Bioinspired graphene aerogel for oil spills

Originally appeared on Materials Today

Marine mussels may not be an obvious first step on the route to developing a material to soak up oil spills or act as a chemical sensor, but a team from China’s Xiamen University did just that. Combining the adhesive properties of mussel with the mechanical properties of graphene, they produced a bio-inspired aerogel with high absorption capacity.

Graphene’s unique combination of electrical, thermal and mechanical properties positions it firmly at the top of the nanomaterials agenda. One route to transferring its properties into larger scale structures is to prepare graphene sheets in the form of an aerogel. To do this, the researchers, led by Xi Chen, looked to the properties of dopamine, a molecule that mimics the adhesive proteins found in marine mussels.

Published in Carbon (DOI:10.1016/j.carbon.2014.08.054), Chen’s paper reports on the low-cost development of a nitrogen-doped graphene structure. Because dopamine spontaneously polymerizes, and can modify virtually all material surfaces, it can be a good adhesive. It also a source of nitrogen atoms, which dopes graphene, enhancing its electrocatalytic properties.

A graphene-dopamine gel was first prepared and annealed at 800 °C, to form an ultra-low density aerogel. Structural characterisation showed that the aerogel consisted of a network of twisted and cross-linked graphene sheets that formed nano- and micro-pores. The nitrogen atoms from the dopamine were shown to be incorporated into the carbon–carbon bonds of the graphene, and the aerogel exhibited excellent electrochemical activity. The mechanical properties of the aerogel were also remarkable. A 10 mg piece could sit on a delicate flower without causing any damage, but could also support 5000 times its own weight.

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(a) Photograph of two NGAs (cylinder size: diameter 1.9 cm, length 1.2 cm) standing on a Calliandra haematocephala flower. (b) SEM image of the sample in (a). (c) Typical TEM image of the NGA. (d) HRTEM image of the NGA.

The surface of the aerogel was found to be hydrophobic, so when combined with its remarkable mechanical stability, demonstrated that the aerogel would be an ideal candidate for highly efficient extraction of organic pollutants and oils. In tests, the aerogel was shown to absorb liquids (including pump oil, chloroform and diesel) of up to 156 times its own weight. The absorbed liquids could also be removed by direct combustion in air.

The team are confident that their graphene-aerogels have a wide range of potential applications, from use as a suction skimmer in marine oil spillage, to an electrode material for electrochemical sensors.

This paper was originally published in Carbon 80 (2014) 174–182

To read more about this article, click here.

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Engineering a room-temperature multiferroic, in theory…

Appeared on Materials Today on 14 October 2014 (Be warned, it’s a bit more technical than most of my posts)

A group of theoreticians have demonstrated that the key to producing a room temperature multiferroic may lie with a new family of perovskite materials.

Often described as the “holy grail” of data storage, room temperature multiferroic materials have been at the forefront of functional materials research for two decades. And the reason is that they are ‘adaptable’. Multiferroic materials simultaneously exhibit two often contradictory properties – they can be both electrically charged (ferroelectric) and maintain a permanent magnetic field (ferromagnetic). In principle at least, it is possible to control the magnetic phase of multiferroic materials with an applied electric field, and to control their electric polarization with an applied magnetic field.

A collaboration of Chinese and US scientists now report that by inducing structural distortions in a specific family of perovskite superlattices, it is possible to create a new room-temperature multiferroic. Published in Computational Materials Science [DOI: 10.1016/j.commatsci.2014.09.011], the paper describes the first-principles approach used by Xifan Wu and his colleagues to explore the functionalities of this material group, ATcO3 (A = Ca, Sr, Ba). In 2011, ATcO3 was experimentally shown to be antiferromagnetic. In this work, density functional theory investigations of the structural instabilities in perovskites found that a mismatch between BaTcO3 and CaTcO3 could induce ferroelectricity at the interface. The researchers also found that the Néel temperature of their superlattice – that is, the temperature above which ferromagnetic order is lost – is 816K, making this theoretical material a multiferroic at room temperature.

A mismatch between two different materials can be induced either because of epitaxial strain – a result of different lattice spacing between crystals – or by “engineering” the interface. Earlier work has shown that epitaxial strain in perovskite superlattices can result in ferroelectricity. But Wu and his team used a thorough theoretical approach to demonstrate that enhanced ferroelectricity can be induced by interface engineering. The Néel temperature of both BaTcO3 and CaTcO3 is well above room temperature, meaning that the superlattice maintains its unique magnetic ordering and ferroelectric properties at vastly-elevated temperatures relative to most multiferroics.

This paper presents a theoretical approach, so the team now await experimental confirmation of their results. If successful, this discovery may lead to a material whose magnetic properties can be easily controlled at room temperate, and, eventually, to a new generation of extremely low-power magnetic storage devices.

