Ballistic Ejection of Microdroplets from Overpacked Interfacial Assemblies
Ballistic Ejection of Microdroplets from Overpacked Interfacial Assemblies
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DOI：
10.1002/adfm.202213844
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发表时间：
2022-07
影响因子：
19
通讯作者：
Xuefei Wu;Gautam Bordia;R. Streubel;J. Hasnain;C. Pedroso;B. Cohen;B. Rad;P. Ashby;A. Omar;P. Geissler;Dong Wang;Han Xue;Jianjun Wang;Thomas P. Russell
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文献类型：
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作者：
Xuefei Wu;Gautam Bordia;R. Streubel;J. Hasnain;C. Pedroso;B. Cohen;B. Rad;P. Ashby;A. Omar;P. Geissler;Dong Wang;Han Xue;Jianjun Wang;Thomas P. Russell
自发乳化是由于表面活性剂在液-液界面上的聚集和积累而产生的，是一种界面不稳定性，微液滴从界面上产生并扩散扩散，直到完全乳化。研究表明，外部磁场可以调节顺磁性纳米颗粒表面活性剂（nps）在液-液界面上的组装，从而触发nps在界面上的面密度过饱和，界面张力γ显著降低，这证明了这一点，并与静磁连续体理论相证实。尽管γ显著降低，但磁场的存在不会导致稳定界面变得不稳定。然而，在快速去除电场后，从表面产生一束微滴的爆炸喷射，这是一种动态界面不稳定，称为爆炸乳化。这一爆炸事件迅速将nps的面密度降低到场前的水平，从而稳定了界面。从外部抑制或触发爆炸乳化的能力，以及控制成千上万微滴的产生，揭示了一种有效的能量存储和释放过程，这在化学物质的控制和定向输送以及远程控制软微型机器人方面具有潜在的应用，利用微滴的铁磁性。
Spontaneous emulsification, resulting from the assembly and accumulation of surfactants at liquid–liquid interfaces, is an interfacial instability where microdroplets are generated and diffusively spread from the interface until complete emulsification. Here, it is shown that an external magnetic field can modulate the assembly of paramagnetic nanoparticle surfactants (NPSs) at liquid–liquid interfaces to trigger an oversaturation in the areal density of the NPSs at the interface, as evidenced by a marked reduction in the interfacial tension, γ, and corroborated with a magnetostatic continuum theory. Despite the significant reduction in γ, the presence of the magnetic field does not cause stable interfaces to become unstable. Upon rapid removal of the field, however, an explosive ejection of a plume of microdroplets from the surface occurs, a dynamical interfacial instability which is termed explosive emulsification. This explosive event rapidly reduces the areal density of the NPSs to its pre‐field level, stabilizing the interface. The ability to externally suppress or trigger the explosive emulsification and controlled generation of tens of thousands of microdroplets, uncovers an efficient energy storage and release process, that has potential applications for controlled and directed delivery of chemicals and remotely controlled soft microrobots, taking advantage of the ferromagnetic nature of the microdroplets.