Sunscreen patches for wounded skin!!

Latex could one day find its way into
specialised sunscreens © Shutterstock

Scientists in France have made a water-resistant latex film loaded with a UVB filter that could be applied as a thick, uniform layer of sunscreen to wounded skin, which is more susceptible to UV damage.

The film, made of nanostructured latex, was built up of soft-core and hard-shell layers by Aggeliki Triftaridou and colleagues at ESPCI-ParisTech, Paris. An amino acid-based surfactant was used as an emulsifier in the place of volatile organic compounds (VOCs).

Elimination of VOCs, traditionally used for their plasticiser effect, is the concept of this work, as Triftaridou explains: ‘The use of an amino acid-based surfactant as an emulsifier rendered the film environmentally friendly and biocompatible, and conferred better mechanical properties to it.’ In the absence of VOCs, the film was cast by water-evaporation, which meant loading an organic UV absorber was going to be challenging.

The team chose 2-ethylhexyl-4-methoxycinnamate (EMC) as their UV absorber over aesthetically less pleasing inorganic absorbers, such as titanium dioxide, which causes whitening of the skin through UV reflectance.

 EMC is used in more than 75% of sunscreens, is highly water insoluble and rarely results in photoallergic reactions. Triftaridou and her team fed EMC directly into the monomer mixture in the reactor in either the core- or the shell-forming step, successfully loading EMC directly into the films without the need for VOCs.

When exposed to UV light, the EMC-loaded film gave zero transmittance values, which demonstrates its sunscreen properties.

Also, the film was able to completely block UV light after being soaked in water for one month or soaked for one month and exposed to sunlight for four days. The water-resistant property of the film is particularly exciting as Triftaridou points out that ‘unlike common sunscreen formulations, the UVB shielding ability remains intact, even after soaking in water’.

 The film also adapts easily to skin motion and is non-sticky to the touch, which as Triftaridou says originates ‘partially from their lightly cross-linked nature and partially from the presence of a continuous hard phase formed by the shells of the soft-core hard-shell particles’.

Jean-François Lutz, head of the precision macromolecular chemistry group at the Institut Charles Sadron, Strasbourg, France, thinks that ‘there are two main innovations in the work: the water-borne core–shell latex that is easy to make and is environmentally friendly; and the utilisation of these latex films as sunscreens’. He thinks the films provide an ‘excellent alternative to all existing commercial products’, adding that ‘this is a clever material with a real commercial potential’.

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Indistinguishable electrons Produced!!

A chip off the semiconductor dot

A new method to produce indistinguishable and coherent electrons has been developed by scientists in France.

The researchers have created a small, electron-emitting chip and used it to produce two single electrons emitted from different sources that are in the same quantum state. This technique is a key step for developing electron-based quantum-information-processing techniques.

Fermionic rules:

Electrons are fermions and so must obey Pauli's exclusion principle that prevents identical fermions from occupying the same state, which leads to anticorrelations or "antibunching". Although this was recognized decades ago, it has proved difficult to perform such an antibunching experiment because electron beams are not coherent – there are many electrons in any system and they all interfere with each other, as well as the environment.

This is what encouraged Erwann Bocquillon and Gwendal Fève at the Ecole Normale Supérieure in Paris, along with colleagues from the Laboratory for Photonics and Nanostructures near Paris and from the Ecole Normale Supérieure de Lyon, to see if indistinguishable electrons could be generated by independent sources, as is done in optics.

"We now understand how electrons move in a system – a very fundamental issue – a lot better. Of course, it is also important to produce such electrons to encode quantum information in the future, but we were most interested in the fundamental proof of concept, in this case," explains Fève.

Restricted movement:

The researchers' electron-emitting "chip" was built using a "very clean" micron-sized bulk-semiconductor sample in which the electrons propagate in very straight lines for several microns in 2D before getting scattered, limiting their interactions. This can be seen as the green plane in the artist's illustration above.

