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By disrupting the thermodynamic balance of liquids, physicists made them behave very differently from how they do in nature – successfully coaxing liquids into squares and hexagons with right sides, and patterns of networks.
This is not only fascinating in itself, but it could help us better understand how liquids behave under different conditions, which has implications in many fields, from physics to medical research.
“Things in balance tend to be pretty boring,” said physicist Jaakko Timonen from Aalto University in Finland.
“It’s fascinating to drive systems out of balance and see if the out-of-balance structures can be controlled or be of use. Biological life itself is a good example of really complex behavior in a group of molecules that are out of thermodynamic equilibrium. “
You probably regularly see thermodynamic equilibrium without even realizing it. This is the phenomenon that allows your cold milk to mix evenly into your hot coffee, because the temperatures – and therefore the kinetic energy in the molecules – of the two liquids equalize.
But when the thermodynamic equilibrium is upset, interesting things can happen, such as the spontaneous emergence of ordered states. This interests scientists and engineers. It can help us not only to understand thermodynamic equilibrium itself, but also various materials.
The research team, led by Aalto physicist Geet Raju, designed an experiment to explore this. They placed two liquids, oils, of different conductivities and relative permittivities under confinement between two non-wetting flat surfaces to induce an almost two-dimensional plane. Then they applied an electric field.
“When we activate an electric field on the mixture, an electric charge builds up at the interface between the oils,” said physicist Nikos Kyriakopoulos of Aalto University. “This charge density shears the interface out of thermodynamic equilibrium and into interesting formations.”
In nature, liquids are sinuous. In the absence of a container, they form small round and fleshy droplets, linked by their surface tension which contains them in the smallest possible surface. In the team’s experiments, they were led to organize themselves according to patterns that never occur in the liquids of nature.
These included the aforementioned rectilinear geometric shapes, as well as interconnected networks. The team also created tori (donut shapes) that typically don’t occur in nature, as liquid tends to fill the hole in the middle, as well as networks of filaments. They even saw filaments spinning around an axis.
“All of these strange shapes are caused and maintained by being prevented from returning to equilibrium by the movement of electrical charges building up at the interface,” Raju said.
The ability to control the shapes generated by the application of a finely tuned electric field has a wide range of very exciting applications, the researchers said.
For example, it can be used to assemble objects at specific locations in larger structures and for liquid self-assembly. Spinning filaments have implications for particle physics. Last, but not least, is the potential of optics.
“The two-phase system studied here offers interesting possibilities as optical devices due to the exceptional control of the liquid-liquid interface and the fluidic structures with electric field,” the researchers wrote in their paper.
“This will immediately lead to unbalanced voltage-controlled optical diffusers and technologically relevant structural colors based on crystals and photonic glasses by controlling the formation, interactions and self-assembly of the various fluidic structures demonstrated here. . “
The research was published in Scientists progress.
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