1070-4272/03/7610-1651 $25.00 C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 10, 2003, pp. 1651!1654. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 10, 2003,
Original Russian Text Copyright + 2003 by Galikhanov, Eremeev, Deberdeev.
AND POLYMERIC MATERIALS
Electret Effect in Compounds of Polystyrene with Aerosil
M. F. Galikhanov, D. A. Eremeev, and R. Ya. Deberdeev
Kazan State Technological Institute, Kazan, Tatarstan, Russia
Received June 9, 2003
Abstract-Coronoelectrets based on polystyrene and composites of polystyrene with Aerosil were studied.
The electret state is characteristic of virtually all
insulators . In recent years, the field of application
of electrets, i.e., insulators producing strong electro-
static field in the surrounding space, has expanded
rapidly. Their applications range from home facilities
to special-purpose equipment; they include acoustic
converters, dosimeters, gas filters, systems for elec-
tron focusing, elements of friction units, gaskets, sys-
tems for corrosion protection, etc. . New fields
of application of electrets have appeared recently in
medicine and biotechnology .
For the most part, electrets with stable external
electric field are produced from nonpolar polymers in
which the presence of deep levels trapping charge
carriers plays an important role. Impurity ions, inter-
faces between crystalline and amorphous phases, and
free volume of the polymer serve as energy traps.
However, highly stable electrets with good service
characteristics can be produced only from a limited
set of materials. Straight polymers as main material
for electrets do not have the mechanical, thermal, and
other characteristics required for their practical use.
To produce electret materials with prescribed char-
acteristics, it is appropriate to use formulations com-
posed of a polymeric binder and various fillers. How-
ever, the general pattern of variation of electret charac-
teristics of polymers upon filling was not determined.
As a result, progress in practical development of poly-
mer composite electrets is ahead of their theoretical
analysis. In this context, it is of interest to study the
features of polarization of various composites.
We used polystyrene (PS) of the PSM 115 grade
[GOST (State Standard) 20282386] with density of
1.06 g cm
, viscosity-average molecular weight of
3 0 10
, and electrical resistivity of 2 010
W m and
Aerosil of the A175 grade (GOST 14922377) with
diameter of the initial aggregates of 14 nm and spe-
cific adsorption surface area of 175 + 20 m
The polymer and filler were blended on laboratory
microrolls at 175 + 5oC for 3 min. Plates 1.13
1.2 mm thick were manufactured by pressing at 170 +
5oC for 5 min (GOST 12 019366). Polymer plates
were polarized in the field of a corona discharge with
the use of an electrode containing 196 sharp needles
uniformly arranged on a 7 0 7cm
area. The distance
between the plates and electrode was 20 mm; polar-
ization voltage, 35 kV; polarization duration, 60 s.
Before polarization, the plates were kept in a ther-
mostat at 90oC for 10 min.
The surface potential of the electrets, V
, was meas-
ured every 24 h for 150 days by the vibration electrode
method (noncontact induction method) according to
GOST 25209382 (measuring error 0.15%). The time
interval from polarization of the plate to the first meas-
urement of its surface potential was 1 h. The electrets
were stored in nonshorted state in paper pacages.
The surface charge density s
was calculated by
is the compensation voltage; e, the relative
permittivity of the composite; e
, the permittivity
of free space, equal to 8.854 0 10
the electret thickness .
The error in s
calculation was 0.18%.
Thermally stimulated depolarization currents were
measured after 150 days of storage under linear heat-
ing at a constant rate of 5 deg min
, using an elec-
tronic recorder of small currents with special measur-
ing cell with blocking aluminum electrodes and Teflon
gasket . The thermally stimulated depolarization
(TSD) spectrum was recorded and visualized on a PC
using NVL 03 Driver software.