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Temperature calibration of an electrical compensation DSC on cooling using thermally stable high purity liquid crystals

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Abstract

Temperature calibration of DSCs is usually carried out on heating. In order to accurately control the temperature during cooling experiments, the calibration has to be carried out on cooling. Therefore, three high-purity, thermally stable liquid crystals were used to perform a temperature calibration of an electrcial compensation DSC on cooling. All three liquid crystals have several liquid crystalline phases, and they all were purified to a 99.9% lovel. Temoperatures of the isotropic to nematic or cholesteric and the mesophase to mesophase transitions were used. It was verified that these liquid crystals have sufficient thermal stability for carrying out the calibration on cooling. The dependence of the real temperature on the indicated temperature has been established for all the combinations of the heating and cooling rates of practical interest. It is also shown that the vant's Hoff equation can only be applied to the crystal to a liquid crystal transition, but not to the liquid crystal to liquid crystal or liquid crystal to isotropic transitions.

Zusammenfassung

Die Temperaturkalibrierung von DSC' s erfolgt immer während des Aufheizens. Um die Temperaturesteuerung auch bei Abkühlversuchen präziese zu steuern, muß die Kalibrierung beim Abkühlen erfolgen. Aus diesem Grunde wurden drei hochreine, thermisch stabile Flüssigkeitskristalle benutzt, um beim Abkühlvorgang die Temperaturkalibrierung eines elektrischen Kompensations-DSC auszuführen. Alle drei Flüssigkeitskristalle haben unterschiedliche flüssig-kristalline Phasen und alle besitzen die Reinheit von mindestens 99.9%. Es wurden die Temperaturen für die isotropisch/nematische bzw. isotropisch/cholesterische beziehungsweise meso/meso-Phasenumwandlungen verwendet. Es wurde gezeigt, daß diese Flüssigkeitskristalle thermisch ausreichend stabil sind, um die Kalibrierung während des Kühlprozesses vorzunehmen. Für alle Aufheiz- und Abkühlgeschwindigkeitskombinationen von praktischem Interesse wurde die Abhängigkeit der tatsächlichen Temperatur von der angezeigten Temperatur ermittelt. Au\erdem wurde gezeigt, da\ die van't Hoffsche Gleichung nur bei Kristall/Flüssigkeitskristall-Umwandlungen, nicht aber bei Flüssigkeitskristall/Flüssigkeitskristall- oder bei Flüssigkeitskristall/isotrope Phase-Umwandlungen.

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Authors and Affiliations

  1. Hoechst celanese research division, Robert L. Mitchell Technical Center, 86 morris avenue, 07901, summit, NJ

    J. D. Menczel

  2. The university of Alabama, 35899, Hunstville, AL, USA

    T. M. Leslie

Authors
  1. J. D. Menczel
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  2. T. M. Leslie
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Menczel, J.D., Leslie, T.M. Temperature calibration of an electrical compensation DSC on cooling using thermally stable high purity liquid crystals. Journal of Thermal Analysis 40, 957–970 (1993). https://doi.org/10.1007/BF02546855

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