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Modulated differential scanning calorimetry

Transitions between monotropic and enantiotropic phases of a cholesteric liquid crystal

Journal of Thermal Analysis and Calorimetry
Authors: F. Roussel and J. M. Buisine

The Modulated Differential Calorimetry (MDSC) is applied to the determination of the reversibility in the cholesteryl chloride, which presents a cholesteric monotropic phase between the isotropic and crystalline states. The experimental modulation parameters that govern this method i.e. frequency, amplitude and heating/cooling rate, are determined. MDSC curves and complementary thermomicroscopical observations assign melting, crystallization and liquid cholesteric transition as ‘non reversing’, and clarification as ‘reversing’.

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The amplitude-energy relationships for surface barrier detectors were measured for4He and12C particles, as well as the corresponding energy resolutions. It is shown that the use of12C beams presents no marked advantage for increasing mass or depth resolution. On the other hand pile-up phenomena are drastically reduced by using12C backscattering. Applications are shown to the determination of trace amounts of Sb or Yb near the surface of iron. Gold contaminations of silicon surfaces were precisely measured within minutes down to 5·1011 gold atom/cm2, the limiting sensitivity being of the order of 1010 atom/cm2 for traces of heavy elements, such as Au, Hg, Pb, etc. Sensitivities for lighter elements are discussed.

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