十六烷基三甲基溴化铵水溶液热致相变的红外光谱研究

在280～320K的温度范围内考察了30％十六烷基三甲基溴化铵水溶液的红外光谱随温度的变化。结果表明该体系的凝聚胶-液晶相转变温度为300K。在300K以下的凝聚胶相,分子的极性头部基团处于高度“固定”的状态,分子的碳氢链以有序的相互平行方式排列,极性头与碳氢链之间有一定的倾斜角。在300K以上的液晶相,极性头内部CH_3-(N~+)基团以及整个极性头与碳氢链之间发生了旋转,碳氢链变为以六方亚晶胞填充形式存在,旦扭曲式构象异构体数量显著增多,极性头与碳氢链之间已不存在倾斜角,分子的亲水极性头和疏水碳氢链部分都处于“融化”状态。

Study on the Thermotropic Phase Transition of Cetyltrimethylammonium Bromide Aqueous Solution by Fourier Transform Infrared Spectroscopy

Fourier transform infrared spectroscopy has been used to study the thermotropic phase transition of 30% cetyltrimethylammonium bromide aqueous solution. The band specific to the hydrophobic hydrocarbon chain CH_2 CH_3 groups, and to the hydrophilic CH_3(N~+) groups were monitored. A coagel to liquid crystalline phase transition was observed at 300K. The spectra show that the packing of the methylene chains is parallel with each other in the coagel phase. The rotations of the terminal methyl group and the head methyl groups all are restricted. In the liquid-crystalline phase, experimental data indicate high conformational disorder of the hydrocarbon chains. The rotational motion of the methylene chain as a whole around the chain axis and the internal rotations of hydrophilic N~+(CH_3)_3 groups occur in hexagonal lattice. Both the hydrophilic part and the hydrophobic part are in a fused state.