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Researchers Control Surface Tension of Liquid Metals

Researchers from North Carolina State University have developed a technique for controlling the surface tension of liquid metals by applying very low voltages, opening the door to a new generation of reconfigurable electronic circuits, antennas and other technologies. The technique hinges on the fact that the oxide “skin” of the metal – which can be deposited or removed – acts as a surfactant, lowering the surface tension between the metal and the surrounding fluid.The researchers used a liquid metal alloy of gallium and indium. In base, the bare alloy has a remarkably high surface tension of about 500 millinewtons (mN)/meter, which causes the metal to bead up into a spherical blob. “But we discovered that applying a small, positive charge – less than 1 volt – causes an electrochemical reaction that creates an oxide layer on the surface of the metal, dramatically lowering the surface tension from 500 mN/meter to around 2 mN/meter,” says Dr. Michael Dickey, an associate professor of chemical and biomolecular engineering at NC State and senior author of a paper describing the work. “This change allows the liquid metal to spread out like a pancake, due to gravity.”The researchers also showed that the change in surface tension is reversible. If researchers flip the polarity of the charge from positive to negative, the oxide is eliminated and high surface tension is restored.  The surface tension can be tuned between these two extremes by varying the voltage in small steps.SourceAlso: Learn about Gradient Metal Alloys Fabricated Using Additive Manufacturing.

Posted in: News, Electronics, Power Management, Metals, Antennas

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'Squid Skin' Metamaterial Yields Vivid Color Display

The quest to create artificial "squid skin" — camouflaging metamaterials that can "see" colors and automatically blend into the background — is one step closer to reality, thanks to a color-display technology by Rice University's Laboratory for Nanophotonics (LANP).The new full-color display technology uses aluminum nanoparticles to create the vivid red, blue, and green hues found in today's top-of-the-line LCD televisions and monitors.The breakthrough is the latest in a string of recent discoveries by a Rice-led team that set out in 2010 to create metamaterials capable of mimicking the camouflage abilities of cephalopods — the family of marine creatures that includes squid, octopus, and cuttlefish.LANP's new color display technology delivers bright red, blue, and green hues from five-micron-square pixels that each contains several hundred aluminum nanorods. By varying the length of the nanorods and the spacing between them, LANP researchers Stephan Link and Jana Olson showed they could create pixels that produced dozens of colors, including rich tones of red, green, and blue that are comparable to those found in high-definition LCD displays.

Posted in: News, Displays/Monitors/HMIs

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Untethered Soft Robot Walks Through Flames

Developers from Harvard’s School of Engineering and Applied Sciences and the Wyss Institute for Biologically Inspired Engineering have produced the first untethered soft robot — a quadruped that can stand up and walk away from its designers.The researchers were able to scale up earlier soft-robot designs, enabling a single robot to carry on its back all the equipment it needs to operate — micro-compressors, control systems, and batteries.Compared with earlier soft robots, which were typically no larger than a steno pad, the system is huge, measuring more than a half-meter in length and capable of carrying as much as 7½ pounds on its back.Giving the untethered robot the strength needed to carry mechanical components meant air pressures as high as 16 pounds per square inch, more than double the seven psi used by many earlier robot designs. To deal with the increased pressure, the robot had to be made of tougher stuff.The material settled on was a “composite” silicone rubber made from stiff rubber impregnated with hollow glass microspheres to reduce the robot’s weight. The robot’s bottom was made from Kevlar fabric to ensure it was tough and lightweight. The result was a robot that can stand up to a host of extreme conditions.SourceAlso: Learn about a Field-Reconfigurable Manipulator for Rovers.

Posted in: News, Composites, Motors & Drives, Machinery & Automation, Robotics

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Researchers Create See-Through Solar Concentrator

A team of researchers at Michigan State University has developed a new type of solar concentrator that when placed over a window creates solar energy.The device is called a transparent luminescent solar concentrator and can be used on buildings, cell phones, and any other device that has a clear surface.And, according to Richard Lunt of MSU’s College of Engineering, the key word is “transparent.”The solar harvesting system uses small organic molecules developed by Lunt and his team to absorb specific nonvisible wavelengths of sunlight.The “glowing” infrared light is guided to the edge of the plastic where it is converted to electricity by thin strips of photovoltaic solar cells.“Because the materials do not absorb or emit light in the visible spectrum, they look exceptionally transparent to the human eye,” said Richard Lunt of MSU’s College of Engineering.SourceAlso: Learn about High-Efficiency Nested Hall Thrusters for Robotic Solar System Exploration.

Posted in: News, Renewable Energy, Solar Power, Plastics

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Toughened Uni-piece Fibrous Reinforced Oxidation-Resistant Composite (TUFROC)

Ames Research Center, Moffett Field, California TUFROC has an exposed surface edge design and an appropriate materials combination for a space vehicle that will survive the mechanical stresses induced in the initial ascent, and will subsequently survive the extreme heating and mechanically stressful environment of re-entry. It provides a thermal protection tile attachment system, suitable for application to a space vehicle leading edge, and for other uses in extreme heating environments [up to 3,600 °F (1,982 °C), and possibly higher, for short time intervals].

Posted in: Briefs

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High-Efficiency Tantalum-Based Ceramic Composite Structures

Ames Research Center, Moffett Field, California High-efficiency tantalum-based ceramic (HETC) composite structures are suitable for use in thermal protection systems. These composite structures have high-efficiency surfaces (low catalytic efficiency and high-emittance), thereby reducing heat flux to a spacecraft during planetary reentry. These low catalytic efficiency and high-emittance ceramic materials were developed in order to increase the capability of a Toughened Uni-Piece Fibrous Insulation (TUFI)-like thermal protection system, with its high-impact resistance, to temperatures above 3,000 °F (≈1,650 °C). These ceramics have been applied to various aerodynamic configurations, such as wedge, wing-leading segment, and conventional tile shapes used on high-speed atmospheric entry vehicles. In addition, this family of tantalum-based ceramics exhibits low catalytic efficiency to atom recombination during exposure to highenergy dissociated hypersonic flow.

Posted in: Briefs

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Use of Solvent-Free Conditions/Dry Mixing for Functionalizing Carbon Nanotubes

Lyndon B. Johnson Space Center, Houston, Texas Two methods have been developed for functionalizing carbon nanotubes in solvent-free conditions. In one method, purified single-walled carbon nanotubes (SWNTs) and a diazonium salt are added to a metal vial, which is loaded with a stainless steel ball bearing. The metal vial is clamped into a mill mixer, and is mixed for one hour. The unreacted diazonium salt is then dissolved in a volume of acetonitrile that efficiently solubilizes the salt to remove the unreacted functionalization reagent. The functionalized nanotubes are then collected by filtration.

Posted in: Briefs

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