Evaporating mixtures of two liquids create hypnotic designs
When liquids containing small particles evaporate, those fluids often leave behind fingerprints like coffee rings or whiskey webs (SN: 10/31/19). But liquids mixed with other liquids leave their own distinct residue patterns. An evaporating droplet that contains two fluids can sprout fingerlike protrusions or a chain of smaller droplets around its edge, depending on the liquids in the mixture, researchers report February 14 in Physical Review Letters. The researchers caught these phenomena on video using droplets of isopropanol, a component of rubbing alcohol, mixed with either an antifreeze ingredient called ethylene glycol or another chemical called dodecane. Similar patterns appear in other evaporating fluid mixtures, too. Researchers deposited 1-microliter drops of isopropanol, mixed with either ethylene glycol or dodecane, on a smooth surface. As each drop spread out, the isopropanol evaporated quickly at the edge, where the puddle was thinnest — leaving a higher concentration of either ethylene glycol or dodecane around the puddle’s perimeter. That distending rim ultimately splintered into a ring of smaller droplets. In...