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Dear Ada

It is Thursday 14th October 2014, and I’m writing you this letter to you from the comfort of my desk. But I’m not using paper and ink, I am using a laptop computer – an electronic device that translates magnetic zeroes and ones into images, text, symbols and music. It does all of the things that you and Charles Babbage envisioned in his Analytical Engine, and much more. This letter won’t be sent by post either, instead it will be instantly viewable from all over the Earth, thanks to a worldwide network of cables that transmit information as packets of light (yes, really!) and electronic platforms that orbit the Earth – they’re called satellites, but we don’t have time to go into that!

Really, I want to use this opportunity to try to express just how important you have been to women like me, and to help you realise the role you’ve had to play in forging the path for us. The world has changed a lot since you left it – the 14th October is now officially known as Ada Lovelace Day, a global celebration of your legacy and of all women working in science, technology, engineering and mathematics (STEM for short). Your mother did the world a great service in raising you surrounded by science, mathematics and machines, unlike so many of your contemporaries. These days, millions of young women study maths and science subjects at school. Whilst we’ve not yet reached parity in all STEM subjects – this year, 2 out of every 5 students who took A-level maths (exams taken aged ~18) were female – progress is slowly being made.

Women are no longer banned from universities and can earn degrees, with record numbers now graduating in STEM subjects. There are thousands of female professors scattered across the science landscape (not as many as I’d like!), and their skills and talent have not gone unnoticed – there are schemes and campaigns across the world that aim to encourage more women to study and work in STEM sectors. Engineering is becoming so popular that over 50,000 people have watched engineers dance around the streets of London, and every week, scientists and mathematicians speak to millions of people across the globe.

Fifty years after your death, an inventor and visionary from Sweden, Alfred Nobel, founded the Nobel Prizes, which aimed to reward scientists whose discoveries “…have conferred the greatest benefit on mankind.” If only you had been around to see it, you’d have been in with a shot :) As it stands, sixteen women have been awarded Nobel Prizes in the fields of medicine, physics and chemistry – far too few in my estimation. But I am hopeful that in time, we’ll see changes there too.

Today, STEM-women are developing the world’s fastest car, building some of its tallest structures, and searching out and inventing “the next big thing“. They lead the world’s largest computing companies and govern some of its major nations. Many of us fail to make quite that impact, but have forged valuable careers – across the world, millions of women are working at various levels in the STEM-world. Some of us found a home-away-from-home in writing about science, while others solve challenges in the lab every day. But we do it because we love it – science simply makes me happy.

200 years after your birth, you may not have expected your name to live on. But it has, and today is the day we all remind ourselves why. To my mind, what you, and the generations of female STEM-pioneers who followed you, did was to open the door, so that the rest of us can pass through. Sir Issac Newton was once quoted as saying “If I have seen further it is by standing on ye shoulders of giants”, and for me, that is true for all women now working in  science, technology, engineering and mathematics – we owe a great debt of gratitude to you Ada. Thanks for being the first.

Highest Regards,

Laurie Winkless

** Written for Ada Lovelace Day 2014 **

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Wearable, stitchable photovoltaics

Originally appeared here

Korean researchers have created a textile-based organic photovoltaic cell that can be stitched into fabric and used as a wearable power source for personal electronic devices.

Organic photovoltaics (OPVs) have been of interest to researchers for years, but recently, they entered the commercial and industrial sectors, for use in energy harvesting applications. OPVs are flexible, easy to produce and lightweight, allowing companies to develop and deploy self-powered wireless sensors at a low cost. But, a collaboration between Kyung Hee University and electronics giants Samsung may have an impact on a very different audience – individual consumers. Published in Nano Energy [doi: 10.1016 /j.nanoen.2014.06.017], the team report on the development of a textile-based OPV that can be stitched directly into clothing, and could be used to power the next-generation of wearable devices.

Producing power from materials that are both lightweight and flexible, involves complex materials engineering. Recent work on photovoltaic wires (fibres that act as individual solar cells) has shown potential, but the process remains slow and costly. And film-based OPVs have shown low compatibility with textiles. Dukhyun Choi and his team took a different approach, by developing an inexpensive polymer-blend-based OPV, which sits on a large-area woven textile electrode that can be stitched directly onto standard textiles.

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Choi and his team developed a novel fibre architecture for the electrode materials. Consisting of polyethylene terephthalate (PET), coated with copper, nickel and gold, each individual fibre is 10um in diameter, and flexible enough to be assembled into bundles. These bundles were then woven into a 5cm2 square and added to the fabric of a child’s t-shirt. The fibre was found to be mechanically durable, but that it formed into a curved surface, rather than the ideal flat electrode surface. The OPV itself consists of layers of oxides and two blended polymers, with a thin layer of indium tin oxide (ITO) acting as the top electrode.

Although the textile-based OPV performed well mechanically, its power conversion efficiency was found to be relatively low, at ~1.8%. The team believe that this can be explained by the poor contact between the textile electrode and the polymer OPV. However, their device showed a short circuit current density higher than that of a typical OPV. With some design changes, the team believe that their approach will open the way to a power source for next-generation of wearable electronics.

