8CB, 9CB VE 8OCB MEZOGENLERİNİN SICAKLIK VE DALGA BOYUNA BAĞLI OPTİK ÖZELLİKLERİ VE DSC ANALİZİ

Yıl 2025, Cilt: 11 Sayı: 2, 76 - 84, 31.12.2025

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

https://doi.org/10.22531/muglajsci.1790471

Öz

Bu çalışma, 8CB, 9CB ve 8OCB sıvı kristal mezojenlerinin sıcaklık ve dalga boyuna bağlı kırılma indisleri (n, no, ne) ile çift kırılma (Δn) davranışlarını kapsamlı biçimde incelemektedir. Ölçümler λ = 0.465 μm, 0.525 μm, 0.625 μm ve beyaz ışık altında hem ısıtma hem de soğutma döngülerinde gerçekleştirilmiş, böylece doğrudan ve ters yönlü SmA–N–I faz geçişlerinin optik özellikler üzerindeki etkileri değerlendirilmiştir. Ayrıca, Diferansiyel Taramalı Kalorimetri (DSC) analizleri yapılarak faz geçiş sıcaklıkları sistematik olarak belirlenmiş ve tarama hızına bağlı termal davranışlar ayrıntılı olarak incelenmiştir. Bulgular, izotropik kırılma indisi n’de sıcaklığa bağlı doğrusal bir azalma, olağanüstü kırılma indisi ne’de faz geçişlerine duyarlı güçlü değişimler ve olağan kırılma indisi no’da daha sınırlı bir sıcaklık bağımlılığı ortaya koymuştur. Δn değeri sıcaklıkla birlikte azalmış ve izotropik fazda sıfırlanarak moleküler düzensizliğe işaret etmiştir. DSC sonuçları ile birlikte değerlendirilen veriler, ters geçişlerde belirgin termal histerezis gözlendiğini ve bu faz geçişlerinin birinci mertebeden karakter taşıdığını doğrulamaktadır. Sonuçlar, siyanobifenil türevlerinin sıcaklığa duyarlı optoelektronik uygulamalardaki potansiyelini vurgulamakta ve sıvı kristallerin faz geçiş davranışına ilişkin literatüre önemli katkılar sunmaktadır.

Anahtar Kelimeler

Sıvı kristaller , Siyanobifenil , Çift kırılma , Kırılma indisi , DSC , Faz geçişleri , Termal histerezis

Teşekkür

Bu çalışma kısmen Muğla Sıtkı Koçman Üniversitesi Bilimsel Araştırma Vakfı'nın 16/056 numaralı hibesi tarafından desteklenmiştir.

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

Öz

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.

Anahtar Kelimeler

Liquid crystals , Cyanobiphenyl , Birefringence , Refractive index , DSC , Phase transitions , Thermal hysteresis

Teşekkür

This work has been partially supported by the Scientific Research Foundation of Mugla Sitki Kocman University, Grant No. 16/056.

