22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Plasma assisted polymerization of fluorinated monomer in ethanol
R. Molina Mansilla1, J.M. Teixidó1, C.W. Kan2 and P. Jovančić3
1
Plasma Chemistry Group, Department of Chemical and Surfactants Technology, Institute of Advanced Chemistry of
Catalonia (IQAC), Consejo Superior de Investigaciones Científicas (CSIC), Jordi Girona 18-26, 08034 Barcelona,
Spain
2
Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
3
Textile Engineering Department, Faculty of Technology and Metallurgy, University of Belgrade,
Karnegijeva 4, 11120 Belgrade, Serbia
Abstract: Hydrophobic fluorinated coatings on cotton were carried out via atmospheric
plasma assisted polymerization of fluorinated monomer solutions in ethanol. Chemical
structure of monomer is retained after plasma treatment and a complete polymerization
seems to occur. Water repellent films were successfully formed on cotton substrates and
the amount of film deposited increases as a function of monomer concentration.
Keywords: plasma in liquids, plasma polymerization, ethanol, hydrophobic coatings
1. Introduction
Plasma polymerization is a well known method that
results in the formation and deposition of polymeric thin
films on a diversity of solid substrates. The intact
monomer may be conventionally free radical polymerized
on the surface from active species present in the plasma.
Different methods are usually employed in order to
promote plasma polymerization of a monomer on a solid
substrate.
The common method consists in the
introduction of the monomer in the plasma gas phase and
polymerization takes place as a result of the free radicals
generated during the plasma treatment. Plasma initiated
polymerization can be promoted in gas phase by both, low
and atmospheric pressure plasmas [1-3].
Recently, atmospheric dielectric barrier discharge
(DBD) plasma has been employed to polymerize
monomer aqueous solutions of hydrophilic vinyl
monomers N-isopropylacrylamide (NIPAAm) and acrylic
acid) [4-5] or to facilitate the gelation of biopolymer
chitosan [6]. In situ plasma polymerization of aqueous
monomer solutions results in high retention degree of
monomer
chemical
composition
whereas
the
polymerization process is partial as both linear and crosslinked polymer chains are present in the coatings obtained
[4]. However, the final coating is hydrophilic in nature
and a different solvent than water is need in order to
dissolve hydrophobic monomers and finally obtain a
hydrophobic surface. For this reason, in this work
fluorinated monomer dissolved in ethanol was exposed to
non-thermal atmospheric pressure DBD plasma to follow
monomer polymerization and to obtain water repellent
cotton coatings. The resulting polymer cotton coatings
are characterized by FTIR, XPS and SEM analysis. The
water repellency of cotton coatings is also evaluated by a
simple water repellency test.
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2. Experimental
Cover glass and cotton fabric (plain weave, bleached
without optical brightener (Article 210) from EMPA)
were use as substrates. Cotton fabric was previously
washed with Tanatex® (Tanatex Chemical) to remove any
existing impurities. A precursor, fluorinated monomer
(MF) know as 1H, 1H, 2H, 2H -Heptadecafluorodecylmethacrylate (97%) (Sigma Aldrich) previously dissolved
in ethanol at different concentrations ranking from 0.2 to
100% (w/v), was subjected to the plasma polymerization
in a DBD reactor. DBD reactor operating at atmospheric
pressure was used in this work (Fig. 1).
Fig. 1. In situ liquid phase polymerization of fluorinated
monomer in ethanol initiated by atmospheric plasma.
Gas mass flow meter and controllers (Bronkhorst,
Ruurlo, Netherlands) were used in order to introduce
helium gas (5 Ln min-1) in the reactor chamber. A 100
kHz signal was generated with a GF-855 function
generator (Promax, L’Hospitalet de Llobregat, Spain)
connected to a linear amplifier AG-1012 (T&C Power
Conversion Inc., Rochester, NY, USA). The incident
power in the plasma reactor was kept constant at 30 W.
A matching network and two transformers (HR-Diemen
S.A., Sant Hipòlit de Voltregà, Spain) were connected to
the amplifier output in order to increase the voltage up to
≈20 kV. The distance between the two electrodes was
kept constant approximately at 5 mm. Cover glasses
and/or cotton fabrics were introduced into the plasma
1
Table 1. Effect of monomers concentration on MF
polymerization yield.
