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 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 dynamic 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 an ultrahigh negative pressure was present 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 structural organization, especially in channels with small channel widths. On the other hand, the hydrogen bond lifetime was increased due to the prolonged stability of the hydrogen bond under stretching. The remarkably increased diffusion coefficients of confined water with the increasing stretching coefficient result from the faster diffusion of interfacial water along the channel surface regardless of channel width. At last, the oscillating tangential pressure profile inside the nanochannels demonstrated that the confined water under stretching consists of multiple layers exhibiting alternate positive and negative pressures, which is reduced with the increase of stretching coefficient, corresponding to the enhanced diffusion.