Anomalous thermal behavior of salicylsalicylic acid and evidence for a monotropic transition to a nematic phase

The temperature of maximum intensity of the isotropization peak of salicylsalicylic acid, obtained by differential scanning calorimetry (DSC), is reported to display a strong dependence on the heating rate. A detailed analysis of the DSC results combined with polarizing optical microscopy (POM) observations and X-ray diffraction (XRD) measurements, as a function of temperature, gives evidence for a nematic phase that appears when the sample is heated. In the present work, some experimental results are presented that suggest that the thermal behavior of the salicylsalicylic acid and the formation of the nematic phase are associated with a process that has slow kinetics. The molecular mobility in the crystalline phase of salicylsalicylic acid was studied by thermally stimulated depolarization currents.