Ph.D. thesis (pdf) - dirac

5.3. Spectral shape 81
4
2
0
This work
Nielsen
Dixon 90
Sekula 04
230 MPa this work
−2
log 10
(τ α
)
−4
−6
−8
−10
−12
0.4 0.6 0.8 1
T g
/T
Figure 5.8: Arrhenius plot of the alpha-relaxation time of DBP at atmospheric pressure
and at 230 MPa, when the temperature is scaled with the pressure dependent
T g , T g (Patm) = 176 K and T g (230 MPa)=200 K. As in figure 5.2, 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groups are also included: unpublished data from Nielsen et al.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) in [Dixon et al., 1990].
atmospheric pressure data in the course of the same experiment, in order to eliminate
the extra uncertainty from differences in absolute temperature scale and possible in
the purity of the sample.
We assume that the scaling is possible. Moreover, we describe e(ρ) by a simple
power law, e(ρ) = ρ x . We find the exponent x by exploiting the fact that the scaling
variable X = e(ρ)/T is uniquely fixed by the value of the relaxation time; applying
this at T g , namely setting X g (Patm) =X g (216K), leads to x = 2.3 and gives a ratio
of m P /m ρ = 1.2.
5.3 Spectral shape
Our main aim in the study of the spectral shape is to analyze the possible correlation
between the degree of departure from Debye relaxation and the fragility (see also
section 2.3). In the end of this chapter we discuss this correlation in the frame