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European Journal of Applied Sciences – Vol. 10, No. 1
Publication Date: February 25, 2022
DOI:10.14738/aivp.101.11533. Goodson, M., Xu, K. G., & Guggilla, P. (2022). Effects of Non-Thermal Plasma Jet Treatment of Pure/Doped Polystyrene Thin Films
on UV-Vis Optical Properties. European Journal of Applied Sciences, 10(1). 81-87.
Services for Science and Education – United Kingdom
Effects of Non-Thermal Plasma Jet Treatment of Pure/Doped
Polystyrene Thin Films on UV-Vis Optical Properties
Mersaydes Goodson
Alabama A&M University Physics, Chemistry, and Math Department
Kunning G. Xu
University of Alabama Huntsville Mechanical and Aerospace Engineering
Padmaja Guggilla
Alabama A&M University Physics, Chemistry, and Math Department
ABSTRACT
Non-thermal Cold Atmospheric Plasma (CAP) to improve optical property of pure
and doped polystyrene (PS) thin films using He and Ar gas. These thin films were
fabricated using the solution cast method. Surface treatment of PS thin films were
performed by CAP. To analyze the effect of plasma treatment, the optical properties
of the thin films were measured and derived by UV-Vis spectroscopy in wavelength
range of 300-700 nm. Absorbance, transmittance, extinction coefficient, energy
band gap, and optical conductivity before and after Cold jet plasma treatment (CJT)
were compared. The results from Ar and He were similar in effectiveness. The
treatment did have an impact on the optical properties of these PS thin films. This
data will help to substantiate the use of CJT to enhance optical properties of polymer
thin films.
Keywords: UV-Vis absorption spectra, polystyrene thin film, nonthermal plasma jet
treatment, cold plasma, Cold atmospheric pressure CAP), Cold jet plasma treatment (CJT)
INTRODUCTION
Many efforts have been directed into the modification of surface roughness resulting in the
improvement in grain size and surface energy. As it is the first interface of material which may
encounter other materials and an external environment, one of the most important parameters
in nanotechnology and thin films is surface and roughness (Hosseinpour et al., 2019). Plasma
functionalization is the process by which a bondable surface is treated to improve its adhesive
properties, bondability, and pairability. Functionalization enhances properties to
characteristics of nanomolecules through surface modifications.
Cold atmospheric pressure has attracted high research interest recently as one of the most
versatile non-thermal techniques in surface modification. CAP are discharged plasma that can
extend beyond the plasma generation region into the surrounding ambient environments. They
can be generated at a discharge voltage around 2kV with discharge gaps in the order of
millimeters and are highly energetic photons in the ultraviolet range 100-400 nm (Golda et al.,
2020; Yahaya et al., 2021).
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 1, February-2022
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Cold plasma jet treatment (CJT) only affects the surface of the treated film and may improve
different surfaces for various materials (dielectric, polymers, and metals). CJT has been
implemented to reduce etching and chain scission in some polymers. However, sometimes
usage of various solvents and different acids may damage the surface and leak into the interior
of the material, affecting the interior properties as well (Zendham et al., 2018; Tabares & Junkar
2021).
For example, in some sensor devices, the metallic sensing layer has a short life span that
depends on the environment within which the sensor operates (Hosseinpour et al., 2019).
Cold plasmas can be characterized as high pressure, atmospheric pressure, and low pressure
according to the pressure conditions and nonequilibrium characteristics. They are an effective
source of reactive species such as radicals, mestables, and photons. Due to their high reactivity,
they are used in many applications, such as varying on surface roughness for polymer
activation, thin film deposition, nanostructuring of surfaces, and for the treatment of biological
substrates.
Sometimes warm or hot plasma are used for hardening and smoothing surfaces from friction
and erosion point of view. CAP is known as non-thermal because it is a weakly ionized gas that
can operate under atmospheric conditions near or just above room temperature Golda et al.,
2021; Yahaya et al., 2021; Zendhnam et al., 2018; Tabares & Junkar 2021; France & Short 1998).
Plasma is the predominate state of matter in the known universe belonging to the large family
of cold atmospheric pressure plasmas. When energy is added to a solid, in the form of heat or
electromagnetic radiation, it transforms into a liquid state, from which gas is obtained through
an additional supply of energy. Plasma is created when extra energy is continuing to be added
to the gas, it will become partially or completely ionized. Electrons are removed from the atoms
that constitute it. Eventually reaching a new state of matter, plasma, made up of free electrons,
atoms, molecules (carriers of heat), and ions further exciting ionization and dissociations. One
of the most peculiarities of plasma is that hey conduct electricity microscopically. On a
macroscopic scale, plasmas are electrically neutral (Yahaya et al., 2021; Zendhnam et al., 2018;
Tabares & Junkar 2021).
The surface of polymer thin films have been widely studied as well as the properties of
inorganic/organic nanocomposite materials. Polystyrene as a polymer has attracted much
attention specifically due to its interesting and superior physical and chemical properties. Thin
films constructed of inorganic nanoparticles and organic polymers have shown improvements
in these same properties and add additional properties. (Ellis et al., 2009; Sangawar & Golchha
2013; Tsuruoka et al., 2013).