The team then uses a strong magnetic field to further restrict the movement of the electrons to only 1D along the edge of the plane (denoted by the arrows in the illustration), such that single electrons may be guided to each of the emitters – the two small islands of the electron gas located on each side of the picture.

The gold sections next to the emitters represent metallic electrodes deposited on top of the electron gas.
By applying a voltage pulse to the metallic electrode deposited on top of the emitter, the researchers trigger the emission of a single electron to an electronic beamsplitter that is made up of two input and two output arms. Fève told physicsworld.com that their sample is capable of emitting billions of single electrons per second – one electron per nanosecond.

Perfectly synchronized:

"The two sources are perfectly synchronized such that both particles arrive simultaneously on the splitter and perfect antibunching occurs, meaning the two electrons always exit in different outputs," explains Fève.

 That means that if a single electron is sent in one of the input arms with the other input being empty, for example, the electron would escape randomly in one of the outputs. But in the experiment, the two electrons, generated by the two identical, synchronized but otherwise independent emitters would arrive simultaneously at the two input arms of the splitter and would always emerge in two distinct outputs, obeying Pauli's principle.

"This electron antibunching effect can only be explained by quantum mechanics. So it is a quantum interference between two particles and that relates to their indistinguishability. This would only happen for two electrons in the same pure quantum state that has not been affected by interactions with the environment, making the electrons indistinguishable and coherent," says Fève.

But he is also quick to point out that while the team did achieve a high degree of indistinguishability, the electrons were not completely so, meaning that some minimal environmental interaction did occur. "To be able to entangle the electrons, wherein they would violate Bell's inequality, they need to be completely indistinguishable – so this is something we are currently investigating and working on," says Fève.

The researchers are looking at making their sample even smaller so that the electrons travel even shorter distances, while keeping in mind the effects of temperature at such sizes.

Fève says their method shows that it is indeed possible to produce well-controlled single electrons. "Our technique also provides a lot of tenability in terms of the energy and rate at which one would want to produce electron wavepackets, on demand, in the lab," he explains, saying that the degree of control their source offers is its main advantage.

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Nanosilicon produces Hydrogen Instantly!!

Silicon nanoparticles

Silicon nanoparticles could be used to produce hydrogen almost instantly, as they react with water, according to researchers at the University at Buffalo (SUNY) in New York. The reaction does not require any heat, light or electricity and the hydrogen generated could be used to power small fuel cells.

The technology could come in handy as a "just add water" approach to produce hydrogen on demand, says the team. In essence, the technique recovers some of the energy that goes into refining the silicon and producing the nanoparticles in the first place.

Splitting water to produce hydrogen is a clean and renewable way to produce energy, and traditional techniques to split water include electrolysis, thermolysis and photocatalysis.

Water can also react with bulk silicon to produce hydrogen, but this route has been little studied because it is slow. In theory, silicon can release two moles of hydrogen gas per mole of silicon (or 14% of its own mass in hydrogen). Silicon is also abundant on our planet, has a high energy density and does not release any carbon dioxide when it reacts with water.

Faster reaction rates:

Thanks to their high surface to volume ratio, silicon nanoparticles should naturally generate hydrogen much more quickly than bulk silicon. Now, a team led by Paras Prasad and Mark Swihart at Buffalo has shown that the increase in reaction rate is much greater than would be expected based on increased surface area alone.

In fact, nanoparticles 10 nm in diameter appear to produce hydrogen in under a minute, compared with around 45 minutes for nanoparticles that are 100 nm. The 10 nm particles are also 1000 times faster at producing hydrogen than is bulk silicon.

A large group of silicon nanoparticles

 

According to the SUNY team, the difference in hydrogen production rates between the 10 and 100 nm-sized silicon particles is much greater than can be accounted for by the difference in the surface areas of the particles.

To understand this difference, the researchers conducted experiments in which they stopped the reaction before all of the silicon had been fully consumed. As the reaction proceeds, the 10 nm silicon particles reduce in size but do not change shape and remain roughly spherical.

