Ph.D. thesis (pdf) - dirac

76 Alpha Relaxation
4
2
0
This work
Nielsen
Dixon 90
Sekula 04
230 MPa this work
−2
log 10
(τ α
)
−4
−6
−8
−10
−12
2 3 4 5 6
1000/T
Figure 5.2: Temperature dependence of the alpha-relaxation time (from dielectric
measurements, τ α = 1/ω peak ) of liquid DBP at atmospheric pressure and at 230
MPa (Arrhenius plot). Data from other groups are also included: unpublished data
from Nielsen et al. [2006], the VTF fit of Sekula et al. [2004] shown in the range
where it can be considered as an interpolation of the original data, and data taken
from figure 2(a) [Dixon et al., 1990].
log 10
τ α
2.5
2
1.5
1
0.5
0
−0.5
−1
−1.5
−2
data
new fit, m=82 Tg=176.6 K
Sekula 04, fit, m=84 Tg=177.4 K
m estimate, m=70 Tg=176 K
−2.5
5.2 5.3 5.4 5.5 5.6 5.7
1000./T
Figure 5.3: Atmospheric-pressure data of figure 5.2 with relaxation times longer
than a millisecond. Also shown are the VTF fit of Sekula et al. [2004] extrapolated
to low temperatures (dashed-dotted line), a new VTF fit made by using data in the
10 −6 s −10 2 region (dashed line), and estimated slope of the data in the long-time
region (full line). The Tg’s estimated from these three methods are very similar,
whereas the fragility varies significantly from m = 65 to m = 85.