Molecular Dynamics Simulation Of Multilayer Graphene Peeling Excited By High Heat Flux

Because graphene has excellent properties in heat,mechanics,electricity and other aspects it has a very broad application prospect in many fields,and become a scientific research hotspot.However,the key problems hindering the wide application of graphene are the preparation,dispersion and stable existence of graphene.Since the discovery of graphene,many preparation methods of graphene have been produced,such as chemical vapor deposition,redox,epitaxial growth,etc.But these preparation methods have certain deficiencies,such as poor repeatability,harsh preparation conditions,and production small scale,etc.In this paper,the method of high heat flux excitation is used.Firstly,the movement of graphene in water is studied,which paves the way for the study of graphene stripping.Secondly,the mixed system of graphene and water is established to explore the stripping rule of graphene in water under different heat flux and graphene lamellar spacing.The high heat flux temperature is very high,the action time is very short,and the thermal conductivity of graphene is high,which can produce explosive boiling and promote the movement of graphene sheet.In this paper,molecular dynamics simulation is used to study the separation process and mechanism of graphene in water.This paper mainly carried out the following research work:The first part is to study the movement of graphene in water under thermal excitation.The pure water model and the mixture model of graphene and water were established.The simulation was carried out at 1000K.At last,the density,atom,temperature and pressure distribution of the system are analyzed,and the following conclusions are drawn:graphene can accelerate the heat transfer and make water molecules obtain greater kinetic energy.The boiling is deeper and the heat distribution is more uniform.Graphene can be peeled off in water under ultra-high temperature thermal excitation.The second part is to study the stripping rule of graphene in water under different thermal excitation.The lamellar spacing of graphene is 3.35 A,and the three thermal excitation temperatures are 373 K,773 K and 1000 K,respectively.The average force potential,mean square displacement,pressure distribution,temperature distribution and atom distribution of the system are studied.The results show that the higher the temperature is,the smaller the tensile energy barrier of graphene is.That is to say,the smaller the force between two layers of graphene is,the greater the separation trend of graphene is.The dispersion effect of 773 K is the best,followed by 373 K and 1000 K.Calculation of temperature,pressure and atom distribution shows that the temperature is very high and the explosive boiling is very violent when the thermal excitation temperature is 1000 K,which makes the bottom water molecules agglomerate and push upward before the phase transition.At 773 K,the graphene is the farthest to be peeled,followed by 373 K and 1000 K.The third part is to study the stripping rule of graphene in water under different spacing.The thermal excitation temperature is 1000 K,and the lamellar spacing is 3.35 A,6 A and 10 A,respectively.The average force potential,mean square displacement,pressure distribution,temperature distribution and atom distribution of the system are studied.The following conclusions are drawn:the larger the distance between graphene sheets is,the smaller the tensile energy barrier of graphene is,that is,the smaller the force between two layers of graphene is,the greater the tendency of graphene separation is.It is found from the final atomic distribution that the best peeling effect is obtained when the distance between graphene sheets is 10 A,followed by 6 A and 3.35 A.It can be seen from the calculation of the mean azimuthal shift that at the final time,the mean azimuthal shift is the largest when the distance between graphene sheets is 10 A,followed by 3.35 A and 6 A.Combined with the temperature and pressure distribution,it is found that the water molecules with graphene spacing of 3.35 A boil fast and disperse fast,so the average azimuthal shift is larger.However,with the increase of thermal excitation time,the water with graphene lamellae spacing of 6 A and 10 A keeps boiling,and the graphene disperses,and the average azimuthal shift increases.