#immiscibility

Scientists discover method to prevent coalescence in immiscible liquids

A team of chemical engineers from Université PSL, CNRS, Harvard University and chemical company Calyxia, has discovered a way to prevent or delay coalescence in some immiscible liquids. In their paper published in the journal Science, the group describes how experiments they conducted led to the discovery of a way to get some fluids such as water and oil, to remain as an emulsion for long periods of time without the use of surfactants. It is widely known that when two immiscible liquids, such as water and oil are mixed, they do not remain so for very long—they slowly separate into two layers. This is because they never really mix to begin with; instead, they coexist as droplets that coalesce when they come into contact with one another.

Improving alloys: Researchers successfully establish a strong mechanical bond of immiscible iron and magnesium

Conventional transportation equipment relies heavily on steel. But steel is heavy, and scientists are turning to alternatives in the quest to improve the safety and speed of transportation, while simultaneously lessening its environmental footprint.

Magnesium alloys, with their low density and excellent strength-to-weight ratio, are considered the next-generation base metal for multi-material design and have been touted as a possible replacement for conventional steels when appropriate.

Although progress has been made in overcoming certain weaknesses associated with magnesium alloys, such as flammability, developing bonding technology that bonds magnesium alloys with structural steels has been severely limited because magnesium and iron are immiscible and do not form at the alloy phase.

Yet, a research group from Tohoku University has succeeded in establishing a dealloying bonding technology that obtains a strong mechanical bond between iron and magnesium. The findings are published in the journal Scripta Materialia.

Chemists tackle the tough challenge of recycling mixed plastics

Plastics are everywhere in our daily lives, but not all plastics are created equal—far from it.

Take, for instance, polyethylene terephthalate, a plastic used to make soda bottles and clothing fibers. Then there's high-density polyethylene, from which shampoo bottles, milk jugs and cutting boards are derived. Don't forget polystyrene for packaging, or low-density polyethylene, which gives us cling wrap and grocery bags.

All of these are plastics, which are the most widely used types of polymers—macromolecules made of repeating units of small molecules called monomers. Post-consumer plastics are almost always collected as a mixed stream of waste, and products are often manufactured from two or more types of plastics.

The bad news is that these items, though all "plastics," are chemically and physically incompatible, and there's no good industrial method for reusing or re-processing them into other useful products. That's why most of those "recyclables" you're throwing into bins every week are going to a landfill. Even after careful sorting and separation into individual plastics, mechanical recycling usually yields inferior products, termed down-cycling.

Can oil and water mix?

Common experience tells us that oil and water do not mix. Yet, it turns out that they can mix when oil is dispersed as small droplets in water. This strange behavior has long vexed scientists because there is no explanation for it. A team of EPFL and ICTP scientists have studied this question using novel optical technology and discovered the mechanism by which these two neutral and immiscible compounds can in fact mix together and form emulsions. The answer lies in the electrical charge distribution at the interface.

For more than hundred years, chemists have wondered about this question: How can tiny oil droplets exist in water without any stabilizing molecules? "After all, water molecules have such strong and favored interactions with one another that they do not like to incorporate molecules that do not participate in these interactions," says Prof. Sylvie Roke, the lead investigator of the study.

Indeed, oil and water segregate from one another when simply mixed. However, with sufficient input of energy in the form of ultrasound, droplets of oil with sizes less than 1 micron form in pure water and continue to exist for several weeks or months. Curiously when placed in an electric field, the droplets move towards the positive electrode. Thus, mixing neutral oil and neutral water results in negatively charged oil droplets. Unsurprisingly, the source of this unexpected charge has been heavily debated.

Maryland engineers open door to big new library of tiny nanoparticles: A new study expands the landscape of nanomaterials -- and what we can do with them

The development of bimetallic nanoparticles (i.e., tiny particles composed of two different metals that exhibit several new and improved properties) represents a novel area of research with a wide range of potential applications. Now, a research team in the University of Maryland (UMD)'s A. James Clark School of Engineering has developed a new method for mixing metals generally known to be immiscible, or unmixable, at the nanoscale to create a new range of bimetallic materials. Such a library will be useful for studying the role of these bimetallic particles in various reaction scenarios such as the transformation of carbon dioxide to fuel and chemicals.

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The study, led by Professor Liangbing Hu, was published in Science Advances on April 24, 2020. Research Associate Chunpeng Yang served as first author on the study.

"With this method, we can quickly develop different bimetallics using various elements, but with the same structure and morphology," said Hu. "Then we can use them to screen catalytic materials for a reaction; such materials will not be limited by synthesizing difficulties."

Unique interface and unexpected behavior help explain how heavy metals act

Refining platinum, plutonium, or certain other metals often depends on how the metal behaves at liquid interfaces. The challenge? Scientists have limited ways to analyze the details of liquid interfaces. Now, researchers described in significant detail how water molecules surround a platinum-based ion. Their description includes an unexpectedly complex structure that forms on the liquid's surface. The team noticed no less than three different forms of water wrapping around the ion. The complex water structure is unexpected and it creates unusual behaviors compared to those observed around smaller and lighter ions under similar conditions.

Refining platinum and other precious metals involves moving the desired metal from one liquid to another. But little is known about how that transfer works on the molecular scale. This work helps explain how platinum and other heavy metals move and react across liquids.

Solvent extraction, the go-to technology for reprocessing nuclear waste or refining rare earths and precious metals, involves the preferential transfer of a targeted chemical species between two immiscible phases through a liquid-liquid interface. Relatively little molecular-scale information is known about the mechanism or mechanisms of this transfer across an interface. Why? In large part, the knowledge gap is because most experimental probes cannot interrogate liquid interfaces directly. Even the best surface sensitive probes are only sensitive to limited components of interfacial structure.

Oil and water really do mix—simulating the world of micro-hydrodynamical phenomena

Have you ever wondered why milk is so white or why mayonnaise appears so thick and yet it can flow out of the bottle?

Are you aware that these such substances are just oil and water mixed together though they look and feel like neither of them?

It turns out that these delightful little mysteries often cause major headaches for chemical engineers designing a shampoo production process or running an oil recovery facility in the North Sea. IBM Research and the Science and Technology Facilities Council's (STFC) Hartree Centre are using mathematics and high-performance computing to help these engineers understand the science behind this conundrum.

Understanding the behaviour of colloids – macroscopic mixture of insoluble particles – remains a challenging task of immense practical importance. We find systems all around us, in these seemingly mundane products such as milk, mayonnaise or shampoos, through everyday weather events like mist, clouds or (alas!) pollution, up to large industrial processes in chemical engineering. Often these mixtures exhibit some surprising behaviours where the whole is more than just a sum of the parts. The scientific research into this area has a long and illustrious history but the recent addition of HPC to our science toolkit allows us to explore cases which are either too difficult for classical analysis or too expensive for experimentation.