Solid-liquid phase transition inside van der Waals nanobubbles: an atomistic perspective.

Area of Science:

• Materials Science
• Physical Chemistry
• Condensed Matter Physics

Background:

• Understanding phase transitions under nanoscale confinement is crucial for materials science.
• Van der Waals bubbles, particularly graphene nanobubbles (GNBs), offer a unique system for studying confined fluids.
• Previous studies have not fully explored the melting behavior of confined simple fluids like argon.

Purpose of the Study:

• To investigate the liquid-solid phase transition of argon confined within a graphene bubble.
• To determine the melting curve of trapped argon under confinement.
• To characterize any novel phase behaviors, such as semi-liquid states.

Main Methods:

• Molecular dynamics simulations were employed to model argon inside a graphene bubble.
• A novel methodology was developed to prevent metastable states, ensuring accurate melting curve derivation.
• Simulations analyzed the structural and dynamic properties of argon at varying temperatures and confinement ratios (H/R).

Main Results:

• The melting curve of confined argon shifts to higher temperatures by approximately 10-30 K compared to bulk argon.
• The height-to-radius ratio (H/R) of the graphene nanobubble decreases with increasing temperature.
• A distinct semi-liquid phase was observed, characterized by layered atomic structures with significant atomic mobility.

Conclusions:

• Confinement within a graphene bubble significantly alters the phase transition behavior of argon.
• The observed temperature shift and semi-liquid state highlight unique properties of confined fluids.
• These findings have implications for designing nanostructured materials and understanding fluid behavior at the nanoscale.