Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Attraction or Repulsion?

23.04.2020

Interactions of chemically active particles can be as complex as human relationships

Researchers at the Max Planck Institute for Dynamics and Self-Organization show that two microscopic non-equilibrium chemically active particles, such as enzymes or catalytically active colloids, can have a vast range of complex interactions reminiscent of human relationships, instead of just simple attraction and simple repulsion.


Comparison between the exact and approximate solutions for interaction of two chemically active particles.

© MPIDS / B. Nasouri & R. Golestanian

Chemically active particles, such as enzymes or colloids, can propel in a liquid by converting chemical energy into mechanical work. A special characteristic of these particles is that they can violate Newton's third law: for a system of two particles, action and reaction are not necessarily equal, nor are they always in opposite directions.

Despite this peculiarity, however, the relative interaction of these particles when they are in their simplest possible form, i.e. isotropic and equally sized, was previously thought to be straightforward: either purely attractive (in which case particles come together and form a complex), or purely repulsive (wherein the particles separate indefinitely), as in positive and negative charges in electrostatics.

In a new paper, just published in Physical Review Letters, Babak Nasouri and Ramin Golestanian from the Department of Living Matter Physics at the Max Planck Institute for Dynamics and Self-Organization (MPIDS) show that the interaction between such particles through chemical signalling and modification of their surrounding liquid is much more complex.

Not just a simple attraction or repulsion: it’s complicated!

When it comes to studying the behaviour of these particles, the complexity of the underlying mechanisms often hinders thorough theoretical investigations and one has to resort to approximations.

A widely used approximation scheme in this context that has so far informed our theoretical understanding of the behaviour of this system is the so-called 'far-field' approximation, which assumes that the distance between the particles is always considerably larger than their sizes.

The far-field approximation predicts that the interaction between two such chemically active particles can be non-reciprocal, which is very non-intuitive, but despite that, it is always either purely attractive or repulsive, when gauged relatively.

“Non-reciprocity of interactions is a rather remarkable feature that we are familiar with at the level of human interactions – e.g. B might like A but A might not like B – but is fundamentally new for microscopic particles, and is a manifestation of their non-equilibrium activity”, says Golestanian, director of the Department of Living Matter Physics at MPIDS.

Although the widely used approximate far-field solution simplifies the governing equations quite significantly, in many cases, it can lead to incorrect predictions for the behaviour of the system.

According to Nasouri and Golestanian, the relationship between two chemically active particles cannot always be categorized as purely attractive or repulsive. For example, the particles may move together as a stable bound-state with a constant nonzero equilibrium distance maintained between them.

In this case, the particles repel each other if they get any closer than a certain distance, and attract each other if they separate any farther. They may also do the exact opposite, which can lead to the formation of an unstable complex that can be broken apart under sufficient perturbations or agitations. Nasouri and Golestanian show that the existence of these two new regimes of behaviour is due to the 'near-field' effects, which are completely ignored in the far-field description of the system.

“It is very difficult to decide what can or cannot be ignored in modelling these complex systems,” says Nasouri, the first author of the study. “Approximate solutions are very useful for shaping our basic understanding of a system,” Golestanian adds, “but we cannot get the full picture without accurately, and if possible exactly, solving the governing equations.”

The underlying mechanism

Through an exact theoretical approach (which accounts for both near-field and far-field interactions), the authors show that the emergence of these two new regimes is due to a self-generated neighbour-reflected effect. When the particles are close to one another, each particle is affected by its own activity reflected back from its neighbour.

“It is as if each particle acts as a mirror for its neighbour,” says Nasouri. He adds, “This reflection can work against the attraction or repulsion coming from the neighbouring particle, and that creates these new regimes of behaviour.”

Wissenschaftliche Ansprechpartner:

Babak Nasouri, Ramin Golestanian, MPIDS Göttingen, Germany

Originalpublikation:

"Exact Phoretic Interaction of Two Chemically Active Particles", Babak Nasouri and Ramin Golestanian, Phys. Rev. Lett. 124 (2020) 168003, doi 10.1103/PhysRevLett.124.168003

Carolin Hoffrogge | Max-Planck-Institut für Dynamik und Selbstorganisation
Further information:
http://www.ds.mpg.de/

More articles from Physics and Astronomy:

nachricht FAST detects neutral hydrogen emission from extragalactic galaxies for the first time
02.07.2020 | Chinese Academy of Sciences Headquarters

nachricht First exposed planetary core discovered
01.07.2020 | Universität Bern

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electrons in the fast lane

Solar cells based on perovskite compounds could soon make electricity generation from sunlight even more efficient and cheaper. The laboratory efficiency of these perovskite solar cells already exceeds that of the well-known silicon solar cells. An international team led by Stefan Weber from the Max Planck Institute for Polymer Research (MPI-P) in Mainz has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell. Clever alignment of these "electron highways" could make perovskite solar cells even more powerful.

Solar cells convert sunlight into electricity. During this process, the electrons of the material inside the cell absorb the energy of the light....

Im Focus: The lightest electromagnetic shielding material in the world

Empa researchers have succeeded in applying aerogels to microelectronics: Aerogels based on cellulose nanofibers can effectively shield electromagnetic radiation over a wide frequency range – and they are unrivalled in terms of weight.

Electric motors and electronic devices generate electromagnetic fields that sometimes have to be shielded in order not to affect neighboring electronic...

Im Focus: Gentle wall contact – the right scenario for a fusion power plant

Quasi-continuous power exhaust developed as a wall-friendly method on ASDEX Upgrade

A promising operating mode for the plasma of a future power plant has been developed at the ASDEX Upgrade fusion device at Max Planck Institute for Plasma...

Im Focus: ILA Goes Digital – Automation & Production Technology for Adaptable Aircraft Production

Live event – July 1, 2020 - 11:00 to 11:45 (CET)
"Automation in Aerospace Industry @ Fraunhofer IFAM"

The Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM l Stade is presenting its forward-looking R&D portfolio for the first time at...

Im Focus: AI monitoring of laser welding processes - X-ray vision and eavesdropping ensure quality

With an X-ray experiment at the European Synchrotron ESRF in Grenoble (France), Empa researchers were able to demonstrate how well their real-time acoustic monitoring of laser weld seams works. With almost 90 percent reliability, they detected the formation of unwanted pores that impair the quality of weld seams. Thanks to a special evaluation method based on artificial intelligence (AI), the detection process is completed in just 70 milliseconds.

Laser welding is a process suitable for joining metals and thermoplastics. It has become particularly well established in highly automated production, for...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International conference QuApps shows status quo of quantum technology

02.07.2020 | Event News

Dresden Nexus Conference 2020: Same Time, Virtual Format, Registration Opened

19.05.2020 | Event News

Aachen Machine Tool Colloquium AWK'21 will take place on June 10 and 11, 2021

07.04.2020 | Event News

 
Latest News

Rising water temperatures could endanger the mating of many fish species

03.07.2020 | Life Sciences

Risk of infection with COVID-19 from singing: First results of aerosol study with the Bavarian Radio Chorus

03.07.2020 | Studies and Analyses

Efficient, Economical and Aesthetic: Researchers Build Electrodes from Leaves

03.07.2020 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>