ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 1, pp. 86 !90. C Pleiades Publishing, Ltd., 2008.
Original Russian Text C M.F. Galikhanov, D.E. Temnov, A.A. Kozlov, A.A. Petrova, Yu.A. Gorokhovatskii, R.Ya. Deberdeev, 2008, published in Zhurnal
Prikladnoi Khimii, 2008, Vol. 81, No. 1, pp. 90 !94.
AND POLYMERIC MATERIALS
Specific Features of the Electret Effect
in Two-Layer Polymeric Films
M. F. Galikhanov, D. E. Temnov, A. A. Kozlov, A. A. Petrova,
Yu. A. Gorokhovatskii, and R. Ya. Deberdeev
Kazan State Technical University, Kazan, Tatarstan, Russia
Herzen Russian State Pedagogical University, St. Petersburg, Russia
Received April 4, 2007
Abstract-Two-layer film corona-electrets based on low-density polyethylene and copolymers of ethylene
with vinyl acetate of various brands were studied. The dependence of the electret characteristics of two-layer
corona-electrets on the percentage content of polar groups in the copolymer constituting the bottom layer was
analyzed. Data on thermally stimulated depolarization and thermally stimulated relaxation of the surface
potential served as a basis for suggesting a mechanism of depolarization of two-layer corona-electrets.
The wide use of polymeric electrets in numerous
electric instruments and devices, friction and sealing
units, and gas and liquid filters [1, 2] predetermines
the unremitting interest in studies of the electret effect
in polymeric insulators. Particular attention is given to
a search for new electret materials by combining
the already known materials, i.e., by obtaining com-
posites, to which belong multilayer electrets whose
layered structure can give rise to specific features
uncharacteristic of single-layer materials .
A practical application of two-layer films is their
use as anticorrosive coatings whose quality is deter-
mined both by the electret properties of polymeric
films and by the adhesion between a film and a met-
allic substrate. As shown in [6, 7], presence of a sur-
face charge improves the anticorrosive properties
of a coating, whereas an increase in the content of
polar groups in the lower layer improves the adhesion,
but impairs the electret properties of corona-electrets.
Thus, studies of the stability of the electret state and
elucidation of the depolarization mechanism are of
interest and can determine the optimal content of polar
groups in the lower layer to provide the best quality of
As objects of study were chosen low-density poly-
ethylene (LDPE) of 11 503-070 brand [GOST (State
Standard) 16 337377] and ethylene3vinyl acetate
copolymers (EVAC) with varied content of vinyl ace-
tate (VA) groups, of 11 106-030, 11 306-075, 11 507-
070, 11 808-240 [TU (Technical Specification) 6-05-
1636378], 12 306-020, and 12 506-150 (TU 301-05-
56390) brands. The characteristics of the polymers
are given in Table 1.
Single-layer films of thickness 0.25 mm were pre-
pared by compaction in accordance with GOST
12 019366 at 170+ 5oC and compaction time of 5 min.
The films were doubled at 170+ 5oC in a restricting
frame of height 0.5 mm in the absence of pressure for
10 min. Then, the composites obtained were heated at
90oC for 10 min and cooled in the field of a negative
corona discharge. The corona discharge was created
with an electrode comprising 196 pointed needles
evenly arranged over an area of 49 cm
in the form of
a square. The polarization voltage and time were
35 kV and 60 s.
The electret characteristics were measured daily
with an IPEP-1 meter whose working principle is
based on a periodic shielding of the measuring probe
situated at a certain distance from the electret surface.
The error in measuring the surface potential V
tric field strength E, and surface density s
tric charges did not exceed 3%.
Spectra of thermally stimulated currents (TSC)
were measured under heating at a constant rate of
5 deg min
in a special measuring cell equipped with
blocking aluminum electrodes and a fluoroplastic
The films were also studied by the method of ther-