Effects of Wavelength on Strain-Induced Birefringence of Polymers

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Abstract

Strain-induced birefringence, Δn, was measured at wavelengths 400nm<λ<800nm for uniaxially elongated films of polystyrene (atactic and syndiotactic), bisphenol A polycarbonate, poly(ethylene terephthalate), and poly(ethylene naphthalate). The magnitude of Δn was always higher at lower λ: the reduced birefringence, k(λ)≡Δn(λ)/Δn(633 nm), was a decreasing function of λ. The strain-induced crystallization in poly(ethylene terephthalate) (PET) and syndiotactic polystyrene (sPS) did not significantly affect k(λ). For polycarbonate (PC) and PET λ-dependence was much stronger when the strain was applied in the melt state (corresponding to the stress-optical coefficient, SOC) than in the glassy state (corresponding to the photoelastic coefficient, PEC); the difference was very small for atactic polystyrene (aPS). These results may be explained with a model theory in which the SOC is associated solely with the chain orientation while the PEC is affected also by the rotation of repeating units around the chain axis induced by deformation of the material glassy state.

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Inoue, T., Kuwada, S., Ryu, D. et al. Effects of Wavelength on Strain-Induced Birefringence of Polymers. Polym J 30, 929–934 (1998) doi:10.1295/polymj.30.929

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Keywords

  • Birefringence
  • Stress-Optical Coefficient
  • Photoelastic Coefficient
  • Polymer Film

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