Large Interfacial Tension Research Articles

Physicochemical and emulsification properties of okara-derived soluble dietary fiber modified by steam explosion

The effective utilization of by-products still poses a challenge in the food industry. In this work, soluble dietary fiber (SDF) extracted from okara was modified by steam explosion (SE) via adjusting steam pressure (1.0, 1.5, and 2.0 MPa) and SE duration (60 and 120 s). The structural and emulsification properties of modified SDF were studied. The untreated SDF exhibited a low yield (5.17%) and poor emulsification properties due to its large molecular weight (162.67 kDa), compact structure, and high interfacial tension (14.27 mN/m). SE increased SDF content by a maximum of 30.31%, 4.86 times higher than that of untreated SDF. Under mild SE conditions (1.0 MPa for 60 s), SDF displayed a loose structure with abundant side chains and a higher glyoxylate content (26.77%). Its near-neutral contact angle (82.0°) and lower interfacial tension (12.69 mN/m) endowed it with higher emulsification capacity, smaller emulsion droplet size, and enhanced emulsifying stability. The molecular weight of SDF decreased and the specific surface area enlarged with increasing SE intensity. Notably, SDF exhibited the best interfacial adsorption characteristics under SE of 2.0 MPa for 120 s, attributed to its low molecular weight (46.99 kDa) and higher protein content (7.58%). Overall, the improved emulsification properties of SDF were attributed to the synergistic effects of amphiphilic equilibrium, electrostatic repulsion, spatial resistance, and enhanced droplet-to-droplet interactions.

Formation characteristics and acoustic regulation of liquid metal droplets in low-aspect-ratio channels

The uniformity in size of liquid metal droplets is crucial in determining the accuracy of flexible circuit printing as well as the stability in signal transmission. In this study, the numerical simulation and the experiment method are combined to analyze the droplet preparation process of liquid metal. Furthermore, the mechanism of the surface acoustic wave as an external force dominating the breakup of the liquid metal interface is investigated. The results show that the squeezing pressure and the capillary force are the dominant forces of the interface evolution in the low-aspect-ratio (height/width) channel. When the dispersed phase flow rate is low, the interface will retract upstream of the channel under the influence of large interfacial tension after breakup, resulting in fluctuations in flow rate, and therefore, the stability of droplet size is weak. When the dispersed phase flow rate is high, the interface randomly breaks up under the influence of the Rayleigh–Plateau instability, which also leads to uneven droplet size. As the acoustic intensity increases, the acoustic radiation pressure gradually becomes the dominant force responsible for the squeezing and breakup of the interface. It increases the radial contraction rate of the interface, shortens the droplet generation period, and ultimately reduces the droplet size. Additionally, the size deviation value is significantly reduced from 10.13% to 1.05%. This study is useful in elucidating the evolution mechanism of liquid metal interfaces in low-aspect-ratio channels, improving the fundamental theory of interface breakup caused by acoustic radiation pressure, and providing theoretical guidance for the controlled and stable production of liquid metal droplets.

Effect of surfactant on oil displacement efficiency of imbibition/huff and puff in low permeability reservoirs

ABSTRACT Low permeability and tight reservoirs are rich in microscale and even nanoscale pores, resulting in a large interfacial tension between oil and water in the pores. Surfactant can effectively improve the oil displacement efficiency during imbibition and huff and puff. In this paper, the low permeability cores with different permeability are taken as the research object, and the effects of surfactant and distilled water on the oil displacement efficiency of imbibition/huff and puff are compared and analyzed using the nuclear magnetic resonance technology. Results show that: (a) Huff and puff can significantly improve displacement efficiency, and there are mainly three reasons: the soaking time, surfactants improve infiltration efficiency, and elastic energy. (b) Imbibition is a spontaneous phenomenon in tight reservoirs, while huff and puff is artificially manipulated. (c) Due to the slow infiltration process, as the soaking time increases, the oil displacement efficiency increases. (d) when the pressure is increased from 0.1 MPa to 12 MPa, the oil recovery and displacement efficiency are increased by about 2 times. (e) Compared with imbibition displacement, huff and puff can significantly improve displacement efficiency. (f) The T2 spectrum shows that the oil displacement efficiency of surfactant imbibition is higher, and the oil displacement efficiency of imbibition is significantly lower than that of huff and puff.

