Molecular Dynamics Simulation Of Intercalation Of Kaolinite With Urea And Water

Polymer/Layered Silicate (PLS) is one of important nanocomposites. Kaolinite are often used to prepare PLS nanocomposite. In order to obtain PLS materials, One must intercalate some suitable organic chemicals into the interlayer space of them and make basic distance bigger, which enables polymer molecules to intercalate into the interlayer space easily and to form nanocomposites. Urea is widely used to intercalate into the interlayer space of kaolinate. The advantage is that urea is an environment friendly substance. Therefore, it is necessary to study the structure and dynamics properties of the interlayer of urea and kaolinite in molecular level.Molecular dynamics simulation of water, urea and mixture of them was performed at T=300K. The results indicate that the of hydrogen bondexists between urea molecules is 2．4 (?). While the length between the water molecules is 1．77 (?). In the mixture, the effect of hydrogen bond is intensified. The hydrogen bond between urea O and urea H is weak, and the hydrogen bond between urea H and water O is stronger with the length of this hydrogen bond of 1．75 (?). As a result, the self-diffusion coefficient of water is lower in the mixture than that for pure water. Therefore, water can form stable Hydrogen bond with urea and reduce the energy of the system.Molecular dynamics simulation of urea and kaolinite system was performed at T=300 K in order to elucidate the relation between quantity of the urea molecules and basal distance of the system. The results indicate that the basal distance of the system increases with urea molecules number, while the increasing rate is gradually decreasing. The urea molecules are divided into two layers in the space between kaolinite. Most urea molecules are located near the hydroxide surface of kaolinite at low concentrations of urea molecules, connecting with the surfaces of kaolinite by hydrogen bond through C=O-H…O-Al interaction. With the growth of quantity of urea molecule, more urea molecules distribute near the silicate surface of kaolinit, and connect with surfaces of kaolinite by hydrogen bond through N-H…O-Si. The energy of the system is mainly influenced by the energy beteen urea and kaolinate.Molecular dynamics simulation of water, urea and kaolinite system was performed at T=300K in order to elucidate the relation between the mole fraction of urea and the rate of intercalation of urea into kaolinite. The results show that the system has the biggest basal distance at the mole fraction of urea of 0．58, and the self-diffusion coefficient of urea reaches a maximum in the interlayer space at this mole fraction. The water molecules are divided into three layers in the space between kaolinite. There is a part of water adsorbed by silica-surface of kaolinite when the mole fraction of urea lower than 0．58．...