Unique polymer fibres that are strong, tough and light as a feather

Electrospinning of a multifibrillar polyacrylonitrile fiber.
University of Bayreuth / Jürgen Rennecke.

Strong and tough yet as light as a feather – materials with this exceptional combination of properties are urgently needed in many industrial sectors and in medicine, as well as being of great interest for scientific research.

A research team from the University of Bayreuth has now developed polymer fibres with precisely these properties. Together with partners in Germany, China and Switzerland, the polymer fibers were characterized. The scientists have published their results in the journal Science.

“The fibres we discovered can be produced easily using high-tech processes that are already established in the industry – and on the basis of polymers that are readily available worldwide. One individual fibre is as thin as a human hair, weighs less than a fruit fly, and yet is very strong: It can lift a weight of 30 grams without tearing. This corresponds to about 150,000 times the weight of a fruit fly. Experiments on the high tensile strength of these fibres have furthermore revealed their high toughness. This means that each individual fibre can absorb a lot of energy,” explains Prof. Dr. Andreas Greiner, who is the head of the research group Macromolecular Chemistry II at the University of Bayreuth, and who guided the research work. Also involved were researchers at the Forschungszentrum Jülich, the Martin Luther University Halle-Wittenberg, the Fraunhofer-Institute for Microstructure of Materials and Systems (IMWS), the Rheinisch-Westfälische Technische Hochschule Aachen University, the Jiangxi Normal University, Nanchang, and the ETH Zürich.

Due to their unique properties, the polymer fibres are ideally suited for technical components that are exposed to high loads. They enable innovative applications in a wide variety of fields, for example in the textile industry or medical technology, in automotive engineering, or in the aerospace industry. In addition, the polymer fibres can be recycled well.

“We are certain that our research results have opened the door to a new, forward-looking class of materials. Practical applications on the part of industry can be expected in the near future. In polymer science, our fibres will be able to provide valuable services in the further research and development of high-performance functional materials,” says Greiner.

The chemical basis of these promising fibres is polyacrylonitrile. A single fibre with a diameter of about 40,000 nanometres consists of up to 4,000 ultra-thin fibrils. These fibrils are linked by small amounts of an additive. Three-dimensional X-ray images show that the fibrils within the fibre are almost always arranged in the same longitudinal direction.

“We prepared these multifibrillar polyacrylonitrile fibers in a laboratory for electrospinning at the University of Bayreuth and extensively tested them for their properties and behaviour. Their unique strength in combination with high toughness never ceased to fascinate us,” reports the Bayreuth polymer scientist Prof. Dr. Seema Agarwal. The lead author of the study published in Science is Xiaojian Liao, a doctoral researcher in chemistry in Bayreuth. “I am very pleased that I was able to contribute to this research success in materials science as part of my doctoral thesis. The intensive interdisciplinary contact between chemistry, physics, and material sciences on the Bayreuth campus has provided some critical impetus in recent years,” says Liao.

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Artificial synapses made from nanowires function in much the same way as a biological nerve cell

Image captured by an electron microscope of a single nanowire memristor (highlighted in colour to distinguish it from other nanowires in the background image). Blue: silver electrode, orange: nanowire, yellow: platinum electrode. Blue bubbles are dispersed over the nanowire. They are made up of silver ions and form a bridge between the electrodes which increases the resistance.
via: Forschungszentrum Jülich

Scientists from Jülich together with colleagues from Aachen and Turin have produced a memristive element made from nanowires that functions in much the same way as a biological nerve cell.

The component is able to both save and process information, as well as receive numerous signals in parallel. The resistive switching cell made from oxide crystal nanowires is thus proving to be the ideal candidate for use in building bioinspired “neuromorphic” processors, able to take over the diverse functions of biological synapses and neurons.

Computers have learned a lot in recent years. Thanks to rapid progress in artificial intelligence they are now able to drive cars, translate texts, defeat world champions at chess, and much more besides. In doing so, one of the greatest challenges lies in the attempt to artificially reproduce the signal processing in the human brain. In neural networks, data are stored and processed to a high degree in parallel. Traditional computers on the other hand rapidly work through tasks in succession and clearly distinguish between the storing and processing of information. As a rule, neural networks can only be simulated in a very cumbersome and inefficient way using conventional hardware.

Systems with neuromorphic chips that imitate the way the human brain works offer significant advantages. Experts in the field describe this type of bioinspired computer as being able to work in a decentralised way, having at its disposal a multitude of processors, which, like neurons in the brain, are connected to each other by networks. If a processor breaks down, another can take over its function. What is more, just like in the brain, where practice leads to improved signal transfer, a bioinspired processor should have the capacity to learn.

