Research Journal of Recent Sciences _________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 238-243 (2012)
Res.J.Recent Sci.

The Study of Mechanisms of Charge Production in
Pure and Sensitized Polymer Films
Bhardwaj M.K.1 and Khare P.K.2
Department of Physics, Govt. College Khategaon, Dist. Dewas, MP, INDIA
2
Dept. of PG Studies and Research in Physics and Electronics, RD University, Jabalpur, MP, INDIA
1

Available online at, www.isca.in
(Received 15th October 2011, revised 10th January 2012, accepted 25th January 2012)

Abstract
The mechanisms of charge production in pure and malachite green sensitized Polyvinyl chloride (PVC) samples have been studied
by short circuit thermally stimulated depolarization current (TSDC) measurement and ultraviolet spectroscopy (U.V.) studies. The
samples were prepared by the casting from solution technique whose thickness measured around 30µm. The samples were
sandwiched between similar aluminum electrodes and polarized at temperature 105 oC with polarizing fields 20, 30, 40 and
50kV/cm. Two peaks current maximum found around at 63±8 and138±7°C for pure, 06 and 7.5% sensitized PVC samples, while for
higher concentration (i.e.10 and 15%) one peak was measured around ≈65 oC in positive direction and the other peak around
≈140oC in the negative direction. The TSDC spectra have been used to calculate activation energy by initial rise method .The
calculated activation energies are 0.389-0.719ev for pure PVC and 0.298-1.09ev for sensitized PVC samples. The magnitude of
peak current increases with polarizing field and temperature, dipolar, space charge and charge transfer complexes mechanisms
may be responsible for this nature. In the case of UV spectra no band appears in pure PVC however the addition of malachite
green, gives rise four absorption bands around 260, 310, 440, and 630nm.The average effect has been observed in the intensity of
third (400-450nm) and fourth bands (550-700nm). The formation of charge transfer complexes is evidenced in the UV-visible
absorption spectra by the appearance and change in the intensity of absorption bands.
Keywords: Thermally stimulated depolarization current (TSDC), ultraviolet spectroscopy, pure and sensitized polyvinyl chloride,
casting from solution technique, thermo electrets, dipolar, space charge and CTC`S mechanisms.

Introduction
The thermally stimulated depolarization current (TSDC) is
an effective tool for extracting information about internal
structure and molecular relaxation as well as the
establishment and decay of the space charge due to trapping
of charge carriers and their subsequent thermal release from
trap in polymer1-4. The total charge stored in a polymeric
electrets and the different mechanisms which contributed to
these charge are sensitive to the structure of the forming
material .Charge storage may be due to either dipolar
orientation or space charge, there must be free equilibrium
charges in the electrets which are responsible for its intrinsic
ohmic conductivity. The reorientation of all aligned dipoles
at random due to the thermal agitation, the motion of excess
charges origination from space limited drift and diffusion and
ohmic conduction result in the decay of the net charge of an
electrets during TSDC. The TSDC of polar dielectrets
usually shows different peaks indicating thereby the
depolarization of thermo-electrets are realized by several
processes two of these are the relaxation of aligned impurity
point defect complex5 and relaxation of the space charge
caused by mobile defects accumulated at the electrodes6,7.
It is known that a dielectric medium takes a long time to

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relax to the steady state at low temperature. Therefore it is
useful to stimulated the discharge of the polarized dielectric
at a higher temperature. If the temperature of the dielectric is
increased at a constant rate glow peaks will be obtained at a
particular temperature which are related to the activation
energy of the relaxation process. The carrier mobility in
polymer is extremely small because the carrier are
predominantly located in trap 8 increased the mobility in the
polymer by impregnating the material with impurity 9.
Basically three kinds of phenomena can occur in thermal
charging10,11.
We have studied the depolarization behaviour of pure and
sensitized PVC samples using the short circuit thermally
stimulated discharge current technique and formation of
charge transfer complex by Ultraviolet Spectroscopy.

Material and Methods
The polyvinyl chloride (PVC) and malachite green used in
the present work were procured from M/s Robert Jonson,
England. Dimethyl formamide (D.M.F.) was used as the
solvent. PVC 100 mg was dissolved in DMF 10 ml by
stirring at 60oC for 4 hours to get a homogenous and
transparent solution. The solution thus, prepared was then
poured onto a cleaned glass plate floating on mercury pool.
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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 238-243 (2012)
Res.J.Recent Sci.
The solvent was allowed to evaporate in an oven at 60 oC for
6 hours to yield the desired samples. The films so prepared
were dried for 18 hours in a dust free chamber. For further
period of time to remove by residual solvent, dried sample
thus obtained was uniformly smooth and could be easily
peeled. The samples approximately 30µm in thickness were
sandwiched between the two aluminum electrodes. The
sample holder was placed in a furnace and heated up to the
poling temperature of 105oC. The sample was allowed to
remain at that temperature for about 60 minute. Then electric
field of desired strength was applied for 60 minute at fixed
poling temperature. The sample was allowed to cool down at
room temperature in the presence of applied field. Total time
of polarization was adjusted to be 180 minutes in each case.

