'Dancing' holes in droplets submerged in water-ethanol mixtures

June 30, 2018

Tokyo, Japan - Researchers from Tokyo Metropolitan University have observed the formation of holes that move by themselves in droplets of ionic liquids (IL) sitting inside water-ethanol mixtures. This curious, complex phenomenon is driven by an interplay between how ionic liquids dissolve, and how the boundary around the droplet fluctuates. Self-driven motion is a key feature of active matter, materials that use ambient energy to self-propel, with potential applications to drug delivery and nano-machine propulsion.

Most people are familiar with how things mix or dissolve. For example, we know that water and ethanol mix very well at room temperature; take alcoholic beverages. How well they mix depends on the environment the mixture is in, like temperature and pressure.

However, dissolution takes a complex turn when we add another component. A team led by Associate Professor Rei Kurita, Department of Physics, Tokyo Metropolitan University, were studying how an ionic liquid (IL) dissolved in a mixture of water and ethanol. Ionic liquids are liquids composed entirely of ions in ambient conditions; properties like their resistance to drying and ability to dissolve otherwise difficult materials have led to their being referred to as a "solvent of the future" [1], with a focus on how they might play a role in industrial processes e.g. battery production, pharmaceuticals, and recycling.

The team placed a small droplet of IL at the bottom of a mixture of ethanol and water. With the temperature and particular ratio of ethanol to water they used, they expected a boundary or interface to form between the IL and the water-ethanol above it, and for the two to mix gradually. Yet, what they saw was startling: over time, holes emerged inside the IL droplet, and the holes could propel themselves inside the droplet.

They found that this curious phenomenon was the result of how the composition of the water-ethanol mixture naturally fluctuated around the interface. The conditions were such that the mixture is close to a critical point, where small variations in composition can have major consequences. In this case, they were enough to locally promote mixing of the IL into the water-ethanol mixture; the unique way in which ILs interact with water led to even further local changes in composition, leading to a positive feedback loop, or instability. The effect was so drastic that they led to variations in the surface tension, driving the surface to become spontaneously bumpy, form holes, and generate the large flows required to move them around. These holes have been dubbed active holes.

Their discovery paves the way for a broad new class of synthetic active matter, materials that can spontaneously take energy from its surroundings and convert it into motion. With possible applications to drug delivery and propulsion at the nanometer scale, this new phenomenon might inspire investigations into novel industrial uses as well as further accelerate academic interest in active phenomena.
-end-
This work was supported by a JSPS KAKENHI Grant-in-Aid for Scientific Research (B) (17H02945), Scientific Research into Innovative Areas (16K13865) and for Young Scientists (17K14356). The study has been published online in the journal Soft Matter and selected for the back cover of the issue (28 June 2018, Issue 24).

[1] R D Rodgers and K R Seddon, 2003, Science, 302, 5646, 792-793 Issue 24, 2018

Tokyo Metropolitan University

Related Ethanol Articles from Brightsurf:

Spraying ethanol to nanofiber masks makes them reusable
A joint research team from POSTECH and Japan's Shinshu University evaluates the filtration efficiency of nanofiber and melt-blown filters when cleaned with ethanol.

Anaerobically disinfect soil to increase phosphorus using diluted ethanol
Anaerobic disinfection of soil is an effective method to kill unwanted bacteria, parasites and weeds without using chemical pesticides.

Fractionation processes can improve profitability of ethanol production
The US is the world's largest producer of bioethanol as renewable liquid fuel, with more than 200 commercial plants processing over 16 billion gallons per year.

Ethanol fuels large-scale expansion of Brazil's farming land
A University of Queensland-led study has revealed that future demand for ethanol biofuel could potentially expand sugarcane farming land in Brazil by 5 million hectares by 2030.

Measuring ethanol's deadly twin
ETH Zurich researchers have developed an inexpensive, handheld measuring device that can distinguish between methanol and potable alcohol.

Modified enzyme can increase second-generation ethanol production
Using a protein produced by a fungus that lives in the Amazon, Brazilian researchers developed a molecule capable of increasing glucose release from biomass for fermentation.

Scientists develop a chemocatalytic approach for one-pot reaction of cellulosic ethanol
Scientists at the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences have developed a chemocatalytic approach to convert cellulose into ethanol in a one-pot process by using a multifunctional Mo/Pt/WOx catalyst.

New core-shell catalyst for ethanol fuel cells
Scientists at Brookhaven Lab and the University of Arkansas have developed a highly efficient catalyst for extracting electrical energy from ethanol, an easy-to-store liquid fuel that can be generated from renewable resources.

Yeast makes ethanol to prevent metabolic overload
Why do some yeast cells produce ethanol? Scientists have wondered about this apparent waste of resources for decades.

Corncob ethanol may help cut China's greenhouse gas emissions
A new Biofuels, Bioproducts and Biorefining study has found that using ethanol from corncobs for energy production may help reduce greenhouse gas emissions in China, if used instead of starch-based ethanol.

Read More: Ethanol News and Ethanol Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.