̽��ֱ�� of Cambridge - crystals

New form of ice is like a snapshot of liquid water

cr696 — Thu, 02 Feb 2023 19:00:00 +0000

̽��ֱ��new form of ice is amorphous. Unlike ordinary crystalline ice where the molecules arrange themselves in a regular pattern, in amorphous ice the molecules are in a disorganised form that resembles a liquid.

In their paper, published in Science, the team created a new form of amorphous ice in experiment and achieved an atomic-scale model of it in computer simulation. ̽��ֱ��experiments used a technique called ball-milling, which grinds crystalline ice into small particles using metal balls in a steel jar. Ball-milling is regularly used to make amorphous materials, but it had never been applied to ice.

̽��ֱ��team found that ball-milling created an amorphous form of ice, which unlike all other known ices, had a density similar to that of liquid water and whose state resembled water in solid form. They named the new ice medium-density amorphous ice (MDA).

To understand the process at the molecular scale the team employed computational simulation. By mimicking the ball-milling procedure via repeated random shearing of crystalline ice, the team successfully created a computational model of MDA.

“Our discovery of MDA raises many questions on the very nature of liquid water and so understanding MDA’s precise atomic structure is very important,” said co-author Dr Michael Davies, who carried out the computational modelling. “We found remarkable similarities between MDA and liquid water.”

A happy medium

Amorphous ices have been suggested to be models for liquid water. Until now, there have been two main types of amorphous ice: high-density and low-density amorphous ice.

As the names suggest, there is a large density gap between them. This density gap, combined with the fact that the density of liquid water lies in the middle, has been a cornerstone of our understanding of liquid water. It has led in part to the suggestion that water consists of two liquids: one high- and one low-density liquid.

Senior author Professor Christoph Salzmann said: “ ̽��ֱ��accepted wisdom has been that no ice exists within that density gap. Our study shows that the density of MDA is precisely within this density gap and this finding may have far-reaching consequences for our understanding of liquid water and its many anomalies.”

A high-energy geophysical material

̽��ֱ��discovery of MDA gives rise to the question: where might it exist in nature? Shear forces were discovered to be key to creating MDA in this study. ̽��ֱ��team suggests ordinary ice could undergo similar shear forces in the ice moons due to the tidal forces exerted by gas giants such as Jupiter.

Moreover, MDA displays one remarkable property that is not found in other forms of ice. Using calorimetry, they found that when MDA recrystallises to ordinary ice it releases an extraordinary amount of heat. ̽��ֱ��heat released from the recrystallization of MDA could play a role in activating tectonic motions. More broadly, this discovery shows water can be a high-energy geophysical material.

Professor Angelos Michaelides, lead author from Cambridge's Yusuf Hamied Department of Chemistry, said: “Amorphous ice in general is said to be the most abundant form of water in the universe. ̽��ֱ��race is now on to understand how much of it is MDA and how geophysically active MDA is.”

Reference:
Alexander Rosu-Finsen et al. 'Medium-density amorphous ice.' Science (2023). DOI: 10.1126/science.abq2105

A collaboration between scientists at Cambridge and UCL has led to the discovery of a new form of ice that more closely resembles liquid water than any other and may hold the key to understanding this most famous of liquids.

Our discovery of MDA raises many questions on the very nature of liquid water and so understanding MDA’s precise atomic structure is very important

Michael Davies

Christoph Salzmann

Part of the set-up for creating medium-density amorphous ice: ordinary ice and steel balls in a jar (not amorphous ice)

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Harnessing the possibilities of the nanoworld

sc604 — Wed, 28 Sep 2016 23:00:02 +0000

̽��ֱ��laws of thermodynamics govern the behaviour of materials in the macro world, while quantum mechanics describes behaviour of particles at the other extreme, in the world of single atoms and electrons.

But in the middle, on the order of around 10–100,000 molecules, something different is going on. Because it’s such a tiny scale, the particles have a really big surface-area-to-volume ratio. This means the energetics of what goes on at the surface become very important, much as they do on the atomic scale, where quantum mechanics is often applied.

Classical thermodynamics breaks down. But because there are so many particles, and there are many interactions between them, the quantum model doesn’t quite work either.

And because there are so many particles doing different things at the same time, it’s difficult to simulate all their interactions using a computer. It’s also hard to gather much experimental information, because we haven’t yet developed the capacity to measure behaviour on such a tiny scale.

This conundrum becomes particularly acute when we’re trying to understand crystallisation, the process by which particles, randomly distributed in a solution, can form highly ordered crystal structures, given the right conditions.

