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Spider silk dissipates energy to prevent spinning
NEWS
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using natural materials designed to take advantage of this approach. They opted for Polydimethylsiloxane (PDMS) for the soft layer as it is inexpensive, inert, and non-toxic. It also dries clear, making it easy to observe the liquid bubbles they wanted to encapsulate, for which they picked gallium as it is liquid at room temperature. By curing the PDMS slowly, the team evolved a process to which they could add gallium droplets of different sizes, with some having one large inner chamber and others up to a dozen discrete droplets.
Materials Today
Each sample was tested, with a dynamic mechanical analysis instrument measuring the deformation under load and measures such as stiffness, toughness, and elasticity were taken under different conditions. The liquid reinforcement in natural materials has the characteristics of high viscous and bulk modulus, and is arranged in a hierarchical manner similar to the skin membrane of ocean fish. As researcher Chandra Sekhar Tiwary told Materials Today, “we hope our work showing an improvement of mechanical behavior by addition of a soft reinforce-
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Volume 20, Number 9
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November 2017
ment should spur other researchers[. . .] We believe there are numerous natural materials which may offer more insights in how to design even better composite based on this mechanism.” As well as new systems waiting to be discovered, they hope to design pure hierarchical systems based on the approach and to look at other liquids with similar or even better properties than liquid metals as reinforcement.
Laurie Donaldson 1369-7021/https://doi.org/10.1016/j.mattod.2017.09.016
Spider silk dissipates energy to prevent spinning Researchers from China and the UK have explained why dragline silk doesn’t twist and spiral out of control when spiders use it to lower themselves from a height and are able to maintain control. Based on the study of two species of golden orb weaver spiders, they showed how spider silk has the ability to resist twisting forces by slightly yielding when twisted, helping to quickly dissipate the energy that would otherwise send the spider spinning uncontrollably on the end of its dragline. The work on the “torsion dynamical response” of spider silk, which has appeared in Applied Physics Letters [Liu et al. Appl. Phys. Lett. (2017) DOI: 10.1063/1.4990676], describes how dragline silk – which is used to create the outside edges and spokes of webs and acts as a safety line when spiders drop to the ground – does not behave in the same way as more conventional materials such as human hair, metal wires, or synthetic fibers as it hardly twists at all due to its tor-
sional properties. A better understanding of how dragline silk could help in the development of biomimetic fibers that mimic such properties, with potential uses in improved synthetic ropes, helicopter rescue ladders, parachute cords, and even violin strings. The team used a torsion pendulum technique to assess the properties of the silk. This involved gathering strands from captive spiders before hanging them inside a cylinder with two washers placed at the end to mimic a spider. The cylinder acted to isolate the silk from being disturbed and maintained the silk at constant humidity since water can cause the fibers to contract. A rotating turntable then twisted the silk, which was recorded using a high-speed camera as the silk oscillated over hundreds of cycles. The silk was shown to partly deform when twisted, discharging more than 75% of its potential energy, with the oscillations quickly slowing down. After twisting,
the silk also somewhat snaps back into place. As yet, the researchers are unsure if this behavior is due to the complex physical structure of the silk, which is made up of a core of multiple fibrils inside a skin, with each fibril containing segments of amino acids in organized sheets and others in unstructured looping chains. They think that torsion could result in the sheets stretching like elastic, and warping the hydrogen bonds that connect the chains, which deform in the same way as plastic. It is the sheets that recover their original shape while the chains stay somewhat deformed. The team will now further explore how spider silk reacts to twisting and is able to maintain its stiffness during torsion, as well the effect of humidity and the extent to which air helps dissipate the energy.
1369-7021/https://doi.org/10.1016/j.mattod.2017.09.015
When methanol crosses from the anode to the cathode through the cell’s proton exchange membrane (PEM), there is an inherent degradation of fuel cell performance. This has been a significant obstacle in the development and the commercialization of DMFCs. “In general, dilute methanol solutions (<4 M) are often used as fuel for DMFCs in order to inhibit methanol crossover. However, to compete with lithium-based rechargeable batteries
that currently dominate the portable power market, the use of high-concentration methanol (9 M or higher) as fuel is highly demanded to capitalize the high energy density of DMFCs,” Yang told Materials Today. Scientists have investigated several ways to improve DMFC performance when high concentrations of methanol are being used, such as improving the fuel-feed system, developing more robust membranes, modification of the
Laurie Donaldson
Methanol means power A new approach to stabilize direct methanol fuel cells (DMFCs) that use high-concentration methanol as their fuel supply has been developed by a research team at the Institute of Process Engineering (IPE), part of the Chinese Academy of Sciences. The method not only boosts fuel cell performance but might also shed light on the design of clean and affordable alternative energy sources for portable electric devices.