Fluorinated
monomer, MF (%)
0.2
2
20
100
Dried Weight
(mg)
0.1
0.4 ± 0.2
2.7 ± 0.2
20.5 ± 2.2
Polymerization
yield, PY [%]
45.6 ± 19.7
32.5 ± 1.8
56.4 ± 6.0
Since these preliminary results demonstrated a
successful polymerization of MF, the plasma
2
Fluorinated monomer polymerized on cotton
6
5
100%
20%
2%
0.2%
Cotton
4
CFx
3
1
0
1800
C-O
2
C=O
3. Results
In order to determine the weight of fluorinated
monomer that has been polymerized during the DBD
plasma treatment using cover glass as a substrate, the
weight of the MF solution before plasma treatment as
well as the weight of the coating obtained after plasma
treatment were recorded. As expected, the weight of the
coatings increases as a function of monomer
concentration (Table 1). Polymerization yield, evaluated
as the percentage of the weight of the dried coating
obtained after plasma treatment and the weight
corresponding to monomer precursor, does not vary
proportionally with monomer concentration as almost
50% of the monomer cursor has been evaporated during
the plasma treatment.
polymerization of fluorinated monomers has been carried
out afterwards onto cotton fabric. Fig. 2 shows the FT-IR
(ATR) spectra of cotton coatings obtained after plasma
assisted polymerization of fluorinated monomer at
different concentrations (0.2% - 100%). It can be
observed that with an increase in concentration of
fluorinated monomer, characteristics bands of bleached
cotton corresponding to OH (1200 - 1336 cm-1) and C-O
(1000 - 1030 cm-1) decreases whereas characteristic bands
of fluorinated polymerized monomer corresponding to
CF x (1149, 1205 and 1245 cm-1) and C=O (1731 cm-1)
increases. The results clearly indicated that the amount
and probably a thickness of polymer coatings formed
could increase depending on concentration of fluorinated
monomer. Vinyl peak (1635 cm-1) corresponding to the
non-reacted fluorinated monomer is scarcely observed
suggesting that the polymerization process could be
almost completed.
Normalized absorbance (a.u.)
reactor and ≈ 100 µl of the fluorinated monomer ethanol
solutions of different concentration were placed over.
The plasma reaction time was kept to 15 min in order to
obtain completely dried macroscopic coatings. The
plasma polymerization process was made in triplicates.
Polymerization yield (PY (%)) was calculated as
percentage of the weight of the MF solution before
plasma treatment relative to the weight of the coating
obtained after plasma treatment. The morphology of the
dried NIPAAm films obtained was studied by scanning
electron microscopy (Hitachi S-3500N). Samples were
previously coated with Au/Pd (thickness coating about
20 nm) in a sputtering device Polaron SC500. The FT-IR
(ATR) spectra were recorded by a Nicolet AVATAR 360
spectrometer. A total of 32 scans were collected for each
measurement at a resolution of 4 cm1. XPS analysis was
done using a PHI Model 5500 Multitechnique System
with an Al Kα monochromatic X-ray source operating at
350 W. The measurements were done at a normal
emission angle. Survey scans were taken in the range
0 - 1100 eV, with pass energy of 187.85 eV. High
resolution scans were obtained on the C 1s , O 1s , N 1s and
F 1s photoelectron peaks, with pass energy of 23.5 eV.
Binding energies were referenced to the C 1s
photoelectronpeak position for C–C and C–H species at
285.0 eV or C–O species at 286.4 eV for bleached cotton
[7].
1600
1400
1200
1000
Wavenumber (cm-1)
Fig. 2. FTIR (ATR) spectra of untreated and polymerized
fluorinated monomer solutions in ethanol at different
concentrations (%) on cotton.
Whereas the infrared spectroscopy in ATR mode is
sensitive to the chemical functional groups present at
microscopic scale, XPS is sensitive to the upper 10 to
30 nm of a material surface, exactly where the plasma
polymerization process takes place, and where the
intimate contact of fluorinated monomer with plasma
active species is occurring. Therefore, possible surface
chemical modifications such as functionalization or
degradation have been additionally studied by XPS.
Atomic chemical composition corresponding to cotton
substrate and plasma assisted polymerized cotton coatings
are shown in Table 2. For plasma assisted polymerization
samples it is observed that the value of carbon and
fluorine is lower than the expected composition for
fluorinated monomer. However, no significant changes in
oxygen atom are observed. These results suggest that
during plasma treatment not only polymerization
processes occurs but also other reactions are involved.
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Table 2. Elemental composition (%) at the surface
determined by XPS.
