NDLI: Kinetics of phase transitions and dielectric relaxations in poly-bis(trifluorethoxy- phosphazene) (PBFP)

Content Provider	Springer Nature Link
Author	Mourik, P. Veldman, E. rder, B. Turnhout, J. W¨bbenhorst, M.
Copyright Year	2005
Abstract	The kinetics of the high temperature (isotropic → mesophase) and low temperature (mesophase → crystalline) transition of PBFP at T$_{m}$ and T(1), respectively, and its local dynamics were studied by differential scanning calorimetry (DSC) at variable heating and cooling rate and by dielectric relaxation spectroscopy (DRS). While on heating no substantial effect of the rate on both transition temperatures was found, T(1) and T$_{m}$ showed a strong dependence on the cooling rate. The high temperature transition revealed thermally activated behaviour with an activation energy of E$_{a}$ = 400 kJ/mol, whereas the transition at T(1) showed the typical signature of supercooling. This finding is consistent with the picture that the isotropic/mesophase transition at T$_{m}$ is controlled by long-range, strongly hindered, chain diffusion that leads to the long-range orientational mesomorphic order. In contrast, the low temperature transition, the enthalpy of which is far larger and the temperature of which depending linearly on the cooling rate, indicates a kinetical control by nucleation as characteristic for a (2D → 3D) crystallization process.Complementary information about the molecular dynamics in the various phases was obtained by DRS that revealed three relaxation processes, which were assigned to the dynamic glass transition (α), local motions of CF$_{3}$—groups in the glassy state (β -process) and cooperative fluctuations of side-groups both in the mesophase and crystalline state (λ -process). Interestingly, both the Arrhenius-type β- and λ -relaxation are characterised by a non-zero activation entropy, which indicates the cooperative nature of the underlying molecular dynamics.
Starting Page	1661
Ending Page	1671
Page Count	11
File Format	PDF
ISSN	00222461
Journal	Journal of Materials Science
Volume Number	40
Issue Number	7
e-ISSN	15734803
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	2005-01-01
Publisher Place	Boston
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Polymer Sciences Industrial Chemistry/Chemical Engineering Characterization and Evaluation Materials Mechanics
Content Type	Text
Resource Type	Article
Subject	Ceramics and Composites Mechanics of Materials Mechanical Engineering Polymers and Plastics

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