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Mesogenic Properties of Noncollinear (Bent) Liquid Crystals

Mesogenic Properties of Noncollinear (Bent) Liquid Crystals. Applications to Environmental Sensing David Davis, Kent State University Advisor: Dr. Robert Twieg. Bent Core Liquid Crystals.

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Mesogenic Properties of Noncollinear (Bent) Liquid Crystals

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  1. Mesogenic Properties of Noncollinear (Bent) Liquid Crystals Applications to Environmental Sensing David Davis, Kent State University Advisor: Dr. Robert Twieg

  2. Bent Core Liquid Crystals • Historically, liquid crystal synthesis has been most concerned with structures incorporating a rigid core bearing one or more flexible tails in what’s known as a calamitic (rod-like) liquid crystal. • Since the early 1990’s much effort has been spent on the synthesis of bent core (noncollinear) liquid crystals, and the study of their properties1. Here the bend exists between ring components in the core.

  3. Properties of Bent-Core Liquid Crystals • Bent-core LCs exhibit new and unique but by now very well documented phases. • Bent core LCs may also possess more controversial phases, e.g. the biaxial nematic phase. • Posesses increased flexoelectricity- capable of spontaneous electrical polarization in response to strain (2 orders of magnitude higher than calamitic LCs)2. • Create strain on a liquid crystal layer to achieve a measurable electrical polarization (induce electron flow and measure current), create foundation for a sensor3. First instance of a Biaxial Nematic phase reported in bent-core liquid crystals (2004)4.

  4. Are There Other Types of Noncollinear Liquid Crystals? • While studies have focused on the synthesis of materials with the bend in the core, can the bend be placed elsewhere to observe similar properties? • Current area of study: Synthesis of materials with the bend at the tail-core juncture (e.g., meta-substituted alkoxy tails). • Target: 28 unique terphenyl-core compounds with differing permutations of meta-, para-, and null substitution of methoxy (C1), hexyloxy (C6), and dodecyloxy (C12) tail lengths. Bent-core liquid crystal Bend at tail-core juncture

  5. Examples of Materials Synthesized(Identical Length Tails) Cr 67.9 Cr 74.8 Cr 191.6 Sm 225.1 Sm 246.3 Iso Liq Iso Liq 244.9 Sm 223.6 Sm 188.5 Cr 72.5 Cr 63.4 Cr Cr 48.7 Cr 76.8 Iso Liq Iso Liq 59.3 Sm 45.1 Cr Cr 112.7 Iso Liq Iso Liq 102.9 Cr

  6. Examples of Materials Synthesized(Non-Identical Length Tails) Phase data TBD Cr 69.2 Iso Liq Iso Liq 99.9 Cr Cr 93.8 Cr 105.2 Iso Liq Iso Liq 100.5 Cr 88.2 Cr Cr 105.9 Iso Liq Iso Liq 99.9 Cr

  7. Terphenyl Compound Set

  8. Sample Synthetic Pathways

  9. Future Direction of Project • Explore other series of cores for bent molecules to discover possible mesogenic activity and flexoelectric properties. • Quaterphenyls (work underway Summer ’10) • 1,4-bis(phenylethynyl)benzenes • 1,4-dibenzoyloxybenzenes

  10. References • 1. Link, D.L. et. al. Spontaneous Formation of Macroscopic Chiral Domains in a Fluid Smectic Phase of Achiral Molecules. Science. 1997, 278, 1924-1927. • 2. Tschierske, C. Liquid Crystals Beyond Display Applications. J. Mater. Chem.2008, 18, 2869-2871. • 3. Jakli, A.I. et. al. Methods and Systems for Determining Flexoelectric Effect in a Liquid Crystal. US Patent Appl. 20100182026, July 22, 2010. • 4. Madsen, L.A. et. al. Thermotropic Biaxial Nematic Liquid Crystals. Phys. Rev. Lett.2004, 92, 14505/1-14505/4

  11. Additional References • Dierking, I. Angew. Chem. Int. Ed. 2010, 49, 29-30. • Lehmann, M. et. al. Chem. Eur. J. 2010, 16, 8275-8279. • Bisoyi, H.K. et. al. Beil. J. Org. Chem.2009, 5, No. 52. • Reddy, R. A.; Tschierske, C. J. Mat. Chem. 2006, 16, 907-961. • Takezoe, H.; Takanishi, Y. Jpn. J. Appl. Phys.2006, 45, 597-625. • Etxebarria, J.; Ros, M.B. J. Mat. Chem. 2008, 18, 2919-2926.

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