Molecular dynamics study of the influence of aggregation and percolation in Al2O3/polyethylene oxide nanofluids on the effective thermal conductivity

Nanocomposites and nanofluids have the potential to be used widely as effective coolant materials. The motivation for this study is a belief that aggregation and percolation of nanoparticles in coolants could help explain the considerable variability in the values of thermal conductivity observed in systems containing similar components. This paper reports the results of the molecular dynamics study of the impact of aggregation and percolation of nanoparticles on the thermal conductivity in nanofluids containing aluminum oxide (α-alumina) nanospheres surrounded by polymer, polyethylene oxide (PEG400). The Reverse Non-Equilibrium Molecular Dynamics (RNEMD) [1] approach implemented in the open source code Molecular Dynamics Simulator LAMMPS [2] was utilized for the simulations. The values of the effective thermal conductivities obtained from the RNEMD simulations increased with growing aggregation from 0.4 W/m·K to 0.8 W/m·K for the structures with no aggregation and with a percolation channel, respectively. Equilibrium Molecular Dynamics (EMD) simulations of these system were also performed as an alternative method to study the thermal conductivity. The existence of the elastic modes in the nanoparticles/matrix superstructure was confirmed. These non-propagating elastic modes do not influence directly the heat flow but their presence in nanocomposites and nanofluids affects the applicability of EMD as an adequate tool for determining the value of thermal conductivity in such systems.