Particle-assisted formation of oil-in-liquid metal emulsions.

Gallium-based liquid metals (LMs) have surface tension an order of magnitude higher than water and break up into micro-droplets when mixed with other liquids. In contrast, silicone oil readily mixes into LM foams to create oil-in-LM emulsions with oil inclusions. Previously, the LM was foamed through rapid mixing in air for an extended duration (over 2 h). This process first results in the internalization of oxide flakes that form at the air-liquid interface. Once a critical fraction of these randomly shaped solid flakes is reached, air bubbles internalize into the LM to create foams that can internalize secondary liquids. Here, we introduce an alternative oil-in-LM emulsion fabrication method that relies on the prior addition of SiO2micro-particles into the LM before mixing it with the silicone oil. This particle-assisted emulsion formation process provides a higher control over the composition of the LM-particle mixture before oil addition, which we employ to systematically study the impact of particle characteristics and content on the emulsions' composition and properties. We demonstrate that the solid particle size (0.8µm to 5µm) and volume fraction (1%-10%) have a negligible impact on the internalization of the oil inclusions. The inclusions are mostly spherical with diameters of 20-100µm diameter and are internalized by forming new, rather than filling old, geometrical features. We also study the impact of the particle characteristics on the two key properties related to the functional application of the LM emulsions in the thermal management of microelectronics. In particular, we measure the impact of particles and silicone oil on the emulsion's thermal conductivity and its ability to prevent deleterious gallium-induced corrosion and embrittlement of contacting metal substrates.

Mechanism of Oil-in-Liquid Metal Emulsion Formation.

Gallium-based liquid metals (LMs) combine metallic properties with the deformability of a liquid, which makes them promising candidates for a variety of applications. To broaden the range of physical and chemical properties, a variety of solid additives have been incorporated into the LMs in the literature. In contrast, only a handful of secondary fluids have been incorporated into LMs to create foams (gas-in-LM) or emulsions (liquid-in-LM). LM foams readily form through mixing of LM in air, facilitated by the formation of a native oxide on the LM. In contrast, LM breaks up into microdroplets when mixed with a secondary liquid such as silicone oil. Stable silicone oil-in-LM emulsions form only during mixing of the oil with LM foam. In this work, we investigate the fundamental mechanism underlying this process. We describe two possible microscale mechanisms for emulsion formation: (1) oil replacing air in the foam or (2) oil creating additional features in the foam. The associated foam-to-emulsion density difference demonstrates that emulsions predominantly form through the addition of oxide-covered silicone oil capsules to the LM foam. We demonstrate this through density and surface wettability measurements and multiscale imaging of LM foam mixed with varied silicone oil contents in air or nitrogen environments. We also demonstrate the presence of a continuous silicone oil film on the emulsion surface and that this oil film prevents the embrittlement of contacting aluminum.

COVID-19 Testing Crisis Management Through a Public-Private Partnership in Sindh, Pakistan.

As the coronavirus disease (COVID-19) pandemic spread, meeting the testing needs to control the spread of infection became a major challenge worldwide. In Pakistan, the lack of the requisite infrastructure and training compounded the acute shortage of testing kits and other consumables. Against this backdrop and to urgently improve province-wide access to high-quality COVID-19 polymerase chain reaction (PCR) testing with rapid turnaround times, the Government of the Sindh (GoS) province of Pakistan entered into a public-private partnership with Indus Hospital & Health Network (IHHN). Under this partnership, the GoS undertook sample collection and Indus Hospital in Karachi, Sindh, centralized testing. We describe the implementation strategies adopted by the partnership, as well as the challenges, opportunities, and lessons learned. Notably, up to 40% and 22% of total COVID-19 PCRs done in Sindh in the first 2 months of the pandemic, respectively, were performed at Indus Hospital in Karachi, though this percentage declined gradually as other centers caught up with their testing capacities. The rapid scaling up was achieved through a combination of mechanisms and factors including building on preexisting partnerships between the GoS and IHHN, pooling resources and harnessing distinct and complementary roles, relocating existing resources, introducing automation and information technology system changes, establishing risk mitigation strategies, and introducing quality measures within testing processes. The primary outcome of the partnership was rapid province-wide access to quality COVID-19 PCR testing with short turnaround times and at no cost to the patient. Furthermore, implementation of the partnership goals established new mechanisms as well as strengthened existing ones to enable rapid response to the future global health security challenges in Sindh, Pakistan.

Gallium oxide-stabilized oil in liquid metal emulsions.

Gallium based liquid metals (LM) have prospective biomedical, stretchable electronics, soft robotics, and energy storage applications, and are being widely adopted as thermal interface materials. The danger of gallium corroding most metals used in microelectronics requires the cumbersome addition of "barrier" layers or LM break-up into droplets within an inert matrix such as silicone oil. Such LM-in-oil emulsions are stabilized by native oxide on the droplets but have decreased thermal performance. Here we show that mixing of the silicone oil into an LM-air foam yields emulsions with inverted phases. We investigate the stability of these oil-in-LM emulsions through a range of processing times and oil viscosities, and characterize the impact of these parameters on the materials' structure and thermal property relationships. We demonstrate that the emulsion with 40 vol% of 10 cSt silicone oil provides a unique thermal management material with a 10 W m-1 K-1 thermal conductivity and an exterior lubricant thin film that completely prevents corrosion of contacting aluminum.

Oxide-mediated mechanisms of gallium foam generation and stabilization during shear mixing in air.

Foaming of gallium-based liquid metals improves their processability and-seemingly in contrast to processing of other metal foams-can be achieved through shear-mixing in air without addition of solid microparticles. Resolving this discrepancy, systematic processing-structure-property characterization demonstrates that many crumpled oxide particles are generated prior to air bubble accumulation.