The hexagonal to discotic phase transition in 1,4,8,11,15,18,22,25-octahexylphthalocyanine studied by differential scanning calorimetry.

The phase change in metal-free 1,4,8,11,15,18,22,25-octahexylphthalocyanine compound with eight non-peripheral hexyl chains was investigated under non-isothermal conditions by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Two endothermic changes were reported. The first one between 332 and 350 K relates to the transition from the hexagonal columnar mesophase to a less ordered crystalline phase, P1. The second endothermic transition from 408 to 417 K is due to the transition to the discotic columnar mesophase, P2. The isoconversional methods of Friedman, and Kissinger, Akahira and Sunose (KAS) were used to determine the variation of the activation energy for crystallisation with temperature, E α(T). Using the Friedman method the average values of E α(T) were 121.31 and 352.77 kJ mol-1 for the first and second peaks, respectively. The KAS method gave higher values of E α(T) with averages of 173.25 and 411.44 kJ mol-1, respectively. The specific heat was measured and found to vary with temperature. [ABSTRACT FROM AUTHOR]