Regulating nanoscale directional heat transfer with Janus nanoparticles.

Janus nanoparticles (JNPs) with heterogeneous compositions or interfacial properties can exhibit directional heating upon external excitation with optical or magnetic energy. This directional heating may be harnessed for new nanotechnology and biomedical applications. However, it remains unclear how the JNP properties (size, interface) and laser excitation method (pulsed vs. continuous) regulate the directional heating. Here, we developed a numerical framework to analyze the asymmetric thermal transport in JNP heating under photothermal stimulation. We found that JNP-induced temperature contrast, defined as the ratio of temperature increase on the opposite sides in the surrounding medium, is highest for smaller JNPs and when a low thermal resistance coating covers a minor fraction of JNP surface. Notably, we discovered up to 20-fold enhancement of the temperature contrast based on thermal confinement under pulsed heating compared with continuous heating. This work brings new insights to maximize the asymmetric thermal responses for JNP heating.