Research On The Surface Adsorption And Wetting Properties Of Graphene

Graphene as a quasi two-dimensional material,had excellent thermal,electrical,mechanical and optical properties.When the graphene as an interface between different media,its surface properties was particularly important.Wettability,as one of the surface properties of solid materials,had a wide application prospect in the fields of building self-cleaning coating materials,metal corrosion protection and mechanical lubrication.In this thesis,by means of molecular dynamics simulation,we analyzed the relaxation characteristics of graphene on smooth surface with different aspect ratio,and the influence of temperature and defect on the relaxation properties of graphene.From the angle of adsorption energy,we analyzed the surface adhesion property of graphene on the stepped substrate and the peeling-off behavior of graphene from the stepped microstructure surface.Studies had shown that the bigger the aspect ratio of graphene,the more violent fluctuations in the relaxation process.The higher temperature could shorten the time when the graphene reached equilibrium state,and the existence of the defect aggravated the fluctuation in the relaxation process.The absorption configurations of graphene on stepped substrate were divided into three kinds.When we peeled graphene from stepped substrate,the peeling force would be cyclical fluctuations,we also gave the theoretical formula that the average peeling force changed with the size of the micro-structure parameters and it fitted well with the simulation results.The larger the angle of peeling force became,the smaller the average peeling force became.graphene with SW defect structure could make the peeling force become large.Secondly,we studied the wetting characteristics of graphene coating on the surface of the metal aluminum,we analyzed the spreading property of nano water droplets on graphene surface,from the angle of spreading radius and force on contact line.Research showed that regardless of the monolayer graphene coating substrate surface is hydrophobic or hydrophilic,water droplets ' spreading radius on graphene was directly proportional to the 1/2 party of time,the spreading of nano water droplets on the surface of the graphene could be divided into three stage,graphene could reduce kinetic energy peak of water molecules' and made the change of kinetic energy more gentle.in addition,we also analyzed the relationship between water surface tension and wettability,it was concluded that the more hydrophilic surface,the smaller the solid-liquid surface tension.We studied the evolution rule of water drops under static electric field on the surface of graphene,and we also discussed the influence of water molecules' number on the contact angle under the vertical electric field,it showed that with the increase of vertical electric field strength,the contact angle first increased and then decreased.Under the influence of horizontal electric field,the more hydrophilic the substrate was,the greater the influence of water droplets on symmetry.The impact on water molecules which were near the substrate and at the liquid gas interface position was small.The solid-liquid interaction parameters had no obvious effect on water molecules' average number of hydrogen bond.Finally,the experimental study on the effect of graphene on the substrate wettability fitted well with the simulation results that the contact angle on graphene coating substrate.The contact angle hysteresis experiments indicate d that graphene could enhance the self-cleaning properties.We also analyzed the influence of contact angle measurement from different angles.