Chemistry Reference
In-Depth Information
By using different precursors, the UV stability and the
transparency of the superhydrophobic surfaces were altered. The
most UV unstable and less transparent layer was substrate coated
with
-decane. The low stability and non-transparent property were
attributed to the significant amount of double bonds in decane that
can be easily oxidised. The
p
p
-TEOS layer exhibited much higher
UV stability than the
-decane. It was also very transparent and,
with the naked eye, looked like uncoated glass. The increase in the
transparency as well as its stability was due to a lower percentage
of carbon atoms per molecule which was logical as the
p
p
-TEOS
had less double bond than the
-decane. It is well known that C-F
bonds are much stronger than C-H and C-C bonds [66]. Therefore,
fluorocarbon-based polymers are known to be UV stable and, as a
consequence, substrate coated with
p
was UV stable and
showed the highest superhydrophobicity (CA = 170
p
-C
F
10
18
). However,
this coated substrate showed a relatively low transparency in the
visible region. The use of C
°
as a precursor could help to improve
the transparency since the amount of doped carbon was reduced.
However, the substrate coated with
F
9
20
exhibited smooth
surface leading to low hydrophobicity. This problem was solved by
coating the substrate with silica before further coating with
p
-C
F
9
20
.
This surface was the most UV stable and most transparent layer,
compared with others. Furthermore, it was found that the CA of the
surface could be increased by re-deposition of the surface with the
precursor. However, the transparency of the surface was decreased.
p
-C
F
9
20
5.5.4 Superhydrophobic Surfaces with Tuning
Wettability
Searching for materials that may change their contact angle in a
reversible and controllable way has also been a challenge in many
of the applications. Examples of them are self-cleaning surfaces,
intelligent microfluidic devices, and lab-on-a-chip systems.
Tuning the surface wettability—reversible transition between
superhydrophobicity and superhydrophilicity—is therefore of great
interest for scientific research.
Borras et al. have developed a tunable superhydrophobic-
superhydrophilic Ag-TiO
composite mat having silver as a substrate
2
and Ag-TiO
core-shell nanofibers as supported vertical fibers on
the mats (Fig. 5.13) [67].
2
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