Heat Capacity of Nanoconfined Liquid: A Molecular Dynamics Simulation

Abstract

Equilibrium molecular dynamics (EMD) simulations aiming to investigate the effect of confinement gap thickness on constant volume molar heat capacity (Cv) of the confined liquid in nanoscale have been carried out by simultaneously controlling the density and temperature of the liquid domain. Simplified Lennard-Jones (LJ) molecular model is used to model the system where the liquid is entrapped between two flat solid surfaces separated by a distance varying from 0.585 nm to 27.8 nm. Molar heat capacity of the bulk liquid has been evaluated using fluctuation formula which matches greatly with the NIST data and published literatures. But in case of confined liquid, molar heat capacity is observed to vary significantly with the gap thickness. For a specific range of gap thickness, molar heat capacity of the confined liquid is found higher than that of the bulk. But molar heat capacity of the nanogap confined liquid becomes independent of the gap thickness and approaches to that of the bulk liquid as gap thickness is greater than this specific range (6.14 nm for 100 K temperature of the confined liquid).

Atomistic simulation of size‐dependent heat capacity of liquid in molecular scale confinement at different temperatures

“…However, for nanoconfined liquid, modified Debye model fails to predict its heat capacity [13]. The anomalous behaviour of heat capacity of the nanoconfined liquid obtained experimentally and through simulation is attributed to some of its key aspects such as (i) non‐uniformity in the distribution of liquid molecules’ density; (ii) enhanced contribution of ballistic phonon transmission; (iii) reduction in molecular motion for the thermal energy transportation; and (iv) increased contribution of interfacial thermal resistance [25].…”