Morphology-sensitive infrared absorption bands of polymers derived from surface polaritons

Naoto Nagai,Hideki Okada,Takeshi Hasegawa

doi:10.1063/1.5116280

Abstract

Infrared (IR) spectroscopy is mostly used for analysis of normal modes, which provides rich chemical information of molecular structure at each chemical group. In practice, however, we sometimes encounter an unusually broad peak that cannot be assigned to a normal mode or overlapped multiple normal modes. This unusual peak can readily be understood by taking the concept of polariton into account even for a polymeric material. In general, however, ‘polariton’ is used for discussing inorganic crystals, in which the real part of the relative permittivity falls in negative. Here, we show some polymeric materials exhibit apparent negative relative permittivity in an IR region, which yields the unusual peaks. Through the measurements and theoretical simulations of spectra of polymer thin films, polariton is found to be necessary to comprehensively understand IR spectra of a polymer not only for a thin film, but also for powder dispersed in a KBr pellet, since the polariton peaks are found to be deeply correlated with the surface morphology.

Highlights

Infrared (IR) spectroscopy is powerful for analyzing molecular vibrations at a localized chemical group, with which molecular structures are revealed
As found in the former section, some strong IR absorbing bands of a polymer are readily explained by the LO frequency, and their intensity is influenced by the surface morphology, the εr,1 remains in the positive region
A radiative-type response of the surface polariton depending on the surface morphology is considered to be a general phenomenon in polymers

Summary

Introduction

Infrared (IR) spectroscopy is powerful for analyzing molecular vibrations at a localized chemical group, with which molecular structures are revealed. IR spectroscopy probes, the localized normal modes, and propagating vibrations over the molecular aggregate such as the phonon in a crystal. This analytical function is highly useful even for a material with a poor crystallinity, which is often found in a polymeric matter. The extraordinary high reflectance was found in a frequency region where the real part of the RP was apparently negative.. The extraordinary high reflectance was found in a frequency region where the real part of the RP was apparently negative.2 These optical characteristics indicate that a ‘polariton mode’ exists in the polarized spectrum The extraordinary high reflectance was found in a frequency region where the real part of the RP was apparently negative. These optical characteristics indicate that a ‘polariton mode’ exists in the polarized spectrum

Results

Discussion

Conclusion