Dispersion Of Oxidized Modified Nano-diamond And Molecular Dynamics Simulation On Their Surface

Nano-diamond（ND）,as a kind of material which combines the characteristics of nano materials and the excellent properties of diamond,has been concerned and applied in more and more fields.In many application fields,nano-diamond is required to have good dispersion.However,because of its small primary particle size,large specific surface area and high surface energy,agglomeration is very easy to occur.In order to improve the dispersion stability and dispersion of nano-diamond,this article adopts the method of air heat treatment to modify the nano-diamond surface,through experimental characterization and reaction based on ReaxFF molecular dynamics method,dispersion,surface properties of diamond nanoparticles were studied and microscopic and chemical reaction,reveals the nano-diamond dispersion and dispersion stability after heat treatment,and the surface evolution mechanism.The main research contents of this paper are as follows:（1）High-Temperature and High-Pressure nano-diamond（HTHP ND）and detonation nano-diamond（DND）were characterized by appropriate characterization methods.The particle size,phase structure,surface groups,surface elements and thermal stability of nano-diamond are analyzed.The results show that nano-diamond is easy to agglomerate,and there are abundant oxygen-containing functional groups on its surface.（2）The reaction molecular dynamics method was introduced into the simulation of surface adsorption,and the models of diamond solid surface and homogeneous gas molecules were constructed.The simulation results show that both water and oxygen molecules will be adsorbed on the diamond surface in the form of molecular adsorption and dissociation adsorption,and the adsorption of water molecules will form C-H₂O,hydroxyl（C-OH）and hydrocarbon（C-H）structures;the adsorption of oxygen molecules will form C-O₂,ketone（C=O）,ether bond（C-O-C）,dioxetane structure（C-O-O-C）.（3）A series of high temperature heat treatment was carried out on nano-diamond in air atmosphere.The effect of temperature on the surface chemistry and dispersion behavior of nano-diamond in water was studied.The results show that proper heat treatment can increase the content of hydrophilic groups on the surface of nano-diamond,increase the absolute value of Zeta potential on the surface,reduce the average particle size of nano-diamond,and improve the dispersion and stability.The results show that the optimal heat treatment temperature of HTHP ND is 420℃,while that of DND is 480℃.In the process of heat treatment,the surface of nano-diamond will undergo three stages:dehydrogenation,oxygen adsorption and combustion.（4）The MD model of high temperature oxidation of nano-diamond was established,and the evolution mechanism of diamond surface during high temperature oxidation was studied.The simulation results show that the adsorption structures of oxygen and water molecules on the diamond surface at high temperature are basically the same as those at low temperature,and the changes of these structures mainly occur on（111）surface when the temperature is increased,which is reflected by the increase of the number of ketone groups.The C atom on the diamond surface will be removed in the form of CO,CO₂ and graphitization when it is oxidized at high temperature.By comprehensive comparison,the most resistant to oxidation is（100）surface,and the most susceptible to oxidation is（111）surface.