Molecular modeling and atomistic simulation strategies to determine surface properties of perfluorinated homopolymers and their random copolymers

Abstract

Molecular mechanics (MM) and molecular dynamics (MD) simulations on ten perfluoroalkyl methacrylates and four copolymers derived from methyl methacrylate (MMA) and 1,1-dihydroperfluorohendecyl methacrylate (F10MA) in different ratios have been performed to predict surface properties. 1,1-Dihydroperfluorohendecyl methacrylate, which contained highest number of fluorine atoms, exhibited lowest surface energy, a trend that is in accordance with experimental observations. Density calculations on selected perfluoroalkyl methacrylates have been performed using NPT dynamics, for which no experimental data are available. Computations were performed to obtain bulk properties like cohesive energy density and solubility parameter through MM and MD simulations in the NVT ensemble under periodic boundary conditions. From the equilibrated structures, surface energies were computed, which compared well with the experimental data reported in the literature. Surface energies of copolymers decreased with increasing number of perfluoroalkyl groups. Various components of energetic interactions have been examined in detail in order to gain a better insight into interactions between bulk structure and the film. The dominant contributions are from van der Waals and Coulombic energy terms. The computed mass density profile for thin films gave an indication whether the film is of sufficient thickness so that the interior of the film is indistinguishable from the bulk structure. The total pair correlation and bond correlation functions have been analyzed to confirm the amorphous nature of the simulated structures.