Micro and nano texturing of polymers and other materials to produce smart surfaces of tuned wetting and reflectivity

Producing smart polymer surfaces by tuning of their properties is of extreme importance in nanomanufacturing, as well as microfluidic applications. It is desirable that modern smart surfaces mimic nature by being self-cleaned (lotus leaf like), antireflective and transparent etc. Such properties can be given to a surface by producing tailored dual scale micro / nanotopography, and appropriate surface chemistry. Their combination can lead to superhydrophobic or superhydrophilic and / or graded refractive index optical surfaces with minimal reflection. In this field, we explore plasma processing as a route for fast and cost-efficient nanofabrication technology. We are studying a variety of polymeric substrates (PDMS, PMMA, PEEK, etc.) and silicon with respect to their surface topography modification upon plasma exposure, and we can obtain superhydrophobic or superhydrophilic as well as surfaces of controllably defined wetting properties (from hydrophilic to hydrophobic), depending on the plasma processing details. We can also tune the transparency.

Available videos:
• Super-hydrophilic plasma processed polymers.
• Super-hydrophobic plasma processed polymers.

- Superhydrophobic PMMA (See Vourdas et al. Nanotechnology 2007)

PMMA surface after 1min etching in Oxygen plasma. This surface is superhydrophilic. Deposition of 20nm Teflon like polymer from fluorocarbon plasma renders the surface supehydrophobic.	PMMA surface treated in oxygen plasma for 1min to become antireflective (right) and overtreated for 5min to become milky-like. Both surfaces are superhydrophobic.
Contact angle and contact angle hysterisis on PMMA Superhydrophobic surfaces versus etching time in oxygen plasma.	Reflectance of PMMA surfaces versus etching time in Oxygen plasmas. Surfaces after 3min etching time are just starting to become milky.

- Superhydrophobic PDMS (see Tserepi et al Nanotechnology 2007)

- Nanotexturing and control of wetting properties of PDMS by oxygen plasma treatment. (see Tsougeni et al., Plasma Processing and Polymers 2007, Japanese Journal of Applied Physics 2007)

Very hydrophobic nanotextured PDMS surface (Wenzel type) after O₂ plasma and AFM showing the nanotexture of such a surface after Oxygen plasma treatment.

- Nanotexturing of Silicon in SF6 plasmas (G. Kokkoris et al Phys Rev B 2007)

Etching of silicon in SF6 plasmas produced interesting nanotexture shown below. Although this nanotexture is small compared to etched depth (etch rate approximately 4 microns/min) it grows with time both in height and diameter.