Investigating the Effect of Smectic A Temperature Range Variation on De Vries Properties

Authors:	Song, Qingxiang
Files in This Item: File Description Size Format Song_Qingxiang_200911_MSc.pdf 8.02 MB Adobe PDF
Keywords:	Liquid Crystals de Vries Character
Issue Date:	2009
Series/Report no.:	Canadian theses
Abstract:	Ferroelectric liquid crystals (FLCs) have been investigated as the basis for a new type of liquid crystal display because of their fast switching times. Commercial FLC materials are mixtures consisting of a small amount of chiral dopant in an achiral liquid crystal host with an isotropic-nematic-smectic A-smectic C (INAC) phase sequence, which is required to achieve proper alignment between glass slides with rubbed polyimide alignment layers. However, the layer contraction occurring at the SmA-SmC phase transition on cooling from isotropic liquid is a severe problem that leads to a buckling of the smectic layers and results in zigzag defects that drastically degrade the optical quality of FLC films. To solve this problem, we are focusing on a new class of liquid crystal molecules with minimal or no smectic layer shrinkage at the SmA-SmC transition which is referred to as ‘de Vries-like.’ Previous work in the Lemieux group has shown that combining structural elements promoting SmA and SmC phases in a single molecule increases de Vries-like behavior. Giesselmann et. al. suggest that a correlation exists between the temperature range of the SmA phase and de Vries-like behavior. In the study described herein, two homologous series of molecules with 2-phenylpyrimidine cores with siloxane-terminated side-chain (SmC promoting element) and a chloro-terminated side-chain (SmA promoting element)are synthesized and characterized by polarized optical microscopy, differential scanning calorimetry and small-angle X-ray diffraction (SAXS). The reduction factor R for series 1.13 from 0.36 to 0.46 and for series 1.14 from 0.47 to 0.54. Results show that, although there is some correlation between % layer contraction and SmA temperature range, it can be explained primarily by differences in tilt angle θ. When θ is taken into account in the R values, there is no correlation. Another aspect of the study described herein, two siloxane-terminated 2-phenylpyrimidine chiral dopants are synthesized and characterized by polarized optical microscopy, differential scanning calorimetry and small-angle X-ray diffraction (SAXS).