Chemists don’t really understand how this works. How do around 10¹⁸ molecules, moving around in solution at random, come together to form a micro- to millimetre size ordered crystal? Most remarkable perhaps is the fact that in most cases every crystal is ordered in the same way every time the crystal is formed.

However, it turns out that different conditions can sometimes yield different crystal structures. These are known as polymorphs, and they’re important in many branches of science including medicine – a drug can behave differently in the body depending on which polymorph it’s crystallised in.

What we do know so far about the process, at least according to one widely accepted model, is that particles in solution can come together to form a nucleus, and once a critical mass is reached we see crystal growth. ̽��ֱ��structure of the nucleus determines the structure of the final crystal, that is, which polymorph we get.

What we have not known until now is what determines the structure of the nucleus in the first place, and that happens on the nanoscale.

In this paper, the authors have used mechanochemistry – that is milling and grinding – to obtain nanosized particles, small enough that surface effects become significant. In other words, the chemistry of the nanoworld – which structures are the most stable at this scale, and what conditions affect their stability, has been studied for the first time with carefully controlled experiments.

And by changing the milling conditions, for example by adding a small amount of solvent, the authors have been able to control which polymorph is the most stable. Professor Jeremy Sanders of the ̽��ֱ�� of Cambridge's Department of Chemistry, who led the work, said “It is exciting that these simple experiments, when carried out with great care, can unexpectedly open a new door to understanding the fundamental question of how surface effects can control the stability of nanocrystals.”

Joel Bernstein, Global Distinguished Professor of Chemistry at NYU Abu Dhabi, and an expert in crystal growth and structure, explains: “ ̽��ֱ��authors have elegantly shown how to experimentally measure and simulate situations where you have two possible nuclei, say A and B, and determine that A is more stable. And they can also show what conditions are necessary in order for these stabilities to invert, and for B to become more stable than A.”

“This is really news, because you can’t make those predictions using classical thermodynamics, and nor is this the quantum effect. But by doing these experiments, the authors have started to gain an understanding of how things do behave on this size regime, and how we can predict and thus control it. ̽��ֱ��elegant part of the experiment is that they have been able to nucleate A and B selectively and reversibly.”

One of the key words of chemical synthesis is ‘control’. Chemists are always trying to control the properties of materials, whether that’s to make a better dye or plastic, or a drug that’s more effective in the body. So if we can learn to control how molecules in a solution come together to form solids, we can gain a great deal. This work is a significant first step in gaining that control.

Reference:
A. M. Belenguer et al. 'Solvation and surface effects on polymorph stabilities at the nanoscale.' Chemical Science (2016). DOI: 10.1039/c6sc03457h

Originally published on the Royal Society of Chemistry website.

Scientists have long suspected that the way materials behave on the nanoscale – that is when particles have dimensions of about 1–100 nanometres – is different from how they behave on any other scale. A new paper in the journal Chemical Science provides concrete proof that this is the case.

It is exciting that these simple experiments, when carried out with great care, can unexpectedly open a new door to understanding the fundamental question of how surface effects can control the stability of nanocrystals.

Jeremy Sanders

Peter Gorges

Snow Crystal Landscape

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New understanding of how shape and form develop in nature

sc604 — Wed, 09 Dec 2015 18:01:07 +0000

Researchers have developed a new method for generating complex shapes, and have found that the development of form in nature can be driven by the physical properties of materials themselves, in contrast with earlier findings. ̽��ֱ��results, reported in the journal Nature, could enable the construction of complex structures from simple components, with potential applications in pharmaceuticals, paints, cosmetics and household products such as shampoo.

Using a simple set-up – essentially droplets of oil in a soapy water solution which were slowly frozen – the researchers found that recently-discovered ‘plastic crystal’ phases formed on the inside surfaces of the droplets causes them to shape-shift into a wide variety of forms, from octahedrons and hexagons to triangles and fibres.

Previous efforts to create such complex shapes and structures have used top-down processing methods, which allow a high degree of control, but are not efficient in terms of the amount of material used or the expensive equipment necessary to make the shapes. ̽��ֱ��new method, developed by researchers from the ̽��ֱ�� of Cambridge and Sofia ̽��ֱ�� in Bulgaria, uses a highly efficient, extremely simple bottom-up approach to create complex shapes.

“There are many ways that non-biological things take shape,” said Dr Stoyan Smoukov from Cambridge’s Department of Materials Science & Metallurgy, who led the research. “But the question is what drives the process and how to control it – and what are the links between the process in the biological and the non-biological world?”

