Thin Surface Layer of Plasma Treated Polyethylene
This paper reports on the effect of argon plasma on the high density polyethylene surface. The aim is to alter the surface in a manner and scale resulting in a stronger metal/polymer valence. The specimens are exposed to the direct current discharge, the irradiation time and power being variables. E...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2008
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| Назва видання: | Проблемы прочности |
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| Цитувати: | Thin Surface Layer of Plasma Treated Polyethylene / V. Kotal, P. Stopka, P. Sajdl, V. Svorcik // Проблемы прочности. — 2008. — № 1. — С. 97-100. — Бібліогр.: 13 назв. — англ. |
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irk-123456789-484502013-08-19T19:35:13Z Thin Surface Layer of Plasma Treated Polyethylene Kotal, V. Stopka, P. Sajdl, P. Svorcik, V. Научно-технический раздел This paper reports on the effect of argon plasma on the high density polyethylene surface. The aim is to alter the surface in a manner and scale resulting in a stronger metal/polymer valence. The specimens are exposed to the direct current discharge, the irradiation time and power being variables. Electron paramagnetic resonance and X-ray photoelectron spectroscopy (EPR and XPS, respectively) are employed to determine the plasma effect. The surface wettability is studied by goniometry. The plasma treatment leads to radical generation and activation of such agents as oxygen, thus the surface wettability is significantly increased. The evolution ofthe treated surface in different media is studied. The influence of an increased oxygen concentration and the storage medium on the concentration gradient within the surface monolayers is proved. The EPR data show a gradual and very slow decrease in the number of radicals present on the treated surface after 2000 h. Also evidence is given for partial dissolution of the treated surface in water. Представлены результаты изучения влияния плазмы аргона на поверхность полиэтилена высокой плотности. Целью исследования является изменение поверхности таким образом, чтобы увеличить валентность металла/полимера. Образцы подвергали воздействию разряда постоянного тока, при этом время воздействия и мощность являлись переменными величинами. Для определения влияния плазмы использовали электронный парамагнитный резонанс (ЭПР) и фотоэлектронную рентгеновскую спектроскопию. Смачиваемость поверхности изучали с использованием гониометрии. Плазменная обработка ведет к образованию радикалов и активизации таких реагентов, как кислород и таким образом, значительно увеличивается смачиваемость поверхности. Исследована эволюция обработанной поверхности в различных средах. Приведено подтверждение влияния повышенной концентрации кислорода и среды на градиент концентрации в поверхностных монослоях. Данные ЭПР свидетельствуют о постепенном и очень медленном уменьшении количества радикалов на обработанной поверхности после 2000 ч. Приведены также данные о частичном растворении обработанной поверхности в воде. 2008 Article Thin Surface Layer of Plasma Treated Polyethylene / V. Kotal, P. Stopka, P. Sajdl, V. Svorcik // Проблемы прочности. — 2008. — № 1. — С. 97-100. — Бібліогр.: 13 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/48450 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Kotal, V. Stopka, P. Sajdl, P. Svorcik, V. Thin Surface Layer of Plasma Treated Polyethylene Проблемы прочности |
| description |
This paper reports on the effect of argon plasma on the high density polyethylene surface. The aim is to alter the surface in a manner and scale resulting in a stronger metal/polymer valence. The specimens are exposed to the direct current discharge, the irradiation time and power being variables. Electron paramagnetic resonance and X-ray photoelectron spectroscopy (EPR and XPS, respectively) are employed to determine the plasma effect. The surface wettability is studied by goniometry. The plasma treatment leads to radical generation and activation of such agents as oxygen, thus the surface wettability is significantly increased. The evolution ofthe treated surface in different media is studied. The influence of an increased oxygen concentration and the storage medium on the concentration gradient within the surface monolayers is proved. The EPR data show a gradual and very slow decrease in the number of radicals present on the treated surface after 2000 h. Also evidence is given for partial dissolution of the treated surface in water. |
| format |
Article |
| author |
Kotal, V. Stopka, P. Sajdl, P. Svorcik, V. |
| author_facet |
Kotal, V. Stopka, P. Sajdl, P. Svorcik, V. |
| author_sort |
Kotal, V. |
| title |
Thin Surface Layer of Plasma Treated Polyethylene |
| title_short |
Thin Surface Layer of Plasma Treated Polyethylene |
| title_full |
Thin Surface Layer of Plasma Treated Polyethylene |
| title_fullStr |
Thin Surface Layer of Plasma Treated Polyethylene |
| title_full_unstemmed |
Thin Surface Layer of Plasma Treated Polyethylene |
| title_sort |
thin surface layer of plasma treated polyethylene |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2008 |
