Researchers from Cambridge University, UK have shown that a specially designed mixture melts in dark and crystallizes in light.
Researchers showed that by using light to heat up the mixture, they were able to lock particles in place and force them to clump together as if they were frozen.
The research team carried out an experiment on a colloid made up of water, polystyrene, and small droplets of oil-coated in DNA to better understand the dynamics taking place between them when warmed by light.
Before getting into how this weird and counter-intuitive thing works, you need to know about Marangoni Effect
What is Marangoni Effect?
The Marangoni effect (also called the Gibbs–Marangoni effect) is the mass transfer along an interface between two fluids due to a gradient of the surface tension. In the case of temperature dependence, this phenomenon may be called thermo-capillary convection (or Bénard–Marangoni convection).
Putting it simply, the contrasting surface tension between oil and water makes each susceptible to variations in temperature in slightly different ways, forcing their particles to scatter.
So, in the current experiment, soft matter physicist Alessio Caciagli and his team coated 20 to 30 micrometer-wide blobs of oil in a polymer that was heavily dusted with single strands of DNA.
These fuzzy oil balls were then combined in a suspension with polystyrene spheres roughly half a micrometre in diameter. The DNA connected the polystyrene to the outer surface of the oil drops, so when the material was suspended in water it formed a loosely bound colloid.
When the team threw light on the interface between the oil and the water, a single polystyrene clump got formed. The laser light caused an increase in temperature of Polystyrene by 5 degrees Celcius which made a temperature gradient against surrounding water.
Although this all sounds like some weird alien stuff but this follows the fundamental laws and doesn’t violate any physics.
As miniaturization increase, we would need more such tools and the research team hopes to find more precise tools to poke things at the nanoscale with the power of light.
“Controlled Optofluidic Crystallization of Colloids Tethered at Interfaces” Physical Review Letters DOI: doi.org/10.1103/PhysRevLett.125.068001