Interfacial Reliability Study Of Copper-Aminated Graphene/Epoxy Nanocomposite Based On Molecular Dynamics

Epoxy and epoxy matrix composites are used as adhesives and fillers in the electronics industry.The two-dimensional structure of graphene in sp² hybrid plane gives it a strong stiffness and elastic modulus.The thermal and dynamic performance of epoxy can be significantly improved by adding only a small amount of graphene.In this thesis,amino functional groups are grafted onto the surface of graphene by random distribution method based on the molecular dynamics simulation method to obtain aminated graphene（AG）.AG is embed into the epoxy resin.The AG and epoxy are connected by C-N covalent bonds and the AG/epoxy nanocomposite model of different sizes is constructed.From the microscopic perspective,the thermal and dynamic properties of AG/epoxy nanocomposite are studied under different parameters（such as functional group type,mass fraction and crosslinking degree,etc.）.The properties of AG/epoxy nanocomposite have an impact on the interfacial mechanical properties of the Cu-AG/epoxy nanocomposite.Therefore,there is a further study on the interfacial mechanical properties of the Cu-AG/epoxy nanocomposite.The interface failure mechanism of the Cu-AG/epoxy nanocomposite materials is studied to improve the interface reliability.The main conclusions are as follows:（1）To obtain the crosslinking AG/epoxy nanocomposite model,the crosslinking script is rewrite based on the epoxy model and the force field parameters of this model is supplemented and adapted.The Thermal properties of AG/epoxy nanocomposites are investigated by molecular dynamics:glass transition temperature（T_g）and coefficient of thermal expansion（CTE）.The effects of crosslinking degree,mass fraction and functional groups are also discussed.The simulation results show that T_g in AG/epoxy nanocomposites increases with the increase of crosslinking degree or mass fraction.The hydroxyl group have a weakening effect on the T_g of the nanocomposite,while the carboxyl group had a strengthening effect on the T_g of the nanocomposite,but none of them enhanced as much as AG.On the other hand,the CTE of AG/epoxy nanocomposite gradually decreases with the increase of crosslinking degree,and the reduction of CTE decreases with the increase of crosslinking degree to a certain extent.As the mass fraction increases,the CTE of AG/epoxy nanocomposites increases and then decreases.Compared with other epoxy composites,the CTE of AG/epoxy nanocomposites is lower.（2）The uniaxial tension of AG/epoxy nanocomposite is carried out,and the mechanical properties(elasticity modulus（E）,poisson’s ratio and interfacical energy(E_int))of AG/epoxy nanocomposite are studied.The effects of crosslinking degree,mass fraction,tensile rate,tensile direction and functional groups are discussed.The simulation results show that the E of AG/epoxy nanocomposite increases with the increase of the crosslinking degree and reaches its maximum value at about 70%crosslinking degree,after that,the E of the AG/epoxy nanocomposite decreases.While the poisson’s ratio is consistent with the trend of E.AG/epoxy nanocomposite have an extremely low E until the AG mass fraction is 1.2%.After the mass fraction of AG was 1.2%,the E and poisson’s ratio of the composite materials both declined with the increase of mass fraction.When the tensile strain rate reaches about 5×10⁸s^-1,the E and poisson’s ratio of AG/epoxy nanocomposite reach the maximum value.If the tensile strain rate is higher or lower than 5×10⁸s^-1,the E and poisson’s ratio of AG/epoxy nanocomposite decrease correspondingly.The yield strength of the AG/epoxy nanocomposite increases with the increase of tensile strain rate.The E and poisson’s ratio obtained by the tensile simulation of AG/epoxy nanocomposite along the normal direction perpendicular to the graphene plane are both small,and the higher E and poisson’s ratio can be obtained by tension along the graphene plane direction.Compared with hydroxyl and carboxyl functional groups,the amino functional group can significantly improve the mechanical properties of epoxy nanocomposite.（3）The mechanical properties（yield limit and strength limit）of Cu-AG/epoxy nanocomposite bi-material interface are studied by molecular dynamics（MD）simulation method,and the influence of crosslinking degree and temperature is discussed.The simulation results show that the yield limit of materials increases with the increase of crosslinking degree,and the yield limit of 70%and 90%crosslinking degree is not much difference.The strength limit increases with the increase of the crosslinking degree and reaches its the maximum at about 70%crosslinking degree,then decreases gradually.With the increase of temperature,the yield strength and tensile strain length of the material decrease gradually.The tensile ratio of Cu-epoxy bi-material model,Cu-Gr/epoxy nanocomposite bi-material model and Cu-AG/epoxy nanocomposite bi-material model gradually increase,and Cu-AG/epoxy nanocomposite bi-material model shows higher elasticity and toughness.