Design and Synthesis of Ferroelectric Liquid Crystals: 1) Studies on the de Vries Phase, and 2) Bent-core Achiral Ferroelectrics

Gong, Tao

Graduate Thesis Or Dissertation

Design and Synthesis of Ferroelectric Liquid Crystals: 1) Studies on the de Vries Phase, and 2) Bent-core Achiral Ferroelectrics Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/rn3011631

Abstract

Two separate projects in the field of ferroelectric liquid crystals are described, in which target molecules are synthesized to fulfill specific goals: obtaining a better understanding of de Vries liquid crystal behaviors through synthesis of new mesogens; and design, synthesis and characterization of novel polar achiral phases of bent-core liquid crystals. de Vries liquid crystals are famous for their minimal layer shrinkage on transition from the SmA into the SmC phase. Since such layer shrinkage causes problems for photonics applications such as LCDs, de Vries materials have considerable potential in the display industry. In the de Vries project, work aimed at developing an improved understanding of the de Vries phase by design and synthesis of new compounds possessing de Vries characters. Thus, by incorporating a carbosilane tail, which is expected to suppress out of layer fluctuations in the smectics, into the formally "anti-de Vries" liquid crystal W317, de Vries phases were obtained as evidenced by the "diagnostic" double peak profile in the polarization reversal current. This property, along with other characterization techniques such as differential scanning calorimetry (DSC), X-ray scattering, and polarized light microscopy (PLM), provide insight into the molecular packing in de Vries phases. In addition, a family of binary smectic mixtures of de Vries/anti-de Vries materials was studied to exam the "cone model" of de Vries phases. The polar phases of achiral bent core liquid crystals have been a topic of intense investigation since their discovery in 1997. In this project, a family of "one-tail" bent core liquid crystals with polar group on one side of the aromatic core, and a carbosilane tail on the other, were synthesized and studied by means of DSC, X-ray, PLM, and other techniques. A novel structure designed to test a popular model for formation of the SmAPF phase refuted the model, as hoped, and provided a new material with very high polarization, and showing "ideal" electrostatic V-shaped electro-optic switching. Such behavior could be potentially applied in devices exhibiting optical latching (no or little power required to maintain a gray level). Furthermore, another novel low temperature phase, denoted as the SmX phase since the structure is not understood, was discovered in one of the family. This SmX phase seems to be similar to the B4 helical nanofilament phase.

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