238
S. Napolitano
be representative of gradients in mobility steeper than those in mass transport, and
the condition ξ > 1 would originate from the opposite case.
4 Conclusion
In conclusion, in this chapter we have summarized the outcome of the experimental
work on the crystallization of thin polymer films performed via broadband dielectric
spectroscopy. We have discussed on the common issues related to sample preparation and showed that this technique was able to answer to a fundamental question
of interest to the large and broad group of researchers working on the effects of
nanoconfinement on the formation of polymer crystals. Differently that what previously speculated, the enormous reduction in crystallization rate cannot be associated
with slower segmental mobility: The crystallization time can increase at constant
dynamic glass transition temperature. We have shown that an analysis of the time
evolution of the dielectric strength—an experimentally accessible parameter, sensitive to immobilization—can be used to determine the timescale of crystallization, and
to estimate if adsorption of chains is concurrently taking place concurrently. In this
regard, an analytical expression for the time dependence of the dielectric strength has
been discussed. We have also discussed on the analysis of the thickness dependence
of the crystallization time and indicated an expression capable to link the timescale
of the formation of ordered structures to that of segmental mobility. The link between
these two timescales was built up considering the role of finite size effects on nucleation and appropriately modified version of the Debye–Stokes–Einstein relation for
bulk melts. Finally, we have shown that extending the latter equation, valid in the
temperature domain, to nanoconfinement yield an exotic and intriguing condition,
where mass transport along the film is more inhibited than what expected from a
gradient in segmental mobility.
Acknowledgements SN acknowledges financial support from the Action Concerté Recherche–
ULB under project “SADI.”
References
1. Liu YX, Chen EQ (2010) Polymer crystallization of ultrathin films on solid substrates. Coord
Chem Rev 254(9–10):1011
2. Beiner M, Rengarajan GT, Pankaj S, Enke D, Steinhart M (2007) Manipulating the crystalline
state of pharmaceuticals by nanoconfinement. Nano Lett 7:1381
3. Massa MV, Carvalho JL, Dalnoki-Veress K (2006) Confinement effects in polymer crystal
nucleation from bulk to few-Chain systems. Phys Rev Lett 97:247802
4. Vanroy B, Wubbenhorst M, Napolitano S (2013) Crystallization of thin polymer layers confined
between two adsorbing walls. Acs Macro Lett 2(2):168
S. Napolitano
be representative of gradients in mobility steeper than those in mass transport, and
the condition ξ > 1 would originate from the opposite case.
4 Conclusion
In conclusion, in this chapter we have summarized the outcome of the experimental
work on the crystallization of thin polymer films performed via broadband dielectric
spectroscopy. We have discussed on the common issues related to sample preparation and showed that this technique was able to answer to a fundamental question
of interest to the large and broad group of researchers working on the effects of
nanoconfinement on the formation of polymer crystals. Differently that what previously speculated, the enormous reduction in crystallization rate cannot be associated
with slower segmental mobility: The crystallization time can increase at constant
dynamic glass transition temperature. We have shown that an analysis of the time
evolution of the dielectric strength—an experimentally accessible parameter, sensitive to immobilization—can be used to determine the timescale of crystallization, and
to estimate if adsorption of chains is concurrently taking place concurrently. In this
regard, an analytical expression for the time dependence of the dielectric strength has
been discussed. We have also discussed on the analysis of the thickness dependence
of the crystallization time and indicated an expression capable to link the timescale
of the formation of ordered structures to that of segmental mobility. The link between
these two timescales was built up considering the role of finite size effects on nucleation and appropriately modified version of the Debye–Stokes–Einstein relation for
bulk melts. Finally, we have shown that extending the latter equation, valid in the
temperature domain, to nanoconfinement yield an exotic and intriguing condition,
where mass transport along the film is more inhibited than what expected from a
gradient in segmental mobility.
Acknowledgements SN acknowledges financial support from the Action Concerté Recherche–
ULB under project “SADI.”
References
1. Liu YX, Chen EQ (2010) Polymer crystallization of ultrathin films on solid substrates. Coord
Chem Rev 254(9–10):1011
2. Beiner M, Rengarajan GT, Pankaj S, Enke D, Steinhart M (2007) Manipulating the crystalline
state of pharmaceuticals by nanoconfinement. Nano Lett 7:1381
3. Massa MV, Carvalho JL, Dalnoki-Veress K (2006) Confinement effects in polymer crystal
nucleation from bulk to few-Chain systems. Phys Rev Lett 97:247802
4. Vanroy B, Wubbenhorst M, Napolitano S (2013) Crystallization of thin polymer layers confined
between two adsorbing walls. Acs Macro Lett 2(2):168