Azimuth Angle Dependence of Polarized Infrared Spectra of Injection-Molded Polyoxymethylene

Abstract

Injection-molded polyoxymethylene (POM) has molecular chains mainly oriented in the injection direction. We investigated the directional dependence of the polarized infrared reflection and attenuated total reflection spectra by rotating the anisotropic POM sample. Because of the strong absorption and large frequency dispersion of the C–O vibration in the main-chain direction, we found phenomena such as shoulder wing generation that resulted from the mixing of optical responses attributed to the vibration in the main chain and that in the direction perpendicular to the main chain. The spectra of the directional dependence can be explained qualitatively because of the anisotropy of the mode with large frequency dispersion.

Electrospun Materials with High Reflectance and Polarization Contrast for Sensing Applications in the Mid-Infrared Atmospheric Window

“…The dipole moment of the 900 cm −1 mode is better aligned with the main axis of the polymer chain than that of the 936 cm −1 mode, such that it naturally presents a higher DOLP value for a given level of anisotropy. 46 This behavior contributes, along with the enhanced fiber alignment itself, to the increased R // and DOLP values measured at this new reflectance maximum. An SEM image of the mat (Figure S9) confirms the high fiber density and alignment.…”

“…It should be noted that the position of the reflectance maximum has shifted to 900 cm –1 , compared to 936 cm –1 for the mat treated solely by compression (Figure A). The dipole moment of the 900 cm –1 mode is better aligned with the main axis of the polymer chain than that of the 936 cm –1 mode, such that it naturally presents a higher DOLP value for a given level of anisotropy . This behavior contributes, along with the enhanced fiber alignment itself, to the increased R // and DOLP values measured at this new reflectance maximum.…”

“…31,42−44 While certain MIR optical properties and the robustness of electrospun POM mats have been applied previously, notably for passive radiative cooling, 45 the ability of these materials to exhibit exceptional reflectance and an anisotropic optical signature have not, to the best of our knowledge, been simultaneously harnessed in any applications, given that the polaritonic response of polymers is a recent discovery still under active fundamental investigation. 40,46 Herein, we synergistically leverage the polaritonic response of POM and the molecular anisotropy induced by electrospinning to prepare flexible fiber mats suitable for MIR polarimetric sensor development. The as-spun fiber mats were subjected to a variety of post-treatments, mainly compression and drawing (but also exposure to a nonsolvent and incorporation of a refractive index-matching medium) to optimize their optical response in the MIR.…”

“…It also possesses good durability thanks to its thermal resistance (high melting point of 175 °C) and recognized insensitivity to most chemicals, making it a viable option for field use where rigorous conditions are expected. , Recent studies by Nagai et al have revealed that certain polymers, most notably POM, exhibit radiative phonon polaritons that arise from the resonant coupling between light and a collective vibrational mode originating from interactions between strong permanent dipole moments within the material . These polaritons result in highly reflective features in the MIR range. − POM stands out because its polaritonic modes are exclusively localized within the AW, and they can reach considerable reflectance values, as previously demonstrated on rigid porous plates. , The intensity, width, and spectral position of these features depend on the topology of the material, including the size and shape of the pores and interstitial spaces. − In a recent study, our group has shown that POM can be readily formed into fibers with high molecular orientation by electrospinning, an effective processing method for the development of advanced polymer materials. ,− While certain MIR optical properties and the robustness of electrospun POM mats have been applied previously, notably for passive radiative cooling, the ability of these materials to exhibit exceptional reflectance and an anisotropic optical signature have not, to the best of our knowledge, been simultaneously harnessed in any applications, given that the polaritonic response of polymers is a recent discovery still under active fundamental investigation. , …”