Chemistry Reference
In-Depth Information
a fluorocarbon surface layer, which is absent in the case of CF
4
-treated alumina, increases
from C
3
F
8
to c-C
4
F
8
treatments.
In the case of C
3
F
8
fluorinated sample, an inhomogeneity of the layer composition is
noticeable on both F1s and C1s spectra. New components at a high BE are indeed present
(at 688.6 and 293.7 eV), which account for the presence of overfluorinated -CF
3
groups
with respect to CF
2
and CF groups, which constitute most species of the c-C
4
F
8
fluorinated
sample. Moreover, for similar deposition conditions, it is necessary to etch the c-C
4
F
8
fluorinated layer upon 10 nm before observing the presence of aluminium, whereas this
element is observed during the surface analysis of the C
3
F
8
fluorinated sample. It is clear
that the polymerized layer is thicker using the c-C
4
F
8
than the C
3
F
8
medium and leads to
more homogeneous and less crosslinked layers.
19.6 Conclusion
In conclusion, by rf-plasma fluorination the outmost surface of the hydrophilic anodized
aluminium support is hydrophobized, or in other words, the hydrophilic support is con-
verted into a support with hydrophobic properties, as shown in Figure 19.5. This conver-
sion from a hydrophilic to a hydrophobic state is characterized by an increase of the contact
angle measured on the surface, indicating an increase in the hydrophobic-to-hydrophilic
ratio. The most adapted route to drastically switch from a pristine hydrophilic surface of
porous alumina into a hydrophobic layer is clearly the c-C
4
F
8
treatment. It has been shown
θ
γ
SV
=
γ
+
γ
L
cos
SL
γ
SV
: surface energy solid/liquid vapour
γ
L
γ
SL
: interfacial energy solid/liquid
γ
SV
θ
γ
L
: superficial tension of the liquid
γ
SL
θ
: contact angle of the liquid on the solid
substrate
Untreated substrate
CF
4
rf plasma
C
4
F
8
rf plasma
Contact angle
θ
≈
20
°
≈
60
°
≥
130
°
hydrophilic
hydrophobic
Figure 19.5 Contact angles of pristine and plasma-treated porous alumina. Reproduced by
permission of Science China, Ser. E-Technolog. Sciences 52, pp. 104-110, Springer (2009)
Copyright Science in China Press
