Zhu Jianxi, He Hongping, Zhu Lizhong, Wen Xiaoyan, Deng Feng
Department of Environmental Science, Zhejiang University, Hangzhou 310028, People's Republic of China.
J Colloid Interface Sci. 2005 Jun 1;286(1):239-44. doi: 10.1016/j.jcis.2004.12.048.
The molecular conformation and mobility of the intercalated surfactant molecules cetyltrimethylammonium bromide (CTMAB) have been studied using Fourier transform infrared spectroscopy (FTIR) and high-resolution single-pulse 13C magic angle spinning nuclear magnetic resonance (13C SP MAS NMR) spectroscopy. The conformation and mobility of alkyl chains were found to be a function of the surfactant concentration. The splitting of the methylene scissoring mode at 1473-1463 cm(-1) and the rocking mode at 730-720 cm(-1) in FTIR are considered to be diagnostic of the packing density increase of the intercalated surfactants within the clay gallery. Compared with the 13C SP MAS NMR spectrum of CTMAB in the bulk state, 1-3 ppm upfield chemical shifts for end-methyl (deltaC16) and methylene (deltaC15, deltaC2-14) of the intercalated surfactant molecules in the hybrids indicate a freer conformational situation. For these hybrids, the conformational freedom decreases with increased of surfactant concentration. In addition, on approximately 2 ppm downfield shift for the C1 carbon atom in the hybrids with higher surfactant content suggests a special local environment. This study demonstrates the different mobility of carbon atoms in the intercalated alkyl chain.
利用傅里叶变换红外光谱（FTIR）和高分辨率单脉冲13C魔角旋转核磁共振（13C SP MAS NMR）光谱研究了插层表面活性剂十六烷基三甲基溴化铵（CTMAB）的分子构象和流动性。发现烷基链的构象和流动性是表面活性剂浓度的函数。FTIR中1473 - 1463 cm(-1)处亚甲基剪式振动模式和730 - 720 cm(-1)处摇摆振动模式的分裂被认为是插层表面活性剂在粘土层间堆积密度增加的诊断依据。与本体状态下CTMAB的13C SP MAS NMR光谱相比，杂化物中插层表面活性剂分子的末端甲基（δC16）和亚甲基（δC15，δC2 - 14）的化学位移在高场有1 - 3 ppm的变化，这表明构象更自由。对于这些杂化物，构象自由度随表面活性剂浓度的增加而降低。此外，表面活性剂含量较高的杂化物中C1碳原子有大约2 ppm的低场位移，这表明存在特殊的局部环境。本研究证明了插层烷基链中碳原子的不同流动性。
