Biomedical Engineering Reference
In-Depth Information
Fig. 9.5
Schematic outline of the heat- and pressure-driven nanoimprint pattern transfer process
for nanofabricating the surface of the thick polymer substrate with (
a
) aligned nanoemboss,
(
b
) nanopost array with embossed base, and (
c
) aligned nanofibers. (Images reprinted with
permission from Lee et al. [
102
] Copyright 2004, American Chemical Society)
rolling off even it is upside down. This super sticky effect is attributed to the van
der Waals' forces between the water molecules and the highly dense nanotubes,
generating a strong adhesion in similar principle with the gecko's mechanism [
103
].
Such a sticky surface is applied as a mechanical hand to transfer a water droplet.
Through extrusion with AAO membranes with pores of average diameter of
68.7 nm [
104
], the researchers have successfully accomplished the fabrication
of superhydrophobic poly(vinyl alcohol) (PVA) nanofibers. Although PVA is a
hydrophilic material, the produced nanofibers exhibited superhydrophobicity with
WCA of 171
ı
, mainly due to the orientation of the PVA molecules that leads to
hydrophobic backbones exposed to the surface as verified by angle dependent X-
ray photoelectron spectroscopy study.
As shown above, templation is a useful technique in preparing superhydrophobic
surfaces with tunable surface morphology. Hence, many features can be fabricated
depending on the type of templates. Furthermore, the diverse polymeric materials
available have endowed templation a versatile approach. However, the attainable
geometry is limited by the available templates and not every material is suitable for
the templation approach.
9.3.1.2
Photo Lithography
In photolithographic approaches, light is radiated through a mask with required
features to the substrates such as silicon with a photoresist. Succeeding developing
and etching steps generate the desired patterned surfaces. There are two kinds of
photolithography, X-ray lithography and E-beam lithography, depending on the
