The deposition characteristics of PAN/PPY on SiO2 substrate by density functional theory (DFT) calculations

The oxides with abundant functional groups on the surface (such as SiO2), have been specifically applied for synthesis of polymer composites like polyaniline (PAN) and polypyrrole (PPY) to improve the adsorption capacity. In this work, we investigated how α-quartz SiO2 surface influences the deposition characteristics of PAN/PPY through density functional theory (DFT) calculations. The PAN/PPY polymer chain has stable adsorption performance on the unoccupied SiO2 substrate due to the hydrogen bond interactions. When two overlapped polymer chains are packing on SiO2 surface, PAN and PPY exhibits different performances. For PAN, the physisorption between the two packed chains is fairly weak (0.07 eV/cell), so PAN prefers to adsorb on the unoccupied SiO2 surface and cannot pack on the as-deposited chain until the surface is fully covered. Differently, the PPY polymer won’t exhibit uniform deposition on SiO2 surface as PAN does, attributing to its more flexible chain configuration. The following calculations reveal that there is significant charge transfer between polymer chain and the silica substrate, which helps to understand the origin of different adsorption performances for PAN and PPY. This investigation provides theoretical insight into the experimental observation of PAN on SiO2 substrate, and helps to understand the microscopic mechanism in polymer-oxide composites.