Molecular Simulation on Thermodynamic Swelling Behavior of Bilayer Graphene Oxide in Solvents

Solvation swelling for graphene oxide (GO)-layered materials is a key property that determines the capacity for species permeation and adsorption inside GO interlayers, which hold great promise for wide applications. Currently, diverse variations and controversies for the measured interlayer spacings appear in the literature. While experimental measurement could provide a macroscopic image of interlayer spacings for layered GOs, a theoretical simulation of the interlayer swelling for GO-layered materials in solvent media is very essential, which is able to provide a fundamental basis for further understanding the complicated interlayer swelling behavior. Herein, we used metadynamics (MTD) molecular dynamics (MD) simulation to explore the swelling free-energy profiles for layered GO structures immersed in solvents. The stable spacings have been simulated for layered GOs in typical solvents, which appears to be quite consistent with experimental results. The effects of surface oxidization degrees and initial water contents on the GO swelling behavior have been investigated. The simulation results can be applied to elucidate the diverse experimental results. Our research provides thermodynamic insight into the swelling behavior of GO-layered structures in solvent media.