The 100 nm particles, on the other hand, do not uniformly reduce in size but form hollow shells or capsules with walls consisting of a few monolayers of silicon. These walls then slow down the water–silicon reaction because they provide an extra layer through which the reactants must diffuse. Particles that are initially larger also have less surface area per unit volume.

Ideal for powering portable devices:

"With further development, this technology could be ideal for powering small portable devices and might even replace bulky gasoline or diesel generators in the future," says Prasad.

"A typical silicon generator could comprise a small hydrogen fuel cell and some plastic cartridges of silicon nanopowder, to which water would be added when needed, to produce energy," adds team member Folarin Erogbogbo.

Although the technique could probably not be used to generate large amounts of hydrogen, the overall efficiency of the process could be quite competitive with primary batteries and other sources of portable power, which makes it interesting for these applications, Swihart told physicsworld.com.

The researchers have already successfully tested their technique in a small fuel cell that they used to power a fan. They are now planning to study the hollow nanostructures formed by the reaction of the larger silicon particles in more detail and look at how hydrogen can be produced when silicon nanoparticles are mixed with other materials, such as alkali hydrides.

"These hollow 'nanoballoons' may have interesting applications in other areas such as anodes for lithium-ion batteries," explains Swihart. "Alkali-metal hydrides react with water to release hydrogen and produce alkali-metal hydroxides (such as sodium hydroxide, for example) needed to catalyse the silicon reaction with water.

On their own, the metal hydrides are air reactive and unstable, but coating them with silicon nanoparticles might let us increase the hydrogen generation capacity of the system while maintaining an air-stable, easy-to-handle material."

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Environmentally friendly alternative to toxic heavy metals in paint !

An enzyme system could be an environmentally friendly alternative to toxic heavy metal drying agents in paints

 Austrian scientists have shown that an environmentally friendly enzyme, laccase, can be used to replace toxic drying agents in paint.

Currently, water-based paints contain heavy metals that dry the alkyd (polyester) resin films that are used as binding agents by catalysing the oxidative cross-linking of unsaturated fatty acid moieties in the films.

Heavy metals are often toxic, and the commonly used cobalt-based catalysts have recently proved to be carcinogenic, and so alternative materials are being sought.

Enrique Herrero Acero at the Austrian Centre of Industrial Biotechnology, Graz, and colleagues, decided to replace the heavy metal catalysts with a laccase enzyme–mediator-based, non-toxic biocatalyst. Laccases, found in fungi, bacteria and plants, can catalyse the oxidation of mainly phenolic substances, and are already used in other fields, including the food, pulp and paper, and textile industries.

Mediators are small molecules that can be used to broaden the substrate scope of an enzyme by acting as ‘electron shuttles’ between the enzyme and substrate. Herrero Acero faced a challenge in ‘selecting the most effective mediator based on a novel rapid screening procedure’.

The team used a fluorescent sensor system to measure the oxygen concentration in the film as the oxygen is consumed in the cross-linking reaction. The sensor system uses an indicator dye, immobilised in polystyrene, whose luminescence is quenched by oxygen, allowing the progress of the reaction to be monitored in both the emulsion and in the drying film.

1-Hydroxybenzotriazole proved to be an effective mediator for laccase in the oxidation of the alkyd resin, and measurements of the oxygen consumption during the reaction  showed that it proceeded by a two-phase radical mechanism, via peroxy-cross-linking. Using the novel screening technique, Herrero Acero intends to ‘search for novel mediators with higher performance and from renewable sources’.

Andrew Laws, of the University of Huddersfield, UK, and an expert in enzyme catalysis and bioorganic reaction mechanisms, says that ‘the enzyme performs remarkably well considering the environment that it is in’. He anticipates further research into the kinetics of the reaction, as it is not yet as fast as the cobalt-catalysed drying process. Both Laws and Herrero Acero expect future work to involve engineering the laccase enzyme to improve its stability and activity.

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