100
A. Sanz
0.5
1.0
1.5
2.0
2.5
3.0
I (Q)
Q (Å
-1
)
Fig. 8 Neutron diffractograms of deuterated ethanol (CD 3 CD 2 OD) corresponding to the stable
monoclinic crystal (115 K), metastable plastic crystal (115 K) and metastable supercooled liquid
(105 K). Data collected on the D1B instrument (ILL)
105 K, although excluding kinetic factors, the formation of the PC phase should be
possible between T g and 115 K approximately. It was reported that the dielectric
spectra for the two PC and SCL phases were rather similar, with the exception of
the time constant, indicating that the slow dynamics of PC and that of SCL ethanol
probed by dielectric spectroscopy are basically identical.
The transformation of SCL ethanol into the PC phase at a fixed temperature
of 105 K is discussed here below. Selected simultaneous ND patterns and DS
spectra are displayed in Fig. 9. A remarkable observation is the transformation of the
dielectric relaxation upon annealing. The main relaxation associated with the liquid
phase is centred around 1 Hz and decreases in intensity as the metastable PC phase
grows. In parallel, a new relaxation appears at lower frequencies due to the mobile
nature of the plastic crystal phase. This process induced by pure reorientations of
ethanol molecules presents slower relaxation times than that of SCL because of the
translational constraints imposed by the BCC lattice.
In order to elucidate unequivocally the fraction of sample transformed into the
PC phase, the diffraction patterns can be described as a linear combination of two
contributions, corresponding to ordered (N PC ) and disordered (N SCL ) phases:
I (Q, t) = I PC (Q) + [1 − N PC (t)]I SCL (Q),
(4)
A. Sanz
0.5
1.0
1.5
2.0
2.5
3.0
I (Q)
Q (Å
-1
)
Fig. 8 Neutron diffractograms of deuterated ethanol (CD 3 CD 2 OD) corresponding to the stable
monoclinic crystal (115 K), metastable plastic crystal (115 K) and metastable supercooled liquid
(105 K). Data collected on the D1B instrument (ILL)
105 K, although excluding kinetic factors, the formation of the PC phase should be
possible between T g and 115 K approximately. It was reported that the dielectric
spectra for the two PC and SCL phases were rather similar, with the exception of
the time constant, indicating that the slow dynamics of PC and that of SCL ethanol
probed by dielectric spectroscopy are basically identical.
The transformation of SCL ethanol into the PC phase at a fixed temperature
of 105 K is discussed here below. Selected simultaneous ND patterns and DS
spectra are displayed in Fig. 9. A remarkable observation is the transformation of the
dielectric relaxation upon annealing. The main relaxation associated with the liquid
phase is centred around 1 Hz and decreases in intensity as the metastable PC phase
grows. In parallel, a new relaxation appears at lower frequencies due to the mobile
nature of the plastic crystal phase. This process induced by pure reorientations of
ethanol molecules presents slower relaxation times than that of SCL because of the
translational constraints imposed by the BCC lattice.
In order to elucidate unequivocally the fraction of sample transformed into the
PC phase, the diffraction patterns can be described as a linear combination of two
contributions, corresponding to ordered (N PC ) and disordered (N SCL ) phases:
I (Q, t) = I PC (Q) + [1 − N PC (t)]I SCL (Q),
(4)