Simultaneous Synchrotron X-ray Diffraction and Stress-Strain or Stress-Relaxation Experiments for the Study of Parallel and Perpendicular Orientation in a Liquid Crystalline Polymer
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- 作者：Juan P. Ferná ; ndez-Blá ; zquez ; Antonio Bello ; Marí ; a L. Cerrada ; Ernesto Pé ; rez
- 刊名：Macromolecules
- 出版年：2008
- 出版时间：January 22, 2008
- 年：2008
- 卷：41
- 期：2
- 页码：421 - 428
- 全文大小：287K
- 年卷期：v.41,no.2(January 22, 2008)
- ISSN：1520-5835
文摘
The orientational behavior of a thermotropic polybibenzoate exhibiting a low-ordered smecticmesophase has been studied by real-time simultaneous synchrotron X-ray diffraction and stress-strain or stress-relaxation experiments. It follows from the stress-strain test (conducted at 105 
C and with a nominal strain rateof 3.33 min<SUP>-1) that during the initial elastic region and around the yielding point, exclusively anomalousperpendicular orientation is obtained, with the molecular axes perpendicular to the uniaxial deformation direction.However, at the end of the necking region and the beginning of the strain-hardening process, parallel orientationbegins to be obtained, and its intensity increases with the strain hardening. The intensity and spacing of thesmectic spots and the layer order parameters for the two kinds of orientation have been obtained from thecorresponding radial and azimuthal integrations of the photographs. One interesting finding is the observation ofa 4% maximum expansion of the smectic spacing for the parallel orientation. In the subsequent stress-relaxationexperiment, very little influence has been found on the smectic regions showing perpendicular orientation, but aprogressively better parallel ordering is observed with an intensity increase by a factor of 3.2, with a very importantincrease of the order parameter, and with a simultaneous decrease of the smectic layer spacing. This decreaseshows a perfect match with the stress-relaxation curve, in such a way that the two magnitudes, stress and smecticspacing, can be fitted to stretched exponential KWW functions with rather similar parameters.
C and with a nominal strain rateof 3.33 min<SUP>-1) that during the initial elastic region and around the yielding point, exclusively anomalousperpendicular orientation is obtained, with the molecular axes perpendicular to the uniaxial deformation direction.However, at the end of the necking region and the beginning of the strain-hardening process, parallel orientationbegins to be obtained, and its intensity increases with the strain hardening. The intensity and spacing of thesmectic spots and the layer order parameters for the two kinds of orientation have been obtained from thecorresponding radial and azimuthal integrations of the photographs. One interesting finding is the observation ofa 4% maximum expansion of the smectic spacing for the parallel orientation. In the subsequent stress-relaxationexperiment, very little influence has been found on the smectic regions showing perpendicular orientation, but aprogressively better parallel ordering is observed with an intensity increase by a factor of 3.2, with a very importantincrease of the order parameter, and with a simultaneous decrease of the smectic layer spacing. This decreaseshows a perfect match with the stress-relaxation curve, in such a way that the two magnitudes, stress and smecticspacing, can be fitted to stretched exponential KWW functions with rather similar parameters.