| topic_facet |
Научно-технический раздел |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/48450 |
| citation_txt |
Thin Surface Layer of Plasma Treated Polyethylene / V. Kotal, P. Stopka, P. Sajdl, V. Svorcik // Проблемы прочности. — 2008. — № 1. — С. 97-100. — Бібліогр.: 13 назв. — англ. |
| series |
Проблемы прочности |
| work_keys_str_mv |
AT kotalv thinsurfacelayerofplasmatreatedpolyethylene AT stopkap thinsurfacelayerofplasmatreatedpolyethylene AT sajdlp thinsurfacelayerofplasmatreatedpolyethylene AT svorcikv thinsurfacelayerofplasmatreatedpolyethylene |
| first_indexed |
2025-07-04T08:57:49Z |
| last_indexed |
2025-07-04T08:57:49Z |
| _version_ |
1836706137443926016 |
| fulltext |
UDC 539. 4
T h in S u r fa c e L a y e r o f P la s m a T r e a te d P o ly e th y le n e
V . K o ta l,1a P . S top k a ,2 P . S ajd l,3 and V . Svorcfk 1
1 Department o f Solid State Engineering, Institute o f Chemical Technology, Prague, Czech Republic
2 Institute o f Inorganic Chemistry, Academy o f Sciences o f the Czech Republic, Rez, Czech
Republic
3 Department o f Power Engineering, Institute o f Chemical Technology, Prague, Czech Republic
a vladimir.kotal@vscht.cz
This paper reports on the effect o f argon plasma on the high density polyethylene surface. The aim
is to alter the surface in a manner and scale resulting in a stronger metal/polymer valence. The
specimens are exposed to the direct current discharge, the irradiation time and pow er being
variables. Electron paramagnetic resonance and X-ray photoelectron spectroscopy (EPR and XPS,
respectively) are employed to determine the plasma effect. The surface wettability is studied by
goniometry. The plasma treatment leads to radical generation and activation o f such agents as
oxygen, thus the surface wettability is significantly increased. The evolution ofthe treated surface in
different media is studied. The influence o f an increased oxygen concentration and the storage
medium on the concentration gradient within the surface monolayers is proved. The EPR data show
a gradual and very slow decrease in the number o f radicals present on the treated surface after
2000 h. Also evidence is given fo r partial dissolution o f the treated surface in water.
K eyw ords: argon plasma, h igh density polyethylene, goniom etry, X -ray photoelectron
spectroscopy, electron paramagnetic resonance.
In trod u ction . Polym ers have been applied su ccessfu lly in m any fields such as
adhesion, biom aterials, protective coatings, friction and wear, com posites, m icroelectronic
devices, and thin-film technology. In general, special surface properties w ith regard to
chem ical com position, hydrophilicity, roughness, crystallinity, conductivity, lubricity, and
cross-linking density are required for successfu l applications in various fie ld s. H ow ever,
the “raw-pristine” polym er surface is inert and the m odification techniques need to be
used [1].
Plasm a treatment, w hich is know n to m odify chem ical and physical states o f the
surface w ithout altering the bulk properties, has becom e an important tool used in industry
[2, 3]. Plasm a effect is versatile and strongly depends on the experim ental conditions
chosen. Take for exam ple polyethylene, its plasm a treatment leads to creation o f new
chem ical groups, branching and crosslinking o f m acrom olecules [2 ], and to formation o f
low m olecular w eight oxid ized structures. O w ing to ablation, the surface topography o f
the polym er is affected too. These alterations are also w ell know n to result in the
formation o f reactive sites for the interaction w ith the m etal atom s such as copper and
aluminum. The m etal polym er adhesion has been o f h ighest interest recently and every
attempt to elucidate their interaction is greatly appreciated.
The aim o f this study is introduction o f reactive sites to the high density polyethylene
(H D PE ) surface by argon plasm a treatment. Further, the evolution o f wettability, radical
concentration, and chem ical structure is thoroughly investigated. The surface w ettability is
studied by goniometry. X -ray photoelectron spectroscopy (X P S ) is carried out to observe
the surface chem ical structure and electron paramagnetic resonance spectroscopy is
em ployed for determination o f the radical number. The experim ent and the above
m entioned m ethods y ield a com plex insight into the evolution o f the H D PE plasm a treated
surface.
© V. KOTAL, P. STOPKA, P. SAJDL, V. SVORCIK, 2008
ISSN 0556-171X. Проблемы прочности, 2008, № 1 91
mailto:vladimir.kotal@vscht.cz
V. Kotal, P. Stopka, P. Sajdl, and V. Svorcik
E xp erim en ta l. P olym er an d P lasm a P aram eters Specification . Oriented H DPE in
the form o f 50 jum thick fo ils w as used in the present experiment. The fo ils were supplied
by Granitol Ltd., C zech Republic. The sam ples w ere treated in a direct current discharge
generated using Balzers SC D 050 device. The further discussed plasm a effect was
obtained under the fo llow ing conditions (gas purity 99.997% and the flow rate 0.3 l/s,
pressure 10 Pa, electrode distance 50 m m and its area 48 cm , chamber volum e approx.