Ferrofluidic aqueous two-phase system with ultralow interfacial tension and micro-pattern formation

Ferrofluids are magnetic liquids known for the patterns they form in external magnetic fields. Typically, the patterns form at the interface between a ferrofluid and another immiscible non-magnetic fluid with a large interfacial tension γ ∼ 10−2 N m−1, leading to large pattern periodicities. Here we show that it is possible to reduce the interfacial tension several orders of magnitude down to ca. γ ∼ 10−6 N m−1 by using two immiscible aqueous phases based on spontaneous phase separation of dextran and polyethylene glycol and the asymmetric partitioning of superparamagnetic maghemite nanoparticles into the dextran-rich phase. The system exhibits classic Rosensweig instability in a uniform magnetic field with a periodicity of ∼200 μm, significantly lower than in traditional systems (∼10 mm). This system paves the way towards the science of pattern formation at the limit of vanishing interfacial tension and ferrofluid applications driven by small external magnetic fields.

A Kinetic Model for Precipitation of TiN Inclusions From Both Homogeneous and Heterogeneous Nucleation During Solidification of Steel

Complex TiN + oxide inclusions which nucleate and grow on the surface of the primary oxide inclusions, e.g. MgO, have been frequently observed in various steel grades after solidification. To describe the precipitation kinetics of TiN and TiN + MgO inclusions, a model accounting for both heterogeneous and homogeneous nucleation was proposed in this work. The model was validated by employing the literature data, and good agreement has been achieved between experimental data and calculation data. The influence of nitrogen and titanium concentrations, the interfacial tension between TiN and steel, cooling rate, and size distribution of primary oxides on the size distribution of TiN and TiN + MgO inclusions were investigated by the model calculations. It was found that nitrogen and titanium concentrations, the interfacial tension between TiN and steel, and the number density of primary MgO inclusions have an impact on the final size distributions of TiN and TiN + MgO inclusions. In contrast, the effects of cooling rate and size of MgO inclusions on the final inclusion size distribution are negligible. The large interfacial tension between TiN and steel would suppress the homogeneous nucleation and is favorable to heterogeneous nucleation. The increase of the number density of primary MgO can significantly suppress the homogeneous nucleation and reduce the size of TiN + MgO inclusions. The present model can be extended to describe the heterogeneous precipitation of other complex inclusions providing that the secondary inclusion has a low lattice mismatch with the primary inclusion. Combining the present model with our previous model for the size distribution of primary inclusions, the size distribution of inclusions in solidified steel can be well described and controlled.

Numerical study of droplet thermocapillary migration behavior on wettability-confined tracks using a three-dimensional color-gradient lattice Boltzmann model

Thermocapillary migration describes the phenomenon whereby liquid droplets move from warm to cold regions on a nonuniformly heated hydrophilic surface. Surface modifications can be applied to manipulate this migration process. In the present study, a three-dimensional color-gradient lattice Boltzmann model is used to investigate the droplet migration behavior on a series of wettability-confined tracks subject to a uniform temperature gradient. The model is validated by simulating the thermocapillary-driven flow with two superimposed planar fluids in a heated microchannel and the capillary penetration of a wetting fluid in a capillary tube. An in-depth study of the wettability-confined tracks confirms the capacity to manipulate the droplet migration process, that is, the wettability-confined tracks can accelerate thermocapillary migration compared with a smooth surface. The effects of changes in the viscosity ratio and interfacial tension are investigated, and it is found that a lower viscosity ratio and larger interfacial tension cause the droplet to migrate faster. Moreover, a systematic study of the track vertex angle is conducted, and the mechanism through which this parameter influences the droplet migration is analyzed. Then the effect of the track wettability on droplet migration is explored and analyzed. Finally, a serial wettability-confined track is designed to realize long-distance droplet migration, and the narrow side width of the connection region is found to play a key role in determining whether the droplets can migrate over long distances. The results provide some guidance for designing tracks that enable precise droplet migration control.

