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Dynamics of Cetyltrimethylammonium Bromide Head Groups in Bulk by Solid-State Deuterium NMR Spectroscopy
Langmuir ( IF 3.7 ) Pub Date : 2018-08-22 00:00:00 , DOI: 10.1021/acs.langmuir.8b02193 Madhubhashini Maddumaarachchi 1 , Yohan L. N. Mathota Arachchige 1 , Tan Zhang 1 , Frank D. Blum 1
Langmuir ( IF 3.7 ) Pub Date : 2018-08-22 00:00:00 , DOI: 10.1021/acs.langmuir.8b02193 Madhubhashini Maddumaarachchi 1 , Yohan L. N. Mathota Arachchige 1 , Tan Zhang 1 , Frank D. Blum 1
Affiliation
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Variable temperature, solid-state deuterium (2H) NMR spectroscopy has been used to probe the rather complex head group dynamics of the surfactant cetyltrimethylammonium bromide-d9 (CTAB-d9) in bulk. Heating and cooling runs were made as the surfactant underwent supercooling. 2H NMR line shape simulations were used to identify the hierarchy of the molecular motions of CTAB as a function of temperature. Fast continuous methyl rotations about the N–Cmethyl axes and 3-fold jumps about the main chain C–N axis were present at all of the temperatures from −40 to 120 °C. With heating, the spectra were consistent with CTAB molecules starting 180° flips about the hydrocarbon chain molecular axis around 0 °C, which continued to flip with increasing flip rates up to 80 °C. At 90 °C, the flips changed to rotation of the CTAB molecules about the hydrocarbon chain axis and that rotation continued to 120 °C. Comparison of spectra of bulk CTAB at different temperatures from heating and cooling runs revealed that the rotation about the long axis of the hydrocarbon chains started at around 90 °C on heating, however, it does not freeze out until between 70 and 80 °C because of supercooling.
中文翻译：
固态氘核磁共振波谱法研究十六烷基三甲基溴化铵头基的动力学
可变温度，固态氘（2 1H）NMR光谱已被用于探测该表面活性剂十六烷基三甲基溴化的相当复杂的头部基团动力学d 9（CTAB- d 9散装）。当表面活性剂进行过冷时进行加热和冷却。2 H NMR线形模拟用于确定CTAB分子运动随温度变化的层次结构。快速连续的围绕N–C甲基的甲基旋转在−40至120°C的所有温度下，均出现绕主链C–N轴的三轴跳变和三倍跳跃。加热后，光谱与CTAB分子一致，始于0°C时围绕烃链分子轴翻转180°，然后随着翻转速率增加而翻转，直至80°C。在90°C下，翻转转变为CTAB分子绕烃链轴的旋转，并且旋转持续到120°C。比较来自加热和冷却运行的不同温度下大体积CTAB的光谱，发现围绕烃链长轴的旋转在加热时始于90°C，但是直到70至80°C时它才冻结。过冷。
更新日期：2018-08-22
中文翻译：
固态氘核磁共振波谱法研究十六烷基三甲基溴化铵头基的动力学
可变温度，固态氘（2 1H）NMR光谱已被用于探测该表面活性剂十六烷基三甲基溴化的相当复杂的头部基团动力学d 9（CTAB- d 9散装）。当表面活性剂进行过冷时进行加热和冷却。2 H NMR线形模拟用于确定CTAB分子运动随温度变化的层次结构。快速连续的围绕N–C甲基的甲基旋转在−40至120°C的所有温度下，均出现绕主链C–N轴的三轴跳变和三倍跳跃。加热后，光谱与CTAB分子一致，始于0°C时围绕烃链分子轴翻转180°，然后随着翻转速率增加而翻转，直至80°C。在90°C下，翻转转变为CTAB分子绕烃链轴的旋转，并且旋转持续到120°C。比较来自加热和冷却运行的不同温度下大体积CTAB的光谱，发现围绕烃链长轴的旋转在加热时始于90°C，但是直到70至80°C时它才冻结。过冷。
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