Aerogels are ultra low density materials that have taken the world by storm recently. they have various scientific applications due to their extremely unique properties. Making these aerogels can be quite challenging as achieving the ideal crystalline structure and purity levels desirable for high value applications can get quite difficult. Scientists are on the lookout for creative methods that can create this material with high accuracy and effectiveness. This new study might just have figured out a creative avenue in this need yet.
When we stir a solid like sugar into a liquid, we typically expect the solid to dissolve, scatter and integrate into the liquid. When we try to replicate this process with an insoluble solid with colloids however, something interesting happens, the solid particles start clustering and forming localized clumps within the colloid. This is termed as the Einstein’s tea leaf paradox.
The paradox named after the famous scientist, Einstein’s tea leaf paradox has its name in the specific example that describes the effect where in a cup of tea that is well stirred, the leaves actually concentrate at the periphery, thickening in a donut shape, and then settle at the center of the cup once the stirring is stopped. Although the paradox has been known for over a century, and explained using the concept of secondary flow effect, the reason for nanoparticles behaving this way in a stirred solution is just as convoluted as tea.
Einstein’s Tea Leaf Paradox in Aerogel
A Science Advances research article describes a method exploring the potential applications of Einstein’s tea leaf paradox phenomena in the production of aerogel. A team of researchers led by Ai Du, School of Physics Science and Engineering, Tongji University, Shanghai authored the paper. It includes the behavior and movement of simulated gold nanoparticle spheres dispersed in water when the solution is stirred.
When the researchers calculated the velocity distribution within the flowing fluid, they discovered that the rate at which the particles move appeared to follow the velocity of the fluid’s flow. When the container was divided into several sectors and observed, it discovered that these local high velocity regions were actually due to the stirrer, and these regions were where the particles aggregated due to the paradox. Du hypothesized the reason for this, “We think that this phenomenon is probably due to direct ‘squeezing’ of the liquid created by the stirrer and comes from the mass differences between the nanoparticles and the liquid phase.”
These localized concentrations basically allow nanoparticles to chain up and aggregate to possibly form aerogels. The process was simulated in Gold nanoparticles and were able to obtain high purity crystalline gold aerogel with potential applications in photocatalysis and other specific examples. Typically metal aerogels are made using three methods and using Einstein’s tea leaf paradox could be an interesting way to obtain these aerogels in high purities with the method properly perfected.
Light Bulb moment of the Lead Author
Du actually discovered the effect by accident, due to his habit of consuming tea, as he was cleaning out cups of tea everyday and wanted to clean them out without wasting much water. He ended up rotating the tea leaves and water mixture by rapidly swirling them around by rotating the mug. He was able to get rid of the waste quickly in this way, and this made him look into the effect of Einstein’s tea leaf paradox as a possible method for metal aerogel production.
Du and his colleagues have already started coming up with specific utilization of this method in the making of several different metal aerogels. The phenomena itself could be used to collect particles or molecules in solutions that are dilute enough, and this could have potential applications in various fields like material sciences, life sciences or even environmental engineering according to Du.