Effect of reservoir permeability on oil recovery using air foam flooding: a case study on Ganguyi oilfield

Air foam flooding is an important technology to enhance oil recovery by improving the swept volume of the fluid and the efficiency of displacement of oil. This study uses a literature review, engineering analysis of reservoirs, laboratory tests, and the data on oil production to clarify the relationship among the efficiency of oil displacement, control of the profile of the mechanism of water blockage, and the permeability of the reservoir. The results show that a highly permeable reservoir has a good pore structure with a large pore throat that helps yield a large swept volume and low interfacial tension to improve the efficiency of oil displacement. It also contains large pores that generate more foam for a higher oil mobility ratio and greater oil displacement. A heterogeneous reservoir has a strong Jamin effect and efficient oil displacement when air foam flooding is applied. The results of experiments yielded similar conclusions. The displacement efficiency of highly permeable and heterogeneous reservoirs is higher, and their injection pressure is lower when air foam flooding is applied. The permeability of reservoirs in oil fields should be higher than 1.5 mD for injection using air foam flooding. The results here can be used in applications of air foam flooding.

Pore-scale study of counter-current imbibition in strongly water-wet fractured porous media using lattice Boltzmann method

Oil recovery from naturally fractured reservoirs with low permeability rock remains a challenge. To provide a better understanding of spontaneous imbibition, a key oil recovery mechanism in the fractured reservoir rocks, a pore-scale computational study of the water imbibition into an artificially generated dual-permeability porous matrix with a fracture attached on top is conducted using a recently improved lattice Boltzmann color-gradient model. Several factors affecting the dynamic countercurrent imbibition processes and the resulting oil recovery have been analyzed, including the water injection velocity, the geometry configuration of the dual permeability zones, interfacial tension, the viscosity ratio of water to oil phases, and fracture spacing if there are multiple fractures. Depending on the water injection velocity and interfacial tension, three different imbibition regimes have been identified: the squeezing regime, the jetting regime, and the dripping regime, each with a distinctively different expelled oil morphology in the fracture. The geometry configuration of the high and low permeability zones affects the amount of oil that can be recovered by the countercurrent imbibition in a fracture-matrix system through transition of the different regimes. In the squeezing regime, which occurs at low water injection velocity, the build-up squeezing pressure upstream in the fracture enables more water to imbibe into the permeability zone closer to the fracture inlet thus increasing the oil recovery factor. A larger interfacial tension or a lower water-to-oil viscosity ratio is favorable for enhancing oil recovery, and new insights into the effect of the viscosity ratio are provided. Introducing an extra parallel fracture can effectively increase the oil recovery factor, and there is an optimal fracture spacing between the two adjacent horizontal fractures to maximize the oil recovery. These findings can aid the optimal design of water-injecting oil extraction in fractured rocks in reservoirs such as oil shale.

Sedimentation Behavior of Liquid Iron Droplets during Smelting Reduction of Converter Slag by Considering the Coalescence of Droplets

To improve the sedimentation efficiency during the smelting reduction process of converter slag for iron extraction, the interaction and sedimentation behavior of liquid iron droplets have been studied under the condition of experimental crucible scale by numerical simulation. The effects of slag viscosity and density difference between slag and iron droplet have also been investigated. The results show that sedimentation process in molten converter slag can be divided into early and latter settling stages, and increasing the coalescence of small droplets in the middle and lower region of slag pool and accelerating the droplet sedimentation at later settling stage are crucial for shortening the settling time of whole iron droplet cluster. During the sedimentation process, the coalescence phenomenon is accompanied, whereas rebound may not happen probably due to the relatively large metal-slag interfacial tension, small slag viscosity and small relative velocities of colliding droplets (≤8×10−3 m·s−1) caused by the creeping flow. The sedimentation velocities for a droplet is increased by about 13%–17% after coalescence. The sedimentation efficiency with interaction is significantly higher than that without interaction when iron droplets coalesce frequently. As the slag viscosity increases from 0.065 Pa·s to 0.195 Pa·s, the sedimentation efficiency decreases from 90% to 59%, while it increases from 89% to 92% with the density difference increasing from 3700 kg·m−3 to 4300 kg·m−3 at the settling time of 24 s. Therefore, molten slags with better fluidity and lower density are favored in the practical iron extraction process.

