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.
plasma processed polymers.
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
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
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
|SEM image of PDMS treated in SF6 plasma
||AFM image of the same PDMS surface showing the nanopilars
created by plasma treatment
||A water drop rolling on such a superhydrophobic (Cassie-Baxter)
surface after plasma deposition of 20nm fluorocarbon thin film.
- 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
Very hydrophobic nanotextured PDMS surface (Wenzel type) after O2
plasma and AFM showing the nanotexture of such a surface after Oxygen
- 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.