TABLE OF CONTENTS The optical measurements presented in the previous chapters can be used to either characterize local, microstructural properties or as probes of bulk responses to orientation processes. In either case, it is normally desirable to make the connection between experimental observables and their molecular or microstructural origins. The particular molecular properties that are probed will naturally depend on the physical interaction between the light and the material. This chapter explores molecular models and theories that describe these interactions and identifies the properties of complex materials that can be extracted from measurements of optical anisotropies. The presentation begins with a discussion of molecular models that are applied to polymeric materials. Using these models, optical phenomena such as birefringence, dichroism, and Rayleigh and Raman scattering are predicted. Models appropriate for paniculate systems are also developed.
Orientation of molecules can normally be detected using polarized light in either transmission or scattering experiments. The prediction of the observed effect (birefringence or dichroism, for example) requires a description of the basic "light-matter" interaction combined with a calculation of the distribution of orientations associated with the individual molecules or segments of molecules.
In this subsection, the connection is made between the molecular polarizability, ?, and the macroscopic dielectric constant, ?, or refractive index, n. This relationship, referred to as the Lorentz-Lorenz equation, is derived by considering the immersion of a dielectric material within an electric field, and calculating the resulting polarization from both a macroscopic...
