Versatile Liquid Metal Composite Inks for Printable, Durable, and Ultra‐Stretchable Electronics

The types of apparatus used to produce liquid sheets are classified according to the manner in which the energy is imparted to the liquid. The factors influencing the development, stability and manner of disintegration of a liquid sheet are examined more particularly with flat sheets produced from the single-hole fan-spray nozzle and the spinning disk. The development of the liquid sheet is influenced by the liquid properties. As the working pressure is raised the width of the sheet increases, but this development is hindered by high surface tension. It is shown that the effect of a surface-active agent on the development is only influential where the surface is not expanding or changing rapidly. Consequently its effect is more pronounced as the liquid moves farther away from the orifice. Increase of viscosity at the same pressure causes the region of disintegration to move away from the orifice, and high viscosity maintains the sheet undisturbed by air friction. Density has little effect on the area of the sheet. The effect of turbulence in the orifice is shown to be responsible for at least two types of disturbance in the sheet which results in holes being formed near the orifice. The depth of the disturbance in the sheet has to be equal to the thickness before disruption occurs. Similar disruption through the formation of holes can be caused by suspensions of unwettable particles. Wettable particles in low concentration, irrespective of their size, have no effect on the manner of disintegration. The most placid, stable and resistant sheet is obtained with a liquid of high surface tension, high viscosity, low density, giving low turbulence in the nozzle. Such a sheet will disintegrate when the velocity is raised and disintegration can occur through air friction. The easiest sheet to disintegrate is obtained with a liquid of low surface tension, low viscosity, low density and with low turbulence in the nozzle. Disintegration will occur near the nozzle at low velocities through waves caused by air friction. Disintegration through the formation of holes in the sheet can occur at low velocity with liquids of high surface-tension, low viscosity and high density where turbulence obtains in the nozzle. The formation of ligaments or threads is a necessary stage before the production of drops. Threads can be formed directly from any free edge or in the boundary. A free edge is formed when equilibrium exists between surface tension and inertia forces. In the spinning disk, at low flow rates, where the sheet is in contact with the surface of the disk, drops are formed at the ends of threads which break down into a limited number of sizes. At high flow rates a free edge of liquid exists outside the periphery of the disk with the formation of more irregular threads and a wider spectrum of drop sizes results. Where perforations occur in the sheet, expansion of the hole by surface tension occurs very regularly so that the holes remain nearly circular until they coalesce forming long threads. These long threads quickly become unstable and break down into drops. Threads being approximately uniform in diameter produce uniform drops, but the irregular areas of liquid which occur when a number of holes expand towards each other produce a wide variety of drop sizes. When the velocity of the sheet in the atmosphere is high, air friction causes slight variations in the sheet to develop rapidly into major wave disturbances, and these can result in holes being blown through the sheet so that disruption starts before the formation of a leading edge. With liquids having visco-elastic properties the sheet disintegrates through the formation of waves, but the rapid increase of viscosity, as the rate of shear is reduced, prevents further break-up of the threads into drops and a web of fine threads only is produced.

Gallium-based liquid metals (LMs) are promising materials for stretchable electronics due to their metallic conductivity and deformability. However, the fabrication of large-area stretchable integrated electronics using LMs on various polymers remains challenging due to their high surface tension, fluidity, and poor wettability. Current techniques, such as selective wetting and lift-off processes, face limitations related to substrate compatibility and Ga/metal alloying, hindering their applicability in integrated electronic systems. To address these challenges, we developed a high-resolution top-down etching-based photolithography combined with a universal cryogenic transfer method for transferring patterned LM particles (LMPs) in various polymer substrates. The cryogenic environment modifies the interfacial bonding between the LMPs and substrates, resulting in a universal transfer. The resulting liquid metal particle network embedded polymer (LNEP) exhibits high electrical conductivity (~1.71 × 10⁶ S/m), stability, and strain-insensitive performance across various polymers. This process is scalable to large-area fabrication, overcoming the limitations of existing LM patterning techniques. Leveraging this approach, we demonstrated the use of LNEP ranging from skin-conformal wearable sensors to hybrid stretchable circuits and implantable devices, demonstrating the universality of the method. This technique establishes a scalable pathway for stretchable electronics in advanced applications.

