Chemistry Reference
In-Depth Information
On the basis of the Eq. (15.5) the relationship was obtained, which allows
to calculate the average distance
r
between two paramagnetic probes [29]:
(
)
1/ 3
H
-
r
=D
, Å
38
(15.6)
dd
where ∆
H
dd
is given in Ersteds.
In Fig. 15.9, the dependence of
d
1
/
d
c
on mean distance
r
between chaoti-
cally distributed in amorphous PC radicals-probes is adduced. For PC at
T
= 77K the values of
d
1
/
d
c
= 0.38 ÷ 0.40 were obtained. One can make an
assumption about volume fractions relation for the ordered domains (nano-
clusters) and loosely packed matrix of amorphous PC. The indicated value
d
1
/
d
c
means, that in PC at probes statistical distribution 0.40 of its volume
is accessible for radicals and approximately 0.60 of volume remains unoc-
cupied by spin probes, that is, the nanoclusters relative fraction
cl
according
to the EPR method makes up approximately 0.60÷0.62.
FIGURE 15.9
The dependence of parameter
d
1
/
d
c
of EPR spectrum on the value of mean
distance
r
between radicals for PC [27].
This result corresponds well to the experimental data of Yech [30] and
Perepechko [31], who obtained the values 0.60 and 0.63 for densely packed
regions relative fraction in amorphous polymers.
The authors of Ref. [11] fulfilled
cl
estimation with the aid of reversed gas
chromatography and obtained the following magnitudes of this parameter
for PC, poly (methyl methacrylate) and polysulfone: 0.70, 0.60 and 0.65,
accordingly (
Table 15.2
).
