Computational Simulations of Nanoconfined Argon Film through Adsorption–Desorption in a Uniform Slit Pore

We performed hybrid grand canonical Monte Carlo/molecular dynamics (GCMC/MD) simulations to investigate the adsorption-desorption isotherms of argon molecules confined between commensurate and incommensurate contacts in nanoscale thickness. The recently proposed mid-density scheme was applied to the obtained hysteresis loops to produce a realistic equilibrium phase of nanoconfined fluids. The appropriate chemical potentials can be determined if the equilibrium structures predicted by GCMC/MD simulations are consistent with those observed in previously developed liquid-vapor molecular dynamics (LVMD) simulations. With the chemical potential as input, the equilibrium structures obtained by GCMC/MD simulations can be used as reasonable initial configurations for future metadynamics free energy calculations.

Nanothermodynamic Description and Molecular Simulation of a Single-Phase Fluid in a Slit Pore

We have described for the first time the thermodynamic state of a highly confined single-phase and single-component fluid in a slit pore using Hill’s thermodynamics of small systems. Hill’s theory has been named nanothermodynamics. We started by constructing an ensemble of slit pores for controlled temperature, volume, surface area, and chemical potential. We have presented the integral and differential properties according to Hill, and used them to define the disjoining pressure on the new basis. We identified all thermodynamic pressures by their mechanical counterparts in a consistent manner, and have given evidence that the identification holds true using molecular simulations. We computed the entropy and energy densities, and found in agreement with the literature, that the structures at the wall are of an energetic, not entropic nature. We have shown that the subdivision potential is unequal to zero for small wall surface areas. We have showed how Hill’s method can be used to find new Maxwell relations of a confined fluid, in addition to a scaling relation, which applies when the walls are far enough apart. By this expansion of nanothermodynamics, we have set the stage for further developments of the thermodynamics of confined fluids, a field that is central in nanotechnology.

Examining Slit Pore Widths within Plasma-Exfoliated Graphitic Material Utilising Barret-Joyner-Halenda Analysis

Plasma-exfoliated multilayer graphitic material (MLG) consists of orderly aligned stacks which contain many partially oxidised graphitic layers. Slit pores are present between successive stacks and their presence allows for improved...

Pore structure characterization and its effect on methane adsorption in shale kerogen

Pore structure characterization and its effect on methane adsorption on shale kerogen are crucial to understanding the fundamental mechanisms of gas storage, transport, and reserves evaluation. In this study, we use 3D scanning confocal microscopy, scanning electron microscopy (SEM), X-ray nano-computed tomography (nano-CT), and low-pressure N2 adsorption analysis to analyze the pore structures of the shale. Additionally, the adsorption behavior of methane on shales with different pore structures is investigated by molecular simulations. The results show that the SEM image of the shale sample obviously displays four different pore shapes, including slit pore, square pore, triangle pore, and circle pore. The average coordination number is 4.21 and the distribution of coordination numbers demonstrates that pores in the shale have high connectivity. Compared with the adsorption capacity of methane on triangle pores, the adsorption capacity on slit pore, square pore, and circle pore are reduced by 9.86%, 8.55%, and 6.12%, respectively. With increasing pressure, these acute wedges fill in a manner different from the right or obtuse angles in the other pores. This study offers a quantitative understanding of the effect of pore structure on methane adsorption in the shale and provides better insight into the evaluation of gas storage in geologic shale reservoirs.