Spontaneous Dispersion and Large-Scale Deformation of Gallium-Based Liquid Metal Induced by Ferric Ions.

A gallium-based liquid metal (LM) exhibits the largest interfacial tension among all the room-temperature liquids, which gives it strong deformability and promises its role in the field of soft machines. Paradoxically, such a material always remains nearly spherical in solution because of large interfacial tension, which in turn hinders the construction of LM-based soft machines. Consequently, it is of significant theoretical and practical value to regulate the interfacial tension of a LM in order to carry out richer deformation. In this study, spontaneous dispersion and large-scale deformation of a bulk LM were disclosed to be induced by ferric ions. It was found that the bulk LM immersed in the FeCl3 solution can spontaneously disperse into a large amount of droplets. In addition, the dispersed LM droplets could move and deform by increasing the concentration of the solution or adding acids. The mechanisms behind the untraditional phenomena lie in the nonuniform interfacial tension over the entire surface of the LM, which is associated with the space-time distribution of the FeCl3 solution. Further, directional locomotion and periodic oscillation occur because of the nonuniform interfacial tension, which leads to the autonomous dispersion and deformation of the LM. Overall, the unique redox reactions between the LM and the FeCl3 solution play an essential role in ensuring the continuity of deformation. The present spontaneous dispersion and deformation capability of the LM signify a paradigm shift and open up new possibilities for the development of chemistry-enabled soft machines in the future.

Patterning and Reversible Actuation of Liquid Gallium Alloys by Preventing Adhesion on Rough Surfaces.

This work reports a simple approach to form, study, and utilize rough coatings that prevent the adhesion of gallium-based liquid metal alloys. Typically, liquids with large interfacial tension do not wet nonreactive surfaces, regardless of surface topography. However, these alloys form a surface oxide "skin" that adheres to many substrates, even those with low surface energy. This work reports a simple approach to render closed channels and surfaces, including soft materials, to be "oxide-phobic" via spray-coating (NeverWet, which is commercially available and inexpensive). Surface spectroscopic techniques and metrology tools elucidate the coatings to comprise silica nanoparticles grafted with silicones that exhibit dual length scales of roughness. Although prior work shows the importance of surface roughness in preventing adhesion, the present work confirms that both hydrophobic and hydrophilic rough surfaces prevent oxide adhesion. Furthermore, the coating enables reversible actuation through submillimeter closed channels to form a reconfigurable antenna in the gigahertz range without the need for corrosive acids or bases that remove the oxide. In addition, the coating enables open surface patterning of conductive traces of liquid metal. This shows it is possible to actuate liquid metals in air without leaving neither metal nor oxide residue on surfaces to enable reconfigurable electronics, microfluidics, and soft electrodes.

An effective compatibilizer for tin fluorophosphate glass/polymer composites obtained from “one pot” KF-RAFT polymerization

Tin fluorophosphate glass (Pglass)/polymer composites have been widely investigated due to their applications in areas including: gas barrier, electronic packaging and fire retardant, etc. The compatibility between Pglass and polymer matrix is rather poor due to the large interfacial tension. Novel method is urgently needed to address this issue so that the interfacial interaction, specific interfacial area as well as aspect ratio of Pglass could be enlarged, which could lead to significant enhancement in various properties. Current study aims to compatibilize Pglass/polymer composites through a newly synthesized compatibilizer: poly(α-aminophosphonate) (polyAPP), using “one pot” Kabachnik-Fields (KF)-Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization. Comparing to commonly used compatibilizer: silane coupling agents 3-Aminopropyltriethoxysilane (KH550) and polydopamine (PDA), polyAPP is found to enhance the interfacial interaction of Pglass and maleic anhydride grafted polypropylene (MA-PP), and decrease the dispersed phase size of Pglass in polymer matrix. It is much smaller than the results reported in literature for polyolefin based systems. Meanwhile, enhanced mechanical performance is also observed in such system, the tensile strength and modulus increased by 22% and 33% comparing to the pristine MA-PP, which can be attributed to the enhancement of the interaction between Pglass and polymer matrix. Such method could provide some guideline for the preparation of high performance Pglass/polymer composites as well as a range of functional polymer composites.

