Anisotropic properties of poly(ethylene terephthalate) by Brillouin spectroscopy: Anisotropic properties of oriented bulk and nanostructured poly(ethylene terephthalate) determined by Brillouin spectroscopy and birefringence experiments

Using Brillouin spectroscopy (BS), the tensor of the elastic constants of oriented poly(ethylene terephthalate) was determined for a variety of morphologies obtained by different uniaxial drawing procedures. The extreme values of the moduli along the drawing direction at frequencies of a few gigahertz were C33 = 40 GPa and C44 = 1.8 GPa. As a result of the invariants of the single‐phase aggregate model, the oriented state is dominated by the Reuss average even at extreme draw ratios and subsequent to a deformation‐induced crystallization. This is documented in both the BS orientation parameter and the BS mode numbers in comparison with birefringence. Additional spectral lines observed at draw ratios larger than 6 are discussed in relation to the formation of nanostructured phases. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1201–1213, 2002