Biomedical Engineering Reference
In-Depth Information
Superhydrophobic films based on micelles depend on the selection of solvents
and the block copolymers, the casting methods, relative humidity of the environ-
ment. Thanks to the diversity of available polymer materials, superhydrophobic
surfaces with different structures can be fabricated by this method [
136
,
137
].
9.3.3.4
Electrospinning
Electrospinning is normally a process extruding polymer nanofibers from the
extrusion nozzle to a grounded collection plate where an electrical bias is applied
[
138
]. A continuous, nonwoven web of electrospun fibers forms films, along the
trajectory of the extruded polymer fiber, where most of the solvents evaporate. The
film properties can also be modified by introducing chemical modification such as
fluorine [
88
].
Electrospinning independently [
88
,
139
] or in combination with other methods,
such as CVD [
92
], have been used in preparing superhydrophobic films of polymers.
The morphology of the electrospun film varies from mostly beads to solely fibers
when the viscosity of the polymer solution is increased [
88
], thus changing the
final wetting behavior. It is observed that surfaces containing beads are more
hydrophobic compared with those with only nanofibers. Therefore, polymers with
lower molecular weight were used to obtain surfaces with higher WCAs due to the
results that more beads can be formed by lower molecular weight polymers, with
the CA reaching as high as167
ı
.
Combination of electrospinning of poly(caprolectone) (PCL) with initiated CVD
(i-CVD) of polymerized perfluoroalkyl ethyl methacrylate were used to fabricate
superhydrophobic surfaces by Ma et al. [
79
]. The inherent hierarchical surface
roughness of the PCL films gained through electrospinning and the considerably low
surface free energy of the coating layer through i-CVD contributes to the remarkably
stable superhydrophobicity with a water CA of 175
ı
and a threshold sliding angle
less than 2.5
ı
.
9.4
Control Wettability on Superhydrophobic Surfaces
via External Stimuli
Increasing attention is paid on the way of manipulating wetting behaviors on su-
perhydrophobic surfaces. Reversible superhydrophobic and superhydrophilic state
transitions controlled by varied external stimuli have been reported. These studies
have revealed that micro/nanostructures of superhydrophobic surfaces and chemical
composition are the key parameters to control wetting behaviors. These superhy-
drophobic surfaces with controllable wettability are of great importance for both
fundamental researches and practical applications
