Molecular Dynamics Simulation Combined with Near-Field Electromagnetic Analysis for Ultrashort-Pulsed Light-Induced Plasmonic Nanobubbles.

Ultrashort-pulsed light-induced nanobubbles gain great attention in research fields such as cancer therapy, optical imaging, and drug delivery. However, the mechanism governing the nucleation and growth of nanobubbles remains controversial. In this study, a molecular dynamics simulation combined with near-field electromagnetic theory is developed to investigate the influence of the localized surface plasmon resonance effect (LSPR) on nanobubble nucleation under various time-length pulsed light and to reveal the energy transfer differences during the nanobubble generation process. The results show that when silver nanoparticles (NPs) are irradiated by a 5 ps shorter-pulsed light, the temperature of the water layer adjacent to the nanoparticle surpasses that of the nanoparticle itself and reaches the spinodal temperature. This leads to nanobubbles' rapid nucleation at approximately 20 ps, which is 80 ps earlier than that irradiated by a 100 ps longer-pulsed light. Comparatively, during longer-pulsed light irradiation, a slower increase in both the temperature of the silver NPs and the water layer results in delayed nucleation of nanobubbles. Therefore, the plasmonic nanobubbles (PNBs) were observed around in 74 and 100 ps when irradiated by 50 and 100 ps longer-pulsed light, respectively. Moreover, the result indicates that the LSPR-induced enhanced electric field by shorter-pulsed light (5 ps) is 2.1 × 1010 V/m, which can accelerate the motion of water molecules surrounding silver NPs, resulting in rapid generation of nanobubbles. However, the intensities of the resonant electric field drop to 5.6 × 109 and 5.0 × 109 V/m when the duration times of pulsed light are 50 and 100 ps, respectively. These results indicate that the energy transfer mechanism of plasmonic nanobubbles (PNBs) under ultrashort-pulsed light irradiation might be very different from that of thermally mediated nanobubbles (TNBs). This work provides new insights into understanding the generation of PNBs induced by ultrashort-pulsed light.

A Molecular Dynamics Analysis on Interfacial Thermal Resistance between Particle and Medium in Light-Induced Heat Transfer of Plasmonic Nanofluid.

Light-induced heat transfer process of plasmonic nanofluids is critical for many applications, but the energy conversion pathway still remains controversial. In this work, we develop a calculation model based on the combination of the electromagnetic theory and molecular dynamics (MD) simulation to investigate the impact of the localized surface plasmon resonance (LSPR) on the heat transfer between nanoparticles and the surrounding medium in gold and silver nanofluids. It is found that the LSPR-induced enhanced electric field (EEF) can obviously reduce the interfacial thermal resistance to promote the heat transfer process, especially in silver nanofluids. The results reveal that the movement of water molecules can be violently perturbed by the EEF to overcome the binding force of nanoparticles, and therefore the energy transfer process in water molecules can be obviously enhanced. The effect of EEF is significant, especially in the initial heating stages when the temperature of the nanoparticles is relatively low. When the silver nanoparticle temperature is 400 K, the relative reduction ratio of the interfacial thermal resistance can reach 19.0% under the effect of the LSPR-induced EEF. The results also indicate that two different energy conversion mechanisms: photothermal and photoexcited electric-field enhancement are likely to coexist and jointly impact the heat transfer process in plasmonic nanofluids, and the effect of the latter cannot be neglected. This work provides some new insights for a deeper understanding of the light-induced heat transfer process in plasmonic nanofluids.