Deposition of hydrocarbon polymer/ZnO nanoparticles nanocomposite thin films by DBDs

22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Deposition of hydrocarbon polymer/ZnO nanoparticles nanocomposite thin
films by DBDs
A.M. Mastrangelo1, F. Fanelli2 and F. Fracassi1,2
1
2
Department of Chemistry, University of Bari “Aldo Moro”, Bari, Italy
Institute of Inorganic Methodologies and Plasmas (IMIP), National Research Council (CNR), Bari, Italy
Abstract: Hydrocarbon polymer/ZnO nanoparticles nanocomposite coatings are deposited by dielectric barrier discharges fed with He and the aerosol of a dispersion of oleate-capped ZnO nanoparticles in n-octane/1,7-octadiene mixtures. The 1,7-octadiene
content in the dispersion highly affects the chemical composition, morphology and wettability of the coatings. The utilization of the films in the field of oil/water separation is
evaluated.
Keywords: DBD, aerosol, nanocomposite coating, nanoparticle, ZnO, oil/water separation.
1.Introduction
The research field of organic/inorganic nanocomposite
(NC) materials is one of the most promising areas in materials chemistry. The combined unique properties offered by both organic and inorganic components on a
nanoscale level make in fact such materials attractive for
a large variety of applications [1-3].
Nowadays, intense efforts are directed towards the development of new methods for the preparation of these
hybrid materials. Over the last years aerosol-assisted
atmospheric pressure cold plasma processes have been
proposed as an attractive route towards the preparation of
NC thin films [4]. These processes have demonstrated to
be particularly convenient when, for instance, the dispersion of preformed nanoparticles (NPs) in a liquid organic
precursor is injected directly in the atmospheric plasma.
This allows the deposition in a single step and at room
temperature of hybrid organic/inorganic nanocomposite
coatings [5, 6] consisting of NPs embedded in the organic matrix formed by the plasma polymerization of the
precursor.
This contribution is focused on the study of the
growth and structure of hydrocarbon polymer/ZnO NPs
nanocomposite coatings [5] deposited in a dielectric barrier discharge (DBD) fed with He and the aerosol of dispersions of oleate-capped ZnO NPs in hydrocarbon precursors, such as n-octane and 1,7-octadiene.
In a previous work the properties of the deposited thin
films were investigated as a function of the NPs concentration in the starting dispersion, using n-octane as organic precursor. It was observed that the increase of the
concentration of the NPs in the dispersion promotes the
increase of the content of ZnO and of ZnO NPs quasi-spherical agglomerates in the coatings. In fact if the
coatings are deposited from a dispersion at the concentration of the ZnO NPs higher than 3 wt % the surface
roughness is less influenced by the morphology of the
polymer and more affected by the NPs agglomerates,
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therefore a hierarchical multiscale surface roughness is
obtained. This structure of the coating affects its wettability, and in fact superhydrophobic surfaces (advancing
and receding WCAs higher than 150°) with very low
contact angle hysteresis (lower than 10°) are obtained
[5].
In this contribution the deposition of the coating is
performed adding a highly polymerizing hydrocarbon
species in the starting dispersion, i.e., 1,7-octadiene. A
comprehensive study on the effect of the amount of
1,7-octadiene in the dispersion on the chemical composition, morphology and wettability of the films is carried
out.
Moreover in this work the potential application of the
deposited coatings for the preparation of materials used
in the field of oil/water separation is evaluated.
Oil/water separation is an important research area in
the field of environmental protection aiming to resolve
industrial oily wastewater and oil-spill pollution [7]. In
recent years, research into the role of wettability of filtration materials used in oil/water separation has attracted
more and more attention. It has been shown for instance
that if a filtration material shows different wetting properties for water and oil, such as superhydrophobic and
superoleophilic behaviour, it can be used to realize the
selective separation of oil from water in oil/water mixtures [7]. Several examples in the literature [7, 8] demonstrate that filtration materials for the selective removal of
oil from water can be prepared by depositing a nanocomposite coating with a hierarchical organized structure
due to NPs incorporation on appropriate supports such
membranes and meshes.
2.Experimental Section
The nanocomposite thin films are deposited in a parallel plate dielectric barrier discharge (DBD) reactor fed
with He and the aerosol of a dispersion of oleate-capped
ZnO NPs in n-octane/1,7-octadiene mixtures [5]. The
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concentration of the NPs in the dispersion ranges between 3 and 10 wt %, while the 1,7-octadiene content in
the n-octane/1,7-octadiene mixtures is increased from 0
to 10 vol %. The NC coatings are deposited for 10 min
on substrates (i.e., borosilicate glass slides and CaF 2
substrates) located in the middle of the DBD region.
The plasma is generated by applying a sinusoidal AC
high voltage (22.0 ± 0.2 kHz, 2.6 ± 0.2 kV rms ) operated
in pulsed mode (20 ms period, 13 ms plasma on-time,
65% duty cycle) [5].
The characterization of the coatings is performed using
X-ray photoelectron spectroscopy (XPS), Attenuated
total reflection-Fourier transform infrared spectroscopy
(ATR-FTIR), scanning electron microscopy (SEM),
contact angle (CA) goniometry.
