Transition enthalpy, liquid crystals

This method is used to locate phase transitions via measurements of the endothennic enthalpy of phase transition. Details of the teclmique are provided elsewhere [25, 58]. Typically, the enthalpy change associated with transitions between liquid crystal phases or from a liquid crystal phase to the isotropic phase is much smaller than the melting enthalpy. Nevertheless, it is possible to locate such transitions with a commercial DSC, since typical enthalpies are... 

An inspection of the transition enthalpies to the plastic state reveals relatively small values, so that one may expect, as in the case of liquid crystals, that some of the enthalpy is gained continuously through increased heat capacity (see Sect. 5.1.2). 

The enthalpies of transition and fusion are also poorly defined. Kantor, et al. ( ) has measured the enthalpy of the crystal and liquid. No data points were obtained in the beta phase region. As a result, we can only derive a combined value for the enthalpy of transition and fusion. Following the suggestion of Abey 12), the enthalpy values of Loasby and Dearden (10) and Abey (1 ) have the same value for the ratio of the transition enthalpy to fusion enthalpy, even though the actual values for each enthalpy are quite different. Thus, using this ratio and the sum of the enthalpies, as determined by Kantor et al. ( ), we calculate the Individual enthalpies of transition and fusion. A much more detailed discussion is in progress. 

Portugall et al. (1982) noticed that the phase transition temperature and enthalpy of the following side-group type liquid crystal polymer, (3.13), were dependent on the degree of polymerization n. The polymer was noncrystalline. If n = 13, the glass transition temperature was 53 °C, the clearing point of the liquid crystal phase was 100 °C, the enthalpy of... 

Typical enthalpy changes between successive liquid-crystal phases or between a liquid-crystal phase and an isotropic liquid are usually small at around 1 kj mol , while transitions between a crystal and a liquid-crystal phase are strongly first order and often in the range of 30-50 kJ mol . Transitions between phases of the same symmetry are always first order and, while all liquid crystal transitions can be first order, the SmC-SmA and SmA-N transitions... 

HEAT CAPACITY AND ENTHALPY OF TRANSITION OF AROMATIC LIQUID CRYSTALS. FROM PROC. INTL. LIQUID CRYSTAL CONF. AT KENT STATE UNIV. AUG. 16-20,1965. 

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