Thermo-optical analysis (TOA) as a tool of melting phenomena investigations

In the work, after preliminary discussion of the complexity of the phenomenon of melting chemical compounds, two basic research methods are presented: calorimetric methods and thermooptical method. The physical basis of the five main calorimetry techniques is now detailed (adiabatic calorimetry, differential thermal analysis – DTA, differential scanning calorimetry with heat compensation – DSC heat compensated, differential scanning calorimetry with heat flow – DSC heat flux and differential scanning calorimetry with temperature modulation – MDSC) and thermo-optical techniques used in phase transitions investigations. The advantages and disadvantages of these methods are shown in numerous examples and the accuracy attainable by the individual measuring techniques is compared

4-Octylphenylazo-4′-phenyl alkanoates – homologous series of azomesogens with extremely rich liquid-crystalline polymorphism

<p>This paper presents synthesis and liquid-crystalline properties of full homologues series (from acetate to arachidate) of 4-octylphenylazo-4′-phenyl alkanoates. All of the 19 synthesised compounds are liquid crystals with extremely rich mesomorphism. The ester chain length strongly influences mesogenic behaviour of presented materials. In some compounds, up to four liquid-crystalline phases have been observed. There were six different mesophases detected: nematic, smectic C, smectic F, smectic I, J and G. Moreover, some homologues display two crystalline forms. This latter phenomenon does not depend on the ester chain length. Identification of such complicated phase sequences was made based on four methods: polarised light microscopy, thermo-optical analysis, differential scanning calorimetry and X-ray measurements.</p