A bimetallic strip is a band of two metals attached in parallel that expand at different rates in response to temperature changes, thus bending the band, often used for measuring temperature. A bike project I'm attempting would be greatly improved if I had a band that bent in response to moisture changes. Specifically, brake/rim dust being fed back into the braking system is considered the top factor for rim wear in wet weather riding, and I've attached a prototype sponge to my brake pads to clean the rim when I brake.
It works well but I don't have the sponge on all the time since it would just be rubbing a dry rim, and it's a pain to engage, so if I want to make it useful to more than just tinkerers it needs to auto-engage. There are a lot of other issues to consider even if I had a material that bent when wet, but this is the thing I know the least about how to design.
I would like to tinker with an arm that closes a 2-5mm gap when wet from rain. A separate sponge or squeegee will deal with brake dust primarily, but some possible contamination from brake dust and road salts should be expected.
The closest thing I've been able to find is a polymer sheet that dances around on a wet surface, which tells me it could be done, but there's got to be a simpler way.
Even using something like a strip of swellstop (a rubber+sand compound for sealing concrete) glued to a non-expanding rubber might work, but I suspect swellstop doesn't contract when dry, and probably doesn't dry quickly either.
It's relatively easy to find materials that expand when wet, but seems hard to find ones that return to their original shape when dry.
Do I really have to resort to "smart" polymers? Is anyone familiar with a material that is less exotic that could fill my need?
Finally, if I can't find one, what's my next step? I'm a dog flying an airplane when it comes to designing something like this from scratch, do I need a team of PhDs? Where would I even start?