(ORDO NEWS) — The idea of freezing particles by heating them is, to put it mildly, contrary to common sense. But physicists have shown how specially designed mixtures “melt” in the dark, but crystallize as soon as the light comes on, thanks to their unique thermal activity.
The researchers showed that by using light to heat the mixture, they were able to hold the particles in place and make them stick together as if they were frozen.
Researchers at the University of Cambridge in the UK have experimented with a colloid composed of water, polystyrene and small oil droplets to better understand the dynamics between them when heated by light.
Thus, it is logical to assume that if we heat the slurries of oil by focusing on the boundary with its aqueous environment, we can expect the mixture of molecules to oscillate moving towards cooler areas and causing the fluids to move.
There is even a term for this flow of oil and water; Marangoni effect.
Simply put, the contrasting surface tension between oil and water makes them susceptible to temperature fluctuations in slightly different ways, causing particles to scatter.
The laser beam raised the temperature of the polystyrene by about 5 degrees Celsius, creating a heat gradient against the surrounding water.
Light has proven to be a fairly versatile tool for manipulating particles.
Harnessing the optical properties of a laser to create a “thermal magnet” is another way we might one day be able to assemble molecular-scale machines.
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