These effects depend on the type of gas used. Most are working with Ar and He with a small
percentage of reactive gasses as O2, N2, He2. Results may also be influenced by the duration of
exposure time and nozzle distance to the sample (Hosseinpour et al., 2019 ; Zendhnam et al.,
2018).
In this paper, after solution cast fabrication of pure and doped PS thin films, they were exposed
to Ar and He non-thermal plasma to investigate the effects on optical and electrical properties.
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Goodson, M., Xu, K. G., & Guggilla, P. (2022). Effects of Non-Thermal Plasma Jet Treatment of Pure/Doped Polystyrene Thin Films on UV-Vis Optical
Properties. European Journal of Applied Sciences, 10(1). 81-87.
URL: http://dx.doi.org/10.14738/aivp.101.11533
EXPERIMENTAL SECTION
Materials
Methyl Ethyl Ketone (C4H8O) was purchased from Reagents. Polystyrene ((C8H8)n) and all
dopants were purchased from Sigma-Aldrich Chemistry as starting materials. Each dopant
contained 99% trace metals. The polystyrene latex beads are uniform in size and morphology.
Fabrication Technique
Thin films were fabricated utilizing solution casting method. All glassware used in this study
for solution casting was subject to rigorous cleaning. This fabrication technique offers many
advantages such as low cost and an easy fabrication technique.
Experimental Set up
The plasma jet set up which can be seen in
schematic 1 consisting of two concentric
electrodes, where the inner electrode is
typically connected to a radio frequency
(RF) power at high frequency resulting in
ionization of the working gas, which exits
the nozzle with a jet-like shape
(Hosseinpour et al., 2019). RF plasma
treatments may be employed to improve
the surface properties of commodity
polymers, increasing tetri range of potential applications for these materials (Tabares et al.,
2021).
With Ar and He being inert gases, would prevent damaging the thin films form oxidation or
carbonation. The reactor is flooded with argon (helium) at a rate of 3 standard liter per minute
(SLM) monitored by a flow meter with a pulse rate of 6 kHz and width of 1 microsec. The
treatment was conducted with a power of 7 kV at a period of 5 minutes for exposure tine for
plasma on the samples. Distance between the surface and plasma jet was constant at and the
films were exposed to CAP perpendicular (normal to the surface). During plasma treatment the
jet temperature was monitored and kept constant.
UV-Vis spectroscopy was measured before CJT of the samples. Acquisition of the optical
properties were carried out within 5 hours of treatment by Cary 3V UV-Vis Spectrophotometer.
The absorption spectra of the samples were recorded in wavelengths 300-700 nm.
RESULTS AND DISCUSSION
Figures 1-5 show UV-Vis of measured thin film samples before and after being exposed to CAP
(using He and Ar plasma gas). Although the samples were treated with both gases, the
difference in values between He and Ar results were same and combined to one graph. The
studey was conducted to see if there would be any effect of using either gas.
UV-Vis spectroscopy is a spectroscopy analysis technique using UV electromagnetic radiation
source and visible light using spectrophotometer instrument. The spectrophotometer consists
of the spectrometer and photometer. The spectrophotometer produces light from spectrum
Schema 1. Schematic set up of cold atmospheric jet plasma
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 1, February-2022
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with certain wavelength and the photometer is a measuring tool of light intensity transmitted
or absorbed (France & Short 1998).
Figure 1. UV-Vis optical absorption spectra for pure PS and doped PS thin films before (L) and
after (R) CJT treatment
The wavelength of UV-Vis light is a result from the process of electron transition. If electron
transition corresponded with the amount of photon energy, it will cause great absorption along
with the amount of energy from the photon (Dewi et al., 2019).
The absorbance peak can be seen to have shifted from wavelength ~350 nm in the untreated
samples to ~550 nm in the treated samples. Perhaps due to the wavelength where in the area
took place high absorbance process and photon energy was greater than energy of visible light
or attributed to an increase in the grains on the surface. PZT and KNbO3 absorption values
decreased with treatment, while LiTaO3 increased dramatically and there were no noted
changes in pure PS and LiNbO3 samples. However, in each sample, as the wavelength increases,
the absorption spectrum slightly increased by 0.04± nm. Optical absorption is an important
property for optoelectrical applications.
0
0.5
1
1.5
2
300 400 500 600
Absorbance (a.u.)
Wavelength (nm)
Pure PS BaEuAlMg
LiNbO3 LiT
kNbO3
0
0.5
1
1.5
2
2.5
3
3.5
4
300 400 500 600
Absorbance (a.u.)
Wavelength (nm)
KNbO3 LiNbO3 LiTaO3
PZT Pure PS
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Goodson, M., Xu, K. G., & Guggilla, P. (2022). Effects of Non-Thermal Plasma Jet Treatment of Pure/Doped Polystyrene Thin Films on UV-Vis Optical
Properties. European Journal of Applied Sciences, 10(1). 81-87.
URL: http://dx.doi.org/10.14738/aivp.101.11533
Figure 2. Transmittance % for pure PS and doped PS thin films before amd CJT treatment
The correlation between absorbance A and transmittance T can be written in the form
A = log $
!
