Molecular dynamics of the α relaxation during crystallization of a glassy polymer: A real-time dielectric spectroscopy study

Abstract

The change of the a relaxation process occurring during isothermal crystallization of a glassy polymer, poly(aryl ether ketone ketone), has been followed in real time through measurement of the dielectric complex permittivity.The dielectric strength has been correlated with the degree of crystallinity derived from real time wide angle x-ray patterns using synchrotron radiation. The phenomenological Havriliak-Negami description has been used to analyze the changes of the dielectric strength, central relaxation time and shape parameters describing the relaxation, as crystallization proceeds. The evolution of the dielectric magnitudes with crystallization time has been interpreted in the light of the Schonhals-Schlosser model. According to this model, a restriction of the long scale motions of the polymeric chains as the material is filled in vrith crystals is observed. The derived dipole moment time correlation functions have been calculated for different crystallization times and fitted by the Kohlrausch-Williams-Watts function. The variation of the stretching parameters with crystallization time can be interpreted in terms of the coupling model assuming an increase of the intermolecular cooperativity of the a relaxation as the polymeric chains are constrained to move between crystalline regions. These results offer a contribution to the understanding of molecular dynamics of a glassy polymer during crystaDization.

Structure-dynamics relationships of the ?-relaxation in flexible copolyesters during crystallization as revealed by real-time methods

“…8 In addition, this model allows one to interpret the observed broadening and symmetrization of the ␣-relaxation in a semirigid polymer during crystallization as due to restriction in the long-scale motions of the polymeric chains as the material is filled in with crystals. 4 Until now, most crystallization studies using dielectric relaxation have been carried out on isothermally crystallized materials from the glassy state after subsequent quenching. Only a few dielectric measurements were performed in real time during crystallization.…”

Translational dynamics of a cold water cluster in the presence of an external uniform electric field

“…A similar decrease of the exponent ␤ has also been observed experimentally during the isothermal crystallization process of a glassy polymer. 41 According to the coupling model introduced by Ngai and León 42,43 and references therein, which assigns a physical significance to the Kohlrausch exponent, by relating it to the existence of cooperative phenomena, 42,43 the decrease of ␤ here can be understood as the increase of cooperativity requirements for the relaxation of the molecular units, because of the restrictions imposed by crystallinity.…”

A systematic study of the isothermal crystallization of the mono-alcohol n-butanol monitored by dielectric spectroscopy

“…[8][9][10][11][12][13]. The sign of crystallization is a decrease in intensity of the signal, and the crystal fraction/concentration of the sample is often obtained by assuming that the relaxation strength is proportional to the volume fraction of liquid in the sample [14][15][16]. But the microscopic interpretation of dielectric spectra is not straight-forward [17], especially when studying a heterogeneous mixture.…”