
Except in exceptional circumstances, polymers do not crystallize in an extended-chain conformation (spaghetti in a box) but instead are repeatedly folded along the chain and re-enter the crystal. You can see this in the blue and green chains above - the red ones appear to be too short to fold over and re-enter. The length of the chain folds depends on the temperature and can be changed by annealing - another topic for another day.
This is from a simulation effort, but it still is better than the idealized hand drawings like this:

2 comments:
John, which book did you get the lower image from? It looks familiar ... I'm guessing Sperling. - Dave
If it is, it isn't directly - my copy of Sperling went AWOL some time ago. I can't remember where I got it from.
Some of these pictures become iconic and take on a life of their own, constantly being reprinted (with permission from the publisher always duely noted).
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