"
% = log 1 − log �.
The phenomenon is that transmittance is reversely proportional to its absorbance value. Figure
2 can be reviewed to see the transmittance percent in each sample slightly increased, except
for LiTaO3 and LiNbO3. As transparency decreases, the sample absorbs more light.
Figure 3. Energy band gap for pure PS and doped PS thin films before and after CJT treatment
The value of the optical energy band gap was determined and plotted. If there is a change in
energy band gap – it is evident that the increased/decreased impact in the optical band gap is
due to the nonthermal plasma treatment. Thus behavior can suggest a change in degree of
disorder in the films due to changes in the polymer structure.
Based on the structure of the energy band, a material can be categorized as a semiconductor,
insulator, or a conductor. The conductor has a valence band (low state) and a conduction band
(lowest excited state) that do not coincide and the interval in between expresses an energy that
cannot be owned by an electron – the band gap. In thin films the optical band gap can be
determined by processing the transmittance and absorbance data.
0
0.5
1
1.5
300 500 700
Transmittance %
Wavelength (nm)
Pure PS BaEuAlMg
PZT LiNbO3
LiT kNbO3
0
0.5
1
1.5
300 400 500 600
Transmittance %
Wavelength (nm)
KNbO3 LiNbO3
LiTaO3 PZT
Pure PS
0
5
10
15
20
25
30
35
40
0 1 2 3 4
Energy Band Gap
Photon Energy (eV)
Pure PS BaEuAlMg
PZT LiNbO3
LiTaO3 KNbO3
0
5000
10000
15000
20000
25000
30000
35000
2 3 4 5
Energy Band gap
Photon Energy (eV)
BaMgAl kNBO3
LiNbO3 LiTaO3
LiZr Pure PS
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European Journal of Applied Sciences (EJAS) Vol. 10, Issue 1, February-2022
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Figure 4. Extinction Coefficient for pure PS and doped PS thin films before and after CJT
treatment
The extinction coefficient, shown in figure 4 shows that each sample increases with CJT. This
may be due to the increase in absorption coefficient. The extinction coefficient is lower at the
longest wavelengths, reverse of the results prior to CJT.
Extinction coefficient, k is related to the absorption coefficient by the relationship:
� = ��
4�
Where � is the incident photon wavelength. k is a measure of how fast the amplitude of the
wave decreases.
Figure 5. Optical conductivity against wavelength before and after exposure to plasma
treatment
The optical conductivity is one of the most powerful tools for studying the electronic states in
materials. Figure 5 shows spectrum indicating peak shift in the samples after CJT treatment. It
is also evident after exposure the optical conductivity increases as the wavelength gets longer.
CONCLUSION
In this article, we have investigated the impact of nonthermal plasma jet treatment on UV-Vis
characteristics of Pure/Doped PS nanocomposites. These thin films were fabricated using the
solution cast method and characterized for their optical properties before and after CJT. From
these results, CJT does have an impact on the surface of these PS samples, also you can note the
0
0.000001
0.000002
0.000003
0.000004
0.000005
300 500 700
Extinction Coefficient
Wavelength (nm)
Pure PS BaEuAlMg
PZT LiNbO3
LiTaO3 KNbO3
0
0.000002
0.000004
0.000006
0.000008
300 500
Extinction Coefficient
Wavelength (nm)
KNbO3 LiNbO3
LiTaO3 PZT
Pure PS
0
500000000
1E+09
1.5E+09
2E+09
2.5E+09
3E+09
3.5E+09
300 500 700
Optical Conductivity
Wavelength (nm)
Pure PS BaEuAlMg
PZT LiNbO3
LiTaO3 KNbO3
0
200000000
400000000
600000000
800000000
1E+09
1.2E+09
1.4E+09
1.6E+09
300 500
Optical Conductivity
Wavelength (nm)
KNbO3 LiNbO3
PZT Pure PS
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Goodson, M., Xu, K. G., & Guggilla, P. (2022). Effects of Non-Thermal Plasma Jet Treatment of Pure/Doped Polystyrene Thin Films on UV-Vis Optical
Properties. European Journal of Applied Sciences, 10(1). 81-87.
URL: http://dx.doi.org/10.14738/aivp.101.11533
impact on these properties due to the additives (dopants). The optical characteristics such as
absorbance, transmittance, energy band gap, optical conductivity, and extinction coefficient (k)
were calculated to analyze the properties. The impact of CJT was demonstrated and can be
clearly seen in the increase in energy bandgap seen in table 1 below.
Table 1. Comparison of energy bandgap before and after CJT.
Sample Energy Bandgap Before Energy Bandgap After
Pure PS 4.3 eV 5.25 eV
PS + LiNbO3 4.35 eV 5.44 eV
PS + LiTaO3 4.27 eV 5.14 eV
PS +_ KNBO3 4.54 eV 4.8 eV
ACKNOWLEDGMENTS
The author expresses gratitude to Title 3 and AL- EPSCoR Foundation for funding for the study
and to faculty of the Physics department at Alabama A&M University.
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