Role of radiation in heat transfer from nanoparticles to gas media in photothermal measurements

The heat transfer from nanoparticles (NPs) to gas of photothermal effect is investigated by taking into account both conduction and radiation. The steady-state and unsteady-state heat transfer processes are studied analytically and numerically, respectively. In contrast to the photothermal effect in liquid with metal NPs, in which the radiation is negligible, we found that the thermal radiation must be taken into account in the nanoparticle–gas system. The reason is that the thermal boundary conductance (TBC) of gas–solid interface is several orders of magnitude smaller than the TBC of liquid–solid interface, especially when the diameter of nanoparticle is comparable to or smaller than the mean free path of gas molecules. We propose a method to measure the ultra-low TBC of interface between nanoparticle and gas based on our investigations.