Biomedical Engineering Reference
In-Depth Information
and carboxyl-terminated poly(2-vinylpyridine) (PVP-COOH). The wettability of
the grafted surface can be switchable by controlling through soaking in different
solvents. This phenomenon was ascribed to the favored component attached on the
surface of the substrate and the other component collapsing into the interior of the
polymeric film.
Apart from the examples shown above, more examples [
70
,
71
,
105
-
107
]
demonstrate that plasma treatment is a dry etching technique for the preparation
of superhydrophobic surfaces. Furthermore, different elements providing additional
functions can be readily introduced in the surface depending on the type of gas,
tetrafluoromethane, ammonia, argon, or oxygen,
9.3.2
Bottom-Up Approaches
Opposite from the top-down approach, bottom-up methods refer to the building of
larger, more complex objects by integrating smaller building units or components.
The bottom-up approach in nanofabrication normally involves self-assembly and
self-organization. Self-assembly and self-organization are normally used inter-
changeably. To be specific, self-organization is a nonequilibrium process while
self-assembly is an integration process leading to equilibrium in which components
assemble spontaneously in solution or the gas phase until they reach a stable
structure with minimum energy. Bottom-up approaches utilized in the preparation
of superhydrophobic surfaces cover chemical deposition methods such as chemical
bath deposition (CBD) [
72
,
79
-
81
], chemical vapor deposition (CVD) [
79
,
80
], and
electrochemical deposition [
77
,
78
,
108
], LBL deposition via electrostatic assembly
[
73
], colloidal assembly [
76
,
85
], sol-gel methods [
83
,
85
,
109
-
117
], hydrogen
bonding [
82
], and chemical synthesis [
118
]. Some important examples will be
introduced and discussed in detail in the following sections.
9.3.2.1
Chemical Deposition
Chemical deposition is generally used for generating thin films of crystalline
inorganic materials, such as ZnS, CuSe, InS, CdS, MnO
2,
etc., with the material self-
assembling and depositing on some appropriate substrates. The chemical deposition
encompasses different methods such as CBD, CVD, and electrochemical deposition,
in regard to corresponding deposition conditions. Various surface morphologies can
be obtained from nanopins, nanotubes to nanorods, by changing the material and
tuning the deposition conditions.
CBD is implemented to create a nanopin film from a solution of CoCl
2
and
NH
2
CO in water by Hosono et al. [
81
]. The nanopin film with the top of the needle
being sharp (a diameter of 6.5 nm) was deposited on borosilicate glass slides in an
autoclave. Besides, the nanopin exhibits single crystalline-like structures because
each metal complex in the solution is singly deposited on the surface owing to
