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Tunable superhydrophobic-superhydrophilic Ag-TiO
Figure 5.13
2
composite mats.
The strategy for the conversion of superhydrophobic to
superhydrophilic is a photoactive activity of the TiO
that can
become hydrophilic when it is irradiated with UV light [68-70]. As
interpreted by Wang et al., this transformation is due to the light-
induced dissociation of water from the atmosphere on the surface
of the TiO
2
[71-73]. The synthesis was done by PECVD technique,
at relatively low temperature (
2
C), where silver substrate was
firstly subjected to preoxidation with plasma of oxygen. TiO
<
250
°
was
then plasma deposited on the surface using a Ti isopropoxide (TTIP)
as a precursor and plasmas of oxygen or mixtures of Ar and O
2
as
2
plasma gas. The Ag core of the Ag-TiO
supported nanofibers had
a width and length of around 20-30 nm and 1-3
2
µ
m, respectively.
The TiO
overlayer had a variable thickness depending on the
deposition time. Water contact angles depended on the width
of the fibers as well as their surface concentration. A completely
superhydrophobic surface of virtually 180
2
C of contact angle was
obtained for sample having a fiber width of 200 nm and a surface
concentration of
°
. The superhydrophobicity was
explained by means of a simple model based on the consideration
of Wenzel. These surfaces became superhydrophilic (i.e., CA = 0
∼
15 fibers per
µ
m
2
)
when they were irradiated with UV light and the transformation was
reversible. Other films containing TiO
°
layer were reported for their
tuning wettability [74,75]. A similar behaviour was also found in the
materials containing ZnO [76-78], SnO
2
[79], and CuO [80].
2
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