For the experiments of oil/water separation, the NC
films are deposited on a polyethylene terephthalate (PET)
mesh with a nominal aperture of 21 µm, a monofilament
diameter of 41 µm and an open area of 12%.
3.Results and discussion
The addition of a small amount of 1,7-octadiene to
n-octane (e.g., 1 vol %) favours the immobilization of the
NPs and hence results in an increase of the ZnO concentration in the coatings. Then, 1,7-octadiene concentrations greater than 5 vol % seem to promote the growth of
the organic component of the coating. Fig. 1 shows, in
fact, that the intensity ratio between the ZnO and the
CH x absorption bands in the ATR-FTIR spectra is maximum at 1 vol % and then decreases with the vol % of
1,7-octadiene in the dispersion.
Fig. 1. ATR-FTIR spectra of NC films deposited by
DBD from 3 wt % oleate-capped ZnO NPs dispersions
as a function of the concentration of 1,7-octadiene (vol
%) in n-octane.
energy organic component and the hierarchical micro-/nano-structured surface morphology of the coatings
induced by NPs incorporation [5, 9, 10]. When the
amount of 1,7-octadiene in the dispersion is greater than
3 vol % the hierarchical micro-/nanostructured surface
morphology of the NC film is lost due to the growth of
the polymeric component that incorporates the NPs agglomerates. As a consequence the advancing and receding WCAs decrease and a concomitant increase of the
hysteresis is observed (Fig. 2a).
Fig. 2. (a) Advancing and receding WCAs of the NC
coatings deposited by DBD as a function of the concentration of 1,7-octadiene (vol %) in octane (concentration
of the NPs in the dispersion = 3 wt %).
(b) Cross-sectional SEM image of NC film deposited at
a concentration of 1,7-octadiene of 3 vol %.
Interestingly, thin films deposited from dispersions
characterized by a concentration of 1,7-octadiene in
n-octane lower than 3 vol %, they show superhydrophobic and superoleophilic properties simultaneously, in fact
water and hexadecane contact angles are greater than
150° and lower than 5°, respectively. Therefore the coatings present wettability selectivity, and they can be exploited in the preparation of filtration materials able to
separate oil from water.
Encouraging preliminary results have been obtained
for the separation of hexadecane/water mixtures when
the nanocomposite thin films are deposited on a PET
mesh. In Fig. 3 pictures of a demonstration separation
experiment for a plasma-treated mesh are reported. As
shown in Fig. 3b, hexadecane (i.e., the transparent liquid)
passes easily through the treated mesh, while water (dyed
with methylene blue for clear observation) can not pass
and remains in the upper reserve; therefore, an effective
separation of the two liquids is obtained.
The amount of 1,7-octadiene in the starting dispersion
significantly affects the wettability of the coatings, and in
fact, as shown in Fig. 2a, with increasing the amount of
1,7-octadiene in the dispersion from 0 to 3 vol %, the
advancing (WCA a ) and receding (WCA r ) contact angles
remain higher than 150° and the hysteresis (i.e., difference between WCA a and WCA r ) is lower than 10° indicating the formation of superhydrophobic surfaces. The
SEM image in Fig. 2b confirms that this superhydrophobic character is due to the combination of the low surface
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Fig. 3. Oil/water separation demonstration experiment
of hexadecane/water mixtures, before (a) and after (b)
separation using the plasma-treated mesh. The water is
dyed with methylene blue for clear observation.
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4.Conclusion
The results obtained in this work demonstrate that it is
possible to deposit organic/inorganic hydrocarbon polymer/ZnO NPs nanocomposite coatings by means of a
single step aerosol-assisted DBD process using dispersions
of
oleate-capped
ZnO
NPs
in
n-octane/1,7-octadiene mixtures. The addition in the
starting dispersion of 1,7-octadiene has a significant
effect on the chemical composition, morphology and
wettability of the thin NC films. A small amount of
1,7-octadiene in the dispersion (e.g., 1 vol %) seems to
promote the immobilization of the NPs in the thin films,
while it is possible to promote the growth of the organic
component by increasing at concentrations of
1,7-octadiene higher than 3 vol %.
The hydrocarbon polymer/ZnO NPs coatings obtained
in the present study can be used in the preparation of
filtration materials that selectively filter oil from
oil/water mixtures.
5.Acknowledgments
The research was supported by the Italian Ministry for
Education, University and Research (MIUR), under
grants PRIN 2009, PON01_02239, PONa3_00369 and
PON02_00576_3333604, and Regione Puglia under
grant no. 51 “LIPP” within the Framework Programme
Agreement APQ “Ricerca Scientifica”, II atto integrativo
- Reti di Laboratori Pubblici di Ricerca. The authors
gratefully acknowledge Savino Cosmai, Danilo Benedetti
and Domenico Benedetti for the skilful technical assistance.
6.References
[1] C. R. Crick, J. C. Bear, A. Kafizas, and I. P. Parkin
Adv. Mater., 24, 3505 (2012).
[2] B. J. Privett, J. Youn, S. A. Hong, J. Lee, J. Han, J. H.
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