TX-100和CTAB交换动力学的核磁共振研究

运用核磁共振(NMR)方法分别测定了表面活性剂辛基苯聚氧乙烯醚(TX-100)和十六烷基三甲溴化铵(CTAB)在不同温度下的临界胶束浓度.阐述了应用1D NMR线型分析方法对表面活性剂快交换体系平均停留时间的定量测量.实验测量了TX-100和CTAB胶束溶液中表面活性剂分子在不同温度下的平均停留时间.结果显示,平均停留时间随温度的增加逐渐减小,说明TX-100和CTAB分子进出胶束的速率随温度的增加逐渐加快.利用阿伦尼乌斯公式拟合,获得了TX-100和CTAB的表观交换活化能,TX-100的表观交换活化能为17.6 k J/mol,CTAB的表观交换活化能为75.3 k J/mol.对TX-100和CTAB平均停留时间和表观交换活化能进行分析,得出平均停留时间和表观交换活化能与分子结构的关系:表观交换活化能反映的是疏水相互作用和静电斥力的大小;而平均停留时间不仅受活化能的影响,还与分子结构有关.

Exchange Kinetics of Surfactants TX-100 and CTAB Investigated by1H NMR Spectroscopy

The critical micelle concentration (CMC) of Triton X-100 (TX-100) and cetyltrimethylammonium bromide (CTAB) was measured by nuclear magnetic resonance (NMR) technologies at different temperature. The average residence time of TX-100 and CTAB were determined by one-dimensional line shape analysis. The average residence time of both compounds decreased with increasing temperature, suggesting that the rate of TX-100 and CTAB molecules entering/leaving the micelles increased with temperature. The apparent activation energy of the exchange process was calculated with the Arrhenius equation, and found to be 17.6 kJ/mol for TX-100 and 75.3 kJ/mol for CTAB. The apparent activation energy likely reflected the strength of hydrophobic interaction; while the average residence time depended not only on the hydrophobic interaction but also on the molecular structure.