TEMPERATURE AND WAVELENGTH DEPENDENT OPTICAL PROPERTIES AND DSC ANALYSIS OF 8CB, 9CB, AND 8OCB MESOGENS

Authors : Atilla Eren Mamuk, Pınar Özden, Çiğdem Elif Demirci, Arif Nesrullazade

Pages : 76-84

Doi:10.22531/muglajsci.1790471

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Publication Date : 2025-12-31

Article Type : Research Paper

Abstract :This study presents a comprehensive investigation of the refractive indices (n, no, ne) and birefringence (Δn) of three cyanobiphenyl-based liquid crystal mesogens—8CB, 9CB, and 8OCB—under varying temperatures and wavelengths. Measurements were conducted at λ = 0.465 μm, 0.525 μm, 0.625 μm, and white light during both heating and cooling cycles, thereby enabling the evaluation of optical responses across direct and reverse SmA–N–I phase transitions. In addition, Differential Scanning Calorimetry (DSC) analyses were performed to systematically determine the phase transition temperatures and to examine the thermal behavior under different scanning rates. The results reveal a linear decrease in the isotropic refractive index n with temperature, pronounced temperature- and transition-dependent variations in the extraordinary refractive index ne, and moderate behavior in the ordinary refractive index no. Birefringence Δn decreased steadily with increasing temperature and vanished at the isotropic phase transition, indicating molecular disordering. When combined with the DSC findings, the data confirm the presence of significant thermal hysteresis during reverse transitions, demonstrating the first-order nature of these phase transformations. Overall, the results emphasize the potential of cyanobiphenyl derivatives for temperature-sensitive optoelectronic applications and contribute valuable insights into the phase transition behavior of liquid crystals.
Keywords : Sıvı kristaller, Siyanobifenil, Çift kırılma, Kırılma indisi, DSC, Faz geçişleri, Termal histerezis

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