Abstract
To assess the Rayleigh light scattering method as a means to determine the elastic constant ratios, we have first reviewed the de Gennes formula for the differential cross section, reexamining the assumptions used and the corrections at the interfaces. Then we have summarized optimum scattering geometries, proposing a new geometry suitable for obtaining K11/K33 directly. Finally we have described experimentals; considerable emphasis has been laid on the stray light level and the delicate adjustment of the experimental setup in determining K11/K22 and K33/K22. The data in each measurement showed a roughly ±3% deviation and there were systematic differences between the three independent measurements. The de Gennes formula appears to be reliable and suitable scattering geometries do in fact exist for obtaining each Kii/Kjj. Accurate determination is prevented by experimental annoyances. The method is inherently susceptible to stray light and the measurement requires delicate critical adjustments of the optical system. The delicacy required for the operation and the susceptibility to stray light may cause the introduction of systematic errors. Photon correlation spectroscopy expected to be resistant to these errors has been suggested for use in determining not only viscosity but also elastic constant ratios.