Thermal and Microstructural Properties of Hydrogen Bonded 8OBA/ADA Binary Complex Liquid Crystal

Abstract

In this study, the phase transition temperatures and enthalpy changes of a novel liquid crystal synthesized from the binary complex of mesogenic 4-octyloxy benzoic acid (8OBA) and non-mesogenic adipic acid (ADA) were investigated by differential scanning calorimeter (DSC) and phase structures by polarized optical microscopy (POM). The hydrogen bonding that occurs between 8OBA and ADA was confirmed by attenuated total reflection- infrared spectroscopy (ATR-IR). In addition, the chemical structure of the 8OBA/ADA liquid crystal complex was studied by 1H-NMR study. The 1H-NMR results also showed that some chemical shifts occurred and a new liquid crystal was synthesized. According to DSC and POM results, it appears that the new liquid crystal complex synthesized exhibits liquid crystalline properties. The 8OBA/ADA binary complex shows phase transition peaks during continuous heating and cooling with DSC. The observed smectic C (SmC) phase during cooling was not observed during continuous heating. The phase transition temperature and enthalpy change values obtained during continuous heating are higher than the phase transition temperature and enthalpy change values obtained during continuous cooling, but the nematic range is lower. Also, the dependence of these values on the heating rate has been investigated. As the heating rate increased, it was seen that the phase transition temperatures increased but enthalpy values decreased. It was observed that the phase transition temperature values measured by DSC are approximately the same as the phase transition temperature values measured by POM. Phase transition activation energies for the phase transitions of the 8OBA/ADA liquid crystal complex were calculated using Kissinger, Ozawa and Takhor equations, and the values obtained indicated that the phase transition activation energies were increased relative to the phase sequence. This result shows that the phase transitions of 8OBA/ADA liquid crystal complex occur regularly during continuous heating.

Keywords

• Hydrogen bonded liquid crystals,Thermal properties,Microstructure,DSC,POM

Hidrojen Bağlı 8OBA/ADA İkili Kompleks Sıvı Kristalin Termal ve Mikroyapısal Özellikleri

Abstract

Bu çalışmada, mezojenik 4-oktiloksi benzoik asit (8OBA) ve mezojenik olmayan adipik asit (ADA)’in ikili kompleksinden sentezlenen yeni bir sıvı kristalin termal özellikleri diferansiyel taramalı kalorimetre (DSC) ve mikroyapı özellikleri polarize optik mikroskop (POM) ile incelenmiştir. 8OBA ve ADA arasında hidrojen bağının oluştuğu zayıflatılmış toplam yansıma-kızılötesi spektroskopisi (ATR-IR) ile doğrulanmıştır. Ayrıca, 8OBA/ADA sıvı kristal kompleksinin kimyasal yapısı 1H-NMR çalışmasıyla incelenmiştir. DSC ve POM sonuçları sentezlenen yeni sıvı kristal kompleksin sıvı kristalik özellikler sergilediğini göstermektedir. 8OBA/ADA ikili kompleksi, DSC ile sürekli ısıtma ve soğutma esnasında faz geçiş pikleri göstermektedir. Soğutma esnasında gözlenen smektik C fazı sürekli ısıtma esnasında gözlenmemiştir. Sürekli ısıtma esnasında elde edilen faz geçiş sıcaklık ve entalpi değişim değerleri, sürekli soğutma esnasında elde edilen faz geçiş sıcaklık ve entalpi değişim değerlerinden daha yüksek, fakat nematik alan daha düşüktür. Ayrıca bu değerlerin ısıtma oranına bağlılığı da araştırılmıştır. Isıtma oranı arttıkça faz geçiş sıcaklıklarının arttığı fakat entalpi değerlerinin azaldığı gözlemlenmiştir. DSC ile ölçülen faz geçiş sıcaklık değerlerinin POM ile ölçülen faz geçiş sıcaklık değerleri ile yaklaşık aynı olduğu görülmüştür. 8OBA/ADA sıvı kristal kompleksin faz geçişleri için faz geçiş aktivasyon enerjileri hesaplanmıştır ve elde edilen değerler, faz sırasına göre faz geçiş aktivasyon enerjilerinin arttığını göstermiştir. Bu sonuç da 8OBA/ADA sıvı kristal kompleksin faz geçişlerinin sürekli ısıtma esnasında düzenli olarak gerçekleştiğini göstermektedir.

