18
J. W. P. Schmelzer and C. Schick
participating in segmental relaxation even if is non-crystalline. The latter is called
rigid amorphous fraction (RAF) [59, 60]. The RAF does not contribute to the glass
transition (segmental relaxation) but to the secondary relaxations like the ß-relaxation
in polyethylene terephthalate [61].
Primary crystal nucleation in polymers shows some peculiarities as described, e.g.,
by Muthukumar [62]. Along one polymer chain (one molecule) several crystal nuclei
may evolve. Due to their coupling through the polymer chain, these nuclei are not
independent and there will be some competition between them. With the introduction
of fast scanning calorimetry (FSC) [63] detailed kinetic studies of homogeneous
nucleation in many polymers became feasible [38] and the often resulting nodular
morphology (crystal size in the order of 10 nm) became accessible for relaxation
studies [64].
Until now, there is a strong controversy regarding the question on how a polymer
crystal lamella is growing. Several models were proposed. An early, widely applied
model is the Hoffman-Lauritzen theory of polymer crystallization [65]. Nevertheless,
the Hoffman-Lauritzen approach was frequently challenged and several competing
theories were developed (for recent reviews see references [55–57, 66–70]). Consequently, also in this respect a broad spectrum of problems remains not finally
settled.
6 Concluding Remarks
Once one is dealing with the theory of different phenomena in nature, one has also
to realize for which purposes the respective analysis is made. The basic desire of
experimenters attempting to apply the theory is that the theory should be as simple
as possible. In contrast, theoreticians always recognize a variety of effects which
may also be of importance tending to advance the theory making it more and more
complex and, consequently, harder to apply. Albert Einstein suggested to make a
compromise in this connection proposing that “everything should be done as simple
as possible but not simpler”. A foundation of the possibility to proceed in such way
was also given by him stating “subtle is the Lord but malicious he is not”. With
respect to the description of crystallization, CNT with its basic assumptions and
its development in different directions can be considered possibly as a realization
of such compromise. However, thinking once again about these problems Einstein
revised his opinion: “I have thought about once again. Quite it could be that God
is malicious”. Consequently, not the theoreticians are responsible for the trouble
they sometimes cause the experimenters demanding and trying to advance a variety
of partly principal improvements of CNT. Hopefully, these developments can be
brought into a form similarly tractable in application to experiment as CNT provides
it now but at a higher level.
J. W. P. Schmelzer and C. Schick
participating in segmental relaxation even if is non-crystalline. The latter is called
rigid amorphous fraction (RAF) [59, 60]. The RAF does not contribute to the glass
transition (segmental relaxation) but to the secondary relaxations like the ß-relaxation
in polyethylene terephthalate [61].
Primary crystal nucleation in polymers shows some peculiarities as described, e.g.,
by Muthukumar [62]. Along one polymer chain (one molecule) several crystal nuclei
may evolve. Due to their coupling through the polymer chain, these nuclei are not
independent and there will be some competition between them. With the introduction
of fast scanning calorimetry (FSC) [63] detailed kinetic studies of homogeneous
nucleation in many polymers became feasible [38] and the often resulting nodular
morphology (crystal size in the order of 10 nm) became accessible for relaxation
studies [64].
Until now, there is a strong controversy regarding the question on how a polymer
crystal lamella is growing. Several models were proposed. An early, widely applied
model is the Hoffman-Lauritzen theory of polymer crystallization [65]. Nevertheless,
the Hoffman-Lauritzen approach was frequently challenged and several competing
theories were developed (for recent reviews see references [55–57, 66–70]). Consequently, also in this respect a broad spectrum of problems remains not finally
settled.
6 Concluding Remarks
Once one is dealing with the theory of different phenomena in nature, one has also
to realize for which purposes the respective analysis is made. The basic desire of
experimenters attempting to apply the theory is that the theory should be as simple
as possible. In contrast, theoreticians always recognize a variety of effects which
may also be of importance tending to advance the theory making it more and more
complex and, consequently, harder to apply. Albert Einstein suggested to make a
compromise in this connection proposing that “everything should be done as simple
as possible but not simpler”. A foundation of the possibility to proceed in such way
was also given by him stating “subtle is the Lord but malicious he is not”. With
respect to the description of crystallization, CNT with its basic assumptions and
its development in different directions can be considered possibly as a realization
of such compromise. However, thinking once again about these problems Einstein
revised his opinion: “I have thought about once again. Quite it could be that God
is malicious”. Consequently, not the theoreticians are responsible for the trouble
they sometimes cause the experimenters demanding and trying to advance a variety
of partly principal improvements of CNT. Hopefully, these developments can be
brought into a form similarly tractable in application to experiment as CNT provides
it now but at a higher level.