A team of physicists at the University of Vermont have discovered a fundamentally new way surfaces can get wet. Their study may allow scientists to create the thinnest films of liquid ever made—and engineer a new class of surface coatings and lubricants just a few atoms thick.
A third way
To understand the new physics, imagine what happens when rain falls on your new iPhone: it forms beads on the screen. They’re easy to shake off. Now imagine your bathroom after a long shower: the whole mirror may be covered with a thin layer of water. “These are two extreme examples of the physics of wetting,” says UVM physicist Adrian Del Maestro, a co-author on the new study. “If interactions inside the liquid are stronger than those between the liquid and surface, the liquid atoms stick together, forming separate droplets. In the opposite case, the strong pull of the surface causes the liquid to spread, forming a thin film.”
More than 50 years ago, physicists speculated about a third possibility—a strange phenomena called “critical wetting” where atoms of liquid would start to form a film on a surface, but then would stop building up when they were just a few atoms thick. These scientists in the 1950s, including the famed Soviet physicist Evgeny Lifshitz, weren’t sure if critical wetting was real, and they certainly didn’t think it would ever be able to be seen in the laboratory.
Then, in 2010, the Nobel Prize in physics was awarded to two Russian scientists for their creation of a bizarre form of carbon called graphene. It’s a honeycombed sheet of carbon just one atom thick. It’s the strongest material in the world and has many quirky qualities that materials scientists have been exploring ever since.
Graphene turns out to be the “ideal surface to test for critical wetting,” says Del Maestro—and with it, the Vermont team has now demonstrated mathematically that critical wetting is real.
Read more: Making quantum puddles
thumbnail courtesy of phys.org