2.6.5. ATR-FTIR Spectroscopy

Fourier transform infrared spectroscopy (FTIR) single spectra were collected in the 600–4000 cm⁻¹ wavelength range using the Tensor 37 FTIR equipment (Bruker, Germany) coupled to the attenuated total reflection (ATR) accessory Golden Gate (Specac, Ltd., Orpington, UK). Spectra were taken by averaging 20 scans at a resolution of 4 cm⁻¹.

A Nicolet Nexus FTIR instrument (Thermo Fisher Scientific, Wilmington, DE, USA) coupled to a variable-temperature single reflection diamond ATR sampling accessory (Specac Ltd., Orpington, UK) was used to collect spectra as a function of temperature. Spectra were collected using the blank ATR crystal at the same temperature as the background by averaging 64 scans at 4 cm⁻¹ resolution. The samples were clamped directly onto the ATR crystal using a calibrated torque wrench (Specac Ltd.) set at 80 cNm, which applies a load of 350 N via the sample accessory anvil, to ensure that any peak intensity changes in the data represented changes to the morphology of the samples. Prior to conducting the variable temperature infrared measurements, reproducibility of the sample contact and resulting spectra intensity were validated. Spectra were collected from 30 to 130 °C at 10 °C intervals and, thereafter, up to 200 °C at 5 °C intervals. Spectra were not collected until the digital reading on the temperature controller had fully stabilized to ensure the validity of the selected temperature.