Uneven heating in a frying pan causes variance in the surface tension of cooking oil and leads to dry patches that can make food to stick to pans
Source:
https://www.newscientist.com/article/2266479-physicists-finally-figured-out-why-food-sticks-to-a-frying-pan/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home