Nano Energy (2014) doi: 10.1016 /j.nanoen.2014.06.017

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Tougher carbon fibre using CNTs

Originally appeared here: http://www.materialstoday.com/composites/news/tougher-carbon-fibre-using-cnts/?sf4650592=1

Engineers from McGill University have definitively demonstrated that multi-wall carbon nanotubes (MWCNTs) can improve the mechanical toughness of carbon fibre laminates.

Carbon fibre composites have been in widespread use for decades – in Formula1, such materials form the chassis of every car, and up to 50% of an aircraft’s structure is now composite-based. It is all about their mechanical properties – when compared to metals, composites offer a superior strength-to-weight ratio, so in mass-critical applications, carbon fibre composites are the material of choice.

But the performance of these materials is not defined by the individual fibres – when it comes to determining damage initiation and growth in the composite, it is the properties of the polymer matrix that dominate. The most widely used polymeric resins tend to provide high stiffness but low fracture toughness, which can result in delamination in the final composite. Now, a team from Quebec’s McGill University have a demonstrated that the inclusion of multi-wall carbon nanotubes (MWCNTs) in the matrix significantly improves its fracture toughness, leading to a new generation of tougher carbon fibre composites.

Published in Carbon 79 (2014) 413-423 [DOI: 10.1016/j.carbon.2014.07.084], this work focused on modifying the brittle thermoset resin used in most carbon-based composites. Two different formulations were used – in the first, functionalised MWCNTs were mixed with the resin. The second formulation combined functionalised MWCNTs with a more traditional acrylate-based toughening agent. A technique called Resin Film Infusion (RFI) was then used to flow the MWCNT-filled resin through layers of carbon fibre mats, to produce the laminated composites. RFI is used in the aerospace industry to produce composites impregnated with rubber particles, but McGill researcher Pascal Hubert used it to ensure an even dispersion of aligned carbon nanotubes throughout the resin.

Fracture toughness tests were carried out on the MWCNT-filled resins and on the final laminates. The mechanical properties of the raw polymer resins were only marginally improved by the addition of MWCNTs. But, the final laminated composites exhibited significant improvement in their delamination properties (up to 143% in the case of Mode II fracture toughness). Hubert and his team believe that when the resin flows through the carbon fibre fabric, the fibres act as a sieve, ensuring a more even dispersion of MWCNTs, and improved mechanical properties. The team believe that this work can lead to a new generation of nano-enhanced carbon fibre composites, but further work on scaling up their system is still needed.

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No Lab Coat Needed logo

What do you think guys? It took me all of 3 mins to do! I am hoping to get a proper designer to create something a bit “sexier” soon, but I think this will do for the moment :)

LOGO

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Vibration filtering in nature: how a spider hears

This article appeared here on 29th August

A collaboration of US and EU researchers has found that the viscoelectric properties of a spider’s leg helps it to detect vibrations

Biological sensory organs help us to receive, interpret and respond to environmental stimuli. In the world of invertebrates, these sensors are remarkably complex – spiders ‘hear’ – or more accurately, sense vibrations – through strain-sensitive grooves, called lyriform organs, distributed along their legs. One species of nocturnal spider found in Central America -Cupiennius salei – optimizes its ‘hearing’ by sitting on mechanically stiff plants, ensuring that vibrations from nearby prey, predators or sexual partners can be easily sensed.

The lyriform organ is extremely sensitive to substrate vibrations – at high frequencies (> 40 Hz) deflections as small as 10-9 – 10-8 elicit a response in the leg. As well as being highly sensitive, the system can also filter out low-frequency background noise – a challenge facing those designing bio-inspired sensing systems. An international team of researchers believe that they have discovered how this ‘filter’ works, and say that their results will establish a basis for bio-inspired sensor design.

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Led by the Georgia Institute of Technology [Acta Biomaterialia (2014) DOI:10.1016/j.actbio.2014.07.023], this work focused on the mechanical properties of a skin-pad close to the sensory organ. The pad is found between the metatarsus (second-last segment) and tarsus of each leg, adjacent to the lyriform organ. Earlier research suggested that this pad contributed to the filtering mechanism, but details were unclear. By using surface force spectroscopy (SFS), the team directly measured the mechanical response of the pad’s viscoelastic surface. By mapping the pad’s surface at a range of temperatures (between 15–40 °C) and frequencies (from 0.05 to 40 Hz), it was possible to define the thermomechanical behavior of the material under typical environmental conditions experienced by the spider.

The group found that the viscoelastic properties of the pad surface were highly temperature-sensitive. At around 20 °C, it became highly viscous, meaning that the spider is particularly sensitive to substrate vibrations at this temperature. This matches closely with the environment Cupiennius – the mountainous region it inhabits has an average night-time temperature of 19 °C. The viscoelastic properties of the pad also define the filtering effect at low frequencies – the mechanical contact between the pad and the tarsus displays a higher effective modulus at high frequencies than at low frequencies. This suggests that mechanical energy is more efficiently transmitted to the sensory grooves at high frequencies.

While more research is needed, the authors believe that this work will help in the design and development of efficient bio-inspired sensors.

To download the article related to this news story, please click here.

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