Tiny Particles Defy Rules of Motion to Move Together

Topic: Physics

Researchers at Tokyo University of Science created a system where tiny particles moved together without pushing each other. This was made possible by nonreciprocal interactions, which are not symmetrical. The team observed that larger particles attracted smaller ones more strongly than vice versa.

Many things in nature and the lab move because they use energy to generate motion. These systems are called active matter. Researchers have been interested in how individual units or agents interact with each other. They want to know how these interactions can lead to new forms of collective motion and self-organization.

A team led by Professor Yutaka Sumino and Assistant Professor Kiwamu Yoshii at Tokyo University of Science, Japan, created a system where particles moved together without pushing each other. This was made possible by nonreciprocal interactions, which are not symmetrical. The team observed that larger particles attracted smaller ones more strongly than vice versa.

To create this system, the researchers suspended tiny polystyrene particles in water between two transparent electrodes. They applied an alternating electric field, which caused electrohydrodynamic (EHD) flows to develop around the particles. These EHD flows increased with particle size, making larger particles attract smaller ones more strongly than vice versa.

The team observed that particles of different sizes spontaneously paired up and formed asymmetric structures. These pairs behaved like self-propelled units, moving through the suspension even though individual particles couldn't propel themselves.

Why It Matters

This research can help us understand how complex systems behave and interact with each other. It also has implications for fields like materials science and engineering, where understanding collective motion is crucial for developing new technologies.

Key Facts

• A team of researchers at Tokyo University of Science created a system where tiny particles moved together without pushing each other.
• The system was made possible by nonreciprocal interactions, which are not symmetrical.
• Larger particles attracted smaller ones more strongly than vice versa due to electrohydrodynamic (EHD) flows.
• The team observed that particles of different sizes spontaneously paired up and formed asymmetric structures.
• This research has implications for fields like materials science and engineering.

Key Terms

Nonreciprocal interactions

Interactions where one particle affects another more strongly than it is affected in return.

Implications

This research can help us understand how complex systems behave and interact with each other. It also has implications for fields like materials science and engineering, where understanding collective motion is crucial for developing new technologies.