Chemistry Reference
In-Depth Information
FIGURE 4.11
The dependence of Grüneisen parameter g
L
on mean number of statistical
segments per one cluster
n
cl
for PC (1) and PAr (2) [43].
Hence, the stated above results shown that polymer yielding process can
be described within the frameworks of the macrothermodynamical model.
This is confirmed by the made in Ref. [44] conclusion about thermodynami-
cal factor significance in those cases, when quasiequilibrium achievement
is reached by mechanical stresses action. The existence possibility of struc-
tures with
D
> 0 (connected with transition “overheated liquid → solid
body” [45] was shown and, at last, one more possible treatment of “cell
'
s ef-
fect” was given within the frameworks of intermolecular bonds anharmonic-
ity theory for polymers [49].
If to consider the yielding process as polymer mechanical devitrification
[36], then the same increment of fluctuation free volume
f
g
is required for
the strain e
Y
achievement. This increment D
f
g
can be connected with e
Y
as
follows [50]:
im
D
f
g
= e
Y
(1−2n).
(4.26)
Therefore,
f
g
decrease results to D
f
g
growth and respectively, e
Y
enhance-
ment.
Let us consider, which processes result to necessary for yielding real-
ization fluctuation free volume increasing. Theoretically (within the frame-
works of polymers plasticity fractal concept [35] and experimentally (by
positrons annihilation method [22]) it has been shown, that the yielding pro-
