In on[4]. Inspiration from natural superhydrophobic surfaces many

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In recent years, 
naturally-occurring super hydrophobic surfaces include water-strider
legs and the leaves of many plants 1which have water contact angles (WCAs) of
more than 150 and water sliding angles (WSAs) of less than 10 2 have
attracted extensive worldwide attention in research purpose as well as
industrial application. The key features of such smart surfaces are based on
two parameters one is nano- and microscale surface roughness and other is low
free surface energies 3. These two key features manifest water droplets to
attain the spherical shape and roll off the surface carrying away the dirt
particles. Such type of surfaces has 
potential applications in many fields including as self-cleaning paints,
coatings for windows, textiles and solar panels, anti-icing, anti-fogging,
protection of electronic devices and so on4. Inspiration from natural
superhydrophobic surfaces many approaches have been developed to design such
type of smart surfaces by creating surface roughness combination with low
surface energy materials such as organic silanes, fluorinated silanes, alkyl amines and silicates5. The popular
approaches are wet chemical reactions 6 sol–gel 7, layer-by-layer
deposition 8 chemical vapour deposition 9 plasma treatment 10 and
electrospinning 11 etc. All of the above processes have focused on the growth
of inorganic materials or nanoparticles. Without using nanoparticle researchers
are also able to impart surface roughness by applying polymerization reaction
on substrate surfaces using organic compound. Between all of organic chemicals,
the fluorocarbon-based products were
found to enhance oil and water repellence by lowering surface energy with
increasing surface roughness 12. Fluorine has a small radius and high electronegativity,
thus the covalent bond between ?uorine and carbon is extremely stable. When
?uorine is replaced by other elements such as H and C, in the order
–CF3 1, which in comparison with a smooth wetted area, can enhance
surface hydrophobicity. So,
SEM images demonstrate that
there are some polymeric layers exist between the fibers stays, which indicated
some adhesion of fluoropolymer occurs
during the polymerization. As a result, the droplet
rests on the top of solid asperities and the gas is left in the voids below the
droplet indicating a shiny, transparent surface underneath the water has also shown in Figure 2. The chemical structure of fluoropolymer has also shown in Figure
5c along with SEM images.

Successful deposition of fluoropolymeric
hydrophobic coatings on the cotton sample was evaluated by comparing the FTIR
spectra of coated cotton samples with the unmodified sample has shown in  Figure 6. In the FTIR spectra of modified
cotton, the minor changes are observed,
indicating in the admicellar process the
internal bonds of in cotton fabric are not destroyed.
FT-IR ATR spectra of untreated fabric and fluoromonomers
treated fabric in Figure 6 showed characteristic cellulose peaks around
1100-1200 cm-1.Other characteristic bands related to the chemical
structure of cellulose were the hydrogen-bonded OH stretching at 3350-3200 cm-1,
the C-H stretching at 2900 cm-1, and the C-H wagging at1314 cm-1.
The OH bending of absorbed water was also observed in 1642cm-1.
Figure 6 shows an absorbance at around
1751 cm-1 in the FT-IR ATR spectrum of fluorinated cotton, which was
attributed to the stretching vibration of the carbonyl group of methacrylates
monomers attached to the fabric. The frequency at 1010 cm-1 is a
characteristic frequency of the C-F bond 23. The C-F stretching frequency is
absent in case of untreated fabric but appears in the treated fabric indicating
polar C-F bond between the cotton fabric and fluoromonomers.
This data indicates that the hydrophobic cotton surface was achieved through
copolymerization of the two monomers and fluorine is attached to the cotton
surface which affects the water repellence behavior of the modified cotton
fabric although the two monomers are different in chemical structure. This
surface polymerization clearly implies that hydrophobicity is strictly related
to the quantities of the attached copolymer to the cotton surface rather than their
chemical composition.

The stabilty of coatings on modified cotton fabric was also
evaluated by the repeated tear test with an adhesive tape . In this test, the
cotton surface was pasted onto an adhesive tape, and then it was peeled off in
Figure 6. Even after repetition of the adhesive test
for 20 cycles the developed material remained hydrophobic, with an almost
constant water contact angle (WCA) of 10. Thus, the results of the
study indicate the stable and long term hydrophobicity of the prepared
fluoropolymer modified cotton fabric

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have successfully created an artificial lotus leaf-like
cotton surface by using a little quantity of fluoromonomer which shows
hydrophobic character with water contact angle1240
  after admicellar polymerization. SEM images
demonstrate the surface roughness occurs after fluoropolymerization
on the cotton surface. FT IR also
confirms the attachment of fluorine moieties on the cotton surface by polymerization.

Categories: Behavior


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