Temperature-Dependent Infrared Refractive Index of Polymers from a Calibrated Attenuated Total Reflection Infrared Measurement

We demonstrate a straightforward method by which a commonly available reference sample such as water can be used to calibrate an attenuated total internal reflection infrared absorbance measurement in order to account for the polarization of the beam incident on the internal reflecting element, and the spread of angles about the nominal angle of incidence. This enables quantitative comparison of attenuated total reflection-derived absorbance data with spectra calculated from optical constants. We then apply this calibration to the measurement of temperature-dependent absorption spectra of a polydimethylsiloxane sample. We illustrate that the extracted optical constants scale with the temperature-dependent changes in the polymer density better than the raw absorbance values on vibrational resonance.

Automated summary

This paper demonstrates a simple method to calibrate attenuated total internal reflection infrared absorbance measurement using a commonly available reference sample such as water. The calibration takes into consideration the polarization of the incident beam and the spread of angles about the nominal angle of incidence. The calibrated measurements enable quantitative comparison with spectra calculated from optical constants, and the method is applied to temperature-dependent absorption spectra of a polydimethylsiloxane sample, showing better correlation between the extracted optical constants and temperature-dependent changes in polymer density than the raw absorbance values on vibrational resonance.