Overcoming Rayleigh Plateau Instabilities: Stabilizing and Destabilizing Liquid Metal Streams via Electrochemical Oxidation

Liquids typically form droplets when exiting a nozzle. Jets – cylindrical streams of fluid—can form transiently at higher fluid velocities, yet interfacial tension rapidly drives jet-breakup into droplets via the Rayleigh-Plateau instability. Liquid metal is an unlikely candidate to form stable jets since it has enormous interfacial tension and low viscosity. We report that electrochemical anodization significantly lowers the effective tension of a stream of metal, transitioning it from droplets to long (long lifetime and length) wires with 100 μm diameters without the need for high velocities. Whereas surface minimization drives Rayleigh-Plateau instabilities, these streams of metal increase in surface area when laid flat upon a surface due to the gravity and low interfacial tension. The ability to tune interfacial tension over at least three orders of magnitude using modest potential (<1 V) enables new approaches for production of metallic structures at room temperature, on-demand fluid-in-fluid structuring, and new tools for studying and controlling fluid behavior.

流体从喷嘴喷出时通常会形成液滴。射流——即圆柱形流体束——在流体流速较高时可暂时形成，但界面张力（interfacial tension）会通过瑞利-普拉托不稳定性（Rayleigh-Plateau instability）快速促使射流断裂为液滴。液态金属本不太可能形成稳定射流，因其界面张力极高而粘度较低。我们的研究表明，电化学阳极氧化可显著降低金属束的有效张力，使其从形成液滴转变为直径100微米、兼具长寿命与大长度的金属丝，且无需高流速。与界面最小化驱动瑞利-普拉托不稳定性的机制不同，这些金属束平铺于表面时，会因重力和较低的界面张力而增加自身表面积。通过施加适度电位（<1 V）即可将界面张力调控至少三个数量级，这一能力为室温下制备金属结构、按需实现液内流体结构化，以及研究与调控流体行为的新型工具开发提供了全新途径。