Kaynakça

• Blinov, L. M. (1993). Electro-optical and magneto-optical properties of liquid crystals. John Wiley and Sons Ltd., New York.
• de Boer, W. (2005). Active-matrix liquid crystal displays: Fundamentals and applications. Elsevier, Burlington.
• Vikari, E. (Ed.). (2003). Optical applications of liquid crystals. Taylor & Francis, London.
• Pochi, V., & Claire, G. (2009). Optics of liquid crystal displays. Wiley, New York.
• Tomilin, M. G., & Pestov, S. M. (2005). Properties of liquid crystalline materials. Politechnika Publ., Sankt-Petersburg.
• Lueder, E. (2001). Liquid crystal displays: Addressing, schemes and electro-optical effects. Wiley, New York.
• Liu, Q. F., Luo, D., Li, S. X., & Tian, Z. (2016). The birefringence and extinction coefficient of positive and negative liquid crystals in the terahertz range. Liquid Crystals, 43(6), 796–802. https://doi.org/10.1080/02678292.2016.1144811
• Zaki, A. A. (2010). Optical measurements of mixture thermotropic liquid crystals. Opt. Lasers Eng., 48, 538–542. https://doi.org/10.1016/j.optlaseng.2009.12.019
• Ozbek, H., Ustunel, S., Kutlu, E., & Çetinkaya, M. C. (2014). A simple method to determine high-accuracy refractive indices of liquid crystals and the temperature behavior of the related optical parameters via high-resolution birefringence data. J. Mol. Liq., 199, 275–286. https://doi.org/10.1016/j.molliq.2014.09.003
• Erkan, S., Çetinkaya, M., Yildiz, S., & Ozbek, H. (2012). Critical behavior of a nonpolar smectogen from high-resolution birefringence measurements. Phys. Rev. E, 87, 041705. https://doi.org/10.1103/PhysRevE.86.041705
• Nesrullajev, A. (2015). Thermotropic, refracting and thermo-optical properties in three homologs of 4-n-alkyl-4’-cyanobiphenyls. Lithuanian J. Phys., 55, 24–34. https://doi.org/10.3952/physics.v55i1.3055
• Nesrullajev, A. (2016). Thermotropic, refracting and birefringent properties in homogeneous mixtures of 4-n-alkyl-4’-cyanobiphenyl mesogens. J. Mol. Liq., 215, 503–511. https://doi.org/10.1016/j.molliq.2016.01.036
• Mamuk, A. E., Nesrullajev, A., & Mukherjee, P. K. (2017). Refractive and birefringent properties of 4-alkyl-4’-oxycyanobiphenyls at direct and reverse phase transitions. Mol. Cryst. Liq. Cryst., 648, 168–181. https://doi.org/10.1080/15421406.2017.1307499
• Nowinowski-Kruszelnicki, E., et al. (2012). High birefringence liquid crystal mixtures for electro-optical devices. Opt. Appl., 52, 167–180. https://doi.org/10.5277/oa120116
• Ma, M., Li, S., Jing, X., Chen, H. (2017), "Refractive indices of liquid crystal E7 depending on temperature and wavelengths," Opt. Eng., 56(11), 117109. https://doi.org/10.1117/1.OE.56.11.117109
• Kedzierski, J., Garbat, K., Raszewski, Z., et al. (2014). Optical properties of a liquid crystal with small ordinary and extraordinary refractive indices and small optical anisotropy. Opto-Electr. Rev., 22, 162–165. https://doi.org/10.2478/s11772-014-0196-9
• Bhowmick, K., Mukhopadhyay, A., & Mukherjee, C. D. (2003). Texture and optical studies of the mesophases of cyanocyclohexyl cyclohexanes. Phase Trans., 76, 671–682. https://doi.org/10.1080/0141159021000008927
• Mamuk, A. E., & Nesrullajev, A. (2016). Refractive and birefringent properties and order parameter of nematic liquid crystal at the direct and reverse nematic ↔ isotropic liquid phase transition. J. Optoelectr. Adv. Mater., 128, 928–937.
• Bhuyan, D., Pardhasaradhi, P., Singh, K. N., et al. (2011). Study of molecular polarizabilities and orientational order parameter in the nematic phase of 6.O12O.6 and 7.O12O7. World J. Condens. Matter Phys., 1, 167–174. https://doi.org/10.4236/wjcmp.2011.14025
• Zakerhamidi, M. S., Ebrahimi, Z., Tajalli, H., et al. (2010). Refractive indices and order parameters of some tolane-based nematic liquid crystals. J. Mol. Liq., 157, 119–124. https://doi.org/10.1016/j.molliq.2010.08.015
• Chandrasekhar, S., & Madhusudana, N. V. (1969). Orientational order in p-azoxyanisole, p-azoxyphenetole and their mixtures in the nematic phase. J. Phys. (Paris) Suppl., 30, C4-24–C4-27. http://dx.doi.org/10.1051/jphyscol:1969406
• Madhusudana, N. V., & Pratibha, R. (1982). Elasticity and orientational order in some cyanobiphenyls. 4. Reanalysis of data. Mol. Cryst. Liq. Cryst., 89, 249–257. https://doi.org/10.1080/00268948208074481
