Terahertz spectroscopy on polymers: A review of morphological studies

Polymers typically show only low absorption in the far-infrared or terahertz (THz) frequency range and are thus often used as window or lens materials for THz spectroscopy and imaging systems. A comprehensive study of the far-infrared properties of polymers yet reveals that THz spectroscopy is a very convenient technology for the investigation of various material properties including the morphology. Here, we report the dielectric parameters refraction index n and absorption coefficient K of various polymers determined by THz time-domain spectroscopy with a very high precision. The observed features are attributed to macromolecular origin. Furthermore, we show that the temperature-dependent lattice mode shifts of highly-crystalline polymers reveal information about thermo-morphological interactions between the amorphous and the crystalline phase. A temperature-dependent refractometric data base of various standard polymers completes the paper. This data base enables the determination of the glass transition temperature T-g of these polymers and allows the extrapolation of the index of refraction across a broad range of temperatures above and below T-g for a given material. (C) 2011 Elsevier B.V. All rights reserved.