Analysis and Transformations of Room‐Temperature Liquid Metal Interfaces – A Closer Look through Interfacial Tension

Abstract

Room-temperature gallium-based liquid metals (e. g. Galinstan) are emerging materials for a wide range of applications spanning from soft robotics to a medium for running chemical reactions. However, Galinstan suffers from rapid oxide formation at the surface, limiting its application. Similarly, this surface oxidation renders it difficult to determine the surface free energy of Galinstan. Herein, the interfacial properties of Galinstan in contact with argon, acid, base, water, and organic solvents were investigated, yielding kinetic information regarding the removal by acids and bases, knowledge about oxo-hydroxide/hydroxide species at the Galinstan/water interface, and an estimated value of the dispersive contribution of the surface free energy. The dispersive contribution of the surface free energy of Galinstan was calculated to be (239.7±9.1) mN/m, around 40 % of the total surface free energy. By employing the dispersive surface tension of Galinstan, the interfacial tension between a liquid and Galinstan can be easily obtained, facilitating the design and application of liquid metal-based devices.

Liquid Metal–Based Soft Microfluidics

“…It has proven to be more practical to remove the oxide skin on demand by employing acidic or alkaline aqueous solutions. By this means, a high surface/interfacial tension is obtained, albeit different from the pristine liquid metal . Interestingly, by this approach, liquid metal can be recovered.…”

“…Zavabeti et al proposed a self‐propelled LM droplet by utilizing the ionic imbalance around the LM droplets. Here, the imbalance in pH (OH − and H + ions) affords an imbalance in interfacial tension on either side of the LM droplet, affording the ability to do work . Miyako et al fabricated a kind of modified LM that can bond to various biomolecules via self‐assembly technique and carbodiimide chemistry.…”

“…By this means, a high surface/interfacial tension is obtained, albeit different from the pristine liquid metal. [29][30][31] Interestingly, by this approach, liquid metal can be recovered. For example, the transient circuit comprising of polyvinyl alcohol (PVA) as substrate and liquid metal Galinstan as electric conductor could be recovered after dissolution of the PVA in water by simply treating with sodium hydroxide solution, yielding in a recovery rate as high as 96%.…”

“…Here, the imbalance in pH (OH − and H + ions) affords an imbalance in interfacial tension on either side of the LM droplet, affording the ability to do work. [31] Miyako et al [137] fabricated a kind of modified LM that can bond to various biomolecules via self-assembly technique and carbodiimide chemistry. After surface modification with catalase, dynamic motion of the LM was achieved by the enzymatic decomposition of H 2 O 2 solution with extensive bubble generation on the base and side surface of LM, which shows the potential to provide soft robotics for biomedical applications.…”

Light‐Induced Shape Morphing of Liquid Metal Nanodroplets Enabled by Polydopamine Coating

“…For example, uniform LM microdroplets can be produced by microfluidics while the oxide layers formed on the droplet surfaces prevent the aggregation of microdroplets . Though, by microfluidics the LM droplet size is limited, among others by viscosity and the high interfacial tension of the LMs in the liquid . Physical vapor deposition method was also employed to fabricate LM nanodroplets on a variety of substrates .…”