Exploring the viscosity and structural behavior of confined hydrogen: A molecular dynamics approach

• Published in: Journal of molecular liquids 2023-11, Vol.390, p.123028, Article 123028
• Main Authors: Yousefi, Farrokh, Farzadian, Omid, Shafiee, Mehdi
• Format: Article
• Language: English
• Subjects: Density profile; Molecular dynamics; Nano-confined hydrogen; Nanochannel; Structural behavior; Viscosity
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2023.123028

[Display omitted] •Equilibrium molecular dynamics (EMD) simulation was used to study the viscosity and structural behavior of hydrogen molecules (H2) confined within a graphene channel.•H2 molecules exhibited a strong propensity for absorption onto the channel wall, forming a dense packed layer near the wall, which greatly impacted the viscosity.•The first picks height in the density profile and radial distribution function show a strong correlation with viscosity.•Nanochannels with a height (h) less than 20 Å showed an astonishing increase in the viscosity from 8 up to 55 µPa.s.•Increasing the channel height, while keeping the number of H2 molecules fixed, led to a notable decrease in the viscosity.•Higher temperatures enhanced the viscosity due to increased collisions between the molecules. In this study, we employ equilibrium molecular dynamics (EMD) simulation to explore the viscosity of hydrogen molecules (H2) when subjected to extreme confinement within a nanochannel made by graphene sheets. We show that the viscosity of confined H2 and, therefore, its flow rate are deeply affected by layered structure of H2 when the nanochannel height (h) becomes less than 20Å. At these heights, we observe a substantial increase in viscosity, ranging from 8 to 55 µPa.s as the h decreases from 20 to 6 Å. To this end, we investigate the impact of structural behavior of H2, the height of nanochannel, the number of H2 molecules (N), and system temperature on the viscosity. Our findings reveal a notable tendency of H2 molecules to adhere to the nanochannel wall, resulting in the formation of a densely packed layer near the wall. Additionally, our observations reveal a robust correlation between the density near the wall and the viscosity. Also, increasing the h, while keeping the N constant, leads to a noticeable decrease in viscosity. Moreover, we investigate the influence of temperature on the viscosity and demonstrate that higher temperatures enhance viscosity making more collisions of molecules to the nanochannel wall and between molecules. Furthermore, we find that viscosity increases linearly with the N due to more collision between the molecules. Exploring the behavior of hydrogen in confined environments provides valuable insights into its transport properties and its potential for applications in the industry.