Chemistry Reference
In-Depth Information
A cluster model of polymers amorphous state structure allows introducing
principally new treatment of structure defect (in the full sense of this term)
for the indicated state [1, 2]. As it is known [3], real solids structure contains
a considerable number of defects. The given concept is the basis of dislo-
cations theory, widely applied for crystalline solids behavior description.
Achieved in this field successes predetermine the attempts of authors num-
ber [4-11] to use the indicated concept in reference to amorphous polymers.
Additionally used for crystalline lattices notions are often transposed to the
structure of amorphous polymers. As a rule, the basis for this transposition
serves formal resemblance of stress - strain (s - e) curves for crystalline and
amorphous solids.
In relation to the structure of amorphous polymers for a long time the
most ambiguous point [12-14] was the presence or the absence of the local
(short-range) order in this connection points of view of various authors on
this problem were significantly different. The availability of the local order
can significantly affect the definition of the structure defect in amorphous
polymers, if in the general case the order-disorder transition or vice versa is
taken for the defect. For example, any violation (interruption) of the long-
range order in crystalline solids represents a defect (dislocation, vacancy,
etc.), and a monocrystal with the perfect long-range order is the ideal defect-
free structure with the perfect long-range order. It is known [15], that suf-
ficiently bulky samples of 100% crystalline polymer cannot be obtained,
and all characteristics of such hypothetical polymers are determined by the
extrapolation method. That is why the Flory “felt” model [16, 17] can be
suggested as the ideal defect-free structure for amorphous state of polymers.
This model assumes that amorphous polymers consist of interpenetrating
macromolecular coils personifying the full disorder (chaos). Proceeding
from this, as the defect in polymers amorphous state a violation (interrup-
tion) of full disorder must be accepted, that is, formation of the local (or
long-range) order [1]. It should also be noted that the formal resemblance of
the curves s - e for crystalline solids and amorphous polymers appears far
incomplete and the behavior of these classes of materials displays principal
differences, which will be discussed in detail below.
Turning back to the suggested concept of amorphous polymer structural
defect, let us note that a segment including in the cluster can be considered
as the linear defect - the analog of dislocation in crystalline solids. Since in
the cluster model the length of such segment is accepted equal to the length
of statistical segment,
l
st
, and their amount per volume unit is equal to the
