Identification of hidden key behind liquid-liquid transition

Structural origin of the liquid-liquid transition.
© 2015 Ken-ichiro Murata, Hajime Tanaka

A University of Tokyo research group has successfully identified a microstructural unit that controls liquid-liquid transition between two phases in a single substance with multiple liquid phases. Identifying this unit is key to understanding liquid-liquid transitions.

It is widely known that even a single-component substance can have more than two crystals, as in the case of carbon (diamond and graphene) and water. Contrarily, it was thought that as a liquid is a disordered state there is only one liquid state for a single-component substance. Liquid-liquid transition in such single-component substances has attracted considerable attention as a new type of phase transition, overturning the conventional view of liquids. However, although much evidence suggestive of its presence has been gathered, the existence of liquid-liquid transitions is still an ongoing debate due to experimental difficulties. To prove the existence of liquid-liquid transitions, it is necessary to experimentally identify the micro structure governing liquid-liquid transition on a microscopic level.

Professor Hajime Tanaka’s research group at the Institute of Industrial Science have successfully identified a structural unit that controls a liquid-liquid transition by using an organic liquid, triphenyl phosphite, which has a transition under ambient pressure. The research group observed the target liquid by irradiating it with X-rays and found that the new liquid formed after the transformation has a higher density of clusters composed of several molecules.

Professor Tanaka says “A liquid state is one of the fundamental states of matter besides gas and solid, and an important physical state universal to a wide range of materials including metals, semiconductors, and organic materials. Thus, our finding not only contributes to our understanding of the underlying mechanism of liquid-liquid transition, but also provides a new insight into the liquid phase, which has been believed to be uniform and random, and leads to a deeper understanding of the very nature of the liquid state.”

Paper

Ken-ichiro Murata and Hajime Tanaka, “Microscopic identification of the order parameter governing liquid-liquid transition in a molecular liquid, "Microscopic identification of the order parameter governing liquid-liquid transition in a molecular liquid", Proceeding of the National Academy of Sciences of the United States of America Online Edition: 2015/4/27 (Japan time), doi: 10.1073/pnas.1501149112. 

Fundamental physicists discover surprise new use for super-chilled neutrons to measure the movement of viruses.

•    First evidence that ultra-cold neutrons interact with moving nano-sized particles provides a new tool for chemists, biologists and engineers

•    Billiard-ball collisions may also explain inaccuracies in 60-year-old experiments to measure the lifetime of the neutron and explain the origin of matter in the universe

Physicists working on a 60-year-old experiment to understand the origin of matter in the universe have uncovered a new tool for studying the movement of tiny particles along a surface, such as a virus travelling along a cell membrane. The new tool utilises ultra-cold neutrons (UCNs) that move slower than most people can run and will allow scientists to map the movement of tiny objects with previously unattainable precision. This discovery, made at the Institut Laue-Langevin, the world’s flagship centre for neutron science and the home of ultra-cold neutron research for over 25 years, is published today in Crystallography Reports.

Since their discovery in 1969, UCNs have been used by experimental physicists to answer fundamental questions about the universe, such as the origin of matter and how gravity fits into the standard model of particle physics. They do this by collecting them in traps and monitoring properties such as their energies or lifetime at high precision.

However, the average storage time of the UCNs in their traps was always much lower than expected, affecting the quality of observations. In 1999 Dr Valery Nesvizhevsky and colleagues at the ILL discovered a new phenomenon that might explain these losses. They found that occasionally a UCN in the trap was given a small thermal ‘kick’. This occurred in just 1 out of every 10,000,000 collisions, but the origin of this ‘kick’ was unknown.
As other hypotheses were ruled out, Dr Nesvizhevsky started to consider the influence of the nanoparticles or nanodroplets which were known to populate a layer immediately above the surface of most materials, including those of the trap’s interior.

To tests this hypothesis Dr Nesvizhevsky and his colleagues returned to the UCN apparatus at the ILL. They placed samples with nanoparticle surface layers of known size distribution into the UCN trap and observed the interactions.
The team discovered that the change in UCN energy was induced by ‘billiard-ball-like’ collisions with moving surface nanoparticles, thus providing the first proof that these nanoparticles are not stationary.

The low energy levels of UCNs means they usually bounce off the inner walls and remain in the trap. However these shots of extra energy caused by the interaction with the nanoparticles gives them just enough energy either to overcome gravity and escape out of the top of the chamber, which is left open, or to pass right through the chamber walls.

This phenomenon has two very dramatic consequences:

1. It could explain discrepancies in the results of 60-year-old experiments measuring the lifetime of the neutron, the results of which differ by about 10 seconds, much more than the reported uncertainties would allow. A precise figure could affect conclusions on the origin of matter in the early universe, as well as on the number of families of elementary particles existing in nature, and could modify models of star formation.
2. It also gives science a brand new and uniquely accurate tool for studying for the very first time how nanoparticles move around and interact with material surfaces, particular through van der Waals/Casimir interactions, in all kinds of natural and man-made systems. Currently no other techniques exist to make these measurements.

