Like their mythological namesake, Janus particles have two faces: one that attracts and one that repels a liquid. Scientists are interested in the nanoparticles' behaviour because they mimic that of many biological and chemical molecules.
When suspended in solution, the repellent faces cluster together, causing the particles to clump. Francesco Sciortino of the University of Rome La Sapienza and his colleagues have now found that this clumping affects gas-to-liquid phase transitions of the particles. Simulations of up to 5,000 particles in solution show that the clumping creates unusual behaviour: contrary to expectation, the gas phase (pictured above) is more ordered than the liquid phase (pictured right) and the material expands as it cools.
The researchers believe that their simulations could prompt new experimental work with Janus particles.