2
$\begingroup$

At the macroscopic level a simple metal file or rasp creates a large amount of friction in one direction and a much smaller amount in the opposit direction. Shark skin displays the same properties due to very fine scales.

Are there any materials with a surface that displays similar behaviour at a microscopic level? also what would this effect/property be called?

I have been searching using 'anisotropic friction' and 'directional friction' but sofar haven't found anything that achieves this due to microscopic effects.

$\endgroup$

3 Answers 3

1
$\begingroup$

It has been engineered, based on observations hair patterns of insects

...

(Droplet slides down when substrate is oriented so that the hairs point downwards, while it was attached in the first two orientations)

In nature, it is useful e.g. for butterflies who need to expel water droplets from their wings: the droplets slide out thanks to the outward pointing hair.

$\endgroup$
0
$\begingroup$

I rather doubt it, depending on the definition of "microscopic." Certainly some theoretical material made up of really large molecules with asymmetric structure might have an asymmetric surface profile as a result.

There is another paradigm you could look at. Certain III-V materials (I may have misremembered and it's II-VI :-( ) cleave asymmetrically in the 1-0-0 plane, always leaving one face of the crystal with one element at the surface, and the opposite face with the opposite element. If you then had some other material whose hydrogen bonding-strength was radically different for the two elements, you'd get different frictional force on the two surfaces. You still wouldn't get a directional difference, though.

$\endgroup$
0
$\begingroup$

As far as sharks go, they have microscopic teeth which lay upon the next layer similar to roof shingles. It is now thought that the scales of fish evolved into what is now known as dermal denticles and those push forward to become teeth. Different species have a smoother grit than others. A blue shark feels like 600 grit sandpaper rubbing it nose to tail, a galapagos is going to feel like 220 grit paper and a tiger will feel like 40 grit. However, running your hand tail to nose, the skin will feel much rougher. This is going against the grain of microscopic shark teeth. Blues will feel like 220, galapagos 100 grit and a tigers dermal denticles will likely cause your hand to bleed.

$\endgroup$
2
  • $\begingroup$ While this is interesting, it isn't an answer to the question. The question specifically asks about behaviour at a microscopic level. In this context shark scales are macroscopic objects. $\endgroup$ Jan 16, 2015 at 11:36
  • $\begingroup$ I was just adding information to a previous comment whereas my profession deals with sharks on a daily basis. Honestly, I wonder about the directional friction between North and South magnetism...That is what I want to know. $\endgroup$
    – Brandon
    Jan 18, 2015 at 20:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.