Keywords

• Hidrojen bağlı sıvı kristaller,Termal özellikler,Mikroyapı,DSC,POM

References

1. Aira H, Ray H, Kohki T, 2004. Effect of non-DC voltage applied during N*-Sc* phase transition on alignment of half-V-shaped switching ferroelectric liquid crystal. Japanese Journal of Applied Physics, 43(9A): 6243-6247.
2. Chen LG, 2007. Thermo-optical properties of polymer dispersed liquid crystals. RMIT University, Australia, Ph.D. Thesis (Printed).
3. Cook AG, Baumeister U, Tschierske C, 2005. Supramolecular dendrimers: Unusual mesophases of ionic liquid crystals derived from protonation of DAB dendrimers with facial amphiphilic carboxylic acids, Journal of Materials Chemistry. 15: 1708-1721.
4. Gray GW, Goodby JW, 1984. Smectic liquid crystals: textures and structures. Leonard Hill, USA.
5. Kang SK, Samulski ET, 2000. Liquid crystals comprising hydrogen-bonded organic acids I. Mixtures of non-mesogenic acids. Liquid Crystals. 27 (3): 371-376.
6. Kavitha C, Prabu NPS, Mohan MLNM, 2012. Design, synthesis and characterization of a linear hydrogen bonded homologous series. Physica B: Condensed Matter. 407 (5): 859-867.
7. Kavitha C, Prabu NPS, Mohan MLNM, 2012. Study of optical shuttering action in supramolecular hydrogen bonded nematogens. Phase Transitions: A Multinational Journal. 85 (11): 973-994.
8. Kissinger HE, 1957. Reaction Kinetics in Differential Thermal Analysis. Analytical Chemistry, 29: 1702-1706.

9. Muniprasada M, Srinivasulub M, Chalapathic PV, Potukuchia DM, 2012. Influence of chemical moieties and the flexible chain for the tilted smectic phases in linear hydrogen bonded liquid crystals with Schiff based pyridene derivatives. Journal of Molecular Structure, 1015: 181-191.
10. Nakamoto K, 2009. Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part B. 6th Edition, John Wiley and Sons, New-Jersey-USA.
11. Naoum MM, Fahmi AA, Alaasar MA, 2008. Supramolecular Hydrogen-Bonded Liquid Crystals Formed from 4-(4′-Pyridylazophenyl)-4″–Substituted Benzoates and 4-Alkoxybenzoic Acids, Molecular Crystals and Liquid Crystals, 482 (1): 57-70.
12. Okumuş M, 2012. Alkil ve alkiloksi siyanobifenil-benzoik asit sıvı kristaller ve karışımlarının faz dönüşümleri, Kahramanmaraş Sütçü İmam Üniversitesi Fen Bilimleri Enstitüsü, Doktora Tezi (Basılmış).
13. Okumuş M, Özgan S, 2014. Thermal and mesomorphic properties of ternary mixtures of some hydrogen-bonded liquid crystals. Liquid Crystals, 41 (9): 1293–1302.
14. Ozawa T, 1970. Kinetic Analysis of Derivative Curves in Thermal Analysis. Thermal Analysis, 2: 301-324.
15. Pavia DL, Lampman GM, Kriz GS, 2007. Introduction to Spectroscopy, Thomson Learning Inc.: pp. 142-145, India.
16. Prabu NPS, Mohan MLNM, 2013. Characterization of a new smectic ordering in supramolecular hydrogen bonded liquid crystals by X-ray, optical and dielectric studies. Journal of Molecular Liquids. 182: 79-90.
17. Prabu NPS, Mohan MLNM, 2015. Thermal Analysis, Calorimetric and Electrical Polarization Studies in Smectic X* Phase of Hydrogen-Bonded Ferroelectric Liquid Crystals. Molecular Crystals and Liquid Crystals, 606 (1): 12-35.
18. Priestley EB, Wojtowicz PJ, Sheng P, 1975. Introduction to liquid crystals. 1st ed. Plenum Press. New York.
19. Sundaram S, Subhasri P, Rajasekaran TR, Jayaprakasam R, Senthil TS, Vijayakumar VN, 2017. Induced Smectic X Phase Through Intermolecular Hydrogen-Bonded Liquid Crystals Formed Between Citric Acid and p-n-(Octyloxy)Benzoic Acid. Brazilian Journal of Physics, 47 (4): 382-392. Takhor RL, 1971. Advances in Nucléation and Crystallization of Glasses; Americal Chemical Society: Columbus, OH. 166-172.
20. Vijayakumar VN, Murugadass K, Mohan MLNM, 2009. Study of intermolecular hydrogen bonding in p-n-alkoxybenzoic acids and alkyl aniline homologous series – part I. Molecular Crystals and Liquid Crystals. 515 (1): 39–48.
21. Vijayakumar VN, Mohan MLNM, 2012. Design and characterization of hydrogen bonded ferroelectric liquid crystals: A study of light modulation in nematic and smectic orderings. International Journal for Light and Electron Optics. 123 (12): 1044-1050.
22. Wang JM, Kim YJ, Kim CJ, Kim KS, 2002. V-Shaped Switching in a Ferroelectric Liquid Crystal with the Phase Sequence of N*-SmC*, Ferroelectrics. 277: 185-195.
23. Wu SL, Lin CY, 2003. V-shaped switching in ferroelectric liquid crystal mixtures induced by an achiral swallow-tailed material, Liquid Crystals. 30(2): 205-210.