The Thermodynamics and Mechanical Properties of Anthracene-Carbazole Alloys

Abstract

Abstract The heat capacities of seven anthracene-carbazole alloys within the homogeneity range of the ordered α′ phase, which extends from 1.5 to 24.5 pet carbazole at room temperature, have been determined over the temperature range 180 to 440 K. At all temperatures, the maximum heat capacity occurred for the 10 pet carbazole alloy. The difference between the enthalpies, and between the entropies, of the alloys and a mixture of the component compounds at 400 K and dilatometry measurements on the 10 pct carbazole alloy indicate that the stability of the α′alloys, with respect to the components, is associated with an increase in vibrational entropy due to a volume change. Heat capacity measurements on quenched and isothermally annealed crystals of a 1.75 pct carbazole alloy give an activation energy of 29.3 kJ mole−1 for the transformation of disordered α to ordered α′ phase. Single crystals of the 1.75 pct carbazole alloys were prepared in the α and α′ condition. The critical resolved shear stress for slip on both the (001) [010] and (001) [110] systems in the disordered α phase is close to that in zonerefined anthracene. The isothermal transformation of α to α′ phase is accompanied by a peak in the curve of critical resolved shear stress against annealing time, which probably corresponds to a critical combination of degree of order and domain size. The overall effect of ordering is to increase the strength of the alloy. The critical resolved shear stress for slip on both basal systems increases as the composition of the α′ alloys is increased to the stoichiometric composition of 10 pct carbazole.