Polarized Raman Spectroscopy Strategy for Molecular Orientation of Polymeric Fibers with Raman Tensors Deviating from the Molecular Frame

Journal article, 2020

Polarized light is frequently used to identify molecular anisotropy in polymers, biological systems, and other materials. The influence of the Raman tensor by polarized light reveals not only the chemical structure but also information on the morphology of polymers. The orientation distribution of molecules in polymers has previously been determined for systems with the principal axis components of the Raman tensor parallel to the molecular frame. In many cases, the Raman tensor principal axis is not parallel to the molecular chain axis. Therefore, the orientation of the Raman tensor, relative to the molecular chain axis, is crucial if accurate information about the molecular orientation distribution is sought for. This work presents a strategy for separating the Raman tensor orientation angles from the molecular orientation angles for polymeric samples with fiber symmetry. Composite polymeric materials often experience signal overlap in the X-ray scattering wide-angle region, where the anisotropy is often resolved. While X-ray scattering investigates intermolecular distances, Raman spectroscopy resolves chemical information, and anisotropy, by the influence of Raman scattering. The quantitative principles presented here may aid in the evaluation of anisotropy in such composite materials.