Investigation of phase transitions of liquid crystals by dielectric spectroscopy method


Thesis Type: Doctorate

Institution Of The Thesis: Yildiz Technical University, Graduate School Of Natural And Applied Sciences, PHYSICS, Turkey

Approval Date: 2019

Thesis Language: Turkish

Student: ALPTEKİN YILDIZ

Principal Consultant (For Co-Consultant Theses): Mustafa Okutan

Co-Consultant: Nimet Yılmaz Canlı

Abstract:

In this thesis, dielectric measurements of different molecules with liquid crystal phase, depending on temperature and frequency, have been taken to include phase transition temperatures. With the completed measurements, the different physical properties of the liquid crystals such as the real and imaginary parts of the complex dielectric constant, dielectric relaxation mechanisms, Cole-Cole curves and behaviors, conductivity mechanisms, and activation energies at selected frequencies have been determined. In the scope of the study, a total of four different liquid crystal molecules have been analyzed: Two liquid crystals having a traditional rod-shaped geometry with Smectic A and C mesophases, and two liquid crystals having a geometry called bent-core, also known as banana-shape, with dark conglomerate mesophase. As a conclusion, with the results obtained, dielectric spectroscopy has proven to be a highly effective tool to determine the phase transition temperatures of the different phases of liquid crystals. In addition, the dielectric analyses of these liquid crystals, which are outstanding in their fields, have been introduced into the literature.