Thursday, December 8, 2011

Controlled disorder: Scientists find way to form random molecular patterns

Scientists at The University of Nottingham have discovered a way to control how tiny flat molecules fit together in a seemingly random pattern.

The researchers have been studying molecules which resemble tiny rhombus/diamond shaped tiles, with a side length of around 2 nanometres -- 2 billionths of a metre.

The fundamental research, published in the journal Nature Chemistry, has shown that they can prompt the 'tiles' to form a range of random patterns by adjusting the conditions in which the experiment is conducted.

Lead author Dr Andrew Stannard, in the University's School of Physics and Astronomy said: "To construct some sort of nanoscale device composed of molecules, one needs to understand how those molecules will interact with one another.

"Typically, a useful device would be one in which the molecules arrange themselves in some perfectly ordered, regular manner. What we have studied here is almost the complete opposite -- we have purposely tried to make the assemblies of molecules as random as possible.

"However, if we can gain a complete understanding of how randomness and disorder arises in these types of molecular structures, we can better understand how to eradicate that disorder when we want to create something functional."

Tilings of various geometrical shapes have interested scientists, mathematicians, and artists for centuries, and a wide range of tilings can be seen adorning many medieval architectural structures, as well as for practical purposes in our more modern kitchens and bathrooms.

But tile effects occur naturally within nature and science too and tilings of rhombuses are of particular interest to physicists, mathematicians and computer scientists because of their ability to form both periodic (regular, repeating patterns) and nonperiodic (random) patterns.

The Nottingham scientists have demonstrated for the first time that the generation of molecular rhombus tilings with varying degrees of orderliness -- some very random, some very ordered -- can be achieved by varying the conditions of the experiment in which they are created.

The achievement is all the more remarkable considering the range of experimental conditions in which this can be achieved is extremely narrow, requiring the scientists to achieve a delicate balance between energy and entropy -- the subjects of the first and second laws of thermodynamics, some of the fundamental laws of physics and, in the case of entropy, are linked to order and disorder within a thermodynamic system.

Story Source:

The above story is reprinted from materials provided by University of Nottingham.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Andrew Stannard, James C. Russell, Matthew O. Blunt, Christos Salesiotis, María del Carmen Giménez-López, Nassiba Taleb, Martin Schröder, Neil R. Champness, Juan P. Garrahan, Peter H. Beton. Broken symmetry and the variation of critical properties in the phase behaviour of supramolecular rhombus tilings. Nature Chemistry, 2011; DOI: 10.1038/nchem.1199

Artificial leaf could debut new era of 'fast-food energy'

In the article, C&EN Senior Correspondent Stephen K. Ritter describes research on electrofuels, made by using energy from the sun and renewable ingredients like water and carbon dioxide, reported at a gathering of experts sponsored by the U. S. Department of Energy's Advanced Research Projects Agency (ARPA-E). Created in 2009 by the American Recovery & Reinvestment Act, ARPA-E is funding electrofuels research, with the goal of developing technologies that improve on nature's approach — photosynthesis. Electrofuels is one of 12 programs funded by ARPA-E.

The artificial leaf is one of the electrofuels technologies. Made of inexpensive materials, the leaf breaks down ordinary water into the oxygen and hydrogen that can power an electricity-producing fuel cell. Just drop the credit-card-sized device into a bucket of water and expose it to sunlight. With the cost-conscious technology, one door-sized solar cell and three gallons of water could produce a day's worth of for a typical American home. The article describes a range of other electrofuel technologies, including ones based on engineered microbes, being developed in the quest for new ways of making fuels.

More information: “Electrofuels Bump Up Solar Efficiency”

Provided by American Chemical Society (news : web)

Spider know-how could cut future energy costs

A report of the research is published this week in the journal .

The finding comes from comparing silk from the Chinese silkworm (Bombyx mori) to molten high density polyethylene (HDPE) - a material from which the strongest synthetic fibres are made. The researchers used polarised light shining through a disk rotating over a plate to study the how fibres are formed as the two materials are spun.

