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The molecular relaxation mechanisms in cork as studied by thermally stimulated discharge currents (1995)

Mano, J. F. ; Correia, N. T. ; Moura Ramos, J. J. ; [et al.]

Springer

Journal of materials science 30 (1995), S. 2035-2041

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ISSN: 1573-4803

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract The dielectric relaxation mechanisms present in cork have been investigated in the temperature range -100 to 100 °C using the technique of thermally stimulated discharge currents. A relaxation mechanism was detected which showed a compensation behaviour as observed for the α-relaxation (or glass transition relaxation) of synthetic polymers and which lead us to attribute to cork a glass transition-like temperature of 18 °C. One lower temperature mechanism was also observed, with low activation enthalpy and entropy, which is presumably originated by local motions (internal rotations) of polar molecular groups. An upper T g relaxation of higher intensity was also detected which was attributed to large-scale non-cooperative motions of polymeric segments.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00353030

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Molecular dynamics of a smectic liquid-crystalline side-chain polymer. The dielectric properties of aligned and nonaligned material studied over a wide range of frequency and temperature (1987)

Attard, George S. ; Moura-Ramos, J. J. ; Williams, Graham

Bognor Regis [u.a.] : Wiley-Blackwell

Journal of Polymer Science Part B: Polymer Physics 25 (1987), S. 1099-1111

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ISSN: 0887-6266

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: The dielectric relaxation behavior of a nonaligned and an aligned liquid-crystalline (LC) polymer are reported for the ranges 10-3.5 to 105 Hz and 274-363 K. Multiple processes (δ and α) are observed that follow a Vogel equation for the temperature dependence related to the apparent glass transition temperature. The occurrence of these processes and the variation in their relaxation strengths as sample alignment is changed is interpreted in terms of a molecular theory for the dielectric behavior of a LC polymer that involves the director order parameter Sd, the mesophase order parameter S, the dipole moment components of the mesogenic head groups, and their associated relaxation functions.

Additional Material: 8 Ill.