Biomedical Engineering Reference
In-Depth Information
Fig. 9.4
Schematic illustration of nanocasting and SEM images of (
a
) a natural lotus leaf and
(
b
) its positive PDMS replica. (Images reprinted with permission from Sun et al. [
100
] Copyright
2005, American Chemical Society)
surfaces with desired features. For example, the surfaces produced by lithographic
approaches and micromachining can be used as a replicating template.
Template methods involve molding and replication steps with the template re-
moved by lifting off [
93
], dissolution [
39
,
89
], or even sublimation as the following
steps [
94
] in order to replicate the desired features. In the lithographic approaches,
irradiation of light through a mask with designed features onto the substrates with
a photoresist is followed by the etching steps, generating the desired patterned
surfaces which correspond to the feature of mask. Silanization is subsequently used
to make these surfaces hydrophobic [
95
,
96
]. In micromachining, surfaces are diced
into the anticipated texture [
8
,
33
,
45
,
90
-
92
]. In the plasma treatments, surfaces
are etched anisotropically, hence yielding rough surfaces. For instance, plasma
treatment of poly(ethylene terephthalate) [
70
,
71
], poly(tetrafluoroethylene) (PTFE)
[
97
], and polyethylene (PE) [
68
]. Pulse-laser treatments of poly(dimethylsiloxane)
(PDMS) for the fabrication of superhydrophobic surfaces have also been developed
[
98
,
99
].
9.3.1.1
Templating
In principle, either 2D or 3D pattern or shape can be replicated via a templating
method. Template methods involve molding and replication steps with the template
removed by lifting off [
93
], dissolution [
39
,
89
], or even sublimation as the
following steps [
94
] in order to replicate the desired features. Templation is a useful
technique to prepare polymeric superhydrophobic surfaces, with a wide range of
materials used as a template containing natural lotus leaves [
100
], a master produced
by lithographic processes as well as commercial inorganic membranes.
Sun et al. [
100
] have obtained a negative replication of the lotus leaf structure
through nanocasting replication process with lotus leaf as the template and PDMS
as the replication media (Fig.
9.4
). This negative template was further applied as