• Sarkar, S. K., Barman, P. C., & Das, M. K. (2013). Determination of optical birefringence and orientational order parameter of four members of alkyl cyanobiphenyls using high resolution temperature scanning technique. Int. J. Res. Appl. Nat. Soc. Sci., 1, 1–7.
• Sarkar, S. K., Barman, P. C., & Das, M. K. (2014). Optical birefringence and its critical behavior in the vicinity of nematic–smectic A phase transition in a binary mixture. Physica B, 446, 80–84. https://doi.org/10.1016/j.physb.2014.04.041
• Patari, S., Devi, Y. K., & Nath, A. (2016). Studies of optical texture, birefringence, order parameter, normalized polarizability and validation of the four-parameter model of a thermotropic mesogen 7OAOB. J. Mol. Liq., 215, 244–252. https://doi.org/10.1016/j.molliq.2015.12.026
• Mitra, M., Gupta, S., Paul, R., & Paul, S. (1991). Determination of orientational order parameter from optical studies for a homologous series of mesomorphic compounds. Mol. Cryst. Liq. Cryst., 199, 257–266. https://doi.org/10.1080/00268949108030937
• Nesrullajev, A., Yurtseven, H., & Kazanci, N. (2000). Liquid Crystals: Structures, Properties, Applications. Ege University Press, Izmir.
• Kuzma, M. R., & Saupe, A. (1997). Structure and phase transitions of amphiphilic liquid crystals. In P. J. Collings & Y. S. Patel (Eds.), Handbook of Liquid Crystal Research (pp. 237–258). Oxford University Press.
• Kimura, H. M., Hoshino, M., & Nakano, H. (1979). Temperature dependent pitch in cholesteric phase. J. de Phys., 40, C174–C179. https://doi.org/10.1051/jphyscol:1979335
• Sonin, A. S. (1984). Introduction to the Physics of Liquid Crystals. Science Publ., Moscow.
• Singh, S. (2000). Phase transitions in liquid crystals. Phys. Repts., 324, 107–269. https://doi.org/10.1016/S0370-1573(99)00049-6
• Oweimreen, G. A., & Morsy, M. A. (1999). DSC studies on p-cyanophenyl p-(n-alkyl) benzoate liquid crystals: Evidence for polymorphism and conformational change. Thermochim. Acta, 325, 111–118. https://doi.org/10.1016/S0040-6031(98)00572-3
• Oweimreen, G. A., & Morsy, M. A. (2000). DSC studies on p-(n-alkyl)-p'-cyanobiphenyl (RCB's) and p-(n-alkoxy)-p'-cyanobiphenyl (ROCB's) liquid crystals. Thermochim. Acta, 346, 37–47. https://doi.org/10.1016/S0040-6031(99)00411-6
• Sharma, M., Kaur, C., Kumar, J., Singh, K. C., & Jain, P. C. (2001). Phase transformations in some homologues of 4-n-alkyl-4'-cyanobiphenyls investigated by positron annihilation spectroscopy. J. Phys.: Condens. Matter., 13, 7249–7258. https://doi.org/10.1088/0953-8984/13/33/306
• Hosaka, S., Tozaki, K., Hayashi, H., & Inaba, H. (2003). Effect of magnetic field on the phase transitions of EBBA by means of a high-resolution and super-sensitive DSC. Physica B, 337, 138–146. https://doi.org/10.1016/S0921-4526(03)00389-2
• Nesrullajev, A., & Bilgin Eran, B. (2005). Mesomorphic, morphologic and thermoptropic properties of 4-Hexyl-N-(4-hexadecyloxysalicilidene) aniline. Mater. Chem. Phys., 93, 21–25. https://doi.org/10.1016/j.matchemphys.2005.02.001
• Cammenga, H. K., Gehrich, K., & Sarge, S. M. (2006). 4,4'-Azoxyanisole for temperature calibration of differential scanning calorimeters in the cooling mode – Yes or no? Thermochim. Acta, 446, 36–40. https://doi.org/10.1016/j.tca.2006.03.015
• Nesrullajev, A. (2010). Changes of thermo-morphologic and thermotropic properties of nematic mesophase ↔ isotropic liquid phase transition: Surface-induced effect. Phase Trans., 83, 326–337. https://doi.org/10.1080/01411591003721635
• Nesrullajev, A., & Avci, N. (2011). Oriented and non-oriented textures of nematic liquid crystals: Comparative peculiarities of the thermotropic behaviour. Mater. Chem. Phys., 131, 455–461. https://doi.org/10.1016/j.matchemphys.2011.10.004
• Lee, C. E., & Yang, S. H. (1998). Thermal hysteresis in the nematic order of a PCH-3 liquid crystal. J. Korean Phys. Soc., 33, L635–L637.
• Pardhasaradhi, P., Prasad, P. V. D., Latha, D. M., Pisipati, V. G. K. M., & Rani, G. P. (2012). Orientational order parameter studies in two symmetric dimeric liquid crystals – an optical study. Phase Trans., 85, 1031–1044. https://doi.org/10.1080/01411594.2012.671323
• Nesrullajev, A., Yörür-Göreci, C., & Bilgin Eran, B. (2012). Thermotropic, thermo-morphologic and thermo-optical properties of new smectogenic calamitic compounds containing imine linking groups. Int. J. Thermophys., 33, 58–68. https://doi.org/10.1007/s10765-011-1108-6
