As you may know, wettability is a characteristic of each surface which determines what the contact angle would be when a droplet is put on the surface (see here for more info). Surface roughness has a significant effect on wettability. For instance, if you increase the roughness of a polymer surface, the contact angle will be increased as well (i.e. it becomes more hydrophobic).
I need to create a surface such that I can control its wettability by an external stimulus (e.g. temperature, etc.). For instance, a polymer (or any other material) in which when I change its temperature, the surface roughness is also changed (due to change in the molecules chains shape or crystallization). I need to know which materials (polymer, etc.) I can use to create such a surface.
Please see the attached image.
Thanks
https://en.wikipedia.org/wiki/Wetting
With one material I'd say it is impossible. Roughness is not really some well defined function of temperature as it is mostly a far-from-equilibrium phenomenon. I would not be surprised if each change of the temperature, up or down, leads to a decrease of the roughness.
But with two materials - why not... Choose two materials, one of very small coefficient of thermal expansion and the other - of very high one. Make a multilayered material of them, with very thin layers. Cut it in direction normal to the layers (with angle different from 90 deg it will be also fun). The surface that you'll get should have the properties you speak about. When you heat it, the expandable material will protrude out of the surface, changing the roughness - see the picture attached.
Do you mean adjustable in in situ experiments?
If not, what about mechanical/electro chemical grinding/polishing? In the case of metals it is easy to achieve a desired surface roughness by selection of paper with adequate grid size or a diamond solution. Also with electrochemical etching it should be possible to create surfaces of desired roughness. There are also articles about grinding/polishing Polymers.
Yes, I mean to be able to adjust roughness of the surface during the experiments (by changing surface temperature for instance, or any other external stimulus)
With one material I'd say it is impossible. Roughness is not really some well defined function of temperature as it is mostly a far-from-equilibrium phenomenon. I would not be surprised if each change of the temperature, up or down, leads to a decrease of the roughness.
But with two materials - why not... Choose two materials, one of very small coefficient of thermal expansion and the other - of very high one. Make a multilayered material of them, with very thin layers. Cut it in direction normal to the layers (with angle different from 90 deg it will be also fun). The surface that you'll get should have the properties you speak about. When you heat it, the expandable material will protrude out of the surface, changing the roughness - see the picture attached.
Sandwiching as proposed by Radomir is a good idea. By using materials of different elasticity and squeezing the stack you may also provide constant temperature conditions.
Maybe to take in account materials with different thermal expansion coefficient. Roughness may be also function of it.
To go with Radomir's idea, I plan to create a pattern of square bars with 0.1 mm * 0.1 mm base and a height of 10 mm and put them together like a chessboard (we can not use permanent adhesive between bars, but I can put the bottom-side into a fixture and use a rubber band around the bars to keep them together at the top). I can use polyethylene (alpha=200e-6) and copper (alpha=17e-6) plates with thickness of 0.1 mm to create the bars. However, I need to cut the plates in 0.1 mm pieces to make the square cross sections and I don't know what kind of cutting technology can give me the appropriate accuracy for that. Please let me know if you have any opinion regarding cutting and my selections for material, dimensions, etc.
Thanks
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