HDPE forms filaments at over 125 C and in addition requires substantial energy input in the form of “shear force” applied to the material in its molten form. Silks, in contrast, in the same set-up forms filaments at ambient temperature and in addition requires only a tenth of the shear force. If the energetic costs of melting HDPE are included for comparison, silks become a thousand times more efficient.

The discovery of low-energy method for fibre formation has led the researchers to view silks as a new class of polymers they call 'aquamelts'.

‘When aquamelts are quickly stretched they lose water, which helps them “lock in” fibre formation like a ratchet,’ said Dr Chris Holland of the Oxford Silk Group, part of Oxford University’s Department of Zoology. ‘This doesn’t happen with your everyday which need to be cooled to preserve the fibres, making them inefficient and harder to process.

‘Silk produced by spiders and silk moths demonstrates combinations of strength and toughness that still outperform their synthetic counterparts. Not only are silks superior to man-made fibres, they are produced at room temperature with just water as a by-product.’

Dr Oleksandr Mykhaylyk, of the University of Sheffield, said: ‘This is in stark contrast to oil-based high performance fibres that require high temperatures and create harmful waste. Whilst the high performance and sustainable credentials of silks are well known, the and silkworm can now add one more to the list, low energy costs.’

Dr Chris Holland said: 'Combining the best of polymer science with biology we were able to determine how much energy is required to form these two fibres. And it seems that we have discovered some fundamental differences between natural and synthetic materials. With hundreds of millions of years of R&D in fibre production it is not surprising that silkworms and spiders have found ways to conserve energy while still making superior fibres.'

However it is not just about saving energy or even money. Dr Oleksandr Mykhaylyk said: ‘The important point of this study are the intellectual advances and fundamental understanding that can be achieved when two normally separate disciplines interact as closely as we did.’

Professor Fritz Vollrath, who leads the Oxford Silk Group at Oxford University, said: ‘This project is about being inspired by Nature to discover and implement things that can help mankind to weather the upcoming storms on our quality of life. This new insight has significant implications for the design and processing of novel bio-inspired synthetic polymers as well as bio-polymer manufacture.’

Provided by Oxford University (news : web)

Bow down to the light: Light-triggered microscale robotic arm makes bending and stretching motions

The tiny robotic arms are made of crystals shaped like micro- or millimeter-sized flat rods. When they are irradiated with (365 nm), the rods bend toward the ; when irradiated with visible light (>500 nm) they stretch back into their original straight shape.

What causes the bending motion? The molecules in the crystals are an organic ring system containing five rings. The central structural unit is a diarylethene group. UV light induces rearrangement of the (isomerization) and causes a ring closure within the molecule. This results in the of each molecule, which leads to a geometry change of the crystal. The crystal contracts, but only where it was exposed to the UV light, that is, on the outer layer of the irradiated side of the rod. This causes bending similar to that of a bimetallic strip. Visible light triggers the reverse reaction, the newly formed sixth ring opens, the original is restored, and the crystal straightens out.

The trick lies in the mixture of two slightly different diarylethene derivatives that are present in just the right ratio. In this type of mixed crystal, the interactions between the individual molecules are weaker than those in a homogeneous crystal. The crystals can withstand over 1000 bending cycles without evidence of fatigue. Depending on the irradiation, it is possible to induce extreme bending—to the point of a hairpin shape.

In contrast to previous concepts for “molecular muscles”, this new approach offers the unique possibility of translating the motion of individual molecules to the macroscopic level. Also, unlike synthetic micromuscles based on polymers, this new microrobotic arm is wireless and responds very fast—even at low temperatures and in water.

If one end of the crystal rod is anchored, alternating irradiation with UV and visible light can be used to induce the loose end to cause a small gear to turn. It can also work as a freight elevator: If attached to a ledge, the rod can lift a weight that is over 900 times as heavy as the crystal itself. This makes it stronger than polymer muscles and equivalent to piezoelectric crystals.

More information: Masahiro Irie, Light-Driven Molecular-Crystal Actuators: Rapid and Reversible Bending of Rodlike Mixed Crystals of Diarylethene Derivatives, Angewandte Chemie International Edition, … ie.201105585

Provided by Wiley (news : web)