• Avci, N., Nesrullajev, A., & Oktik, S. (2010). Thermotropic and thermo-optical properties of nematic mesophase at direct and reverse phase transitions. Braz. J. Phys., 40, 224–227. https://doi.org/10.1007/s10765-010-0865-y
• Anisimov, M. A. (1988). Critical phenomena in liquid crystals – Introduction. Mol. Cryst. Liq. Cryst., A162, 1–96.
• Anisimov, M. A. (1991). Critical Phenomena in Liquids and Liquid Crystals. Gordon and Breach Publ., Amsterdam.
• Toledano, J. C., & Toledano, P. (1987). The Landau Theory of Phase Transitions. World Scientific, Singapore.
• de Gennes, P. G., & Prost, J. (2003). The Physics of Liquid Crystals. Oxford University Press, Oxford.
• Prasad, A., & Das, M. K. (2010). Optical birefringence studies of a binary mixture with the nematic–smectic Ad–re-entrant nematic phase sequence. J. Phys.: Condens. Matter, 22, 1–7. https://doi.org/10.1088/0953-8984/22/19/195106
• Sastry, S. S., Kumari, T. V., Mallika, K., Sankara Rao, B. G., Ha, S.-T., & Lakshminarayana, S. (2012). Order parameter studies on EPAP alkanoate mesogens. Liq. Cryst., 39, 295–301. https://doi.org/10.1080/02678292.2011.643246
• Srivastava, A. K., Manohar, R., & Shukla, J. P. (2006). Refractive indices, order parameter and principal polarizability of cholesteric liquid crystals and their mixtures. Mol. Cryst. Liq. Cryst., 454, 225–234. https://doi.org/10.1080/15421400600654371
• Manohar, R. J., & Shukla, J. P. (2004). Refractive indices, order parameter and principal polarizability of cholesteric liquid crystals and their homogeneous mixtures. J. Phys. Chem. Solids, 65, 1643–1650. https://doi.org/10.1016/j.jpcs.2004.03.012
• Chirtoc, I., Chirtoc, M., Glorieux, C., & Thoen, J. (2004). Determination of the order parameter and its critical exponent for nCB (n = 5–8) liquid crystals from refractive index data. Liq. Cryst., 31, 229–240. https://doi.org/10.1080/02678290310001642540
• Abdoh, M. M., Shivaprakash, S. N. C., & Prasad, J. S. (1982). Orientational order in the nematogenic homologous series trans-4-alkyl (4-cyanobiphenyl) cyclohexane. J. Chem. Phys., 77, 2572–2576. https://doi.org/10.1063/1.444129
• Hauser, A., Pelzl, G., Selbmann, C., Demus, D., Grande, S., & Petrov, A. G. (1983). Order parameter and molecular polarizabilities of liquid crystals with nematic and smectic phases. Mol. Cryst. Liq. Cryst., 91, 97–113. https://doi.org/10.1080/00268948308083078
• de Jeu, W. H., & Bordewijk, P. (1978). Physical studies of nematic azoxybenzenes. II. Refractive indices and internal field. J. Chem. Phys., 68, 109–115. https://doi.org/10.1063/1.435499
• Soorya, T. N., Gupta, S., Kumar, A., Jain, S., Arora, V. P., & Bahadur, P. (2006). Temperature dependent optical property studies of nematic mixtures. Indian J. Pure Appl. Phys., 44, 524–531.
• Kumar, K. (2013). Determination of orientational order and effective geometry parameter from refractive indices of some nematics. Liq. Cryst., 40, 503–510. https://doi.org/10.1080/02678292.2012.761355
• Kumar, A. (2007). Calculation of optical parameters of liquid crystals. Acta Phys. Polonica A, 112, 1213–1221. https://doi.org/10.12693/APhysPolA.112.1213
• Sastry, S. S., Kumari, T. V., Begum, S. S., & Rao, V. V. (2011). Investigations into effective order geometry in a series of liquid crystals. Liq. Cryst., 38, 277–285. https://doi.org/10.1080/02678292.2010.541947
• Gill, P., Moghadam, T. T., & Ranjbar, B. (2010). Differential scanning calorimetry techniques: Applications in biology and nanoscience. Journal of Biomolecular Techniques, 21(4), 167-193. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2977967
• Oweimreen, G. A., & Morsy, M. A. (2000). DSC studies on p-(n-alkyl)-p′-cyanobiphenyl (RCB’s) and p-(n-alkoxy)-p′-cyanobiphenyl (ROCB’s) liquid crystals. Thermochimica Acta, 346, 37-47. https://doi.org/10.1016/S0040-6031(99)00411-6
• Özgan, Ş., & Okumuş, M. (2011). Thermal and spectrophotometric analysis of liquid crystal 8CB/8OCB mixtures. Brazilian Journal of Physics, 41(2-3), 118-122. https://doi.org/10.1007/s13538-011-0034-1
• Sharma, D., MacDonald, J. C., & Iannacchione, G. S. (2006). Thermodynamics of activated phase transitions of 8CB. The Journal of Physical Chemistry B, 110(33), 16679-16684. https://doi.org/10.1021/jp062862d
• Sied, M. B., López, D. O., Tamarit, J. Ll., & Barrio, M. (2002). Liquid crystal binary mixtures 8CB + 8OCB: Critical behaviour at the smectic A–nematic transition. Liquid Crystals, 29(1), 57-66. https://doi.org/10.1080/02678290110093831