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

Öz

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.

Anahtar Kelimeler

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

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

Öz

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.

Anahtar Kelimeler

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

Kaynakça

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