Dynamics of polymeric liquids using polarization-modulated laser Raman scattering

A new experimental technique, ‘polarization-modulated laser Raman scattering’ (PMLRS), is presented for the study of the dynamics of polymeric materials subjected to transient flows. A detailed analysis of the experiment based on Jones-Mueller matrix calculus is presented. Jones and Mueller matrices that take into account the integrated effect of the deformed sample's birefringence are developed for a Raman scattering element, using either the 0° or 180° scattering geometries. To test the predictions of the theory a Raman scattering system, based on high-speed phase modulation (50 kHz) of the incident light coupled with phase-sensitive detection, has been developed. This system is also capable of simultaneously measuring birefringence. Single-step reversal extension and step strain experiments were conducted using a polyisobutylene melt. Experiments were done using the Raman scattered light associated with the v stretching vibration of C-H groups present in the specimen. The results obtained indicate that the Raman signal ratios all depend on the second- and fourth-order moments of the orientation distribution function of polymer segments and on the sample's birefringence.