Two-dimensional infrared correlation spectroscopy on dodecyloxy benzoic acid phase transition

Abstract

Thermal spectra of liquid crystal, dodecyloxy benzoic acid were collected over a temperature range of 26-150 degrees C by FTIR microspectroscopy. By taking investigations of temperature-induced changes in dodecyloxy benzoic acid by means of 2D infrared correlation spectroscopy, it was possible to clearly describe the molecular dynamic mechanism of dodecyloxy benzoic acid aggregates in the phase transitions. The analysis shows that p-dodecyloxy benzoic acid crystallized as multi-molecule aggregates through hydrogen bonds between the carboxylic groups, while the long polymethylene residues intermixed each other in solid state. Premelting phenomena in polymethylene residues were observed with temperature up to melting point. It seems that lots of oxy-benzoic acid part recrystallized to cycle dimer as supermolecular liquid crystal during alkyl chain melting in crystal-smectic phase transition. After temperature over 132 degrees C, oxy-benzoic acid part were melted to open dimer and separate molecule in liquid state.

利用顯微紅外光譜技術在寬范圍的溫度區域跟蹤對十二烷氧基苯甲酸相變過程 ,經二維相關紅外光譜分析 ,來描述對十二烷氧基苯甲酸在不同溫度區間的分子動態變化。結果認為固態由烷基相互纏結以多種羧酸聚集體的狀態存在 ,95℃發生的相轉變主要是非均相的十二烷基熔融和氧基苯甲酸部分重結晶的過程 ,132℃以后的相轉變主要是羧酸聚集體部分氫鍵集中斷裂和羧酸苯醚基團迅速熔融的結果。