Far-infrared reflection–absorption spectroscopy of thin polyethylene oxide films

We report the temperature dependent far-infrared spectrum of ultra-thin films of polyethylene oxide (PEO). Using the orientational specificity of infrared and far-infrared reflection–absorption spectroscopy and in-situ recrystallization, we find that during spin coating the PEO helices are initially in the plane of the film, but on crystallization reorient to be normal to the substrate. A splitting of the C–O torsional mode near 109 cm−1 is identified as arising from a distortion of the normal helical structure of PEO. Comparison with transmission spectra of cast films demonstrates the value of far-infrared reflection–absorption spectroscopy (FIRRAS) in the study of crystalline polymers in the far infrared.