Deyong Zhu

Liquid metal sponges for mechanically durable, all-soft, electrical conductors

Liquid metal sponges were developed by loading liquid metals (GaInSn) into elastomer sponges. The elasticity of 3D-interconnected networks and the fluidic nature of liquid metals led to the formation of all-soft structures for electrical conductors with high electrical conductivity and mechanical flexibility.

Liquid metal droplets with high elasticity, mobility and mechanical robustness

Non-stick, ultra-elastic liquid metal droplets were fabricated by coating polytetrafluoroethylene (PTFE) particles onto the surface of NaOH-treated liquid metal droplets. The liquid metal droplets consisted of a liquid metal core, a thin anti-oxidation layer to maintain the high surface tension of the liquid metal and a particle-interpenetrated shell to enhance the mobility of the droplet.

Recent progress in fabrication and application of polydimethylsiloxane sponges

Owing to their structural advantages in comparison with bulk polydimethylsiloxane (PDMS), porous 3D substrates, which are also known as PDMS sponges, possess immense potential in energy generation, transport and storage, absorption, separation, photocatalysis, wearable electronics and life science applications. Extensive effort has therefore been devoted to the design and synthesis of porous PDMS sponges. The key to excellent performance in high-value applications is a deep knowledge of the beneficial aspects of their porosity, structure and morphology for a specific application. Several new routes for the fabrication of PDMS sponges, as well as novel applications, have been developed recently. Therefore, this review focuses on advances in the field of the fabrication and application of PDMS sponges since 2011. After a concise introduction, which includes remarks on the benefits of PDMS in comparison with other materials, strategies for the synthesis/fabrication of PDMS sponges are presented and their advantages and drawbacks are concisely discussed. A summary of the potential fabrication procedures will be beneficial for those entering the field, as it gives a quick overview of the feasible applications of a PDMS sponge fabricated via a specific method. Afterwards, different high-value applications of PDMS sponges are described in conjunction with specific and detailed examples of all the abovementioned applications. In this regard, suggestions are also made regarding which fabrication method is most beneficial for the application being discussed. Finally, recent advances in the fabrication and application of PDMS sponges are summarized, as well as issues, such as surface functionalization and pore size limitations, which are impeding reasonable future applications. We envision that this review will be helpful to those entering the field, as well as experienced researchers who need rapid access to recent literature, and will give new stimuli for the development of novel porous materials.

Hydrophilic Sponges for Leaf-Inspired Continuous Pumping of Liquids

A bio‐inspired, leaf‐like pumping strategy by mimicking the transpiration process through leaves is developed for autonomous and continuous liquid transport enabled by durable hydrophilic sponges. Without any external power sources, flows are continuously generated ascribed to the combination of capillary wicking and evaporation of water. To validate this method, durable hydrophilic polydimethylsiloxane sponges modified with polyvinyl alcohol via a “dip‐coat‐dry” method have been fabricated, which maintains hydrophilicity more than 2 months. The as‐made sponges are further applied to achieve stable laminar flow patterns, chemical gradients, and “stop‐flow” manipulation of the flow in microfluidic devices. More importantly, the ease‐of‐operation and excellent pumping capacity have also been verified with over 24 hs pumping and quasi‐stable high flow rates up to 15 µL min−1. The present strategy can be easily integrated to other miniaturized systems requiring pressure‐driven flow and should have potential applications, such as cell culture, micromixing, and continuous flow reaction.

Microfluidic Patterning of Metal Structures for Flexible Conductors by In Situ Polymer‐Assisted Electroless Deposition

A low‐cost, solution‐processed, versatile, microfluidic approach is developed for patterning structures of highly conductive metals (e.g., copper, silver, and nickel) on chemically modified flexible polyethylene terephthalate thin films by in situ polymer‐assisted electroless metal deposition. This method has significantly lowered the consumption of catalyst as well as the metal plating solution.

