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amorphous portions of the cellulose in O
plasma and subsequently
depositing the etched surface with a thin fluorocarbon film by
plasma-enhanced chemical vapour deposition (PECVD) using
pentafluoroethane as a precursor [45]. According to the variation
of the plasma treatment conditions, two types of superhydrophobic
surfaces were fabricated: (i) roll-off (CA, 166.7
2
°
±
0.9
°
; CA hysteresis,
3.4
°
±
0.1
°
) and (ii) sticky (CA, 144.8
°
±
5.7
°
; CA hysteresis, 79.1
°
±
). After surface treatment, the bulk properties of the paper
did not change. The superhydrophobic paper surfaces were robust,
flexible, breathable, biodegradable, and could also be recyclable.
Polydimethylsiloxane (PDMS) is frequently used in microfluidic
for lab-on-a-chip applications. Since an accumulation of small
amounts of liquid near the nozzle outlet due to pinning effects may
result in further liquid accumulation or deflection of the droplet
flight direction, superhydrophobicity of the nozzle as well as the
channel of microfluidic system is important. The PDMS chips with
completely superhydrophobic channel walls (both vertical and
horizontal surfaces) were fabricated by a two-step fabrication
process [46]. The fabrication of these microchannels consisted of
two main steps: (i) formation of micro-channels in a composite of
PTFE nanoparticles and PDMS as the matrix material and (ii) CF
15.8
°
-
4
plasma treatment for isotropic PDMS etching to uncover the
hydrophobic multiscale roughness of the PTFE particles. It was
possible to generate both horizontal and vertical superhydrophobic
surfaces in one processing step because the plasma treatment was
responsible for isotropic etching of PDMS.
O
2
5.5.2 Functionalisation Strategy
For the hydrophobic functionality, fluorinated hydrocarbons, such as
CF
, are often used. The basic reason is that fluoride species can lower
the surface energy of the film after they are deposited. Additionally,
the C-F bond can easily be activated in the plasma. Thus, it is easy
to achieve sufficiently high concentration of intermediate species to
form hydrophobic particulate in the gas phase [36].
Kim et al. reported the production of superhydrophobic surfaces
regardless of the substrate nature [47]. The superhydrophobic
coating was produced by an in-line atmospheric RF glow-discharged
plasma process using helium (He) as a carrier gas and a mixture
4
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