电场对高岭石表面水分扩散特性的影响

Influence of electric field on the diffusion of water on the surface of kaolinite

  • 摘要: 为阐明水分子在高岭石表面扩散特性受电场作用影响的微观机理,构建了高岭石超晶胞模型,采用巨正则系综蒙特卡洛(GCMC)及分子动力学(MD)模拟方法,并利用相关Perl程序得到了不同电场条件下高岭石表面水分子极化构象与吸附形态、扩散系数、相互作用能以及氢键的演化规律。模拟结果表明:电场极化作用会使水分子在高岭石表面的吸附形态呈有序的正倒“V”字型,远离高岭石表面羟基,向真空层中扩散。电场强度为1010 V/m时,受库仑作用力影响,水分子H—O—H键的夹角减小3°;水分子在高岭石表面扩散呈各向异性,X,Y方向扩散系数相近,且远大于Z方向,水分子更易在XY平面方向扩散。水分子扩散系数随电场强度增加而增大,电场的正负方向对水分子的扩散系数的影响不大;水分子与高岭石的相互作用能以静电作用能和氢键作用能为主。施加电场后静电作用能和氢键作用能大幅降低,相互作用能与电场强度负相关。电场作用减弱了高岭石表面对水分子的束缚作用,有利于高岭石表面水分子的扩散;随电场强度增大水分子与高岭石表面氢键作用减弱,氢键数量减少,高岭石晶面亲水性降低。

     

    Abstract: In order to clarify the microscopic mechanism of the effect of electric field on the diffusion characteristics of water molecules on the surface of kaolinite, a kaolinite supercell model was constructed, and the grand canonical ensemble Monte Carlo(GCMC) and molecular dynamics(MD) simulation methods were used.The related Perl program was used to obtain the polarization conformation and adsorption morphology, diffusion coefficient, interaction energy and hydrogen bond evolution law of water molecules on the surface of kaolinite under different electric field conditions.The simulation results show that the polarization of the electric field will make the adsorption of water molecules on the surface of kaolinite into a regular upside-down “V” shape, away from the hydroxyl groups on the surface of kaolinite, and diffuse into the vacuum layer.When the electric field intensity is 1010 V/m, the included angle of the H—O—H bond of water molecules decreases by 3° under the influence of the Coulomb force.The diffusion of water molecules on the surface of kaolinite is anisotropic, and the diffusion coefficients in the X and Y directions are similar, and much larger than that in the Z direction.Water molecules diffuse more easily in the XY plane.The diffusion coefficient of water molecules increases with the increase of the electric field intensity, and the positive and negative directions of the electric field have little effect on the diffusion coefficient of water molecules.The interaction energy between water molecules and kaolinite is mainly electrostatic interaction energy and hydrogen bond interaction energy.After the electric field is applied, the electrostatic interaction energy and hydrogen bonding energy are greatly reduced, and the interaction energy is negatively correlated with the electric field strength.The electric field weakens the binding effect of water molecules on the surface of kaolinite, which is beneficial to the diffusion of water molecules on the surface of kaolinite.With the increase of the electric field intensity, the hydrogen bonding between water molecules and the surface of kaolinite weakens, the number of hydrogen bonds decreases, and the hydrophilicity of the kaolinite crystal surface decreases.

     

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