The effect of viscous soluble dietary fiber on nutrient digestion and metabolic responses Ⅰ: In vitro digestion process

Achieving control over the motion of dissolved particles in liquid metals is of importance for the meticulous realization of hierarchical particle assemblies in a variety of nanofabrication processes. Brownian forces can impede the motion of such particles, impacting the degree of perfection that can be realized in assembled structures. Here, we show that light-induced Marangoni flow in liquid metals (i.e., liquid-gallium) with Laguerre-Gaussian (LGpl) lasers as heating sources is an effective approach to overcome Brownian forces on particles, giving rise to predictable assemblies with a high degree of order. We show that by carefully engineering surface tension gradients in liquid-gallium using non-Gaussian LGpl lasers, the Marangoni and convective flow that develops in the fluid drives the trajectory of randomly dispersed particles to assemble into 100 μm wide ring-shaped particle assemblies. Careful control over the parameters of the LGpl laser (i.e., laser mode, spot size, and intensity of the electric field) can tune the temperature and fluid dynamics of the liquid-gallium as well as the balance of forces on the particle. This in turn can tune the structure of the ring-shaped particle assembly with a high degree of fidelity. The use of light to control the motion of particles in liquid metals represents a tunable and rapidly reconfigurable approach to spatially design surface tension gradients in fluids for more complex assembly of particles and small-scale solutes. This work can be extended to a variety of liquid metals, complementary to what has been realized in particle assembly out of ferrofluids using magnetic fields.

Electronic Blood Vessel

Gallium liquid metal alloys (GLMAs) such as Galinstanand gallium–indiumeutectic (EGaIn) are interesting materials due to their high surfacetensions, low viscosities, and electrical conductivities comparableto classical solid metals. They have been used for applications inmicroelectromechanical systems (MEMS) and, more recently, liquid metalmicrofluidics (LMMF) for setting up devices like actuators. However,their high tendency to alloy with the most common metals used forelectrodes such as gold (Au), platinum (Pt), titanium (Ti), nickel(Ni), and tungsten–titanium (WTi) is a major problem limitingthe scaleup and applicability, e.g., liquid metal actuators. Stableelectrodes are key elements for many applications and thus, the lackof an electrode material compatible with GLMAs is detrimental formany potential application scenarios. In this work, we study the effectof actuating Galinstan on various solid metal electrodes and presentan electrode protection methodology that, first, prevents alloyingand, second, prevents electrode corrosion. We demonstrate reproducibleactuation of GLMA segments in LMMF, showcasing the stability of theproposed protective coating. We investigated a range of electrodematerials including Au, Pt, Ti, Ni, and WTi, all in aqueous environments,and present the resulting corrosion/alloying effects by studying theinterface morphology. Our proposed protective coating is based ona simple method to electrodeposit electrically conductive polypyrrole(PPy) on the electrodes to provide a conductive alloying-barrier layerfor applications involving direct contact between GLMAs and electrodes.We demonstrate the versatility of this approach by direct three-dimensional(3D) printing of a 500 μm microfluidic chip on a set of electrodesonto which PPy is electrodeposited in situ for actuationof Galinstan plugs. The developed protection protocol will providea generic, widely applicable strategy to protect a wide range of electrodesfrom alloying and corrosion and thus form a key element in futureapplications of GLMAs.

