Heat a Cold Margarine, Open a Zipper, and Melting Theory

If we heat a solid margarine block or a cheese block on a hot plate, that material will melt starting at a higher temperature surface, the surface that is contact with the surface of the hot plane. The melting process will take place in one direction, from the bottom surface to the top surface. It is impossible for the melting position to jump randomly. Finally, the surface at the farthest position from the hot plate is the last part to melt.

Conversely, if a melted margarine or a melted cheese is contacted to a surface having a very low temperature (for example, touched with ice), then the freezing process will start from the coldest surface. The freezing process will take place in one direction if only one surface is cooled. It is also impossible for the freezing position to jump randomly. In the end, the surface located farthest away from the ice is the last part to freeze.

(left) margarine on a cold plate, (right) margarine just after placed on a hot plate. melting started from the bottom surface and moved upward.

I thought, this phenomenon is similar to opening or closing a zipper. If we open a zipper, the opening location will start from one end and complete at the other end. The opening process always moves in one direction. It is impossible for an open location to jump randomly. Similarly, if we close a zipper, the closed position will move in one direction. Finally, the farthest end will close last. Wow, this is similar to the melting or solidification process of margarine or cheese? Maybe we can model the melting or solidification process by opening or closing the zipper. The closed part of the zipper can be considered as the solid part of the material. The opened part of the zipper can be considered as a melting part of the material. The opening of the zipper can be considered as the melting process of the material. The closing of the zipper can be considered as the solidification process of the material.

I accidentally read an old paper regarding the zipper model for molecules written by Charles Kittel published in the Americal Journal of Physics. I was thinking about how the equation derived by Kittel could be adopted for explaining the melting process of materials. It finally did, and the results have been published in the European Journal of Physics with the title Zipper model for the melting of thin films.  We further developed these results, finally, the second paper has appeared in The European Physical Journal B with the title A new criterion for the melting of nanostructures of arbitrary shapes.

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