Pouring out the remaining tea leaves in one go often reveals that there is always tea left inside the cup wall. Therefore, the cup must be connected to tap water once or multiple times until the tea leaves in the cup are completely removed. How to use the principles of physics to solve this practical problem? Obtained from Einstein's tea paradox, rotating the cup in hand and quickly pouring the cup body, tea and water are simultaneously poured out, and it is found that there is no residue of tea in the cup.

Recently, the internationally famous comprehensive journal Science Advances published the research paper of the aerogel research group online under the title of "Einstein's tea leaf paradox induced localized aggregation of nanoparticles and their conversion to gold aerogels". The emergence of this academic achievement is precisely inspired by pouring tea water. The Physics World news website of the British Physical Society highlighted and reported on this achievement in its headline position.

People usually believe that stirring means dispersion. The famous Einstein tea paradox, born a hundred years ago, tells us that when stirring the tea in a cup, the tea leaves do not scatter towards either side of the cup, but rather gather in a circular area resembling a "donut" under the secondary flow caused by stirring, and gather in the center of the cup after stirring stops. Most people have a good understanding of the secondary flow effects of pure fluids and fluids carrying large-sized particles, but there is still little literature on the effects of nanoparticles in fluids.

At that time, the research on high-purity gold aerogel gel was being carried out to extend the "tea paradox" effect to nanofluids. Simulate the movement of nanoparticles with fluid flow rate under stirring conditions, and conduct laser scattering experiments and analysis of scattered light grayscale values on SiO2 nanoparticles dispersion under stirring conditions. This study not only verified the existence of the "tea paradox" effect in nanofluids, but also found the phenomenon of local particle concentration increase and local aggregation of nanoparticles between laminar flows caused by stirrer driving. The local agglomeration effect in nanofluids is very suitable for promoting the rapid aggregation of particles or molecules in low concentration colloids, "said Du Ai.

Based on the above research findings, the research team realized the rapid preparation of high-purity gold aerogels and other metal aerogels by using a simple and continuous stirring strategy. The multiple aggregation effect of nanoparticles under the action of agitation increases the concentration of nanoparticles in the local space of the liquid, greatly promotes the self-assembly and cross-linking of nanoparticles, thus accelerating the gel process of metal nanoparticles.

If the conventional static sedimentation method is used to prepare metal aerogels, the process of gel usually takes about one week. Now only by stirring, the time of gel can be shortened to about 20 minutes, and the effect is amazing.

It was also found that heating could cause a reversible change in the properties of the precursor chloroauric acid solution, making the skeleton size of the aerogel controllable in the range of 10-200 nm. The obtained gold aerogels have good photocatalytic degradation and surface Raman enhancement properties, and have potential applications in the field of environmental treatment and life science in the future.