Structure and Dynamic Properties of Stretched Water in Graphene Nanochannels by Molecular Dynamics Simulation: Effects of Stretching Extent
Water confined in nanochannels can be stretched with the variation of the external pressure, leading to unusual properties compared with bulk water. In order to unravel the impacts of stretching extent on the structural and dynamical properties of water confined in hydrophobic graphene nanochannels with various channel widths (L = 1 nm, 2 nm and 3 nm), molecular dynamics (MD) simulations were performed in this work. It was found that the ultrahigh negative pressure was presented in the confined space with the increase of stretching extent before cavitation. The interfacial density peak and tetrahedral arrangement were reduced with the increasing hydrogen bond length, indicating the more disordered structure organization, especially in channels with small channel widths. On the other hand, the hydrogen bond lifetime was increased due to the prolonged stability of hydrogen bond under stretching. The remarkably increased diffusion coefficients of confined water with the increasing stretching coefficient, resulting from the faster diffusion of interfacial water along channel surface regardless of channel widths. At last, the oscillating tangential pressure profile inside nanochannels demonstrated that the confined water under stretching consists of the multiple layers exhibiting alternate positive and negative pressures, which is reduced with the increase of stretching coefficient, corresponding to the enhanced diffusion.