When you stretch an elastic band, is it only the intermolecular distances that are increasing, or do the individual molecules that make up the band also stretch to some extent? Or maybe the stretching is due to a completely different mechanism that I’m too stupid to imagine?
I have no idea how a rubber band works, but I know that your skin and underlying flesh is stretchy mostly because of a protein called elastin. It’s pretty hydrophobic, meaning that it doesn’t like to be in water (just like oil that way). Since inside your body is a pretty wet environment, elastin clumps up into something that looks like a pile of yarn. When it’s pulled on, however, it stretches out, as if someone pulled on the two ends of the yarn that had been formerly bunched up. As soon as the stretching force goes away, the elastin bunches back up into its preferred-in-a-watery-environment form, snapping the skin back with it. My WAG would be that rubber molecules also tend to adopt a bunched-up form (for some reason unrelated to hydrophobicity), which is pulled straight when the rubber band is stretched but snaps back as soon as it’s allowed.
The conformation of the molecules (i.e. their 3 dimensional shape) changes when you stretch a rubber band. There’s very little increase in the length of individual covalent bonds. Here’s a more detailed discussion of what goes on during stretching.
Thanks, that was a really, really interesting link, Squink.
I’m a bit confused, though, so let me ask: Is the gain in length of the macro elastic band due to the an “opening up” of the individual molecules, eg. instead of looking like this /__\ a molecule might look like this __/.
Given the entropy-based explanation in the link, am I correct in thinking that it would be harder to stretch an elastic band in a hot room than in a cold room? I wonder this because in a hot room wouldn’t there be a tendency for the rotating segments to get energized (heated) from the environment?
Maybe the mechanism is somewhat similar to that of a coiled telephone cord?
I would think high temperatures (to a point) would make it easier to stretch a rubber band – things tend to get more pliable at high temperatures, possibly because bonds are easier to break. But you might not get the same recoil.