Smoukov’s research proposes a possible answer to the question of what drives this process, called morphogenesis. In animals, morphogenesis controls the distribution of cells during embryonic development, and can also be seen in mature animals, such as in a growing tumour.

In the 1950s, the codebreaker and mathematician Alan Turing proposed that morphogenesis is driven by reaction-diffusion, in which local chemical reactions cause a substance to spread through a space. More recent research, from Smoukov’s group and others, has proposed that it is physical properties of materials that control the process. This possibility had been anticipated by Turing, but it was impossible to determine using the computers of the time.

What this most recent research has found is that by slowly freezing oil droplets in a soapy solution, the droplets will shape-shift through a variety of different forms, and can shift back to their original shape if the solution is re-warmed. Further observation found that this process is driven by the self-assembly of a plastic crystal phase which forms beneath the surface of the droplets.

“Plastic crystals are a special state of matter that is like the alter ego of the liquid crystals used in many TV screens,” said Smoukov. Both liquid crystals and plastic crystals can be thought of as transitional stages between liquid and solid. While liquid crystals point their molecules in defined directions like a crystal, they have no long-range order and flow like a liquid. Plastic crystals are wax-like with long-range order in their molecular arrangement, but disorder in the orientation of each molecule. ̽��ֱ��orientational disorder makes plastic crystals highly deformable, and as they change shape, the droplets change shape along with them.

“This plastic crystal phase seems to be what’s causing the droplets to change shape, or break their symmetry,” said Smoukov. “And in order to understand morphogenesis, it’s vital that we understand what causes symmetry breaking.”

̽��ֱ��researchers found that by altering the size of the droplets they started with or the rate that the temperature of the soapy solution was lowered, they were able to control the sequence of the shapes the droplets ended up forming. This degree of control could be useful for multiple applications – from pharmaceuticals to household goods – that use small-droplet emulsions.

“ ̽��ֱ��plastic crystal phase has been of intense scientific interest recently, but no one so far has been able to harness it to exert forces or show this variety of shape-changes,” said the paper’s lead author Professor Nikolai Denkov of Sofia ̽��ֱ��, who first proposed the general explanation of the observed transformations.

“ ̽��ֱ��phenomenon is so rich in combining several active areas of research that this study may open up new avenues for research in soft matter and materials science,” said co-author Professor Slavka Tcholakova, also of Sofia ̽��ֱ��.

“If we’re going to build artificial structures with the same sort of control and complexity as biological systems, we need to develop efficient bottom-up processes to create building blocks of various shapes, which can then be used to make more complicated structures,” said Smoukov. “But it’s curious to observe such life-like behaviour in a non-living thing – in many cases, artificial objects can look more ‘alive’ than living ones.”

Inset image: Morphogenesis ( ̽��ֱ�� of Cambridge).

Reference:
Denkov, Nikolai et. al. ‘Self-Shaping of Droplets via Formation of Intermediate Rotator Phases upon Cooling.’ Nature (2015). DOI: 10.1038/nature16189.

Researchers have identified a new mechanism that drives the development of form and structure, through the observation of artificial materials that shape-shift through a wide variety of forms which are as complex as those seen in nature.

It’s curious to observe such life-like behaviour in a non-living thing – in many cases, artificial objects can look more ‘alive’ than living ones

Stoyan Smoukov

̽��ֱ�� of Cambridge

Morphogenesis

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Meteorite impact turns silica into stishovite in a billionth of a second

Anonymous — Tue, 13 Oct 2015 12:49:29 +0000

̽��ֱ��Barringer meteor crater is an iconic Arizona landmark, more than 1km wide and 170 metres deep, left behind by a massive 300,000 tonne meteorite that hit Earth 50,000 years ago with a force equivalent to a ten megaton nuclear bomb. ̽��ֱ��forces unleashed by such an impact are hard to comprehend, but a team of Stanford scientists has recreated the conditions experienced during the first billionths of a second as the meteor struck in order to reveal the effects it had on the rock underneath.

̽��ֱ��sandstone rocks of Arizona were, on that day of impact 50,000 years ago, pushed beyond their limits and momentarily – for the first few trillionths and billionths of a second – transformed into a new state. ̽��ֱ��Stanford scientists, in a study published in the journal Nature Materials, recreated the conditions as the impact shockwave passed through the ground through computer models of half a million atoms of silica. Blasted by fragments of an asteroid that fell to Earth at tens of kilometres a second, the silica quartz crystals in the sandstone rocks would have experienced pressures of hundreds of thousands of atmospheres, and temperatures of thousands of degrees Celsius.