Ultrasonic processing in the cavitation mode is used to produce the composite materials based on the metal matrix and reinforcing particles of micro- and nano-sizes. In such a case, the deagglomeration of aggregates and the uniform distribution of particles are the expected effects. Although the particles can not only fragment in the acoustic field, they also can coagulate, coarsen and precipitate. In this paper, a theoretical study of processes of deagglomeration and coagulation of particles in the liquid metal under ultrasonic treatment is made. The influence of various parameters of ultrasound and dispersion medium on the dynamics of particles in the acoustic field is considered on the basis of the proposed mathematical model. The criterion of leading process (coagulation or deagglomeration) has been proposed. The calculated results are compared with the experimental ones known from the scientific literature.

Several gallium-based liquid metal alloys are liquid at room temperature. As 'liquid', such alloys have a low viscosity and a high surface tension while as 'metal', they have high thermal and electrical conductivities, similar to mercury. However, unlike mercury, these liquid metal alloys have low toxicity and a negligible vapor pressure, rendering them much safer. In comparison to mercury, the distinguishing feature of these alloys is the rapid formation of a self-limiting atomically thin layer of gallium oxide over their surface when exposed to oxygen. This oxide layer changes many physical and chemical properties of gallium alloys, including their interfacial and rheological properties, which can be employed and modulated for various applications in microfluidics. Injecting liquid metal into microfluidic structures has been extensively used to pattern and encapsulate highly deformable and reconfigurable electronic devices including electrodes, sensors, antennas, and interconnects. Likewise, the unique features of liquid metals have been employed for fabricating miniaturized microfluidic components including pumps, valves, heaters, and electrodes. In this review, we discuss liquid metal enabled microfluidic components, and highlight their desirable attributes including simple fabrication, facile integration, stretchability, reconfigurability, and low power consumption, with promising applications for highly integrated microfluidic systems.

The natural tendency of liquid metal (LM) droplets to minimize surface energy and form spherical shapes presents a fundamental challenge for synthesizing elongated LM particles in solution. Overcoming this limitation is critical for the development of anisotropic functional materials with potential applications in stretchable electronics and wearable devices. To address this challenge, a solution-based method is presented to synthesize stable, elongated particles of eutectic gallium-indium (EGaIn) by combining a high-intensity mixing process with particle surface modification. Various surface modification agents are investigated, and the elongated LM particles are incorporated into uncured elastomers. In particular, polyvinylpyrrolidone (PVP)-functionalized EGaIn particles retain their high aspect ratio after embedding in silicone elastomers. Furthermore, these elongated particles are aligned within the elastomer matrix via printing and doctor-blading techniques, producing composites with anisotropic internal microstructures. The resulting LM-elastomer composites exhibit enhanced heat dissipation and thermal conductivity compared with isotropic counterparts, with numerical simulations confirming the role of the elongated particle morphology. Beyond thermal management, the elongated, solution-processable LM particles serve as programmable liquid-state functional units compatible with diverse polymer matrices and fabrication methods.

Conductive hydrogel materials are garnering attention for their high flexibility and biocompatibility, establishing them as promising candidates for use in wearable and stretchable electronics. Despite the high conductivity of many reported hydrogel materials, they generally lack intelligent properties such as degradability, stretchability, self-adhesion, and self-healing. This study proposes a stress-assisted conductive networking mechanism for liquid metal (LM)-based gel, which is attributed to the internal stress generated by volume shrinkage during the liquid–solid phase transition, and operates without the requirement of additional energy input. Based on this mechanism, LM particles are subsequently incorporated into a polyvinylpyrrolidone (PVP)-fructose composite (PFC) to fabricate a highly conductive LM-PFC gel. This gel not only achieves high conductivity but also demonstrates excellent intelligent properties, including high stretchability, degradability, high mechanical strength, self-adhesion, self-conforming ability, recyclability, and self-healing ability, which make it highly suitable for applications such as monitoring bioelectric signals, thereby highlighting its immense potential in stretchable electronics and wearable technologies.