PVC14, it must correspond to a molecular motion or dipole
disorientation process rather than a trap depth.

The thermo electret was then short-circuited at room
temperature for 5 minutes to remove the frictional and stray
surface charges. The voltage was applied by high voltage
unit (EC–HV 4800 D). The sample temperature was raised at
a liner heating rate of 5°C/minute, while the current was
recorded by means of a Keithley 610 C electrometer. For
ultraviolet
study
PARKIN
ELMER
UV/VS
spectrophotometer Mambda-12 was used.

Results and Discussion
The TSDC spectra of pure PVC and sensitized samples (i.e.6
and7.5℅) consist of two peaks, located around 63±8 and
138±7°C respectively, represented by figures 1-3. However
on increasing sensitization, the first peak shifts towards
higher temperature side and second peak shifts towards lower
temperature side and current starts appearing in the negative
direction. For the higher concentration (i.e.10 and15℅) both
the peaks merge into one and the corresponding thermograms
are characterized by peaks opposite in polarity observed
around 65 and 140 °C respectively are shown in figures.4-5.
This shows the negative effect of malachite green12. The
peak current increases with the increase in polarizing field.
The activation energy is calculated by the initial rise method
listed in table -1 (results not shown). PVC is known to
exhibit three relaxation processes , α and α’13. The  peak
occurs in the glassy state of the polymer usually below room
temperature and is due to the local reorientation of the polar
side groups while the α peak is found at the glass rubber
transition temperature Tg, where either the segment motion of
the main chain, or the disorientation of the polar side group
carrying a net dipole-dipole moment sets in.
The third process is α’ which is observed at temperature
higher than those for α process probably due to the charge
accumulation (space charge) near the electrodes. In the
present investigation, we have observed two peaks. The first
peak observed just near the glass transition temperature of
PVC corresponds to α relaxation process and the activation
energy associated with this discharge process is 0.3 eV. The
observed activation energy is comparable to that associated
with the molecular motion or the phase transition process in

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Figure-1
TSDC Thermograms of pure polyvinyl chloride (PVC)
samples polarized with various fields at
polarizing temperature Tp=105°C

Figure- 2
TSDC Thermograms of 6% malachite green sensitized
(PVC) samples polarized with various fields
at polarizing temperature Tp=105°C

239

Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 238-243 (2012)
Res.J.Recent Sci.

Figure-3
TSDC Thermograms of 7.5% malachite green sensitized
(PVC) samples polarized with various fields at polarizing
temperature Tp=105°C

Figure-4
TSDC Thermograms of 10% malachite green sensitized
(PVC) samples polarized with various fields at polarizing
temperature Tp=105°C
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Figure-5
TSDC Thermograms of 15% malachite green sensitized
(PVC) samples polarized with various fields at
polarizing temperature Tp=105°C

Figure- 6
UV Spectra of pure and sensitized PVC Samples
Spectrum of pure Polyvinyl chloride sample
Spectrum of 6% sensitized PVC sample
Spectrum of 7.5% sensitized PVC sample
Spectrum of 10% sensitized PVC sample
Spectrum of 15% sensitized PVC sample
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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 238-243 (2012)
Res.J.Recent Sci.
Further the observed peak must be related to the
depolarization of the aligned dipoles connected with the
chain of the polymer rather than to the charge released during
the glass transition temperature. Because the magnitude of
the charge corresponding to this peak increases linearly with
an increase of Ep suggesting a dipolar mechanism is involved
during the depolarization process of peak first. The activation
energy of 1.07 eV for the higher temperature peak α’ is large
and associated with an ionic mechanism rather that with a
dipolar mechanism or some dipolar mechanism of some
dipolar rotation.

depend upon the amount of doping used. The low
temperature peaks may be attributed to the shallow trapping
of mobile charge carriers, while the high temperature peak is
due to the re-orientation of dipoles. On further sensitization,
these carriers are bound to the impurity sites, and this result
the disappearance of these peaks24.
It appears that because of increased intermolecular
interaction on sensitizing, dipoles are entangled in such a
way that the contribution of orientation of dipoles towards
the polarization of the sample in the presence of an applied
field becomes insignificant. It has been stated earlier, the
observed peaks exhibit characteristics of both dipolar as well
as space charge behavior25,26.

