Determination of Smectic-Nematic Phase Transitions in Liquid Crystalline Polymers Using X-ray Diffraction Methods

Abstract

Abstract Phase transitions in liquid crystals are not always easily detectable. Wiegeleben and Demus [1] described methodological aspects in thermal analysis of liquid crystalline substances. There a classification of the detection of phase transitions has been given in which a division in transitions observable only by optical microscopy or/and by DSC has been made. However, there are certain cases known, where phase transitions are not detectable either by polarisation microscopy or by DSC. This is especially true, if the investigated substances have a polymeric nature. Due to polydispersity it is not always possible to obtain clear evidence for phase transitions using both methods. A special hinderence for polarization microscopy investigations is the usually high viscosity of polymeric substances and therefore the difficulties in obtaining sufficiently thin layers for the investigation. Calorimetric studies suffer from the mostly small heat of transition for smectic A- or smectic C-nematic transitions...