486
NEWS
using natural materials designed to take advantage of this approach. They opted for Polydimethylsiloxane (PDMS) for the soft layer as it is inexpensive, inert, and non-toxic. It also dries clear, making it easy to observe the liquid bubbles they wanted to encapsulate, for which they picked gallium as it is liquid at room temperature. By curing the PDMS slowly, the team evolved a process to which they could add gallium droplets of different sizes, with some having one large inner chamber and others up to a dozen discrete droplets.
Materials Today
Each sample was tested, with a dynamic mechanical analysis instrument measuring the deformation under load and measures such as stiffness, toughness, and elasticity were taken under different conditions. The liquid reinforcement in natural materials has the characteristics of high viscous and bulk modulus, and is arranged in a hierarchical manner similar to the skin membrane of ocean fish. As researcher Chandra Sekhar Tiwary told Materials Today, “we hope our work showing an improvement of mechanical behavior by addition of a soft reinforce-
d
Volume 20, Number 9
d
November 2017
ment should spur other researchers[. . .] We believe there are numerous natural materials which may offer more insights in how to design even better composite based on this mechanism.” As well as new systems waiting to be discovered, they hope to design pure hierarchical systems based on the approach and to look at other liquids with similar or even better properties than liquid metals as reinforcement.
Laurie Donaldson 1369-7021/https://doi.org/10.1016/j.mattod.2017.09.016
Spider silk dissipates energy to prevent spinning Researchers from China and the UK have explained why dragline silk doesn’t twist and spiral out of control when spiders use it to lower themselves from a height and are able to maintain control. Based on the study of two species of golden orb weaver spiders, they showed how spider silk has the ability to resist twisting forces by slightly yielding when twisted, helping to quickly dissipate the energy that would otherwise send the spider spinning uncontrollably on the end of its dragline. The work on the “torsion dynamical response” of spider silk, which has appeared in Applied Physics Letters [Liu et al. Appl. Phys. Lett. (2017) DOI: 10.1063/1.4990676], describes how dragline silk – which is used to create the outside edges and spokes of webs and acts as a safety line when spiders drop to the ground – does not behave in the same way as more conventional materials such as human hair, metal wires, or synthetic fibers as it hardly twists at all due to its tor-
sional properties. A better understanding of how dragline silk could help in the development of biomimetic fibers that mimic such properties, with potential uses in improved synthetic ropes, helicopter rescue ladders, parachute cords, and even violin strings. The team used a torsion pendulum technique to assess the properties of the silk. This involved gathering strands from captive spiders before hanging them inside a cylinder with two washers placed at the end to mimic a spider. The cylinder acted to isolate the silk from being disturbed and maintained the silk at constant humidity since water can cause the fibers to contract. A rotating turntable then twisted the silk, which was recorded using a high-speed camera as the silk oscillated over hundreds of cycles. The silk was shown to partly deform when twisted, discharging more than 75% of its potential energy, with the oscillations quickly slowing down. After twisting,
the silk also somewhat snaps back into place. As yet, the researchers are unsure if this behavior is due to the complex physical structure of the silk, which is made up of a core of multiple fibrils inside a skin, with each fibril containing segments of amino acids in organized sheets and others in unstructured looping chains. They think that torsion could result in the sheets stretching like elastic, and warping the hydrogen bonds that connect the chains, which deform in the same way as plastic. It is the sheets that recover their original shape while the chains stay somewhat deformed. The team will now further explore how spider silk reacts to twisting and is able to maintain its stiffness during torsion, as well the effect of humidity and the extent to which air helps dissipate the energy.
1369-7021/https://doi.org/10.1016/j.mattod.2017.09.015
When methanol crosses from the anode to the cathode through the cell’s proton exchange membrane (PEM), there is an inherent degradation of fuel cell performance. This has been a significant obstacle in the development and the commercialization of DMFCs. “In general, dilute methanol solutions (<4 M) are often used as fuel for DMFCs in order to inhibit methanol crossover. However, to compete with lithium-based rechargeable batteries
that currently dominate the portable power market, the use of high-concentration methanol (9 M or higher) as fuel is highly demanded to capitalize the high energy density of DMFCs,” Yang told Materials Today. Scientists have investigated several ways to improve DMFC performance when high concentrations of methanol are being used, such as improving the fuel-feed system, developing more robust membranes, modification of the
Laurie Donaldson
Methanol means power A new approach to stabilize direct methanol fuel cells (DMFCs) that use high-concentration methanol as their fuel supply has been developed by a research team at the Institute of Process Engineering (IPE), part of the Chinese Academy of Sciences. The method not only boosts fuel cell performance but might also shed light on the design of clean and affordable alternative energy sources for portable electric devices.
486