Effect of particle size distribution on near-field thermal energy transfer within the nanoparticle packings

Nanoscale size effects give rise to near-field thermal considerations when heating nanoparticles under high laser power. We solve Maxwell’s equations in the frequency domain to analyze near-field thermal energy effects for three nanoparticle assemblies with different variances in particle sizes and show that heat dissipation generally decreases as the spread in nanoparticle sizes increases within the nanoparticle packing. For this study, log-normally distributed copper nanoparticle packings with a mean radius of 116 nm and three different standard deviations (12, 48, and 84 nm) were created by using a discrete element model in which a specified number of particles is generated. The nanoparticle packings in the simulation are created by randomly placing each nanoparticle into the packing domain with a random initial velocity and a position. The nanoparticles are then allowed to interact with each other under gravitational and weak van der Waals forces until they settle to form a stable packing configuration. A finite-difference frequency-domain analysis, which yields the electromagnetic field distribution, is then applied to the packing by solving Maxwell’s equations to obtain absorption, scattering, and extinction coefficients. This analysis is used to calculate the surface plasmon effects due to the electromagnetic coupling between the nanoparticles and the dielectric medium under the different distributions and show that different particle distributions can create different plasmonic effects in the packing domain, which results in nonlocal heat transport. Overall, this analysis helps to reveal how sintering quality can be enhanced by creating stronger laser–particle interactions for specific groups of nanoparticles.