蒸发过程中的一种新机制被发现

Evaporation is so common that everybody thinks it's a well understood phenomenon. Appearances can be, however, deceptive（迷惑的）. Recently, a new, earlier not predicted mechanism of evaporation was discovered. Experiments and simulations performed at the Institute of Physical Chemistry of the Polish Academy of Sciences and the Institute of Physics of the PAS not only confirm its existence, but also indicate that it plays the crucial role in evaporation process in the nanoscale. Too hot? It's not only because of summer. It's also likely that the sweat on your skin stopped to evaporate efficiently enough. Evaporation affects the "climate" inside our body, but is equally important for the climate of the entire planet -- and for how fast laundry dries or how efficient car engines are, as well. In spite of its omnipresence（无所不在） in the human environment, the physicists still do not fully understand its course after 130 years of research efforts. Now, thanks to experiments and simulations performed by research teams at the Institute of Physical Chemistry of the Polish Academy of Sciences (IPC PAS) and the Institute of Physics of the PAS (IP PAS), the secrets of evaporation finally came to light.

"Usually you can easily predict what will be the beginning or the end of a given physical process. Answering the question, which path is selected by nature to complete the process, is much more difficult. For evaporating droplets, it had since long been known that temperatures -- before the evaporation started and after it was completed -- were the same. But what occurs between these two moments in time, so when all this is happening? That was the question we didn't know a good answer for," says Prof. Robert Hołyst (IPC PAS).

Existing theoretical models of the evaporation process assumed that the rate of evaporation depends on how fast the molecules attach to or detach from the surface of a liquid. The measurements indicated, however, that during evaporation a barrier should be formed on the droplet surface, hindering the molecules to cross the liquid-vapour (or vapour-liquid) interface. Recent experiments carried out by various research groups worldwide have proven, however, that such a barrier does not exist, and virtually every molecule falling on the liquid surface does not detach from it. The researchers noticed also a clear temperature jump at the interface between the droplet and its surrounding, and found that pressure remains constant during evaporation. These effects were not predicted by the existing theoretical models.