Figure 1

(a) Water flow inside a graphene flat nanochannel with a height of $\sim$2 nm. (b) The pluglike velocity profile of the Poiseuille flow along the flow direction (i.e., $x$ direction) observed in our MD simulations. We applied three different accelerations to water molecules to obtain the different steady flow velocities as shown by the different symbols.Reuse & Permissions

Figure 2

(a) Friction shear stress $\tau$ versus slip velocity $v_s$ at the water/graphene interface with graphene deformation strain $\epsilon$ from $-10\%$ to $10\%$ (indicated by the arrow from bottom to top). The solid lines represent the fitted relations $\tau /{\tau }_0=\mathrm{asinh}(v_s/v_0)$, with the fitting coefficients ${\tau }_0$ and $v_0$ summarized in Table . (b) The friction coefficient $\lambda$ and the slip length $l_s$ as a function of the applied strain $\epsilon$. The open square symbols represent the $\lambda$ values calculated from the slopes of curves at $v_s=0.0$ in (a), and the solid circles are calculated by using the Green-Kubo (GK) relation [Eq. (2)] in our equilibrium MD simulations. The slip length $l_s$ is calculated by using $l_s=\mu /\lambda$ [26], where $\mu$ is the viscosity of water.Reuse & Permissions

Figure 3

(a) Density profiles of water across the height ($z$ direction) of the graphene nanochannel. The sharp density peak next to the solid wall represents the first water layer. For graphene layers at zero strain, the density profiles at flow velocity $v_s=0$ m/s and $v_s=100$ m/s have a negligible difference. The density profiles in the strained graphene channels with $\epsilon =-10\%$ (solid line), $0\%$ (dashed line), and $10\%$ (dash-dotted line) indicate the almost same first peak position but different magnitude. The inset shows the density of the first peak as a function of the imposed strains $\epsilon$ on graphene. (b) Two-dimensional radial density function (RDF, normalized by the mean density) of the first water layer in three differently strained graphene channels, $\epsilon =-10\%$ (open square), $0\%$ (open circle), and $10\%$ (open triangle). In comparison, the RDF of the bulk water is also shown. (c) Two-dimensional structure factor $S_1\left(\mathbf{q}\right)$ of the first water layer in the strain-free graphene channel exhibits a clear direction independence. (d) The radial average of the structure factor in the strained graphene channels with $\epsilon =-10\%$ (solid square), $0\%$ (solid circle), and $10\%$ (solid triangle). The solid arrows indicate the positions of the reciprocal lattice vector $|q_{\pm }|$ of the strained graphene planes.Reuse & Permissions

Figure 4

Interfacial potential energy barriers as a function of the strain applied on the graphene walls. The contour plot of potential energy landscape at $\epsilon =0$ is shown in inset with a sixfold symmetry, which is consistent to the atomic structure of graphene.Reuse & Permissions

Figure 5

(a) Functional dependence of the friction coefficient $\lambda$ versus the static root mean square force $\langle F^2\rangle$ [Eq. (3)]. (b) Functional dependence of the friction coefficient $\lambda$ on the computed ${\rho }_1{\left(q_0\Delta E\right)}^2{S}_1$ [Eq. (4)]. Dashed straight lines are guides to the eye. The good linear relations validate the forms of Eqs. (3) and (4).Reuse & Permissions

Figure 6

(a) The normalized energy barrier of the potential profiles from the graphene solid walls as a function of the strains applied. (b) The normalized structural changes as the function of the applied strains on the solid walls.Reuse & Permissions