The Physico‐thermal Stabilities of Dye Solids II—Phase Transitions and Melting Behaviour of Some Disperse and Vat Dyes

Physical changes observed on heating a number of disperse‐dye solids up to and above their melting points have been followed using differential scanning calorimetry and hot‐stage microscopy; the existence of metastable solid states has been verified by X‐ray diffraction. Enthalpy and entropy changes of transition and fusion have been determined and the thermal behaviour of some of the dyes has been compared with and likened to the behaviour of liquid crystals on heating. No evidence was found for similar transitions in vat‐dye solids over the range of temperature employed.