Biomedical Engineering Reference
In-Depth Information
different between silicon wafers and CaCO
3
-loaded hydrogel spheres. Hence, the
silica or polystyrene spheres localize in selective regions, leading to irregular binary
structures possessing a hierarchical roughness. The substrate can also be tuned to
superhydrophobic surface by depositing gold and SAM formation.
9.3.2.3
Layer-by-Layer Deposition
The LBL technique is easy to perform where the thickness of the resulting layer can
be controlled with molecular precision, utilizing the electrostatic charge interactions
between the different layers such as polyanion and polycation. Incorporating
nanoparticles into the multilayer system and additional treatment can be used to
enhance the roughness, rendering multilayer films the hydrophobicity,
Zhai et al. [
123
] have acquired superhydrophobic silicon surfaces with
poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) multilayers via
LBL deposition. Acidic treatments generate pores on the order of 10
manda
microscopic honeycomb-like structure was formed on the PAH/PAA films. Further
coating of silica nanoparticles and a semifluorinated silane leads to the stable
superhydrophobic substrate, with the stability tested by extended immersion in
water. In general, the acid treatments create microstructure and the deposition of
silica nanoparticles induces nanostructure. Both the procedures are important in
creating stable superhydrophobic surfaces.
Another approach for the incorporation of particles in the LBL assembly has been
performed by Han et al. [
73
] in order to prepare superhydrophobic surfaces. PAA-
coated ZrO
2
particles and PAH take turns to be deposited on clean silicon substrates.
Through 20 deposition cycles, the surface displays WCA of 139
ı
with a PAH
exposed as the outermost layer and a huge hysteresis (
40
ı
), which are remarkable
˙
60
ı
). Further deposition of silica nanoparticles
and perfluorinated dodecyltrichlorosilane reduced the contact angle hysteresis of 2
ı
and enhanced the superhydrophobicity of a WCA of 170
ı
significantly. Amidation
through thermal treatment of substrates at an increased temperature of 220
ı
C render
the film additional stability.
The LBL technique is facile to implement and control the film thickness
with molecular precision. However, a hydrophobization is often necessary since
polyelectrolytes are hydrophilic. In addition, some additional steps such as the
incorporating nanoparticles are required to generate rough surfaces, thus making
it a less direct and immediate way in preparing superhydrophobic surfaces.
since PAH is rather hydrophilic (
˙
9.3.2.4
Sol-Gel Methods
Hydrolysis of the corresponding oxide in the presence of solvent produces sol.
Gel is formed when a large amount of solvent are also congested in the network
during the network formation process. The sol can be used either straight way or
