Investigation of the interface between polyethylene and functionalized graphene: A computer simulation study

The effect of surface chemical functionalization of a single graphene layer on its thermodynamic work of adhesion (WA) with polyethylene (PE) chains has been investigated using molecular dynamics (MD) simulation. For this purpose, amine (NH₂), carboxyl (COOH), hydroxyl (OH), and methyl (CH₃) functional groups were distributed randomly throughout the graphene surface using a Monte Carlo (MC) algorithm to achieve graphene functionalized structures with minimized potential energies. The MD simulation results showed that the thermodynamic WA between the PE and the functionalized graphene was larger than that between the PE and the pristine graphene. In fact, the electronegativity of functional groups and Van der Waals forces play influential roles in the thermodynamic WA between the PE and the functionalized graphene. In addition, the amount of thermodynamic WA was increased with increasing the functional group surface density, except for the graphene functionalized with the methyl groups. The segmental density of the PE chains near the single sheet surface was determined based on the density profile calculation. The polymer segments exhibited strong ordering and sharp density variations near the PE/graphene interface. The dynamic of chains was quantitatively characterized by calculating mean square displacement (MSD). Furthermore, the influence of functionality on the glass transition temperature (T_g) of the PE at the PE/graphene interface region was investigated. The results showed that the T_g at the PE/graphene interface was much higher than that of the bulk polymer. In fact, the functionalization of the graphene surface seems to considerably enhance the T_g of the polymer due to lowering the chains mobility.