Zhang Shuai, Liu Qinfu, Cheng Hongfei, Gao Feng, Liu Cun, Teppen Brian J
School of Geosciences and Surveying Engineering, China University of Mining &Technology (Beijing), Beijing 100083, People's Republic of China.
Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, Michigan 48824, United States.
J Phys Chem C Nanomater Interfaces. 2017 Apr 27;121(16):8824-8831. doi: 10.1021/acs.jpcc.6b12919. Epub 2017 Mar 31.
Intercalation and surface modification of clays with surfactants are the essential process to tailor the clays' surface chemistry for their extended applications. A full understanding of the interaction mechanism of surfactants with clay surfaces is crucial to engineer clay surfaces for meeting a particular requirement of industrial applications. In this study, the thermodynamic mechanism involved in the intercalation and surface modification of methanol preintercalated kaolinite by three representative alkane surfactants with different head groups, dodecylamine, cetyltrimethylammonium chloride (CTAC), and sodium stearate, were investigated using the adaptive biasing force accelerated molecular dynamics simulations. In addition, the interaction energies of surfactants with an interlayer environment (alumina surface, siloxane surface, and interlayer methanol) of methanol preintercalated kaolinite were also calculated. It was found that the intercalation free energy of CTAC with a cationic head group was relatively larger than that of stearate with an anionic head group and dodecylamine with a neutral head group. The attractive electrostatic and van der Waals interactions of surfactants with an interlayer environment contributed to the intercalation and surface modification process with the electrostatic force playing the significant role. This study revealed the underlying mechanism involved in the intercalation and surface modification process of methanol preintercalated kaolinite by surfactants, which can help in further design of kaolinite-based organic clays with desired properties for specific applications.
用表面活性剂对粘土进行插层和表面改性是调整粘土表面化学性质以实现其广泛应用的关键过程。全面了解表面活性剂与粘土表面的相互作用机制对于设计满足工业应用特定要求的粘土表面至关重要。在本研究中，使用自适应偏置力加速分子动力学模拟研究了三种具有不同头基的代表性烷烃表面活性剂（十二烷基胺、十六烷基三甲基氯化铵（CTAC）和硬脂酸钠）对甲醇预插层高岭土进行插层和表面改性所涉及的热力学机制。此外，还计算了表面活性剂与甲醇预插层高岭土的层间环境（氧化铝表面、硅氧烷表面和层间甲醇）的相互作用能。结果发现，具有阳离子头基的CTAC的插层自由能相对大于具有阴离子头基的硬脂酸盐和具有中性头基的十二烷基胺的插层自由能。表面活性剂与层间环境的吸引性静电和范德华相互作用有助于插层和表面改性过程，其中静电力起重要作用。本研究揭示了表面活性剂对甲醇预插层高岭土进行插层和表面改性过程中所涉及的潜在机制，这有助于进一步设计具有特定应用所需性能的高岭土基有机粘土。