Sample
Untreated
cotton
Cotton coated
with 20% MF
MF theoretical
composition
C 1s
63.3
N 1s
0.5
O 1s
36.2
F 1s
-
53.8
-
8.9
37.3
42.2
-
6.1
51.5
longitudinal fibril architecture can be easily observed in
untreated cotton (Fig. 4a). As previously demonstrated
(see Table 1), the polymerization yield increases as a
function of monomer concentration. Similarly, at low
monomer concentration (0.2%) structure alterations are
hardly observed despite that a very thin layer is deposited
(Fig. 4b). Increasing the monomer concentration (2%) a
thin coating seems to be completely formed over the
cotton fibre (Fig. 4c). Finally, the increase of the MF
concentration (20%) leads to the thicker and
microscopically well-defined rough coatings (Fig. 4d).
For this reason high resolution spectra corresponding to
carbon functionalities were also studied. Fig. 3 shows the
high-resolution spectra of C 1s corresponding to cotton
fabric and plasma assisted polymerized coatings on
cotton. It can be observed that cotton substrate is mainly
composed of a major peak corresponding to C-O
functionalities (286.6 eV) and a shoulder band at lower
binding energies attributed to aliphatic carbon atoms
(285 eV) as expected for a cellulosic fibre.
High-resolution spectra corresponding to plasma assisted
polymerized coatings on cotton reveals the presence of
fluorinated (CF 2 and CF 3 ) and carbonyl (C=O) species.
C-O
Fig. 4. SEM images of (a) untreated cotton and cotton
treated with MF at (b) 0.2%, (c) 2% and (d) 20%.
C-C
20
15
C - F2
C=O
10
5
C - F3
Normalized intensity (atom %)
Untreated cotton
Plasma coated
0
296
294
292
290
288
286
284
282
280
Binding energy (eV)
Fig. 3. XPS high-resolution C 1s spectra of untreated and
cotton coated with fluorinated monomer (20%).
However, spectrum corresponding to plasma assisted
polymerization of a fluorinated monomer is significantly
different from that we have found previously for a plasma
assisted polymerization in vapour phase of the same
monomer.
In plasma assisted polymerization of
fluorinated monomer in ethanol solution, aliphatic carbon
atoms predominate over fluorinated carbon atoms
(Table 2), suggesting that additional carbon has been
introduced on the surface during plasma treatment. It is
indicated that a possible polymerization or reaction of
ethanol during plasma processes could take place in the
polymerized film. However, the presence of oxygenated
species can also indicate a possible film oxidation during
plasma treatment.
Fig. 4 shows high-resolution SEM images of bleached
cotton and plasma cotton coatings obtained using
different concentrations of fluorinated monomer. Typical
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Water repellency test was performed on the treated side
of the cotton fabric and the results are presented in
Table 3. A water droplet placed on the surface of
untreated cotton fabric sinks completely into the fabric
after just a few seconds, mainly due to capillary forces.
When a water droplet is placed over the cotton fabric
previously impregnated with ethanol and treated with
plasma during 15 minutes a different behaviour was
observed.
Table 3. Water repellency test.
Composition
Untreated cotton
Ethanol
MF 0.2%
MF 2%
MF 20%
MF 100%
Wetting time (min)
0
0
0
60
165
200
Neither the formation of a water droplet, nor an
instantaneous sinking as done by untreated cotton
happened, thus suggesting again that the ethanol may
have functionalized or polymerized itself on cotton fabric.
Wetting properties of plasma treated cotton treated with
3
relatively small concentrations of fluorinated monomer
(0.2%) maintained unchanged. However, at higher
monomer concentrations (2%, 20% and 100%), it is
observed that wetting time significantly increases that is
in good agreement with the presence of thicker coatings
after plasma polymerization as observed by SEM (Fig. 4).
4. Conclusions
Fluorinated monomer in ethanol solutions can be
successfully polymerized using atmospheric pressure
dielectric barrier discharge while the chemical structure of
monomer is almost retained during plasma treatment.
Chemical structure analysis of water repellent coatings
performed by FT-IR (ATR) and XPS implies that almost
complete polymerization of fluorinated polymer took
place during the plasma assisted polymerization process.
Water repellent coatings were successfully formed on
cotton fabric after plasma polymerization of fluorinated
monomers. The thickness of coatings deposited increases
as a function of monomer concentration.
5. Acknowledgment
The work was supported by a grant from the
CSIC/RGC Joint Research Scheme sponsored by the
Research Grants Council of Hong Kong and the Spanish
National Research Council (Reference No. S-HK007/12).
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