Graphs from a study of the thermal characterization of surfactant-modified montmorillonites

The montmorillonite (HM) was obtained from Hebei, China. The sample was purified by sedimentation and the <2 μm fraction was collected and dried at 90°C. The sample was ground through a 200 mesh sieve and sealed in a glass tube for use. As indicated by XRD (Zhu, J.X., He, H.P., Guo, J.G., Yang, D. and Xie, X.D. (2003) Arrangement models of alkylammonium cations in the interlayer of HDTMA+ pillared montmorillonite. Chinese Science Bulletin, 48, 368–372.), the montmorillonite collected contains minor illite and kaolinite. The CEC is 57.9 meq/100 g. The structural formula is [Na0.05Ca0.18Mg0.10] [Al1.58Fe0.03Mg0.39][Si3.77Al0.23]O10(OH)2·nH2O. The surfactant used in this study, provided by YuanJu Chem. Co., China, is hexadecyltrimethylammonium bromide (HDTMAB) with a purity of 99%.

Figure 1 shows DTA (Differential Thermal Analysis) and TG (Thermogravimetric) curves of (a) Na montmorillonite and (b) of neat HDTMAB. Figure 2 shows the DTA curves of the modified montmorillonites with different surfactant-packing density. Figure 3 is the DSC (Differential Scanning Caloimetry) curves of the neat surfactant and HM0.5 CEC, HM1.9 CEC, HM5.0 CEC. Figure 4 is the DSC curves of (a) HM1.9 CEC and (b) HM5.0 CEC, with three cycles of heating and cooling. Figure 5 TG curves of the modified montmorillonites with different surfactant-packing densities. Figure 6 shows the change in the surfactant decomposition temperature for modified montmorillonite as a function of the surfactant-packing density within the montmorillonite interlayer. The surfactant-packing density refers to the amount of the surfactant within the montmorillonite interlayer as shown in Table 1 of the associated text.

蒙脱石（HM）源自中国河北省。该样品经沉降纯化，并收集了小于2微米的颗粒，于90摄氏度下进行干燥处理。样品经过200目筛子研磨，并封装于玻璃管中以备使用。根据XRD分析（朱锦勋、何华平、郭继光、杨德和谢希德，2003年，《HDTMA+插层蒙脱石中烷基铵阳离子的排列模型》，《中国科学通报》，48期，368-372页），所收集的蒙脱石样品含有少量伊利石和高岭石。其阳离子交换容量（CEC）为57.9毫摩尔/100克。其结构式为[Na0.05Ca0.18Mg0.10][Al1.58Fe0.03Mg0.39][Si3.77Al0.23]O10(OH)2·nH2O。本研究中使用的表面活性剂由中国的远举化学有限公司提供，为十六烷基三甲基溴化铵（HDTMAB），纯度为99%。图1展示了（a）钠蒙脱石和（b）纯HDTMAB的差热分析（DTA）和热重分析（TG）曲线。图2展示了不同表面活性剂填充密度的改性蒙脱石的DTA曲线。图3为纯表面活性剂及HM0.5 CEC、HM1.9 CEC、HM5.0 CEC的差示扫描量热法（DSC）曲线。图4为（a）HM1.9 CEC和（b）HM5.0 CEC在三次加热冷却循环中的DSC曲线。图5为不同表面活性剂填充密度的改性蒙脱石的TG曲线。图6展示了改性蒙脱石中表面活性剂分解温度随表面活性剂填充密度在蒙脱石层间变化的关系。表面活性剂填充密度指表面活性剂在蒙脱石层间内的含量，具体数值见相关文本的表1。