TABLE OF CONTENTS The two dimensional infrared technique of Noda and coworkers cussed in section 10.1.4 has proven to be a powerful tool for investigating the local dynamics of multicom-ponent polymer materials. This method of analyzing the Orientational dynamics of different components in a complex liquid is not restricted to dichroism, however, and can be used for other spectroscopic methods, such as Raman scattering. Recently, in the laboratory of the author, two-dimensional Raman scattering has been developed as a tool to examine the local dynamics of polymeric liquids [143]. In this case, the synchronous and asynchronous correlation functions are constructed as described by equation (10.1), except that an appropriate Raman scattering orientation anisotropy signal is used in place of ? n ?. A convenient choice would be the R 2 ? signal given in equation (8.53) since this observable is not affected by birefringence.
As an example, we consider here the orientational dynamics of a simple polymer melt of poly, (isobutylene). The sample used here is a room temperature melt of average molecular weight 300,000, which is well above the entanglement chain length for that polymer. It is first necessary to examine the Raman spectra for this material to determine the extent of sensitivity to the polarization of light by various vibrational modes. In Figure 10.12, both the polarized (with the analyzing polarizer parallel to the incident polarizer) and depolarized (with the analyzer crossed) spectra are shown for an undeformed sample.
