Computational study of laser fragmentation in liquid: Phase explosion, inverse Leidenfrost effect at the nanoscale, and evaporation in a nanobubble
Computational study of laser fragmentation in liquid: Phase explosion, inverse Leidenfrost effect at the nanoscale, and evaporation in a nanobubble
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激光在液体中碎裂的计算研究：相爆炸、纳米尺度下的反莱顿弗罗斯特效应和纳米气泡中的蒸发
DOI：
10.1007/s11433-021-1881-8
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发表时间：
2022-07-01
影响因子：
6.4
通讯作者：
Zhigilei, Leonid, V
中科院分区：
文献类型：
--
作者：
Huang, Hao;Zhigilei, Leonid, V
激光在液体中破碎是一种有效的、环境友好的加工技术，能够生产出粒径分布窄的胶体纳米粒子和原子团簇。这种技术的进步可以通过更好地理解控制纳米颗粒的大小、形状和结构的过程而得到促进。本文研究了激光脉冲在水中照射20 nm金纳米粒子时，其破碎机制与沉积能量密度的关系。模拟结果表明，吸收激光能量的减少导致了从“强”相爆炸的连续转变，当辐照纳米颗粒的爆炸相分解的所有产物被迅速注入纳米颗粒周围形成的纳米气泡周围的水中时，两种不同的纳米颗粒破碎机制导致形成一个大的中心纳米颗粒，周围是较小的卫星碎片。首先，在“温和”相爆炸状态下，中心纳米粒子是由纳米粒子爆炸分解产生的一些热金属液滴从纳米气泡边界反射而产生的。这种反射归因于在纳米尺度上作用的逆莱顿弗罗斯特效应。反射的液滴聚集在纳米气泡的中心，并在纳米气泡破裂后不久凝聚成一个单一的液滴。吸收激光能量的进一步降低使辐照条件低于相爆炸的阈值，通过辐照纳米颗粒表面的强烈蒸发、纳米气泡的演化和金属蒸气凝结成簇和小卫星纳米颗粒的相互作用，导致破碎产物形成核心-卫星结构。计算预测与实验观察相联系，并讨论了破碎机制、纳米颗粒尺寸分布和晶体内部缺陷产生之间的联系。
Laser fragmentation in liquid is an effective and environment-friendly processing technique capable of yielding colloidal nanoparticles and atomic clusters with a narrow size distribution. The advancement of this technique can be facilitated by an improved understanding of processes that control the sizes, shapes, and structures of the produced nanoparticles. In this work, the dependence of the fragmentation mechanisms on the energy density deposited by the laser pulse is investigated in atomistic simulations performed for 20 nm Au nanoparticles irradiated in water by 10 ps laser pulses. The simulations reveal that the decrease in the absorbed laser energy leads to sequential transitions from the regime of "strong" phase explosion, when all products of an explosive phase decomposition of the irradiated nanoparticle are promptly injected into the water surrounding a nanobubble formed around the nanoparticle, to two distinct regimes of nanoparticle fragmentation leading to the formation of a large central nanoparticle surrounded by smaller satellite fragments. First, in the regime of "mild" phase explosion, the central nanoparticle is produced by the reflection of some of the hot metal droplets generated by the explosive decomposition of the nanoparticle from the boundary of the nanobubble. This reflection is attributed to the inverse Leidenfrost effect acting at the nanoscale. The reflected droplets converge in the center of the nanobubble and coalesce into a single droplet that solidifies shortly after the collapse of the nanobubble. Further decrease in the absorbed laser energy brings the irradiation conditions below the threshold for the phase explosion and results in the formation of a core-satellite structure of the fragmentation products through an interplay of the intense evaporation from the surface of the irradiated nanoparticle, evolution of the nanobubble, and condensation of the metal vapor into clusters and small satellite nanoparticles. The computational predictions are related to the experimental observations, and the connections between the fragmentation mechanisms, the nanoparticle size distribution, and the generation of internal crystal defects are discussed.