New form of 'active matter' driven by the dissolution of droplets of an ionic liquid
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" , 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.
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).
 R D Rodgers and K R Seddon, 2003, Science, 302, 5646, 792-793 Issue 24, 2018
Go Totsukawa | EurekAlert!
Researchers develop new lens manufacturing technique
21.05.2019 | Washington State University
Planetologists explain how the formation of the moon brought water to Earth
21.05.2019 | Westfälische Wilhelms-Universität Münster
Engineers at the University of Tokyo continually pioneer new ways to improve battery technology. Professor Atsuo Yamada and his team recently developed a...
With a quantum coprocessor in the cloud, physicists from Innsbruck, Austria, open the door to the simulation of previously unsolvable problems in chemistry, materials research or high-energy physics. The research groups led by Rainer Blatt and Peter Zoller report in the journal Nature how they simulated particle physics phenomena on 20 quantum bits and how the quantum simulator self-verified the result for the first time.
Many scientists are currently working on investigating how quantum advantage can be exploited on hardware already available today. Three years ago, physicists...
'Quantum technologies' utilise the unique phenomena of quantum superposition and entanglement to encode and process information, with potentially profound benefits to a wide range of information technologies from communications to sensing and computing.
However a major challenge in developing these technologies is that the quantum phenomena are very fragile, and only a handful of physical systems have been...
Working group led by physicist Professor Ulrich Nowak at the University of Konstanz, in collaboration with a team of physicists from Johannes Gutenberg University Mainz, demonstrates how skyrmions can be used for the computer concepts of the future
When it comes to performing a calculation destined to arrive at an exact result, humans are hopelessly inferior to the computer. In other areas, humans are...
Scientists develop a molecular recording tool that enables in vivo lineage tracing of embryonic cells
The beginning of new life starts with a fascinating process: A single cell gives rise to progenitor cells that eventually differentiate into the three germ...
29.04.2019 | Event News
17.04.2019 | Event News
15.04.2019 | Event News
21.05.2019 | Materials Sciences
21.05.2019 | Materials Sciences
21.05.2019 | Life Sciences