For this peak released charge show a saturation trend with
increase in Ep. The mechanism of ionic conduction in PVC,
found by several workers15,16 and they confirm the existence
of excessive ions in the bulk of the polymer. These ions must
have come either from the dissociation of some of the
molecules or from the thermal degradation of PVC.

The space charges consisting of charges within the samples
which become mobile above the glass transition temperature
is expected to be responsible for the intensity of polarization.
Moreover, since the second observed peak is above the glass
transition temperature, it will definitely have partial
contribution from the Maxwell-Wagner type space charge at
the crystalline amorphous phase boundaries.

The appearance of a peak with polarity opposite to that of the
dipoles suggests that, in addition to the normal mechanism of
polarization some other mechanism must be operative.
Malachite green is a cationic dye having triphenylmethane
structure 25,2 .The colored ion is charged positively19, the dye
having triphenylmethane structure can easily form charge
transfer complexes (CTC) with the substrate1,20. Malachite
green has one amino group containing an unshared pair of
electrons21,22 which may be responsible for CTC formation.
Also in view of such consideration, malachite green is
supposed to interact strongly with polymer matrices to form
CTC23.

It is interesting to note that the TSDC behaviour of PVC is
modified considerably on sensitization. Ascertaining the
existence of a charge transfer complex in polymeric systems
is often a difficult task. Many charge transfer complexes are
highly colored and therefore spectral studies are more useful.
The formation of charge transfer complexes is evidenced in
the UV-visible absorption spectra by the appearance and
change in the intensity of absorption bands.
Absorption spectra of pure and sensitized PVC (with
different percentage of malachite green i.e. 6, 7.5, 10, and
15%) are shown in figure 6. No bands appears in the spectra
of pure sample however, the addition of malachite green in
PVC gives rise four absorption bands around 260,310,440
and 630 nm. It is clear that an average effect has been
observed in the intensity of third (400-450 nm) and fourth
bands (550-700 nm).

The shift of 140oC peak towards lower temperatures with
increasing concentration of malachite green may be due to
the increase in the mobility of charge carriers. The CTC are
supposed to create localized states of various depths which
will lead to trapping sites and distribute over a considerably
wide energy range. This may be the cause of the merging of
first and second peaks. Thus, we found not only that the
original trapping levels corresponding to the TSC peaks at
63+8 and 138+7oC are quantitatively affected by the addition
of malachite green but also that new peaks appear which

Table-1
Depolarization kinetic data i.e. Activation Energy for pure and
various malachite green sensitized PVC samples
Pure PVC
6% M green
7.5% M green
10% M green
Field
Temperature
(eV)
sensitized PVC sensitized PVC sensitized PVC
o
(kV/cm)
C
(eV)
(eV)
(eV)
20

15% M green
sensitized PVC
(eV)

0.389

0.700

0.359

0.685

0.341

0.671

0.339

1.09

0.317

0.991

0.387

0.719

0.351

0.678

0.339

0.669

0.336

1.07

0.307

0.989

40

0.383

0.714

0.349

0.667

0.337

0.660

0.329

1.00

0.301

0.981

50

0.373

0.704

0.340

0.635

0.340

0.650

0.326

1.00

0.298

0.979

30

105

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Research Journal of Recent Sciences _____________________________________________________________ ISSN 2277-2502
Vol. 1 (ISC-2011), 238-243 (2012)
Res.J.Recent Sci.

SENSITIZED SAMPLES

(A)

ABSORBANCE

(nm)

PEAK POSITION

15%

(A)

ABSORBANCE

(nm)

PEAK POSITION

10%

(A)

ABSORBANCE

(nm)

PEAK POSITION

7.5%

(A)

ABSORBANCE

(nm)

6%
PEAK POSITION

PURE PVC SAMPLES

PEAKS

ABSORBANCE

Table-2
Analysis of UV spectra of pure and sensitized
Polyvinyl chloride samples

FIRST

NOT FOUND

260

1.25

230

3.9

240

4.1

230

4.4

SECOND

NOT FOUND

320

1.00

310

2.9

280

3.1

270

3.5

THIRD

NOT FOUND

430

0.7

430

2.1

430

2.25

430

3.2

FOURTH

NOT FOUND

630

3.4

580

3.5

640

3.7

610

3.6

The intensity of the bands appears in the range of 200-400
nm found to increase with the increases in malachite green
concentration. It is evident from all the figures that width of
the fourth band increases and intensity of the band is found to
decrease with optimum concentration, listed in table 2. The
formation of charge transfer complexes27 is evidenced in the
UV-visible absorption spectra by the appearance and change
in the intensity of absorption bands.

References

Conclusion
Thermally stimulkated discharge current of pure polyvinyl
chloride (PVC) revel a strong dependence on the
sensitization. Which is the source of charge carrier
responsible for conduction and observed polarization of the
polymer. Space charge, ionic conduction, dipolar and charge
transfer complexes mechanisms are operated by these
studies.

