Researchers from the Czech Academy of Sciences have found the cause of a phenomenon that makes life difficult for cooks and casts a shadow on manufacturers of non-stick cookware. This is a typical situation when an abnormal zone forms in the center of the frying pan, in which the food burns as if there is no protective coating and the metal is not oiled. It turned out that the roots of this phenomenon are the same as that of the well-known wine tears effect, it is also the Marangoni effect (the phenomenon of transfer of matter along the interface between two media, which occurs due to the presence of a surface tension gradient - ed. By TechCult).
By itself, Teflon is not a universal protection of products from sticking to metal - on the contrary, the video recorded by Czech researchers clearly shows that the cause of the problem is the formation of a dry spot in the center of the pan. Oil literally flows out of there due to the effect of thermocapillary convection (Benard - Marangoni convection). This usually happens in a mixture of liquids with different surface tensions, where moisture flows to where it is greater. A classic example is alcohol and water in alcohol, which is why drops in a glass of wine are even able to rise up the wall.
In the case of a non-stick coating, the surface tension of the oil changes when heated, so if the pan heats up unevenly and the central area heats up faster, then the oil begins to move towards the walls. This process is not instantaneous, so if you pour more oil, take a frying pan with a thick bottom, heat slowly over the entire bottom area, then the Marangoni effect will not gain strength. Finally, simply stirring the food while cooking and tilting the pan to let the oil flow back and forth saves most of the trouble.