TEMPERATURE CALIBRATION OF HEAT-FLUX DSCS ON COOLING

The temperature calibration of a TA Instruments 3200-2920 DSC has been performed on cooling using the isotropic --> nematic, isotropic --> c holesteric and other liquid crystal --> liquid crystal transitions of thermally stable, high purity liquid crystals. The thermal stability o f these liquid crystals has been verified by measuring the temperature of the mentioned transitions during cyclic heating and cooling experi ments. Correspondence has been established between the real and indica ted temperature during cooling for all combinations of heating and coo ling rates of practical interest: correction values were determined to the indicated temperature in order to obtain the real temperature on cooling. These correction values were calculated as the average from t he temperatures of four or five different liquid crystal transitions f or each heating-cooling rate combination. The accuracy of the temperat ure calibration on cooling is ca. 0.2 degrees C for heating and coolin g rates up to 20 degrees C mid(-1).