1

Khare P.K. and Chandok R.S, Electrical properties of
modified grafted polypropylene, Phys Stat. Solidi, 147,
509-513 (1995)

2

Khare P.K. et al, Transient current in discharge mode in
cellulose acetate, polyvinyl acetate blend films, J.
Polymer Inter, 34, 407-411 (1994)

3

Sessler G.M., Electrets, Topics in Applied Physics,33,
Berlin (1980)

4

Turnhout J. Van: Thermally Stimulated Discharge
Currents of Polymer Electrets, Poly. Intr. 106-130,
(1975)

5

Bucci C., Fieschi R. and Guidi G., The Kerr effect in
KCL, Phys, Rev, 148, 816-821 (1966)

6

Kessler A., and Caffyn J.F: Glass structure and ion
dynamics of led cadmium fluoride metal, J. Phys. C-5,
1134-1138 (1972)

7

Saito S., Sasabe H., Nakajima T. and Yoda K.,
Thermally stimulated depolarization current in studies
in sodium and barium doped potassium titrate fluoride,
J. Polym. Sci., A-26, 1297-1301 (1968)

8

Devis D.K., Electrification IPPS Conf. Ser. No. 4, 29
(1967)

9

Devis D.K., Carrier transport in polythene, J. of Phys
(5), 162-165 (1972)

Acknowledgement
I express my deep sense of gratitude to Prof. J.M. Keller for
his valuable suggestions and kind cooperation throughout the
tenure of research work. I also wish to convey my regards
and heartily thanks to Dr. R.K. Duby, Department of
Postgraduate Studies and Research in Physics and
Electronics, Rani Durgavati University, Jabalpur for constant
encouragement, and tentative help.

10 Grass B, Charge Storage in Solid Dielectric, (1964)

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Vol. 1 (ISC-2011), 238-243 (2012)
Res.J.Recent Sci.
11 Fridkinand V.M. and Gheludev I.S., Photoelectret and
Photographic Process (1961)

20 Piper W.W. and Williams F.F., British J. Appl. Phys., 6,
569-572 (1955)

12 E. Sudova, J. Machova, Z. Svobodova, T. Vesely,
Negative effects of malachite green and possibilities of
its replacement in the treatment of fish eggs and fish, a
review, Veterinarni Medicina, 521(2), 527–539 (2007)

21 Srivastava S., Sinha R. and Roy D., Toxicological
effects of malachite green, Aquat Toxicol 66(3), 319–29
(2004)

13 Adamec V., Kolloid Z, Z. Polym., 237, 219-229 (1970)
14 Rasuvaev G.A., Troitskaya L.S. and Troitskii B.B.:
Effects of addition on photodegradation of polymers:
Addition of typical ketone sensitizers (acetophenone),
J.Polym.Sci. Polym. Chem. Ed., 9, 26,73 (1971)

22 Khare P.K. and Shrivastva A.P, Spontaneous current
emission
in
solution-grown
doped
polymethylmethacrylate films ,Thin Solid films, 208,
233- 236 (1992)
23 Ragehy N.A. et al., Spectroscopy Letters, An Inter. J. for
Rapid Comm., 24(1), 81-97 ( 2006)

15 Verma D.and Bhatnagar C.S., Indian J. Pure Appl.
Phys., 13, 868-871 (1975)

24 Martin E.H. and Hirdh J., Non Crystal Solids, 4, 133136 (1970)

16 Kosaki M., Sugiyama K and Ieda M, J. Appl. Phys., 42,
33-38, (1971)
17 Gutman F. and Lynos L.E., Organic Semiconductor,
John Wieleya, Sons, New-York 434-484 (1967)

25 Prashant Shukla and Mulayam S Gaur, Thermally
Stimulated Discharge Current Spectra and UV-vis
Absorption in Polymethylmethacrylate Electret, Iranian
Polymer Journal, 18(7), 535-541 (2009)

18 Lal Nand and Srivastva Alok kumar, Removal of
triphenylmethane dye, malachite green by Escherichia
Coli K ,ISCA Indore, India, 164, (2011)

26 Schwartz L.M., Hornig J.F., Photocurrents generated by
intense flash illumination, J. of Phys and Chem. of
Solids, 26(12), 1821–1824 (2002)

19 Onoda M., Nakayam H. and Mahendru P., J. phys. D.,
19, 684-689 (1978)

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27 Khare P.K. and Bhardwaj M.K., Thermally stimulated
depolarization and ultraviolet spectroscopy study of pure
and malachite green sensitized polymer film, Asian. J. of
exp. Sci, 25, 59-60 ( 2011)

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