Biomedical Engineering Reference
In-Depth Information
experimental procedure, 2.5 mM KMnO
4
and 10 mM concentrated HCl were
added to 45 mL deionized water to form a precursor solution, which was then
transferred into a teflon-lined stainless steel autoclave with a capacity of 100 mL.
Two types of Si wafers (1
3cm
2
) with and without Pt coating were used as the
substrates to grow high-oriented MLS films with different mesh sizes. The autoclave
was sealed and treated hydrothermally at 140
ı
C for 50 min to obtain MnO
2
MLS
films. The TNS films were synthesized by extending the reaction time to 135 min
to form the
'
-MnO
2
layer. By employing the TNS films as the substrate, BCS
films were obtained via the same procedures as MLS. All the as-fabricated films
were rinsed with deionized water and dried in air overnight. To achieve surface
superhydrophobicity, the as-prepared MnO
2
films were immersed into methanol so-
lution of hydrolyzed 1 wt% PFOTES (1H,1H,2H,2H-perfluorooctyltriethoxysilane
(CF
3
(CF
2
)
5
CH
2
CH
2
Si(OCH
2
CH
3
)
3
)) for 1 h at room temperature. The samples
were rinsed with ethanol and subsequently heated to 140
ı
C for 1 h to remove
nonbonded PFOTES molecules.
In addition, Huang et al. [
120
] have used CVD to prepare aligned carbon
nanotubes (ACNTs) on Fe-N-coated silicon substrates. The substrates deposited
by a ZnO layer showed water CA of 159
ı
, where the wettability is tunable and
the property can be utilized in the application in microfluidic devices. Specifically,
the superhydrophobic surface can be turned into hydrophilic after a long period
of exposure to UV illumination. And the hydrophobicity of the surface can be
recovered after storage in the darkness.
Besides, electrochemical deposition of the zinc oxide [
108
], gold clusters [
121
],
or silver aggregates together with the further modification with SAMs has been used
to fabricate superhydrophobic surfaces [
77
].
9.3.2.2
Colloidal Assemblies
The close-packed particle assemblies formed by monodispersed particles owing to
van der Waals' interactions impart roughness to the underlying substrates. This
roughness can be further improved by the subsequent treatment such as plasma
etching [
122
]. Various colloidal particles ranging from polymer beads to inorganic
spheres can be used in the assembly. Colloidal assembly is widely used in laboratory
research because it is an economic way compared with expensive lithographic
technique and it is easy to master.
Spin coating is a way to assemble monodispersed polystyrene (PS) beads to
closely packed structure [
122
], with the solid-air fraction of these nanostructures
tuned by oxygen plasma etching which can reduce the sizes of beads by controlling
the etching conditions. The surfaces were then coated with a layer of gold and a
layer of octadecanethiol SAM in order to make the surfaces superhydrophobic.
Zhang et al. [
76
] have used binary colloidal assemblies for the production
of superhydrophobic surfaces. CaCO
3
-loaded hydrogel spheres were assembled
on silicon substrates using dip-coating, serving as templates for the subsequent
self-assembly of silica nanoparticles or polystyrene beads. The hydrophilicity is
