Molecular Dynamics Investigation of Structural and Thermophysical Properties of Capric Acid–Silica Nanocomposites Under Varying Initial Pressures

Abstract

The initial thermodynamic condition can influence the organizational behavior of molecules and the energy transportation in nanocomposites of phase change materials, whereas the pressure dependence property behavior of fatty acid-silica is not fully known on the molecular scale. In this work, MD simulations were performed to study the effects of the initial pressure of the first phase range of 1–3 bar, which impacts structural and thermo-physical properties for a capric acid-silica nanocomposite. The simulated system for the second-phase run was divided into two parts: first, an equilibration stage to maintain the system temperature at 300 K; second, a production stage to measure changes in local number density, atom velocity, temperature, heat flux, thermal conductivity, charging time, and discharging time. The consistency during thermal equilibration verified that the system reached a stable state, followed by evaluation. The maximum local number density at the heat reservoir increased from 0.0338 atoms/ to 0.0323 atoms/ under higher initial pressures, with a decrease in maximum velocities and temperatures from 0.0010 to 0.0008 Å/fs and 328.26 to 318.22 K. Concomitant decreases of thermal flux and thermal conductivity can also be observed during this period. The heat flux decreased from 8.10 to 7.79 W/m, and thermal conductivity from 0.29 to 0.23 W/mK, while the charge time slightly increased from 4.68 to 4.88 ns and the discharge time was almost invariant, close to the mean value of 6.19 ns, with slight variance at different initial pressures. In addition, this initial pressure can affect local molecular mobility and local structural properties. The research provides evidence of the influence of initial thermodynamic pressure on structural features, dynamics, and transport of the nanocomposite from a molecular view.