Polymer Optical and Dielectric Properties through Vibrational Spectroscopy

Principles of the refraction and extinction of electromagnetic radiation incident upon homogeneous isotropic condensed phases are reviewed. The relationship between the complex refractive index, n(υ), and the absorption index, k(υ), through the Kramers–Kronig transform is shown as is the relationship of these optical constants to ɛ, the complex dielectric function. The basis of the determination of the optical constants n and k as a function of frequency for polymeric materials by infrared reflection-absorption spectroscopy (IR-RAS) is illustrated with examples as are other external reflection methods. Also discussed is the effect of absorber concentration on the IR-RA spectra. Various methods for the measurement of optical constants and dielectric function of isotropic and anisotropic polymers covered are internal reflection techniques such as attenuated total reflectance (ATR), transmittance-reflectance, transmission, and ellipsometry. The chapter concludes with comments on new spectroscopic techniques with potential application to the determination of optical constants of polymers. Keywords: anisotropic polymers; optical constants; refractive index; absorption index; dielectric function; infrared reflection-absorption spectroscopy; Fresnel coefficients; Kramers–Kronig transform; transmittance; ellipsometry