A serious physics question: why does oil always come to the edge of the pot?

A serious physics question: why does the oil in the frying pan always run to the side?

in a paper this week, the researchers looked at the hot oil on the pan. They poured a thin layer of sunflower oil into ceramic and Teflon-coated pans, heated the oil, and analyzed its changes (the thickness of the oil film in the experiment was 1.5mm). With heating, the evenly spread oil film always breaks suddenly, leaving an oil-free "hole" in the middle-which may make the food in the middle of the pot more likely to stick to the bottom.

(during heating, the oil film on the pan often forms a hole in the center. Alex Fedorchenko)

the researchers say this phenomenon is due to uneven heating and changes in surface tension. In heating, the heating of the pan is not uniform, and the temperature in the center is generally higher than that on the outside. The surface tension of the oil film will change with the temperature: the higher the temperature, the smaller the surface tension. In this way, the temperature gradient leads to the imbalance of surface tension. When the oil film in the center is thin to a certain extent, it will be torn by the surface tension, leaving a hole in the center.

if you don't want to, you can put in more oil, heat it gently, or use a thick pan (of course, you can stir it frequently). In addition, this is also related to the degree of infiltration of vegetable oil on the pan surface (that is, it is related to the material properties of the pot surface).

the purpose of this study is not just to answer kitchen questions. The process of spreading a uniform liquid film can be used in many places, such as forming a coating or lubricating layer. in order for these processes to proceed smoothly, it is also necessary to understand the conditions for the rupture of the liquid film.

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in addition, a video showing the oil film forming a hole is attached to the press release, but I can't see it very clearly.

have you noticed this phenomenon? I have never seen it because there is so little oil in cooking.

it is really interesting to find a phenomenon in life and use science to explain why it happens.