3 31000 cm , plasm a volum e 240 cm , and pow er 8.3 W ). The treated polym er sam ples were
stored under laboratory conditions, exposed to ambient atmosphere.
D iagn ostic M eth ods . The contact angle, characterizing the surface wettability, was
m easured using distilled water at room temperature w ith a Kernco G-1 goniom eter
(Japan). The “static” contact angle dependence on the tim e after treatment w as obtained
[4].
A n O m icron N anotechnology ESCAProbeP spectrometer w as used to observe the
treated surface. The dim ensions o f the area analyzed were 2X 3 mm. The X -ray source was
m onochrom ated at 1486.7 eV. The spectra were measured stepw ise w ith a step in binding
energy o f 0.05 eV. In order to understand the cause forthe decrease in the oxygen content
w ithin several surface m onolayers, the spectra were collected at six angles betw een the
detector and the surface normal (A R X PS). The data were processed by the CasaXPS
program.
The concentration o f free radicals w as determ ined using an electron paramagnetic
resonance spectroscopy w ith an x-band spectrometer o f type E lexsys E -540,
Bruker-Biospin w ith a relative error o f 10%. The sam ples were p laced in a quartz tube and
m easured at room temperature. The experim ental conditions were as follow s: the
m agnetic field range 600 mT, sw eep tim e 180 s, m agnetic m odulation 0.4 mT, field
m odulation 100 kHz. The standards M n/ZnS and Cr/M gO w ere used for the g-factor
calibration and for quantitative evaluation o f the spectra. Identification and determination
o f signals w ere perform ed by com parison w ith the standards.
R esu lts and D iscussion . G oniom etry. The dependence o f the water contact angle on
the plasm a treatment tim e is show n in Fig. 1. The tim e after the plasm a treatment is a
parameter o f the curves. The higher the treatment tim e the low er the contact angle,
namely: the angle decreases from 100° (pristine HD PE) to 10° (240 s treated HDPE). The
increasing tim e after the plasm a treatment leads to an increase in the contact angle. The
increase is more distinct for longer plasm a treatments. A s has been reported in a recent
study [5], the present m easurem ents confirm the dependence o f the contact angle
(wettability) on the tim e after the A r plasm a treatment. The cause for this is the diffusion
o f the low -m ass oxid ized fragments and orientation o f the polar groups towards the
specim en bulk and this phenom enon is referred to as hydrophobic recovery [6 , 7].
E lectron P aram agn etic R esonance S pectroscopy (E PR ). The number o f radicals
form ed on the surface w as m onitored by the EPR. Figure 2 show s the number o f radicals
for sam ples stored in different “m edia.” The “water” sam ple w as stored in water for 12
hours, and then dried and exam ined. The “air” sam ple w as kept in an ambient atmosphere.
The low er number o f radicals for a “w ater” sam ple results from the storage in water,
w hich caused the rem oval o f low -m olecular-w eight oxid ized material from the treated
surface [8 ]. This material contains a portion o f the introduced radicals. Figure 2 also
clearly show s a slow decrease in the number o f radicals during storage. The free radical
centers are “trapped” inside the crosslinked layer and are o f low chem ical reactivity, even
i f the surface is exposed to water [9].
X -ray P hotoelectron Spectroscopy . The chem ical structure o f the plasm a treated
HDPE stored subsequently in air or water w as exam ined using the X PS. It w as reported
that the surface o f the Ar plasm a treated H DPE contains groups o f pristine PE (-C H 2) and
oxygen introduced during the treatment (-C = O , -C O O , and -C O C -) [5].
98 ISSN 0556-171X. npo6n.eubi npounocmu, 2008, N 1
Thin Surface Layer o f Plasma Treated Polyethylene
Fig. 1 Fig. 2
Fig. 1. Evolution o f the contact angle dependence on the plasma treatment time. The numbers
represent hours elapsed after the treatment.
Fig. 2. Dependence o f spin number o f the plasma treated samples on time after the treatment. The
samples were treated successively stored 12 h in water ( • ) resp. air (O ) and measured.
45-
40 -
35 -
30 -
25 -
20 -
HDPE/plasma
Water 24
■/■
/
_ _ . ■
Air 1 "''"'-O'—'' / 1 o
/•
Air 24
•---- ~~~~~~
------
20 40
0 (deg)
60 80
Fig. 3. The dependence o f oxygen concentration on the detector to surface normal angle. The
samples were plasma treated and preceding the measurement stored in air for 1 h (Air 1) and 24 h
(Air 24). The sample (Water 24) was stored 24 h in water.
