Thermal properties of liquid entrapped between hybrid wettability surface

Abstract

Molecular dynamics (MD) simulations were conducted to investigate the impact of hybrid wettability on thermal properties, specifically focusing on the constant volume molar heat capacity and thermal conductivity of Nano-confined liquid (NCL). The simulation domain, maintained at a temperature of 100 K, consisted of a $\sim 3\mathrm{nm}$ — thin film of liquid argon entrapped between two solid copper surfaces with hybrid wettability. Hybrid wettability surfaces were produced by varying the solid–liquid interaction parameter and applying two different wettability factors ($\mu$) to the same surface. In this study, key findings pertaining to the influence of hybrid wettability on heat capacity and thermal conductivity include: (i) The heat capacity of liquid confined within hybrid wettability surfaces surpasses the heat capacity of the liquid in its bulk form. The heat capacity of bulk argon liquid is 20 J/mol k, but the liquid confined in the Hybrid I surface has a maximum heat capacity of roughly $\sim$53.2 J/mol k, which is 2.3 times higher. (ii) Remarkably, liquid confined in patterned wettability surfaces exhibited higher maximum heat capacity compared to the liquid confined inside uniform (Fully hydrophobic or hydrophilic) surfaces. The maximal heat capacity of liquid confined in Hybrid I surface is approximately $\sim$53.2 J/mol K, while the heat capacity of confined argon in a fully hydrophilic surface is around $\sim$30 J/mol K. (iii) Moreover, the heat capacity exhibits intriguing patterns. As the proportion of hydrophilic regions on the hybrid surfaces rose, there was a corresponding increase in heat capacity up to a specific threshold, beyond which the heat capacity dropped. (iv) Unlike Heat capacity, thermal conductivity exhibits a consistent behavior. A gradual decrease of thermal conductivity in the liquid region is observed as hydrophilic portions of the hybrid surface increase. The incorporation of hybrid wettability surfaces transforms the behavior of nano-confined liquid, inducing both structural and dynamic changes. These structural and dynamic variations result in the division of the entire simulation domain into two distinct zones: (i) Solid-like nanolayer zones located near the walls and (ii) Liquid zones located further away from the wall. The behavior of argon molecules in these two zones is completely different. Argon molecules in the solid-like layer exhibit increased density, higher potential energy, less translational motion and vigorous vibration over a frequency range of $\sim$0 to $\sim$ 3 THz. Conversely, the argon molecules in the liquid layer mostly exhibit translational motion. However, this translational motion is hindered as the hydrophilic area of the surface increases resulting in a reduction in overall molecular mobility. The observed variations in heat capacity and thermal conductivity of the Nano-confined liquid were elucidated by taking into account the combined influence of structural modifications of argon molecules occurring in solid-like nanolayer regions and the dynamic alterations of argon molecules in liquid regions. The findings of this study will provide valuable insights for improving cooling systems in electronic chips and nanoscale memory devices, advancing energy storage systems with potential applications in various biological domains in the future.