In a bag of combined nuts, after shaking, smaller nuts fill out the spaces created at the bottom, pressing the bigger Brazil nuts to the top. Credit: Melchoir, CC BY-SA 3.0, by means of Wikimedia Commons
Physicists from the University of Utrecht and the Faculty of Physics at the University of Warsaw have actually observed– for the very first time experimentally– the Brazil nut result in a mixture of charged colloidal particles. Up until now, it was thought that an increase of external energy was needed to develop this effect– but the researchers had the ability to validate that the procedure can take place spontaneously. The findings, published in The Proceedings of the National Academy of Sciences (PNAS), might find applications in a broad range of fields, from geology to soft matter physics.
Have you discovered that after such an action, the biggest nuts in the mix– Brazil nuts– float to the top? The phenomenon of large objects rising to the surface area of a mixture of little items, bearing the professional name of granular convection, is commonly referred to “the Brazil nut impact” and happens frequently in nature.
This uncommon effect contradicts the intuition that heavier items ought to sink to the bottom due to gravity and inertia force. This is the case with the phenomenon of sedimentation, common in nature, a process involving the sinking of strong particles dispersed in a liquid, under the influence of gravity or inertia forces. Sedimentation plays a function in processes such as the formation of sedimentary rocks, and is also utilized to purify water and wastewater or isolate cells from blood.
Physicists from the University of Utrecht and the Faculty of Physics at the University of Warsaw have observed– for the first time experimentally– the Brazil nut impact in a mixture of charged colloidal particles. Have you discovered that after such an action, the biggest nuts in the mix– Brazil nuts– float to the top? Up until now, it was thought that an increase of external energy, such as shaking the bag, was essential to create the Brazil nut result. As the scientists point out, although in both granular (e.g., nut) and colloidal mixtures the “Brazil nut result” occurs, the mechanisms for its formation are entirely various. In the case of a nut mix, as a result of shaking, smaller nuts fill in the spaces created at the bottom, pressing the larger nuts to the top.
Brazil nut result in charged colloids
Up until now, it was believed that an increase of external energy, such as shaking the bag, was needed to produce the Brazil nut effect. The theoretical estimations were validated experimentally for the very first time by a group of speculative and theoretical physicists from the University of Utrecht and the Faculty of Physics at the University of Warsaw.
” We have actually revealed that the Brazil nut effect can happen in a mixture of charged colloidal particles driven exclusively by Brownian motions and repulsion of electrical charges,” highlights Jeffrey Everts from the Faculty of Physics at the University of Warsaw, who, under the instructions of René van Roij of the Institute for Theoretical Physics of the Utrecht University, performed the theoretical estimations for the experiment. Marjolein van der Linden, working under the direction of Alfons van Blaaderen of the Debye Institute for Nanomaterials Science of Utrecht University, was accountable for the speculative part of the research study.
Colloidal mix
The scientists utilized charged polymethylmethacrylate particles with different sizes (large and small) to bring out the experiment. A low-polar solvent, cyclohexyl bromide, was used as a distributing representative.
As the scientists mention, although in both granular (e.g., nut) and colloidal mixes the “Brazil nut effect” happens, the systems for its development are completely various. When it comes to a nut mixture, as an outcome of shaking, smaller sized nuts complete the spaces created at the bottom, pushing the larger nuts to the top. The charged particles in the colloid make Brownian motion as a result of crashes with the surrounding solvent particles.
” Each particle is positively charged. Much heavier but bigger particles have a higher charge, so they push back each other more highly, making them move upward more quickly than smaller however lighter particles,” Jeffrey Everts describes.
The discovery of the “Brazil nut effect” in mixes of colloidal particles can be used in lots of fields from geology to soft matter physics. It can also find application in industry such as in the stability of paint and ink.
Referral: “Realization of the Brazil-nut result in charged colloids without external driving” by Marjolein N. van der Linden, Jeffrey C. Everts, René van Roij and Alfons van Blaaderen, 24 February 2023, Proceedings of the National Academy of Sciences.DOI: 10.1073/ pnas.2213044120.