A Molecular Dynamics Simulation Study On Interfacial Properties Of Multilayer Graphene/Epoxy Resin

Graphene reinforced polymer nanocomposites are received more and more attention in material industry owing to its light weight,promising mechanical,electrical and thermal properties.And it can be used in aircraft,aerospace,and electronic devices.Interface is a key factor affecting the mechanical properties of composite materials,but the microscopic mechanism of composite interface failure is extremely complicated.The traditional test method is difficult to characterize,so the computational simulation methods are widely used in the field of nanocomposite materials.It can realize the microscopic mechanism research,thus solves the problem which the experiment cannot complete.In this paper,through molecular dynamics(MD)simulation,the Compass field is used to simulate the separation of epoxy matrix(Epoxy)from Multilayer graphene(MLG)and functional MLG,and the interaction mechanism between MLG and Epoxy matrix interface is revealed.The micro-mechanism of the interfacial enhancement of the composite system by functional MLG is studied,and the main research contents are as follows:Firstly,the MLG/Epoxy model system was constructed by dynamic cross-linked method,and the process of epoxy matrix detachment from MLG was simulated by steered molecular dynamics(SMD).The variation of stress,mass density,energy term,and the epoxy matrix and MLG microstructure during tensile process were analyzed.The influence of tensile speed and crosslinking degree on interfacial tensile properties was investigated.The results show that the tensile stress first linearly increases with the tensile distance increasing,and then the MLG/Epoxy composite is reduced to 0 after reaching the maximum value,and then the epoxy matrix is completely detached from the MLG.In the initial stage of stretching,the epoxy of the molecules in the matrix can be changed to a certain extent in the linear phase,and the Van der Waals action in the Non-bond energy increases rapidly after yielding.The greater the tensile rate,the greater the tensile strength of the interface.When the cross-linking degree is not large,the greater the cross-linking degree,the greater the adhesion energy of the MLG/Epoxy interface,the greater the interfacial strength,but the excessive cross-linking(87%)will cause the adhesion of the interface to decrease and the interfacial strength decrease.Secondly,the influence of non-covalent bonding on interfacial properties is studied,and the MLG model of different functional(-OH,-NH2,-CH3)processing is constructed.The effect of non-covalent bonding on interfacial properties of MLG/Epoxy system was studied by changing graft density(0.76,1.53,2.29,3.05/nm~2).The results show that the functional treatment will affect the density distribution of the epoxy matrix at the interface.The-OH is the most influential,the-NH2 is the second,and the-CH3 is the weakest.At the same time,-OH,-NH2,-CH3 groups on MLG are embedded in the epoxy matrix.After the MLG functional processing,the stress transfer efficiency between the MLG and epoxy matrix can be improved,and the strength of the interface of the composite is enhanced.The greater the polarity of the functional group,the stronger the interfacial interaction between the MLG and the epoxy matrix,the greater the tensile strength of the interface.With the increase of grafting density,the interfacial tensile strength increases first and then decreases,when the grafting density is0.76/nm~2,the tensile strength of each system reaches the maximum value.Finally,the effects of-NH2 functional groups on the crosslinking degree and tensile strength of the composites were studied by covalent modification of MLG/Epoxy composite system.The changes of mass density,radial distribution function and mean square displacement of MLG/Epoxy composites before and after covalent bonding are analyzed.The results showed that the-NH2 on the MLG can participate in the solidification reaction of the epoxy matrix,reduce the distance between the MLG and epoxy matrix interface,improve the mass density of epoxy matrix at the interface,and enhance the interaction of MLG and Epoxy.The tensile strength at the interface of composite material is improved.In conclusion,the interfacial tensile properties of MLG/Epoxy Composites are studied by means of SMD method,and the deformation mechanism of the composite system in the tensile process is discussed.This study is helpful to understand the internal microscopic mechanism of functional graphene-reinforced polymers,and has a certain theoretical significance for the preparation of new functional graphene/polymer materials.