“With today’s semiconductor technology, these functions are to some extent already achievable. These systems are however suitable for particular applications and require a lot of space and energy,” says Dr. Ilia Valov from Forschungszentrum Jülich. “Our nanowire devices made from zinc oxide crystals can inherently process and even store information, as well as being extremely small and energy efficient,” explains the researcher from Jülich’s Peter Grünberg Institute.

For years memristive cells have been ascribed the best chances of being capable of taking over the function of neurons and synapses in bioinspired computers. They alter their electrical resistance depending on the intensity and direction of the electric current flowing through them. In contrast to conventional transistors, their last resistance value remains intact even when the electric current is switched off. Memristors are thus fundamentally capable of learning.

In order to create these properties, scientists at Forschungszentrum Jülich and RWTH Aachen University used a single zinc oxide nanowire, produced by their colleagues from the polytechnic university in Turin. Measuring approximately one ten-thousandth of a millimeter in size, this type of nanowire is over a thousand times thinner than a human hair. The resulting memristive component not only takes up a tiny amount of space, but also is able to switch much faster than flash memory.

Nanowires offer promising novel physical properties compared to other solids and are used among other things in the development of new types of solar cells, sensors, batteries and computer chips. Their manufacture is comparatively simple. Nanowires result from the evaporation deposition of specified materials onto a suitable substrate, where they practically grow of their own accord.

In order to create a functioning cell, both ends of the nanowire must be attached to suitable metals, in this case platinum and silver. The metals function as electrodes, and in addition, release ions triggered by an appropriate electric current. The metal ions are able to spread over the surface of the wire and build a bridge to alter its conductivity.

Components made from single nanowires are, however, still too isolated to be of practical use in chips. Consequently, the next step being planned by the Jülich and Turin researchers is to produce and study a memristive element, composed of a larger, relatively easy to generate group of several hundred nanowires offering more exciting functionalities.

Learn more: Artificial Synapses Made from Nanowires

 

 

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Facilitating the early detection of glaucoma

via EYES on EYES OPTICAL

This eye disease often leads to blindness — which might be prevented by early intervention

The team headed by Dr. Jacqueline Reinhard and Prof. Dr. Andreas Faissner from the Department of Cell Morphology and Molecular Neurobiology in Bochum, together with colleagues from the University Eye Clinic in Bochum, RWTH Aachen University, the University of Toronto and the University of Denver, has published a report on their findings. The article was released on 12 October 2018 in the online edition of the journal Molecular Neurobiology.

Specific and early intervention

The researchers bred mice in which the gene PTP-Meg2 (protein tyrosine phosphatase megakaryocyte 2) was mutated . As a result, the animals suffered from chronic intraocular pressure elevation. The team successfully demonstrated that, in their model, the intraocular pressure elevation was associated with a loss of optic nerve fibres and retinal cells. Using functional analyses, they observed that retinal cells were unable to function properly, either. Moreover, they made the following discovery: glial cells and certain components of the immune system showed a reaction in the animals’ optic nerve and retina. As both aspects may be relevant for neurodegeneration, specific and early intervention into these cellular mechanisms may inhibit glaucoma.

Testing new therapy options

Making use of a genetic screening, the researchers subsequently identified new potential biomarkers. In future, these biomarkers may facilitate early detection of glaucoma; as a result, it will be possible to start therapy at an early stage, before the optic nerve and retina are damaged. The glaucoma-mouse model may, moreover, be used to test new therapy options. Experiments to date have shown that intraocular pressure was reduced and nerve cells were retained in the mice if they were given a drug that had been administered to treat human patients.

Learn more: Biomarkers facilitate early detection of glaucoma

 

 

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ReRAM memory chips perform computing tasks, greatly increases computing speed and saves energy

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A team of international scientists have found a way to make memory chips perform computing tasks, which is traditionally done by computer processors like those made by Intel and Qualcomm.

This means data could now be processed in the same spot where it is stored, leading to much faster and thinner mobile devices and computers.

This new computing circuit was developed by Nanyang Technological University, Singapore (NTU Singapore) in collaboration with Germany’s RWTH Aachen University and Forschungszentrum Juelich, one of the largest interdisciplinary research centres in Europe.

It is built using state-of-the-art memory chips known as Redox-based resistive switching random access memory (ReRAM). Developed by global chipmakers such as SanDisk and Panasonic, this type of chip is one of the fastest memory modules that will soon be available commercially.

