高岭石层间域有机化合物分子动力学模拟研究
发布时间：2018-03-06 01:35
本文选题：高岭石 切入点：分子动力学模拟 出处：《中国矿业大学(北京)》2017年博士论文 论文类型：学位论文
【摘要】：高岭石是应用比较广泛的黏土矿物之一。在我国高岭土资源储量丰富,质地优良,广泛应用在橡胶、塑料、涂料、造纸、陶瓷及环保等领域。粒度和表面性质是衡量高岭石产品的重要指标,尤其在高新技术领域,高岭石的粒度和表面特性直接影响产品的诸多性能。对高岭石进行插层,剥片及表面改性是实现高岭石颗粒纳米化及表面修饰等精细化加工的必要手段,可显著提高高岭石产品的附加值。到目前为止,实验研究发现只有有限的几种有机小分子可直接进入高岭石层间域。而有机大分子表面改性剂则需要通过间接插层法实现高岭石层间域改性。虽然高岭石/有机物复合体已经通过X射线衍射、红外光谱、拉曼光谱和核磁共振等方法得到广泛研究,但高岭石/有机物层间域在原子尺度范围内的界面结构和界面作用尚无定论,有机化合物进入高岭石层间域的驱动因素尚不明晰。利用有代表性的有机化合物尿素,二甲基亚砜(DMSO),和大分子表面改性剂十二胺对纯化的高岭石进行了液相插层,制备了高岭石/尿素,高岭石/DMSO和高岭石/十二胺插层复合物。在XRD和热重实验分析的基础上构建了高岭石/有机化合物复合分子模型,并对其进行了分子动力学模拟,计算了高岭石层间域表面与有机化合物之间的界面结构和界面作用。采用自适应偏置力(Adaptive Biasing Force)分子动力学模拟计算了表面改性剂对高岭石/甲醇前驱体的插层自由能。通过对自由能的分解计算了表面改性剂与高岭石/甲醇复合体层间域的相互作用能。从理论层面深入剖析了有机化合物在高岭石层间域的界面结构和界面作用机理,阐明了有机化合物对高岭石插层的主要驱动力来源。在高岭石层间域中,尿素分子呈单层结构分布,其C=O官能团作为氢键受体与高岭石铝氧面羟基形成较强的氢键,其NH2官能团作为氢键给体与高岭石铝氧面羟基和硅氧面基面氧原子同时形成氢键。尿素与铝氧面形成的氢键作用大于硅氧面。而且尿素与铝氧面的相互作用能也大于硅氧面,因此铝氧面对诱导尿素进入高岭石层间域起到关键作用。DMSO在高岭石层间域也呈单层结构分布,其S=O官能团与高岭石铝氧面羟基形成较强的氢键作用,甲基则与硅氧面以疏水作用键合在一起。高岭石硅氧面上的复三方孔和铝氧面上的铝氧八面体空穴都是局部高吸附位点,分别对DMSO的甲基和S=O官能团具有较强的吸附作用。高岭石铝氧面和硅氧面都对DMSO分子表现出亲和性,但铝氧面与DMSO的相互作用能高于硅氧面,加之铝氧面羟基与DMSO S=O官能团形成较强的氢键作用,因此对DMSO的插层起到关键作用。自适应偏置力分子动力学模拟计算的改性剂对高岭石/甲醇前驱体插层自由能表明高岭石/甲醇复合体层间域对携带正电荷离子官能团的十六烷基三甲基氯化铵(CTAC)具有较强的亲和性。改性剂对高岭石层间域插层的驱动力主要来源于与层间域铝氧面、硅氧面和层间甲醇相互作用而获得的焓变能量。其焓变能量主要来源于静电势能和范德华能,其中静电势能起主导作用。携带离子官能团的CTAC和硬脂酸钠可通过与高岭石层间域的静电引力作用获得更多的焓变能量,相比于电中性的十二胺更容易实现高岭石插层和改性。高岭石的层间甲醇可使层间域更具疏水性可通过疏水作用、静电引力作用和范德华能作用促进大分子改性剂进入高岭石层间域。大分子表面改性剂十二胺可以高岭石/甲醇插层复合物为前驱体进入高岭石层间域,使高岭石层间距从7.2?扩大到42.9?。分子动力学模拟表明十二胺分子的烷烃链并非呈有序的全反式结构分布于高岭石层间域,而是以类似于石蜡型和无序结构分布于高岭石层间域中心区域和有序的双层结构平行分布于高岭石硅氧面和铝氧面。本论文采用分子动力学模拟与实验相结合的方法阐明了高岭石/有机化合物层间域的界面结构和界面作用,以及有机化合物进入高岭石层间域的驱动机理,为高岭石插层与有机改性的实验设计和制备高附加值高岭石产品提供了理论依据。
[Abstract]:Kaolinite clay minerals is one of the widely used in kaolin resources in China is abundant, fine texture, widely used in rubber, plastic, paint, paper, ceramics and environmental protection. The field size and surface properties of kaolinite is an important indicator of products, especially in the high-tech fields, many properties of particle size and surface characteristics of kaolinite directly affect the products. On kaolinite intercalation and exfoliation and surface modification is a necessary means to realize nano kaolinite particles and surface modification of fine processing, can significantly improve the added value of kaolinite products. So far, the study found that only a limited number of small organic molecules directly into the interlayer of kaolinite while the organic macromolecular surface modifier is required by indirect intercalation method of kaolinite interlayer modified. Although kaolinite / organic complexes has been through X ray Diffraction, infrared spectroscopy, Raman spectroscopy and NMR methods has been widely studied, but the kaolinite / organic interlayer on the atomic scale interface structure and interface effect is inconclusive, driving factors of organic compounds into kaolinite interlayer is not clear yet. The representative organic compound urea, two dimethyl sulfoxide sulfone (DMSO), and the macromolecular surface modifier twelve amine on the purification of liquid phase kaolinite intercalation of kaolinite / urea were prepared, kaolinite and kaolinite / /DMSO twelve amine intercalation compound. XRD and thermogravimetry was established on the basis of kaolinite / organic compound molecular model. And has carried on the molecular dynamics simulation, interfacial structure and interfacial interaction between kaolinite interlayer surface and organic compounds were calculated. The adaptive biasing force (Adaptive Biasing Force) molecular dynamics model The surface modification of kaolinite / methanol precursor intercalation free energy were calculated. The surface modification agent and kaolinite / methanol complex interaction of interlayer energy calculated by decomposition of the free energy. From the theoretical level, in-depth analysis of the interface structure and interface mechanism of organic compounds in the kaolinite interlayer the main driving force, illustrates the sources of organic compounds on kaolinite intercalation. The kaolinite interlayer, urea molecule monolayer distribution structure, the C=O groups form strong hydrogen bond as a hydrogen bond acceptor and surface hydroxyl of kaolinite alumina, the NH2 functional groups as hydrogen bond donor and surface hydroxyl of kaolinite and silica alumina base surface oxygen at the same time the formation of hydrogen bonds. Atomic hydrogen bonding of urea and alumina surface to form larger than silicon oxygen. But the interaction between urea and alumina can also larger than the silica surface, so the face of urea induced into alumina 鍏ラ珮宀煶灞傞棿鍩熻捣鍒板叧閿綔鐢，
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