Deciphering the Liquid Continuum: Thermophysical and Slippage Dynamical Behavior of Water in Graphene Oxide Nanochannels

Abstract

Understanding water behavior within graphene oxide (GO) nanochannels holds paramount significance, especially in the realms of nanofluidics and energy conversion. Presently, flow modeling predominantly relies on simplifications, overlooking phase states. Our study unveils a nuanced reality: the molecular arrangement of confined water mirrors the density fluctuations observed in the liquid phase of water, a behavior contingent on both the degree of oxidation and the proximity to GO membranes. Through an exhaustive analysis encompassing density, viscosity, specific heat capacity, and diffusion coefficient, we establish a robust correlation, revealing the manifestation of continuous liquid behavior tied intimately to thermophysical properties and hydrogen bonding networks. Incorporating boundary slip velocity into the Hagen− Poiseuille equation, we predict pressure-driven flow with remarkable accuracy, validated by molecular dynamics simulations. Our revelations illuminate the continuum nature of water flow in GO nanochannels, with far-reaching implications spanning biomechanics, energy conversion, and desalination. Additionally, our investigation delves into the impact of varying hydroxyl (−OH) group concentrations within GO systems, effectively representing the degree of oxidation. This facet offers profound insights into the consequences of surface functionalization on the water behavior of nanochannels. Notably, our findings underscore the sensitivity of slip velocity to surface modifications, with a striking reduction by a factor of 5 as the −OH group concentration escalates from 5 to 30% under an applied driving pressure of 0.5 GPa. This discovery accentuates the potent influence of increasing hydrophilicity, stemming from higher degrees of oxidation, on water flow behavior, thereby casting fresh perspectives on nanofluidic system design.