Jump-to-contact instability: The nanoscale mechanism of droplet coalescence in air
Jump-to-contact instability: The nanoscale mechanism of droplet coalescence in air
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跳跃接触不稳定性：空气中液滴聚结的纳米级机制
DOI：
10.1103/physrevfluids.3.102001
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发表时间：
2018
影响因子：
2.7
通讯作者：
P. Tordjeman
中科院分区：
文献类型：
--
作者：
V. Chireux;M. Protat;Frédéric Risso;T. Ondarçuhu;P. Tordjeman
本文利用原子力显微镜（AFM）实验研究了半径在0.7 ~ 74 μm之间的两个液滴之间的跳接触不稳定性。这种发生在纳米尺度上的不稳定性是造成液滴聚结的原因。在接触和调频两种模式下进行了AFM实验，监测了两个液滴界面相互靠近时的作用力和频移。用力和频移的理论表达式拟合实验曲线，确定跃迁到接触处的临界距离d_min。结果指出了两种状态的存在。对于亚微米液滴，d_min的尺度为（HReq/γ）^1/3，其中Req为等效液滴半径，H为Hamaker常数，γ为液体的表面张力。对于较大的液滴，d_min不再取决于液滴的大小，其尺度为（H/γ）^1/2。在大多数情况下，第二个尺度是控制液滴聚结的尺度。
We study experimentally by means of atomic force microscopy (AFM) the jump-to-contact instability between two droplets in air, with radii ranging between 0.7 and 74 μm. This instability which occurs at the nanoscale is responsible for droplet coalescence. The AFM experiments were conducted in contact and frequency-modulation modes where the interaction force and the frequency shift are monitored while the two droplet interfaces approach each other. The critical distance d_min at which the jump to contact takes place is determined by fitting the experimental curves by the theoretical expressions for theforce and the frequency shift. The results point out the existence of two regimes. For submicrometer droplets, d_min scales as (HReq/γ)^1/3 where Req is the equivalent droplet radius,H the Hamaker constant, and γ the surface tension of the liquid. For larger droplets,d_min no longer depends on the droplet size and scales as (H/γ)^1/2. This second scaling is the one that controls droplet coalescence in most situations.