010.
8. Peterson, M. S., Georgiev, G., Atherton, T. J., Cebe, P., “Dielectric analysis of the interaction of nematic liquid crystals with carbon nanotubes”, Liquid Crystals, 45, 3, 450-458, 2018.

9. Misra, A. K., Tripathi, P. K., Pandey, K. K., Singh, B. P., Manohar, R., “Dielectric properties and activation energies of Cu: ZnO dispersed nematic mesogen N-(4-methoxybenzylidene)-4-butylaniline liquid crystal”, Journal of Dispersion Science and Technology, 41, 9, 1283-1290, 2020.
10. Mukherjee, S., Electro-optic response of homeotropic, hole patterned, nematic liquid crystal cells under AC and DC voltage. Ph.D. dissertation, Department of Chemical Physics, Kent State University, Ohio, USA, 2016.
11. Nayek, P., Li, G., “Superior electro-optic response in multiferroic bismuth ferrite nanoparticle doped nematic liquid crystal device”, Scientific Reports, 5, 1, 1-9, 2015.
12. Sutormin, V. S., Krakhalev, M. N., Prishchepa, O. O., Zyryanov, V. Y., “Electrically induced anchoring transition in nematics with small or zero dielectric anisotropy”, Liquid Crystals, 44, 3, 577-581, 2017.
13. Kocakülah, G., Önsal, G., Köysal, O., “Electro-optical and dielectric performance analysis: The influence of azo dye on polymer/LC composite structures”, Applied Physics A, 125,1, 1-8, 2019.
14. Deshmukh, R. R., Jain, A. K., “Effect of anti-parallel and twisted alignment techniques on various properties of polymer stabilised liquid crystal (PSLC) films”, Liquid Crystals, 43, 4, 436-447, 2016.
15. Kocakülah, G., Köysal, O., “Electro-optical and dielectric response of quantum dot-doped cholesteric liquid crystal composites”, Journal of Materials Science: Materials in Electronics, 33,8, 5489-5500, 2022.