Observation on Elastic Incoherent Structure Factor for Rotational Aromatic Groups of Thermotropic Copolyester

概要

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By using a combined method of neutron and X-ray scatterings, the rotational motion of aromatic groups in a thermotropic copolyester(Vectra)has been investigated, observing the elastic incoherent structure factor(EISF). Vectra, a random copolyester of p-hydroxybenzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) with a fraction of 73/27 (mol/mol), gives rise to nematic phase above its melting temperature T_m=558 K. Below the melting temperature, Vectra forms semi crystalline phase, i. e., a mixture of a crystalline and a amorphous phases(T_g=393 K). The elastic incoherent cross section obtained by the neutron scattering was successfully decomposed into (i) the Debye Waller factor originating from the vibrational motion of hydrogen, (ii) EISF for the rotational motion of aromatic groups (RM) and (iii) the quasi elastic cross section for RM. In the nematic phase above T_m, the EISF thus obtained was well reproduced by a free rotational model for the aromatic groups, in which a number of residing sites for hydrogen on the rotational circle is infinite. On the other hand, in the solid semi crystalline phase below T_m, EISF becomes less q-dependent with decreasing temperature, which can be well described by a jump rotation having a finite number of residing sites for hydrogen.
理論物理学刊行会の論文
1997-06-27