Enhanced thermal conductivity and electrical insulation properties of polymer composites via constructing Pglass/CNTs confined hybrid fillers

The preparation of thermal conductive and electrical insulating polymer composites has gained extensive interest due to their important applications. The morphological control of functional fillers is thought as an effective approach to achieve this. Herein, a novel method involves the confinement of carbon nanotubes (CNTs) in phosphate glass (Pglass) domains is presented. Due to the large interfacial tension between Pglass and polymer matrix, strong confinement of CNTs can be achieved while CNTs is incorporated into Pglass. Thus, the formation of CNTs conductive networks in polymer matrix can be prohibited in ternary polymer/Pglass/CNTs composites. Comparing with similar composites having high density polyethylene (HDPE) to realize confinement on CNTs, much higher thermal conductivity and much lower electrical conductivity are observed in polymer composites based on polypropylene (PP) containing boron nitride (BN). It is thought that the use of Pglass can provide an effective method for the preparation of thermally conductive and electrically insulating polymer composites.

Controllable dispersion and reunion of liquid metal droplets

Liquid metal (LM) micro-droplets have been widely used in microfluidics, drug-loaded nano-system and micro-nano machine due to its excellent properties. However, there still exist difficulties in succinctly dispersing a bulk of LM into micro-droplets due to the large interfacial tension. Besides, the controllable switching between droplet dispersion and reunion is yet to be realized. Herein, a practical and efficient method for dispersing LM was proposed and the controllable switching between dispersion and reunion of LM droplets was achieved. LM micro-droplets were produced by vibrating the LM immersed in a mixture of N , N -dimethylformamide (DMF) and polyvinyl chloride (PVC). The experimental results show that the size distribution of LM micro-droplets could be tuned by controlling the vibration frequency. More intriguingly, the dispersion and reunion of LM droplets can be switched intelligently through tuning the vibration frequency and amplitude. Furthermore, optical properties of the LM micro-droplet coating were evaluated to display potential applications. A self-driven motion of PVC-coated LM could be achieved by utilizing the produced LM micro-droplets based on the Marangoni effect, which holds promising value for developing future transport tool of LM droplets. The present work suggests an entirely feasible method for dispersing and utilizing LM droplets, which is of great significance for promoting the development of LM micro-droplet science and technology.

Crystallization of hard spheres revisited. I. Extracting kinetics and free energy landscape from forward flux sampling.

We investigate the kinetics and the free energy landscape of the crystallization of hard spheres from a supersaturated metastable liquid though direct simulations and forward flux sampling. In this first paper, we describe and test two different ways to reconstruct the free energy barriers from the sampled steady state probability distribution of cluster sizes without sampling the equilibrium distribution. The first method is based on mean first passage times, and the second method is based on splitting probabilities. We verify both methods for a single particle moving in a double-well potential. For the nucleation of hard spheres, these methods allow us to probe a wide range of supersaturations and to reconstruct the kinetics and the free energy landscape from the same simulation. Results are consistent with the scaling predicted by classical nucleation theory although a quantitative fit requires a rather large effective interfacial tension.

Interfacial rheology of low interfacial tension systems using a new oscillating spinning drop method

When surfactants adsorb at liquid interfaces, they not only decrease the surface tension, they confer rheological properties to the interfaces. There are two types of rheological parameters associated to interfacial layers: compression and shear. The elastic response is described by a storage modulus and the dissipation by a loss modulus or equivalently a surface viscosity. Various types of instruments are available for the measurements of these coefficients, the most common being oscillating pendent drops instruments and rheometers equipped with bicones. These instruments are applicable to systems with large enough interfacial tensions, typically above a few mN/m.We use a new type of instrument based on spinning drop oscillations, allowing to extend the interfacial rheology studies to low and ultralow interfacial tension systems. We present examples of measurements with systems of high and low tension, discuss the possible artifacts and demonstrate the capability of this new technique. We emphasize that the data shown for low interfacial tensions are the first reported in the literature. The instrument is potentially interesting for instance in enhanced oil recovery or demulsification studies.

