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

People usually believe that stirring means dispersion. The famous Einstein tea paradox, which was born a century ago, tells us that when stirring the tea in a cup, the tea does not spread to either side of the cup, but rather gathers in a circular area resembling a "donut" under the secondary flow caused by stirring, and after stirring stops, it gathers in the center of the cup. Most people have a better understanding of the secondary flow effects of pure fluids and fluids carrying large-sized particles, but there is still little literature mentioning the effects of nanoparticles in fluids.

At that time, the research on high-purity gold aerogel gel was being carried out to try to extend the "tea paradox" effect to nanofluids. We simulated and studied the motion law of nanoparticles accompanied by fluid flow velocity under stirring conditions, and conducted laser scattering experiments and analysis of scattered light grayscale values on SiO2 nanoparticle dispersion under stirring conditions. This study not only verified the existence of the "tea paradox" effect in nanofluids, but also found the phenomenon of increased local nanoparticle concentration and localized nanoparticle aggregation between laminar flows caused by agitator driving. The local agglomeration effect in nanofluids is very suitable for promoting the rapid aggregation of particles or molecules in low concentration colloids.

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.