The present study provides a strategy for the determination of the viscosity and surface tension of high-viscosity fluids in the form of ionic liquids (ILs) at equilibrium conditions by combining surface light scattering (SLS) and the pendant-drop (PD) method within one experimental setup. Through the study of the same sample under identical conditions by both methods inside a closed system, the surface tension determined via the PD method can be directly used to evaluate the dynamics of surface fluctuations of ILs with an overdamped behavior probed by SLS for accessing their viscosity. In connection with the SLS experiments, variations in the applied detection geometries in reflection and transmission direction and in the probed wave vectors down to relatively small values were also addressed. The reliability and self-consistency of SLS and the PD method applied within the same sample cell has been proven by investigating the reference fluids tris(2-ethylhexyl) trimellitate (TOTM) and n-dodecane featuring relatively high and low viscosities. For the two studied model ILs of opaque to non-transparent color, i.e., the hydrophobic 1-methyl-3-octylimidazolium hexafluorophosphate ([OMIM][PF6]) and the hydrophilic 1,3-bis(2-(2-methoxyethoxy)ethyl)imidazolium iodide ([(mPEG2)2Im]I), the combination of PD measurements and SLS experiments in reflection direction performed at ambient pressure between (303 and 373) K allowed access to the viscosity and surface tension with typical relative expanded uncertainties of (4 and 2) %. These results agree well with own viscosity data from capillary viscometry and experimental data in the literature, demonstrating the performance of the novel approach for the contactless in-situ measurement of viscosity and surface tension of fluids with relatively high-viscosity such as ILs.

Experimental investigation on molten slag granulation for waste heat recovery from various metallurgical slags

Droplet disintegration behavior on slender cylindrical objects is critical in various applications. This work investigates droplet impact dynamics on hydrophilic cylindrical glass fibers by using a high-speed imaging method. The influences of liquid viscosity, surface roughness, and surface tension are examined, revealing two distinct disintegration patterns: T-shaped and wing-like. T-shaped disintegration is a never-reported phenomenon that only occurs under very low viscosities, whereas wing-like disintegration tends to appear under higher viscosities and challenges the previous understanding that high viscosity promotes liquid wrapping on fibers. A regime map is constructed by varying impact velocity and liquid viscosity, and an empirical threshold model is proposed. Besides, surface roughness can also enhance wing-like disintegration, equivalent to the effect of directly increasing liquid viscosity. Additionally, a second regime map is developed by varying impact velocity and surface tension, and a theoretical threshold model based on the Plateau-Rayleigh theory is established. This work extends the understanding of droplets impacting fibers, illustrating that droplet disintegration is not necessarily favored by low-viscosity droplets or by surface hydrophobicity.

Processes involved in the collision of liquid droplets enhance their atomization. If droplets contain more than one component, these processes become especially strong and intense. In this paper, we describe experiments for heterogeneous droplets of water solutions, emulsions, and slurries typical of fuel, firefighting, and heat and mass transfer technologies. We determine the conditions for a stable occurrence of the four droplet collision regimes: bounce, coalescence, separation, and disruption. We go on to establish how droplet dimensions, velocities, impact angles, component concentrations, as well as liquid viscosity, surface tension, and density affect collision parameters. The experimental results are generalized using collision regime maps produced in the coordinate systems controlling for the variations of Weber, Reynolds, Ohnesorge, and capillary numbers, as well as angular and linear interaction parameters. The results are compared with the scarce data by other authors. The Weber number variation range is not the only factor influencing the droplet collision behavior the form of four interaction regimes. Viscosity and surface tension of the liquid have a significant impact as well. An increase in the viscous forces can provide conditions for droplet breakup into a maximum number of small fragments. Coalescence is the dominating mode at low viscosity and high surface tension. Droplet bounce occurrence does not only depend on the Weber number range but also on phase transformations and thermophysical properties of the liquid. Finally, we determine the droplets interaction parameters for group of liquids that can provide intense droplet atomization through collisions.

Liquid metals and their hybrids as stimulus–responsive smart materials