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^ St. Petersburg State Polytechnical University Journal. Physics and Mathematics No. 4-2(182) 2013 UDC 536.421
E.N. Lushin, R.A. Castro
Herzen State Pedagogical University of Russia 48 Moyka Emb., St. Petersburg, 191186, Russia
DETERMINATION OF THE GLASS TRANSITION TEMPERATURE IN POLYMER COMPOSITES AND SYSTEMS
Е.Н. Лушин, Р.А. Кастро
ОПРЕДЕЛЕНИЕ ТЕМПЕРАТУРЬ! СТЕКЛОВАНИЯ ПОЛИМЕРНых
композиционных материалов и систем
The results of the study of the frequency dependence of the dielectric constant in a wide range of temperature in tetrazole polymers are presented. It has been found that the temperature at which the dielectric constant changes sharply in all systems is the glass transition temperature.
TETRAZOLE POLYMERS, GLASS TRANSITION TEMPERATURE, DIELECTRIC RELAXATION.
Представлены результаты исследования частотной зависимости диэлектрической проницаемости в широком интервале температур в тетразолсодержащих полимерах. Обнаружено, что температура, при которой происходит смена характера зависимости обратной величины диэлектрической проницаемости от температуры, для всех изученных нами систем совпадает с их температурой стеклования.
ТЕТРАЗОЛСОДЕРЖАЩИЕ ПОЛИМЕРЫ, ТЕМПЕРАТУРА СТЕКЛОВАНИЯ, ДИЭЛЕКТРИЧЕСКАЯ РЕЛАКСАЦИЯ.
The physical properties of the polymer in glass state are significantly different from the same properties in rubbery state. The conventional boundary between these two states is the glass transition temperature T , which is the most important characteristic of amorphous polymers introduced by Uberrighter. Under the glass transition temperature we mean the temperature under which the viscosity of the polymer is no less than 1012 Pa-s. This temperature is also understood as the temperature below which the motion of chain segments of polymer molecules is «frozen» [1].
There are many methods of experimental determination of glass transition temperature. The measurement of mechanical and dielectric loss is among them. The use of the dielectric method can be sometimes difficult because measuring the temperature-frequency dependence of the dielectric loss in low-frequency region can cause certain problems. That is why
it is important to expand the possibilities of dielectric spectroscopy method to determine T. This paper suggests using the temperature dependence of the inverse value of the dielectric permeability (1/e1) as a criterion to estimate the value of T.
Fig.
1. The temperature dependence of the specific volume of amorphous solids
a)
b)
0,10-
0,06-
0.04-
0,02-
0,00-
-i-1-'-1-'-1-1-1-1-1-1-1-p-1—
260 280 300 320 340 360 380 400
0,070,06 0,050,040,030,020,01
| V = 1 Hz|
-1-r-1--,--1-1-1-If-1--,--1--I-1-<-1-,-1
260 230 300 320 340 360 3B0 400 420 440
T(K)
T(K)
Fig. 2. Temperature dependences of the inverse of the dielectric constant of the sample #1 (a) and #3 (b)
According to the model suggested by the authors [2], the temperature dependence of the inverse value of dielectric permeability has a linear character. It is experimentally obtained that for many polymer systems in the dependence (1/e1) = f(T) there are at least two regions which correspond to the system being in glass and rubbery state respectively. It means that on condition of certain critical temperature, there is a change in the character of the temperature dependence of (1/e1). The same temperature dependence is also observed for
polymer density (p~1/V) (Fig. 1). That is why the temperature dependence 1 / s' can be used to determine glass transition range.
The dielectric measurements were carried out using an impedance analyzer ALPHA-N Analyzer from Novocontrol Technologies, covering a frequency range from 0.1 Hz to 1 MHz and working at different increasing temperature steps from 173 up to 523 K. A drop of the polymer mixture with two silica spacers of 50 ^m thickness was placed between two gold plated electrodes (20 mm of dia-
A comparison between experimental data of this work and from literature
Number of sample Compound composition (Polymer-plasticizer-[modifier]- hardener) Tg (1/8' = f(7)) T from literature g
K
1 (MPVT-A) (DMF) [KNO3(55%)] (TON-2) 310 310 [3]
2 (MPVT-A) (DMF) [KCl(70%)] (TON-2) 326 326 [4]
3 (MPVT-A) (DMFA) (MeO-TON) 328 329 [5]
4 (MPVT-A) (DMFA) (TON-2) 324 325 [5]
5 (MPVT-A) (DMFA) (Dur-TON) 327 -
(TON-2) — 2,4,6-triethylbenzene-1,3-dicyanobenzene-di-N-oxide (MeO-TON) — 3,6-methoxy-1,4-dicyanobenzene-di-N-oxide (Dur-TON) — 2,3,5,6-methyl-1,4-dicyanobenzene-di-N-oxide (DMFA) - dimethylformamide C3H7NO (DMF) - dimethylphthalate C10H10O4
^ St. Petersburg State Polytechnical University Journal. Physics and Mathematics No. 4-2(182) 2013
meter) of a parallel plate capacitor. The sample cell was mounted on a cryostat and exposed to a heated gas stream being evaporated from a liquid nitrogen Dewar. The temperature control was performed within ±0.5 K, using the Novocontrol Cryosystem. Novocontrol GmbH supplied all these modules.
For polymer composite materials based on poly-N-methylalil-5-vinyltetrazol (MPVT-A) with the modifier KN03 (55 %), the glass transition temperature is Tg = 310 K (Fig. 2, a) (the critical temperature is 310 K); for Meo-ToN, the glass transition temperature is Tg = 328 K (Fig. 2, b) (the critical temperature is 329 K). The experimental results we obtained can allow us to conclude that for a broad class of systems this critical temperature coincides with the glass transition temperature (see Table).
The first region is characterized by the abrupt
decrease of 1 / s'. Such significant changes of the temperature dependence of the dielectric parameters are connected with the main thermal transition from glass state to rubber state (or vice versa). The second region corresponds to rubbery state. The analysis of the temperature dependence shows that this region is characterized by the smooth decrease of the value 1 / s' and the curve flattens out to the steady plateau.
The temperature under which there is a change in the character of the temperature dependence of the inverse value of dielectric permeability for all the systems we studied coincides with their glass transition temperature.
Thus, the measurement of 1/e1 temperature dependence can be used as a new alternative method to determine Tg for polymer systems and composites.
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кАстРо Арата Рене Алехандро — доктор физико-математических наук, профессор кафедры физической электроники Российского государственного педагогического университета им. А.И. Герцена. 191186, Россия, Санкт-Петербург, наб. р. Мойки, 48 [email protected]
ЛУШИН Евгений Николаевич — аспирант кафедры физической электроники Российского государственного педагогического университета им. А.И. Герцена. 191186, Россия, Санкт-Петербург, наб. р. Мойки, 48 [email protected]
© St. Petersburg State Polytechnical University, 2013