In the EPR study it w e found that a portion o f the treated surface is d issolved during
storage in water. In order to confirm this result and also to learn more about the evolution
o f the first surface layers (w ithin approx. 5 nm) after the treatment, the angle-resolved
X PS has been carried out [10, 11]. Figure 3 show s the dependence o f the oxygen
concentration on the angle betw een the surface normal and the detector. The higher the
angle, the thinner layer is studied, i.e ., an angle o f 80° allow s studying the structure o f the
surface m onolayers. Figure 3 show s that the oxygen concentration in the sam ples treated
and stored in air for 1 h and 2 4 h (Air 1 and A ir 24 , respectively) decreases towards the
bulk o f the sam ple. It has already been stated that the surface is oxygenated during the
treatment. The post treatment oxygen incorporation is rather uncertain and som e authors
are in favor o f it [12] w hile others are not [13]. W hat is worth noticing is that the oxygen
concentration o f the “Air 24” sam ple is low er than that o f “A ir 1.” This has been shown
by goniom etry, the results o f w hich proved increasing hydrophobic character after the
treatment, i.e ., during aging. Another important conclusion m ade from the A R X PS data is
that the oxygen concentration in the water stored sam ple “Water 2 4 ” at h igh angles is
ISSN 0556-171X. npoôëeMbi npounocmu, 2008, N 1 99
V. Kotal, P. Stopka, P. Sajdl, and V. Svorcik
low er than that in the “A ir 1”sample. This suggests that a portion o f the surface, especially
o f the oxid ized material, is d isso lved in water. This has been confirm ed by the EPR in this
work, as w ell as by the IR spectroscopy o f the material d issolved in water [8 ]. Finally, the
only explanation for the increase in the concentration o f oxygen w ith a decrease in the
angle for the “Water 24 ” sam ple is that the oxygen concentration increases into the depth
o f the m aterial(within the nm scale). A t a depths o f the order o f 10 nm w e expect a sharp
decrease in oxygen concentration. This is confirm ed by Rutherford back scattering (RBS)
analyses carried out on this sam ple [8 ].
C onclusions. The effect o f the HDPE treatment in the Ar plasm a discharge on its
properties has been studied by different techniques. We have proved that the discharge-
induced surface alterations lead to an im m ediate increase in the surface wettability.
M oreover, this effect is not permanent and the w ettability decreases during the tim e after
treatment. The EPR data show a gradual and very slow decrease in the number o f radicals
present on the treated surface; partial d issolving o f the treated surface in water is also
observed. The backbone o f this report is the X PS observations, w hich revealed an
increased oxygen concentration w ithin the treated surface. Furthermore, it has been
proved that the water storage causes an increase in the oxygen concentration gradient
w ithin the surface m onolayers. On the contrary, w hen the sam ple is stored in air, the
oxygen gradient decreases.
Acknowledgments. This work was supported by the GA ASCR under the project
KAN400480701 and Ministry o f Education of the CR under research program No. LC 06041.
1. C. M. Chan, T. M. Ko, and H. Hiraoka, Surf. Sci. Rep., 24, 3 (1996).
2. M. R. Wertheimer, A. C. Fozza, and A. Hollander, Nucl. Instrum. Meth. B, 151, 65 (1999).
3. P. K. Chu, J. Y. Chen, L. P. Wang, and N. Huang, Mater. Sci. Eng. R, 36, 143 (2002).
4. M. A. Grunlan, N. S. Lee, F. Mansfeld, et al., J. Polym. Sci., 44, 2551 (2006).
5. V. Svorcik, V. Kotal, P. Slepicka, et al., Nucl. Instrum. Meth. B, 244, 365 (2006).
6 . F. Truica-Marasescu, P. Jedrzejowski, and M. R. Wertheimer, Plasma Process. Polym., 1, 153
(2004).
7. S. Guimond and M. R. Wertheimer, J. Appl. Polym. Sci., 94, 1291 (2004).
8 . V. Svorcik, V. Kotal, P. Slepicka, et al., Polym. Deg. Stab. (submitted).
9. M. Kuzuya, T. Kawaguchi, M. Nakanishi, and T. Okuda, J. Chem. Soc. Faraday Trans., 82,
1441 (1986).
10. S. Oswald, R. Reiche, M. Zier, et al., Appl. Surf. Sci., 252, 3 (2005).
11. P. J. Cumpson, J. Elec. Spec. Rel. Phenomena, 73, 25 (1995).
12. M. Kuzuya, S. Kondo, M. Sugito, and T. Yamashiro, Macromolecules, 31, 3230 (1998).
13. O. Ochiello, Proc. o f the 7th Int. Conf. on SIMS (1990), p. 789.
Received 28. 06. 2007
100 ISSN 0556-171X. npo6neMbi npouHocmu, 2008, № 1
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