Potential applications of this technique are vast and include the production of chemicals and semiconductors, catalytic converters, integrated circuits used in electronic devices and silver halide salts used in photographic films. The tool could also be used to study for the first time how biological molecules move along a surface such as viruses along a biological membrane.
For their next experiments, Valery and his colleagues have secured further beam time at the ILL and will be inviting scientists from various disciplines to provide samples from their own research for analysis with UCNs to prove the validity of this new technique.

Quotes

Dr Valery Nesvizhevsky said: “We found this brand new scientific tool by chance. We never thought UCNs might have such practical uses. The implications of these findings for fundamental physics are sure to be a hot topic and I expect there will be some debate as to how much these thermal kicks contribute to the uncertainties around the lifetime of the neutron measurements. However the potential in this new technique for studying nanoparticle dynamics is a certainty and we look forward to working with researchers from across the scientific disciplines to realise its potential.”

Dr Valentin Gordeliy is heads of the Membrane Transportation Group at the Institut de Biologie Structurale and has met with Dr Nesvizhevsky to discuss the possible application of the new ultra-cold neutron technique in his own line of research: “This is a great piece of science and if its feasibility can be verified, a potentially very exciting discovery for my own work in structural biology. In the human body there are a great many nano-scale structures, the motions of those correspond to time-scale of this technique. These include viruses, and various proteins and protein complexes including histones, the scaffolds of DNA that regulate the expression of genes, helping turning them on and off. One of the most attractive objects for study would be membrane proteins that help maintain the health of the whole body and are therefore targeted by 60% of existing drugs. Whilst other tools such as electron microscopes can be used they are not suitable to study dynamics. Also the possibility of watching the evolution of complex interactions such as that of a virus and a membrane protein would provide new insights for drug discovery as well as a better understanding of how our body functions.”

Source: http://www.ill.eu/news-events/press-room/press-releases/fundamental-physicists-discover-surprise-new-use-for-super-chilled-neutrons-to-measure-the-movement-of-viruses-september-2013/

MIT and Harvard create new state of matter: Photonic molecules

MIT and Harvard create new, lightsaber like state of matter: Photonic molecules

The awesomely named Center for Ultracold Atoms, a joint Harvard and MIT venture, has created a new state of matter: photonic molecules. This new state of matter is surprising and interesting, as photons are considered to be massless and incapable of interacting with each other. According to the research group’s leader, who has the unbelievably coincidental surname Lukin, these photonic molecules behave somewhat like lightsabers from the Star Wars universe, with the photons pushing and deflecting each other, but staying linked.

Almost the entirety of our understanding of light is predicated on the knowledge that photons, the elementary particle that makes up the quantum of light and all other electromagnetic radiation, are massless and have no electric charge. If you shine two lasers at each other, because the streams of photons have no mass or charge, the streams of photons simply pass through each other without reacting. It is for this reason that light (and EMR in general) is such a great medium for transmitting data over long distances, and for perceiving visual stimuli with your eyes. If you used almost any other kind of particle to transmit data, it would react violently and fizzle in the atmosphere almost instantly.

Now, however, the Harvard and MIT researchers, led by Lukin, have managed to make photons behave almost as if they’re normal, massive particles. To do this, the researchers pump rubidium atoms into a vacuum chamber, and then cool the vacuum down until it’s a few degrees from absolute zero. Extremely weak laser light — a stream of single photons — is then shone through the rubidium-filled vacuum. As individual photons travel through the medium, it loses energy to the rubidium atoms, slowing down. When the researchers used the laser to fire two photons, instead of one, they found that the photons became a two-photon molecule by the time it left the medium.

A highly informative diagram, showing the attraction (F) between the two photons in a photonic molecule

These photonic molecules have been theorized to exist, through an effect called the Rydberg blockade, but this is the first time that this new state of matter has been physically realized. Unlike a normal molecule, where the constituent atoms are held together by chemical bonds caused by opposite electron or nuclei charges, these photonic molecules aren’t really held together. Basically, as each photon travels through the medium and pushes against the rubidium atoms, they pushed back towards each other, forcing the two photons to coexist. “It’s a photonic interaction that’s mediated by the atomic interaction,” Lukin said. “That makes these two photons behave like a molecule, and when they exit the medium they’re much more likely to do so together than as single photons.”

As with all new effects, and more so with new states of matter, Lukin and co aren’t entirely sure what practical applications these photonic molecules might have. As we mentioned previously, the way these photonic molecules jostle against each other isn’t completely unlike the way two lightsaber clash in Star Wars. There’s also the fact that photons are our best bet for quantum networking — but performing logic with photons, because they don’t like to interact with each other, is hard. These photonic molecules might provide a solution to this problem. Being an entirely new state of matter, though, we really won’t know what’s possible until we perform a lot more research — which is exactly what the Center for Ultracold Atoms plans to do.

Source: http://www.extremetech.com/extreme/167439-mit-and-harvard-create-new-lightsaber-like-state-of-matter-photonic-molecules