Birefringence techniques for the assessment of orientation

• Published in: Polymer testing 1984, Vol.4 (2), p.143-164
• Main Authors: Read, B.E., Duncan, J.C., Meyer, D.E.
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Miscellaneous; Physical properties; Polymer industry, paints, wood; Properties and testing; Technology of polymers
• ISSN: 0142-9418; 1873-2348
• DOI: 10.1016/0142-9418(84)90009-6

Methods are surveyed for the quantitative specification of molecular orientation in solid polymers based on measurements of birefringence (refractive index anisotropy). Reliable estimates are required of the intrinsic birefringence of the fully oriented material and account should be taken of possible contributions to the birefringence from local distortional deformations and other effects not associated with orientation. The in-plane birefringence of sheets or films is usually determined from measurements of the relative retardation between the resolved components of a polarised light beam transmitted normal to the sample plane. Far-infra-red and microwave techniques can eliminate scattering and yield birefringence values on materials opaque to visible radiation. Several methods are reviewed for measuring the through-thickness birefringence of biaxially oriented sheets or films. From birefringence measurements over a temperature range, using a light-scattering retardation technique, estimates have been made of the rubber-elastic orientational stresses and internal distortional stresses frozen into biaxially oriented sheets of cross-linked PMMA.