Defect-free, high resolution patterning of liquid metals using reversibly sealed, reusable polydimethylsiloxane microchannels for flexible electronic applications

This paper describes a simple and reliable approach for high-resolution patterning of liquid metals onto elastomeric substrates and their applications in flexible and wearable electronics. In this method, the liquid metal eutectic gallium indium (EGaIn) alloy was first dispensed into an air plasma-treated polydimethylsiloxane (PDMS) substrate through a reversibly sealed PDMS microchannel. The liquid metal-filled substrate was then placed on a cold plate, where the liquid metal was solidified. Finally, defect-free patterns were obtained by directly peeling off the PDMS microchannel on a hot plate while the liquid metal started to melt. The as-made liquid metal patterns exhibited excellent electrical and mechanical performance. As a proof of concept, the as-made flexible patterns of liquid metals were applied as flexible electrical conductors, capacitive sensors, and touch keyboards.

Bioinspired, Mechano-Regulated Interfaces for Rationally Designed, Dynamically Controlled Collection of Oil Spills from Water

This study describes the fabrication of bioinspired mechano‐regulated interfaces (MRI) for the separation and collection of oil spills from water. The MRI consists of 3D‐interconnected, microporous structures of sponges made of ultrasoft elastomers (Ecoflex). To validate the MRI strategy, ecoflex sponges are first fabricated with a low‐cost sugar‐leaching method. This study then systematically investigates the absorption capacity (up to 1280% for chloroform) of the sponges to different oils and organic solvents. More importantly, the oil flux through the as‐made sponges is controlled by mechanical deformation, which increases up to ≈33‐fold by tensile strain applied to the sponge from 0 to 400%. On the basis of MRI, this study further demonstrates the application of ecoflex sponges in oil skimmers for selective collecting oil from water with high efficiency and durable recyclability. The as‐developed MRI strategy has opened a new path to allow rational design and dynamical control toward developing high performance devices for oil permeation and selective collection of oil spills from water.

Effect of laser energy on the crystal structure and UV response characteristics of mixed-phase MgZnO thin films deposited by PLD and the fabrication of high signal/noise ratio solar-blind UV detector based on mix-phase MgZnO at lower voltage

MgZnO thin films (with Mg0.4Zn0.6O as the target) were fabricated on fused quartz substrates employing PLD method under different laser energy densities. Cubic structured MgZnO thin films were made at laser energy densities of 20 J cm−2 and 22 J cm−2, whilst the MgZnO thin films were deposited along both cubic and hexagonal structures under higher laser energy density condition. When a higher energy density laser was focused on the MgZnO target during the deposition process, the MgZnO thin film was found to be deposited with a more hexagonal structure and a higher Zn composition. There are two response peaks located in the solar-blind UV and visible-blind UV regions within the UV response spectrum of the mixed-phase MgZnO based detector deposited at laser energy over 24 J cm−2. When the deposition laser energy density increased from 24 to 30 J cm−2, the maximum UV responsivity of the mixed-phase MgZnO-based detector increased from 0.06 A W−1 to 1 A W−1 at 40 V bias voltage, and the visible-blind UV response peak of the mix-phase MgZnO based detector was also higher due to the MgZnO adopting a more hexagonal structure; furthermore, a higher internal gain is obtained, which can be attributed to a higher density of interfaces between the MgZnO grains of different structures in the mixed-phase MgZnO thin film. At 5 V bias voltage, the Ilight(230 nm)/Idark ratio of the UV detector based on mix-phase MgZnO deposited at 24 J cm−2 reached 500, and the Ilight(290 nm)/Idark ratio of the UV detector based on mix-phase MgZnO deposited at 26 J cm−2 reached 1100. Therefore, the UV-detector based on mixed-phase MgZnO thin films is sensitive to solar-blind and visible-blind UV light with strong background noise (on Earth) when the boundaries between (111) an (200) cubic MgZnO makes obvious function in decreasing the dark current of the detectors at lower bias voltage.