What the model reveals is that atoms form an immensely dense structure almost instantaneously as the shock wave hits at more than 7km/s. Within ten trillionths of a second the silica has reached temperatures of around 3,000℃ and pressures of more than half a million atmospheres. Then, within the next billionth of a second, the dense silica crystallises into a very rare mineral called stishovite.

̽��ֱ��results are particularly exciting because stishovite is exactly the mineral found in shocked rocks at the Barringer Crater and similar sites across the globe. Indeed, stishovite (named after a Russian high-pressure physics researcher) was first found at the Barringer Crater in 1962. ̽��ֱ��latest simulations give an insight into the birth of mineral grains in the first moments of meteorite impact.

Simulations show how crystals form in billionths of a second

̽��ֱ��size of the crystals that form in the impact event appears to be indicative of the size and nature of the impact. ̽��ֱ��simulations arrive at crystals of stishovite very similar to the range of sizes actually observed in geological samples of asteroid impacts.

Studying transformations of minerals such as quartz, the commonest mineral of Earth’s continental crust, under such extreme conditions of temperature and pressure is challenging. To measure what happens on such short timescales adds another degree of complexity to the problem.

These computer models point the way forward, and will guide experimentalists in the studies of shock events in the future. In the next few years we can expect to see these computer simulations backed up with further laboratory studies of impact events using the next generation of X-ray instruments, called X-ray free electron lasers, which have the potential to “see” materials transform under the same conditions and on the same sorts of timescales.

Simon Redfern, Professor in Earth Sciences, ̽��ֱ�� of Cambridge

This article was originally published on ̽��ֱ��Conversation. Read the original article.

Inset image: Barringer meteor Crater, Arizona (NASA Earth Observatory).

̽��ֱ��opinions expressed in this article are those of the individual author(s) and do not represent the views of the ̽��ֱ�� of Cambridge.

Simon Redfern from the Department of Earth Sciences discusses a study that has recreated the conditions experienced during the meteor strike that formed the Barringer Crater in Arizona.

United States Geological Survey/D. Roddy

Barringer Crater aerial photo

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Scientists create artificial mother of pearl

gm349 — Tue, 24 Jul 2012 16:04:40 +0000

Mimicking the way mother of pearl is created in nature, scientists have for the first time synthesised the strong, iridescent coating found on the inside of some molluscs. ̽��ֱ��research was published today in the journal Nature Communications.

Nacre, also called mother of pearl, is the iridescent coating that is found on the inside of some molluscs and on the outer coating of pearls. By recreating the biological steps that form nacre in molluscs, the scientists were able to manufacture a material which has a similar structure, mechanical behaviour, and optical appearance of that found in nature.

In order to create the artificial nacre, the scientists followed three steps. First, they had to take preventative measure to ensure the calcium carbonate, which is the primary component of nacre, does not crystallise when precipitating from the solution. This is done by using a mixture of ions and organic components in the solution that mimics how molluscs control this. ̽��ֱ��precipitate can then be adsorbed to surfaces, forming layers of well-defined thickness.

Next, the precipitate layer is covered by an organic layer that has 10-nm wide pores, which is done in a synthetic procedure invented by co-author Alex Finnemore. Finally, crystallisation is induced, and all steps are repeated to create a stack of alternating crystalline and organic layers.

Professor Ulli Steiner, of the Department of Physics’ Cavendish Laboratory at the ̽��ֱ�� of Cambridge, said: “Crystals have a characteristic shape that reflects their atomic structure, and it is very difficult to modify this shape. Nature is, however, able to do this, and through our research we were able to gain insight into how it grows these materials. Essentially, we have created a new recipe for mother of pearl using nature’s cookbook.”

Alex Finnemore, also of the Department of Physics’ Cavendish Laboratory, said: “While many composite engineering materials outperform nacre, its synthesis entirely at ambient temperatures in an aqueous environment, as well as its cheap ingredients, may make it interesting for coating applications. Once optimised, the process is simple and can easily be automated.”

Research paves way for tough coatings fabricated from cheap, abundant materials.

Essentially, we have created a new recipe for mother of pearl using nature’s cookbook.

Professor Ulli Steiner, of the Department of Physics’ Cavendish Laboratory

Cavendish Laboratory

Mother of pearl next to artificial nacre

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