Tunable dielectric constant of water confined in graphene oxide nanochannels

Abstract

Dielectric behavior of water in pristine and oxide graphene nanochannels with various separation has been investigated by means of molecular dynamic simulations. The motivation in performing this integrated set of simulations was to provide deep insight into the interaction between the size of the enclosure and the oxidation degree of the membrane sheets on the dielectric properties. It was shown that the dielectric constant of confined water decreased with the reduction of the space of the nanochannel because water molecules in such narrower environments were expected to exhibit a greater degree of spatial and orientational order. With the increase of the oxidation concentration, the influence of the wider interval space on the dielectric constant was greater than that of narrower nanochannls. For the widest channel (d = 1.2 nm), a decrease of dielectric constant was observed with the increase of oxidation concentration on the graphene bilayers, while a non-monotonous tendency of dielectric behavior appeared for the relatively narrow nanochannels (i.e. d = 0.6 nm and d = 0.9 nm). To understand the physical picture behind it, we computated the number of hydrogen bonds for the three nanochannels. Results showed that the number of HBs was the lowest in the 1.2 nm nanochannel, as well as the dynamic stability (corresponding the fastest decay rate), suggesting that water molecules are more unstable in this large nanochannel and then less orderly than in the 0.6 nm and 0.9 nm nanochannels.