Coarse-Grained Computer Simulation of Nanoconfined Polyamide-6,6

Coarse-grained (CG) computer simulation models of polyamide-6,6 (PA-6,6) and graphene have been developed to simulate long chains of polymer confined between suffices. Here, groups of atoms are mapped onto a smaller number of beads, allowing simulation of nanoconfined polymers over the length scales and time scales much longer than what is achievable in atomistic simulations. The CG force field has been obtained using the iterative Boltzmann inversion method, in which the distribution functions for different degrees of freedoms are iteratively matched to the corresponding distributions obtained from atomistic simulations. Taking into account the detailed chemical structures of both polymer and confining surfaces, the resulting CG force field is shown to be transferable and applicable to simulate the confined polymer systems over a wide range of temperatures and intersurface distances. Employing this force field, CG simulations have been performed on long chains of PA-6,6 confined between graphene surfaces, at constant temperature, constant parallel component of pressure, and constant surface area of the confining surfaces. It is shown that the present CG model describes well the layering of polymers confined between the surfaces. The conformations of confined polymers have been analyzed by calculating the radius of gyration and the orientation of end-to-end vectors relative to the surface normal. It is shown that the CG model allows efficient and fast equilibration of even very long chains of PA-6,6 in very narrow pores.