Liquid‐Suspended and Liquid‐Bridged Liquid Metal Microdroplets

Abstract

because it allows for simple on-demand deposition of materials with a reduced number of processes and relatively low amounts of waste compared to conventional lithography, conferring a higher efficiency. Moreover, facile additive manufacturing or "3D printing" of a complicated free-standing structure may be possible using DIW, [25] potentially with high accuracy. Thus far, DIW and 3D printing using materials other than LM have been widely used for applications in various fields, [26][27][28][29][30][31][32][33][34][35][36][37] which often employ an ink-type filament with proper rheological properties.Despite the fluidic nature of LMs and alloys, 3D printing using these materials is not trivial. In addition to fluid-like properties that allow for printing via shear extrusion, the ink-type filament must also be sufficiently solid-like to enable the printed ink to retain its shape and not spread over the previously printed structure or substrate. [24,25] Thus, the ink-type filament for 3D printing should be a viscoelastic fluid possessing both high elastic (G′) and viscous (G′′) moduli, often characterized by a high yield stress (τ y ) value. An oxide passivation layer (1-5 nm), which spontaneously forms on the surface of LMs when exposed to air, can provide some solid-like properties locally. [1,38] However, bulk metals in the liquid state have low viscosities (near that of water) and exhibit Newtonian behavior under a wide range of shear, which complicates 3D printing. [24] To date, several methods have been suggested for 3D printing of LMs and alloys. [24] One possible approach, in which the LMs and alloys can be used directly without modification, is to precisely control the printing parameters, [39] such that the rupture and rapid reformation of the surface oxide layer can occur continually to achieve shape retention of the printed LMs. This requires the printing nozzle to be located in close proximity to a substrate. Once the meniscus of the LM at the nozzle tip, which is formed at an adequately set pressure, adheres to the substrate, the nozzle movement creates mechanical stress, which can rupture the oxide layer, thus allowing for drawings with flowing LM (the shape of which can be retained by the rapid reformation of the oxide layer). The second possible method is to disperse solid particle fillers in the LM (as a continuous-phase medium), which could significantly increase the rheological strength of the LMs, rendering them 3D-printable without sophisticated control of the printing parameters to a degree that is required for the printing of pristine LM. [17,18,21] Liquid metals (LMs) and alloys are attracting increasing attention owing to their combined advantages of high conductivity and fluidity, and have shown promising results in various emerging applications. Patterning technologies using LMs are being actively researched; among them, direct ink writing is considered a potentially viable approach for efficient LM additive manufacturing. However, true LM additive manufacturing with arbitrary printing g...

Vitrification of Liquid Metal‐in‐Oil Emulsions Using Nano‐Mineral Oxides

“…Despite the high Φ of the dispersed phase (Φ LM = 0.55), the resulting emulsion exhibited relatively high fluidity (Figure 1a), consistent with prior studies. [25,50] To the as-prepared LM-in-oil emulsion, silica (SiO 2 , 224.8 ± 105.0 nm; see electron microscopic image in Figure S1 in the Supporting Information) nanospheres were added as rheology modifiers. For the systematic rheology study, Φ for the total dispersed phase was the same as that of the base emulsion, that is, Φ LM+MO = 0.55.…”

“…[45] Thus, the unique tunability of the electronic properties by employing external oxide materials [17,18,[46][47][48] calls for follow-up research on various combinations of LMs and other particulate additives.LM microdroplets, when suspended as discrete particles with a solid oxide skin in a liquid medium, increase the viscosity (ɳ) of the resulting colloidal systems in a loading-dependent manner, and even induce elasticity at high loadings. [24,25,49,50] Such rheological properties of colloidal LM suspensions (or Ga and Ga-based alloys have recently received significant attention as "liquid metals (LMs)" with the combined advantages of a low toxicity, low melting point, high fluidity, and high conductivity. An important method for modifying LMs for enhanced processabilities and new applications is to tailor them into colloidal microdroplets suspended in a liquid medium.…”

Liquid Metal-Based Angle Detection Sensor

“…In recent years, LM has gained widespread use in the preparation of various sensor parts due to its attractive properties, such as fluidity and conductivity, which allow for remarkable adaptability in various applications, particularly under tensile force and pressure. − Gallium-based LM has been successfully integrated into the field of stretchable and wearable electronics. The LM generates an oxide layer that adheres to various materials, making it highly versatile.…”

High-Thermal-Conductivity and High-Fluidity Heat Transfer Emulsion with 89 wt % Suspended Liquid Metal Microdroplets

“…Specifically, EGaIn, which is a focused LM with a melting point below room temperature, was dispersed in liquid paraffin, which is a widely used base fluid for conventional nanofluids. Two different processes were employed in LM dispersion: (1) the previously known and widely used probe-sonication (PS) method − and (2) the rotor–stator homogenization (RSH) method, which has been used to manufacture various emulsion systems of conventional immiscible liquids (e.g., oil-in-water (o/w) or water-in-oil (w/o)) , but not frequently for LMs. The RSH method, based on high shear force, produces anisotropic LM droplets with large dimensions (≥10 μm in major diameter and ≥5 μm in minor diameter), in contrast to the isotropic submicron LM droplets produced via the PS method.…”