SIMULTANEOUS DETERMINATION OF THE HEAT-CAPACITY AND THE HEAT OF THE TRANSITIONS FOR LONG-CHAIN COMPOUNDS WITH A HEAT-FLUX TYPE DSC

The heat capacity method of DSC measurements, for which sapphire was u sed as a standard, was applied to determine simultaneously the heat of the transitions and the heat capacity for long-chain compounds. A hea t-flux DSC was used because of its relatively high sensitivity at slow scanning rates. The data were analyzed with a computer system. Measur ements on indium were performed to obtain information about factors af fecting the accuracy. Fairly satisfactory results were obtained for th e heat of melting and the heat capacity at heating rates of 0.5 and 2 K min-1. Long-chain symmetrical ketones were also used to test the rel iability of the measurement because their thermal behavior is very sim ple. Solution-grown crystals of henpentacontane and dopentacontane cle arly showed high-temperature modifications with a high heat capacity. Analysis by the present method indicates that the heat capacities of t hese modifications have a relatively large contribution to the overall change in enthalpy from the stable crystal at room temperature to the liquid.