COLD FLOW (FORCED HIGHELASTICITY) - Fractal Mechanics of Polymers - page 129

entanglements network are formed. The first from them represents itself a
traditional macromolecular binary hooking's network [35] and the second
- macromolecular entanglements cluster network [18, 23]. For the two in-
dicated types of macromolecular networks the distinctions of their density
temperature dependence are the most characteristic: if a macromolecular bi-
nary hooking's network density n e is independent on temperature and is ap-
proximately the same above an below polymer glass transition temperature
T g [29], then a cluster network density n cl decreases a testing temperature
growth in virtue of its thermofluctuation origin [23] and at T g n cl = 0 [28]. As
it has been shown in Refs. [36, 37], a cluster network at T g forms percola-
tion system, that is, it becomes capable to bear stresses. The authors of Ref.
[38] were elucidated, which from the two indicated above macromolecular
networks defined stress transfer in glass polymers macroscopic samples, us-
ing the mentioned above analogy with conductive bonds net in mixtures
metal-insulator.
As it is known [39], the ability to conduct current with definite conduc-
tivity level g mixtures metal-insulator are acquired at percolation threshold
reaching, that is, in the case, when conductive bonds form continuous per-
colation network. As it was noted above, macroscopic polymer samples are
acquired ability to bear stress at formation in them of macromolecular entan-
glements continuous network. This obvious analogy allows to use modern
physical models of conductivity in disordered systems for description of the
dependence of cold flow plateau stress s p on macromolecular entanglements
network density in amorphous polymers, As it is known [40], the dependent
on length scale L conductivity g ( L ) is described by the relationship:

g ( L ) ~ L b , (6.17)

where the exponent b is determined as follows [41]:

b = d f - 2 - q. (6.18)

In the Eq. (6.18) d f is polymer structure fractal dimension, q represents
itself the exponent in the equation of dependent on distance r diffusivity D r
[41]:

D r ( r ) ~ r -q . (6.19)

As it was noted above, an amorphous glassy polymers structure can be
simulated as a WS clusters large number totality [21, 22], for which the fol-