Report No xxxx - Instytut Fizyki JÄ drowej PAN

MOLECULAR DYNAMICS IN POLY(ETHYLENE OXIDE) (PEO):
1 H-NMR AND DIELECTRIC SPECTROSCOPY STUDIES
Bakyt Orozbaev, Marcin Wachowicz, Stefan Jurga
Institute of Physics, A. Mickiewicz University, Umultowska 85, 61-614 Poznań, Poland
Molecular dynamics in poly(ethylene oxide) (PEO) with molecular weights M=2⋅10 6
and M=1⋅10 5 were studied by T 1 Dispersion NMR and Dielectric Spectroscopy.
T 1 spin-lattice relaxation times were measured by Fast Field Cycling technique in the
frequency range from 10 kHz to 16 MHz for selected temperatures below and above melting
points of 67°C and 63°C, for M=2⋅10 6 and M=1⋅10 5 samples, respectively (Fig. 1). Two
different slopes observed in our experiment are interpreted in terms of the Rouse dynamics of
chain segmental motion [1].
Dielectric relaxation spectra were collected using a Novocontrol BDS-80 broadband
dielectric spectrometer. Experiments were performed in the frequency domain (0.01 Hz – 1.8
GHz) and between –140 and 60 °C with 5 °C increments. Dielectric specimens were 0.4-0.6
mm thick, and were coated on both sides with a thin layer of gold to optimize electrical
contact, then sandwiched between two electrodes having a diameter of 20 mm and 10 mm.
Two relaxation processes, β and γ, were observed, and are similar to those observed in PEO
with molecular weights M=2.8⋅10 6 and M=8.4⋅10 5 [2]. The relaxation process detected at low
temperature and high frequency called β relaxation, is due to the local motions of amorphous
PEO segments. The β process is independent of molecular weight (M) and degree of
crystallinity ( Χ c ). The γ-process was assigned to local twisting in the main chains of PEO
molecule and refers to both crystalline and non-crystalline regions, including amorphous
segments of the folded molecules.
From the temperature shift of β and γ maximum observed in the ε”(T) plot the
activation energies for these two processes were evaluated (Fig. 2) and compared with NMR
data.
1
10
8
22 kJ/mol
PEO 2E6
PEO_2E6 ω 0.27
ω 1.23
6
0.1
log(f) [Hz]
4
γ - process
2
13 kJ/mol
β - process
0 186 kJ/mol
γ '- process
27 kJ/mol
-2
3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5
1000/T max
[1/K]
T 1
[s]
0.01
45 °C
65 °C
90 °C
1E-3
0.01 0.1 1 10
Larmor frequency ω [MHz]
Fig. 1. Larmor frequency dependence of 1 H-NMR T 1 relaxation time for PEO (M=2⋅10 6 )
Fig. 2. Arrhenius plot correlation times for PEO (M=2⋅10 6 )
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