Multiple Cases of Efficient Nonfullerene Ternary Organic Solar Cells Enabled by an Effective Morphology Control Method

AbstractTernary organic solar cells (OSCs) have attracted much research attention, as they can maintain the simplicity of the single‐junction device architecture while broadening the absorption range of OSCs. However, one main challenge that limits the development of ternary OSCs is the difficulty in controlling the morphology of ternary OSCs. In this paper, an effective approach to control the morphology is presented that leads to multiple cases of efficient nonfullerene ternary OSCs with efficiencies of up to 11.2%. This approach is based on a donor polymer with strong temperature dependent aggregation properties processed from hot solutions without any solvent additives and a pair of small molecular acceptors (SMAs) that have similar surface tensions and thus low propensity to form discrete phases. Such a ternary blend exhibits a simplified bulk‐heterojunction morphology that is similar to the morphology of previously reported binary blends. As a result, an almost linear relationship between VOC and film composition is observed for all nonfullerene ternary devices. Meanwhile, by carefully designing a control system with a large interfacial tension, a different phase separation and VOC dependence is demonstrated. This morphology control approach can be applicable to more material systems and accelerates the development of the ternary OSC field.

Oxidation-Mediated Fingering in Liquid Metals.

We identify and characterize a new class of fingering instabilities in liquid metals; these instabilities are unexpected due to the large interfacial tension of metals. Electrochemical oxidation lowers the effective interfacial tension of a gallium-based liquid metal alloy to values approaching zero, thereby inducing drastic shape changes, including the formation of fractals. The measured fractal dimension (D=1.3±0.05) places the instability in a different universality class than other fingering instabilities. By characterizing changes in morphology and dynamics as a function of droplet volume and applied electric potential, we identify the three main forces involved in this process: interfacial tension, gravity, and oxidative stress. Importantly, we find that electrochemical oxidation can generate compressive interfacial forces that oppose the tensile forces at a liquid interface. The surface oxide layer ultimately provides a physical and electrochemical barrier that halts the instabilities at larger positive potentials. Controlling the competition between interfacial tension and oxidative (compressive) stresses at the interface is important for the development of reconfigurable electronic, electromagnetic, and optical devices that take advantage of the metallic properties of liquid metals.

A molecular dynamics study of local pressures and interfacial tensions of SDS micelles and dodecane droplets in water.

To obtain the radial (normal) and lateral (transverse) components of the local pressure tensor, PN(R) and PT(R), respectively, and the interfacial tension of micelles, molecular dynamics (MD) calculations were performed for spherical sodium dodecyl sulfate (SDS) micelles. The local pressure tensor was calculated as a function of radial distance R using the Irving-Kirkwood formula. Similar MD calculations were also carried out for an n-dodecane droplet in water to compare the differences in the local pressure and interfacial tension values with those of the micelles. The calculated interfacial tensions were 20 ± 5 and 44 ± 10 mN/m for the SDS micelles and dodecane droplets, respectively. The excess free energies due to the interfacial tension were 340 and 1331 kJ/mol for the SDS micelle and dodecane droplet, respectively. The micelles are stabilized by 991 kJ/mol by covering their hydrophobic cores with hydrophilic groups. The dodecane droplet has a large interfacial tension caused by the zero or positive values of PN(R) - PT(R) at all values of R. In contrast, the small interfacial tension in the SDS micelles comes from the negative PN(R) - PT(R) values over a wide range of R. The pressure difference between the inside and outside of the oil droplet and its interfacial tension well satisfies the Laplace equation. However, the hydrophobic core of the SDS micelle is quite different from the liquid alkane, and the SDS micelles do not follow Laplace's picture. Decomposing the interfacial tension into contributions from various interactions, it is found that those between charged and polar groups dominate the interfacial tension of the SDS micelles. The positive electrostatic potential (1.3 V) on the micelle surface and the negative potential (-0.15 V) on the oil droplet contribute to the interfacial tensions by 19 and 0.5 mN/m, respectively. Thus, the interfacial tension of the SDS micelles is produced by electrostatic interactions, in contrast to the dodecane droplet.

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension. Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries. Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( ̴500 mN/m to near zero). Furthermore, this method requires only a very modest potential (< 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.