Fractals in a tear of plastic

Mar 13, 2015 • 7:37 PM UTC

China Basin, San Francisco, CA 94107, USA

140x Magnification

Plants

Manu Prakash

I am a faculty at Stanford and run the Prakash Lab at Department of Bioengineering at Stanford University. Foldscope community is at the heart of our Frugal Science movement - and I can not tell you how proud I am of this community and grassroots movement. Find our work here: http://prakashlab.stanford.edu

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“Beauty of science is everywhere around us” – I was caught saying this phrase recently; and I wanted to share more of this beauty with everyone. This time I decided to look at the curious phenomena of what happens when you cut a piece of plastic film; but with a blunt object. Say you decide to open that CD case you just bought (who buys CD’s still – but please, just go with my story). You opened it in a with your key chain or your ball point pen and threw that piece of plastic covering.
Pick it up and look at the edge.

Wow – the edge of freshly cut or torn piece of plastic is actually a fractal structure. The edge is ruffled up in many curvy lines (to me, it looks like a cauliflower leaf edge). Look closely; put it in a foldscope; and you will find that the same pattern is repeated also at the microscale. So it is a true fractal (to a certain magnification); so when you see up close, you see the same pattern repeat as before. Isn’t that funny.
Here are some images of the fractal pttern using a foldscope. It turns out; the reason leaves edges have these fractal pattern is not that far from why a torn piece of thin plastic will also have these patterns. The physics of formation of these wrinkles is not that far from the biology of folding of a leaf edge.
Try this yourself; you will be surprised.
Surprisingly, I was also able to image the stress pattern in a stretched piece of plastic. It forms a beautiful ladder network – this one I really need to think hard about. It seems like the stretching of a piece of plastic is never uniform; and it leads to this ladder network. Now I a really puzzled – what gives rise to this ladder network. I don’t think anyone knows the answer as yet. Can you find out?