22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Atmospheric pressure PECVD of fluorocarbon coatings
on polyurethane foams
F. Fanelli1 and F. Fracassi1, 2
1
National Research Council (CNR), Institute of Inorganic Methodologies and Plasmas, Bari, Italy
2
Department of Chemistry, University of Bari ‘Aldo Moro’, Bari, Italy
Abstract: Fluorocarbon coatings are deposited on polyurethane foams using an
atmospheric pressure dielectric barrier discharge fed with helium and hexafluoropropene.
The ignition of the atmospheric plasma inside the three-dimensional porous structure of the
foams allows depositing a uniform coating within their interior.
Keywords: DBD, PECVD, fluoropolymer, polyurethane foam
1. Introduction
In recent years thin film deposition on complex threedimensional (3D) porous substrates has attracted growing
interest in materials chemistry for the design and
fabrication of biomaterials, heterogeneous catalysts,
special wettable materials, etc. [1-3]. Efforts are directed
towards the preparation of conformal coatings onto the
entire 3D network of the substrates, i.e., onto their outer
and inner surfaces, while leaving the bulk properties and
porous architecture intact.
Several strategies have been developed for the
deposition of thin films on both polymeric and inorganic
foams; they exploit for instance liquid phase reactions as
well as dip-coating, spin-coating and spray-coating
methods [1]. Moreover, among various gas phase
techniques, over the last decade, the low pressure plasmaenhanced chemical vapor deposition (PECVD) has
demonstrated to be a viable approach for the surface
modification of porous materials, as for instance widely
reported in the case of polymeric scaffolds for tissue
engineering applications [3-5]. Diffusion of reactive
depositing species into the scaffold interior is thought to
control thin film deposition in low pressure plasmas;
several studies enlightened, in fact, that limited
penetration of thin film precursors within the porous 3D
substrate can result in gradients of the coating thickness
and of the surface chemical composition moving from the
exterior to the interior of the scaffold [3-5].
To our best knowledge, the atmospheric pressure
plasma deposition of thin films inside complex 3D
materials, such as porous foams, has not been reported so
far. Therefore there is a need to fill this gap and to
evaluate the potential of atmospheric pressure PECVD in
this field. Indeed, the unique possibility of igniting the
atmospheric cold plasma inside the cavities of porous
materials [6, 7] could open
new and exciting
opportunities in plasma processing.
This contribution focuses on the PECVD of
fluoropolymers inside polyurethane (PU) foams using
atmospheric pressure dielectric barrier discharges
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(DBDs). The deposition processes are carried out igniting
the DBD into the porous 3D network of the foams.
2. Experimental
Deposition processes are performed using a DBD
reactor [8] with parallel plate electrode configuration,
lateral injection of the feed mixture into the interelectrode
zone and gas gap of 5 mm (Fig. 1a). The DBD is
generated using a sinusoidal ac voltage (20 kHz, 3.3
kV pp ) and fed with helium-hexafluoropropene mixtures
(He and C 3 F 6 flow rates of 6 slm and 6 sccm,
respectively). Commercial fully interconnected open-cell
PU foams having 30 and 60 pores per linear inch (ppi) are
used as substrates.
The chemical and morphological characterization of the
foams is carried out by X-ray photoelectron spectroscopy
(XPS) and scanning electron microscopy (SEM).
(a)
~
Gas flow
(b)
Fig. 1. (a) Schematic of the parallel plate DBD cell
utilized for thin film deposition on PU foams; (b) picture
showing the discharge into the pores of the 30 ppi foam.
3. Preliminary results
Under the experimental conditions utilized in this work,
the DBD exhibits a filamentary behaviour. During
deposition processes, a strip of PU foam is located in the
middle of the discharge region (Fig. 1a) so that the gas
1
flow is forced to pass through the foam and, as evident in
Fig. 1b, the ignition of the DBD inside the pores of the
foams can be clearly observed.
A representative high resolution C1s XPS spectrum of
the foam cross-section after a deposition time of 30 min is
shown in Fig. 2; the cross-section is obtained cutting the
foam with a scalpel after deposition. The C1s signal
presents the typical components ascribed to the
fluorinated groups (e.g., C-CF, CF, CF 2 and CF 3 ) of the
deposited coating [5, 8]. It is worth mentioning that
similar C1s XPS spectra are obtained for both the inner
and outer surfaces of the plasma-treated foam, indicating
the deposition of a conformal coating onto the entire 3D
network.
CF3
CF2
C-CF
CO
CF
C-C
C-H
298
296
294
292
290
288
286
284
282
Binding Energy (eV)
Fig. 2. Typical high resolution C1s XPS spectrum
corresponding to the cross-section of the plasma-treated
30 ppi foam.
SEM analyses allow to observe that the overall porous
architecture of the foam is not modified by the plasma
treatment (Figure 3a); interestingly, the presence of the
fluorocarbon coating within the interior of the foam can
be clearly appreciated when observations of crosssectioned foam ligaments are performed (Fig. 3b).
(a)
4. Conclusion
In this work a He/C 3 F 6 -fed DBD is used to deposit a
fluorocarbon coating on commercial PU foams. During
depositio, the discharge is ignited inside the porous 3D
network of the material and allows depositing a uniform
coating within its interior as enlightened by XPS and
SEM analyses.
5. Acknowledgements
The research is supported by the Italian Ministry for
Education, University and Research (MIUR), under grants
PRIN 2009, PON01_02239 and PONa3_00369,
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. Danilo Benedetti
and Savino Cosmai are gratefully acknowledged for the
skilful technical assistance.
6. References
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Tsapatsis, S. Al Hashimi, L. F. Francis, Industrial &
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[3] Q. Zhu, Q. Pan, F. Liu, Journal of Physical Chemistry
C, 115, 17464 (2011).
[4] F. Intranuovo, E. Sardella, R. Gristina, M. Nardulli, L.
White, D. Howard, K.M. Shakesheff, M. R. Alexander, P.
Favia, Surface & Coatings Technology, 205, S548
(2011).
[5] M. J. Hawker, A. Pegalajar-Jurado, E. R. Fisher,
Langmuir, 30, 12328 (2014).
[6] M. Kraus, B, Eliasson, U. Kogelschatz, A. Wokaun,
Physical Chemistry Chemical Physics, 3, 294 (2001).
[7] K. Hensel, The European Physical Journal D, 54, 141
(2009).
[8] F. Fanelli, R. d’Agostino, F. Fracassi, Plasma
Processes and Polymers, 8, 557 (2011).
(b)
thin film
Fig. 3. SEM images: (a) interior of the plasma-treated 30
ppi foam (the arrow indicates a cross-sectioned ligament);
(b) detail of the cross-sectioned ligament.
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