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Magnetic fluid mimics biological pattern formation

作者:冒蝙骝    发布时间:2018-01-02 05:00:11    

By Jacob Aron (Image: Jaakko Timonen) How do you get a bunch of ferrofluid blobs to dance? Place them above a wobbling magnet on a water-repelling surface. Ferrofluids – liquids infused with magnetic nanoparticles – can be manipulated in a magnetic field. While studying their properties, Jaakko Timonen of Aalto University in Espoo, Finland, and colleagues put a small drop of ferrofluid on a superhydrophobic surface. When a magnet was placed underneath, the drop became pointed, and moving the magnet closer caused the drop to split in half. Further reducing the gap generated even more droplets that formed symmetrical patterns, as shown in the video above, which surprised Timonen. “It was a lucky stumble,” he says. The newly formed drops are held apart by a combination of magnetic repulsion and the water-repelling surface, which prevents them from joining together again. They even stay separate once the magnet is removed, because the individual drops don’t have enough energy to reform. Similar static systems are often found in nature – for example, the atoms in a crystal or the folds of a protein automatically arrange themselves in the lowest possible energy state. Other natural structures such as the cytoskeleton, the flexible fibres that form the scaffold of cell membranes, require a continuous supply of energy to self-assemble. It is much harder to create such dynamic structures in the lab, but Timonen realised that moving the magnet back and forth beneath the surface on which several droplets sat would provide the droplets with a continuous supply of energy that lets them form new structures. Sure enough, when the magnet moved quickly enough, the droplets began to merge together. However, stopping the magnet made the droplets revert back to their initial state. A better understanding of this behaviour could teach us more about how dynamic biological structures work. According to Timonen, the ability to split and manipulate drops of fluid could also prove useful for lab-on-a-chip applications, for example to analyse water samples. “You could split a droplet into five smaller droplets and perform a different analysis on each one,” he says. Journal reference: Science, doi:

 

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