However, instead of storing information, NTU Assistant Professor Anupam Chattopadhyay in collaboration with Professor Rainer Waser from RWTH Aachen University and Dr Vikas Rana from Forschungszentrum Juelich showed how ReRAM can also be used to process data.

This discovery was published recently in Scientific Reports, a peer-reviewed journal under the prestigious Nature Publishing Group.

Current devices and computers have to transfer data from the memory storage to the processor unit for computation, while the new NTU circuit saves time and energy by eliminating these data transfers.

It can also boost the speed of current processors found in laptops and mobile devices by at least two times or more.

By making the memory chip perform computing tasks, space can be saved by eliminating the processor, leading to thinner, smaller and lighter electronics. The discovery could also lead to new design possibilities for consumer electronics and wearable technology.

How the new circuit works

Currently, all computer processors in the market are using the binary system, which is composed of two states – either 0 or 1. For example, the letter A will be processed and stored as 01000001, an 8-bit character.

However, the prototype ReRAM circuit built by Asst Prof Chattopadhyay and his collaborators processes data in four states instead of two. For example, it can store and process data as 0, 1, 2, or 3, known as Ternary number system.

Because ReRAM uses different electrical resistance to store information, it could be possible to store the data in an even higher number of states, hence speeding up computing tasks beyond current limitations.

Asst Prof Chattopadhyay who is from NTU’s School of Computer Science and Engineering, said in current computer systems, all information has to be translated into a string of zeros and ones before it can be processed.

“This is like having a long conversation with someone through a tiny translator, which is a time-consuming and effort-intensive process,” he explained. “We are now able to increase the capacity of the translator, so it can process data more efficiently.”

The quest for faster processing is one of the most pressing needs for industries worldwide, as computer software is getting increasingly complex while data centres have to deal with more information than ever.

The researchers said that using ReRAM for computing will be more cost-effective than other computing technologies on the horizon, since ReRAMs will be available in the market soon.

Prof Waser said, “ReRAM is a versatile non-volatile memory concept. These devices are energy-efficient, fast, and they can be scaled to very small dimensions. Using them not only for data storage but also for computation could open a completely new route towards an effective use of energy in the information technology.”

The excellent properties of ReRAM like its long-term storage capacity, low energy usage and ability to be produced at the nanoscale level have drawn many semiconductor companies to invest in researching this promising technology.

The research team is now looking to engage industry partners to leverage this important advance of ReRAM-based ternary computing.

Moving forward, the researchers will also work on developing the ReRAM to process more than its current four states, which will lead to great improvements of computing speeds as well as to test its performance in actual computing scenarios.

Learn more: NTU and German scientists turn memory chips into processors to speed up computing tasks

 

 

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Citrus fruit inspires a new energy-absorbing metal structure

300px-Pomelo_cut_one_half

English: One half of a cut honey pomelo Deutsch: Eine Hälfte von einer aufgeschnittenen Pomelo (Photo credit: Wikipedia)

Researchers use a naturally occurring structure to design aluminum materials

It has been said that nature provides us with everything that we need. A new study appearing in Springer’s Journal of Materials Sciencemay lend credence to that claim. Researchers from the Foundry Institute of the RWTH Aachen University in Germany, and Plant Biomechanics Group of the University of Freiburg, Germany, have developed an aluminum hybrid that could be used to optimize technical components and safety materials. And the inspiration came from an unexpected source – the peel of the pomelo fruit (Citrus maxima).

Pomelo fruits have a mass of one to two kilograms, but are able to withstand impact forces resulting from falls of over 10 meters. The fruit’s impact resistance is mainly due to the hierarchical structuring of the peel, which is made up of a graded, fiber-reinforced foam. The new aluminum hybrid is the product of a bio-inspired approach, combining metals with different mechanical properties that reflect these naturally occurring structures and mimic the strength of the pomelo peel.

To make use of the pomelo’s ability to absorb impact energy, the “block mold casting” process was modified, and the pomelo foam’s strut composition was transferred to a metal hybrid. This hybrid consists of highly ductile pure aluminum in the center and a high strength aluminum-silicon alloy in the outer shell.

The composite exhibits a much higher tensile strength (the force needed to break something apart) than pure aluminum, and a much higher ductility (the ability to withstand permanent changes in shape) than the aluminum-silicon alloy. This new combination of materials exhibits a novel behavior under load, and the authors suggest safety materials as the best and most obvious use for the new bio-inspired composite material they’ve created.

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