Scientific sensation: Hungarian researchers discover new state of matter

Researchers at the HUN-REN Wigner Research Centre for Physics have discovered a new state of matter, in which liquid droplets behave as actively moving, interacting particles under the influence of an electric field. Their findings could open new avenues in precision technology.

Researchers Péter Salamon and Marcell Tibor Máthé from the HUN-REN Wigner Research Centre for Physics have been studying a recently discovered special type of liquid known as ferroelectric nematic liquid crystals. They observed that the surface of ferroelectric nematic liquid droplets becomes unstable in an electric field, forming fractal-like liquid extensions.

What is a Ferroelectric Nematic Liquid?

Ferroelectric nematic materials are composed of elongated, asymmetric molecules that are highly polar, meaning their two ends carry opposite electrical charges – one positive and one negative. The uniqueness and rarity of the ferroelectric nematic phase lie in the fact that its molecular arrangement does not cancel out the individual charge distributions. Instead, the molecular polarizations add up, resulting in a spontaneous electric polarization of the material. Although the analogy is not perfect, ferroelectric nematic liquids can be thought of as the electrical counterparts of magnetic fluids (ferrofluids). Although their existence was predicted over a century ago, it was only in 2017 that scientists successfully synthesized such a material for the first time.

During the research, scientists observed that when a higher voltage was applied to the liquid droplets, their behavior became even more extreme: they lost their droplet shape and formed complex, maze-like structures. The researchers also found that when an alternating voltage was applied within a specific frequency range, the droplets began to move while changing shape. During movement, the droplets repelled each other and collided like particles, resembling active objects such as swarming insects, microbes, or microrobots. The researchers were also able to control the motion of the droplets using voltage, suggesting potential applications in new types of microfluidic devices. This discovery could have practical benefits in fields such as medical diagnostics, chemical analysis, and biotechnology.

The researchers also observed that this movement was accompanied by sound emission. The surprising phenomenon was explained through spectral analysis of the sound, which indicated that the droplets undergo mechanical vibrations when exposed to alternating voltage. The characteristic frequencies of these vibrations corresponded to the driving signal’s frequency and its second harmonic. The researchers published their findings in the prestigious journal Nature Communications.