Low-temperature phase transformation studies in the stearic acid: C form

• Temperature dependence polarized Raman spectra in the C form of stearic acid.
• Its structure was refined by Rietveld analysis of XRD data.
• Differential scanning calorimetry measurements.
• The crystal undergone to a phase transition and a conformational change.

This paper reports the temperature-dependent measurements in the C form of stearic acid. Raman scattering, X-ray diffraction, and differential scanning calorimetry measurements were performed at low temperatures. The polarized Raman spectra were measured for temperatures ranging from 8 to 300 K over the spectral range of 30–3000 cm−1. The spectral changes observed in both the lattice vibrational modes and the internal vibrational modes regions of the Raman spectrum, allowed to identify a phase transition undergone by the stearic acid crystal occurring between 210 and 170 K and a change in the structure continues to be observed down to 8 K. The anharmonicity of some vibrational modes and the possible space groups presented by the crystal at low temperatures were also discussed. Low-temperature X-ray diffraction measurements were performed from 290 to 80 K and the results showed slight changes in the lattice parameters at ∼200 K. Furthermore, the evidence of the phase transformation was provided by the differential scanning calorimetry measurements, which identified an enthalpic anomaly at about 160 K.

This study reports temperature dependence in the C form of stearic acid. The phase transition undergone by the crystal occurs between 210 and 170 K and a conformational change in the molecule structure continues occurring down to 8 K. The spectral changes in the Raman spectrum, allowed to identify a phase transition undergone by the stearic acid crystal. The X-ray diffraction results showed slight changes in the lattice parameters at ∼200 K. Furthermore, an evidence of the phase transformation was provided by the differential scanning calorimetry measurements, which identified an enthalpic anomaly at ∼160 K.Figure optionsDownload as PowerPoint slide