FLEXOELECTRIC LIQUID CRYSTALS AND THEIR APPLICATIONS A dissertation submitted to Kent State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy by Yingfei Jiang August 2020 © Copyright All rights reserved Except for previously published materials i Dissertation written by Yingfei Jiang B.S., University of Science and Technology of China, Hefei, China 2014 M.S. Kent State University, USA 2017 Ph.D., Kent State University, USA 2020 Approved by ___________________________________ , Chair, Doctoral Dissertation Committee Dengke Yang ___________________________________ , Members, Doctoral Dissertation Committee Philip J. Bos ___________________________________ Robin Selinger ___________________________________ Elizabeth K. Mann ___________________________________ Xiaoyu Zheng ___________________________________ James Gleeson Accepted by ___________________________________ , Chair, Chemical Physics Interdisciplinary Antal I Jakli Program ___________________________________ , Interim Dean, College of Arts and Sciences Mandy Munro-Stasiuk, Ph.D. TABLE OF CONTENTS TABLE OF CONTENTS ............................................................................................... III LIST OF FIGURES ..................................................................................................... VIII LIST OF TABLES .........................................................................................................XV DEDICATION.............................................................................................................. XVI ACKNOWLEDGEMENTS ...................................................................................... XVII INTRODUCTION ..................................................................................... 1 1.1 Basics of liquid crystal .............................................................................................. 1 1.2 Elastic property of liquid crystal ............................................................................... 3 1.3 Dielectric property of liquid crystal .......................................................................... 4 1.4 Flexoelectric effect .................................................................................................... 5 1.5 Optical properties ...................................................................................................... 8 1.6 Dichroic dye liquid crystals ....................................................................................... 9 1.7 Liquid crystal display modes ................................................................................... 10 1.7.1 Twist nematic (TN) ....................................................................................... 10 1.7.2 Vertical alignment (VA)................................................................................ 12 1.7.3 In-plane-switch (IPS) and Fringe field switching (FFS). .............................. 14 1.8 Polymer stabilized liquid crystals............................................................................ 17 1.9 The overview of the dissertation ............................................................................. 18 EFFECTS OF FLEXOELECTRICITY AND ION ON THE FLICKER OF FRINGE FIELD SWITCHING LIQUID CRYSTAL DISPLAY ............................................................................................................. 22 iii 2.1 Background ............................................................................................................. 22 2.2 Experiment and results ............................................................................................ 23 2.3 Simulation study ...................................................................................................... 26 2.3.1 Effect of flexoelectricity................................................................................ 26 2.3.2 Effects of ion ................................................................................................. 28 2.3.3 Splay and bend deformation values .............................................................. 30 2.3.4 Flexoelectric coefficients on flickering ......................................................... 31 2.4 Conclusion ............................................................................................................... 32 IMAGE FLICKERING-FREE POLYMER STABILIZED FRINGE FIELD SWITCHING LIQUID CRYSTAL DISPLAY ................................... 33 3.1 Introduction ............................................................................................................. 33 3.2 Experiment and results ............................................................................................ 35 3.3 Simulation and results ............................................................................................. 43 3.4 Discussion and conclusion ...................................................................................... 49 IMAGE FLICKERING REDUCTION BY DIMER AND POLYMER STABILIZATION IN FFS LIQUID CRYSTAL DISPLAY ........................... 52 4.1 Introduction ............................................................................................................. 52 4.2 Reduction of image flickering by decreasing flexoelectric coefficient: doping a liquid crystal dimer ........................................................................................................... 56 4.2.1 Simulation study ............................................................................................ 57 4.2.2 Experimental study ........................................................................................ 59 iv 4.3 Reduction of image flickering by decreasing spatial variation of liquid crystal director: polymer stabilization .......................................................................................... 67 4.3.1 Simulation study ............................................................................................ 67 4.3.2 Experimental study ........................................................................................ 70 4.4 Discussion and Conclusion ..................................................................................... 74 DUAL MODE SWITCHABLE SMART WINDOW BY DIELECTRIC AND FLEXOELECTRIC EFFECT OF THE LIQUID CRYSTAL ........................................................................................................... 76 5.1 Introduction ............................................................................................................. 76 5.2 Operation principle .................................................................................................. 80 5.3 Experimental result ................................................................................................. 85 5.3.1 Cell fabrication .............................................................................................. 85 5.3.2 Electro-optic studies ...................................................................................... 86 5.3.3 Transmission spectrum .................................................................................. 93 5.3.4 Demo ............................................................................................................. 95 5.4 Conclusion ............................................................................................................... 96 PRETILT ANGLE INDUCED BY DIMER IN VERTICAL ALIGNMENT LIQUID CRYSTALS ............................................................... 98 6.1 Introduction ............................................................................................................. 98 6.2 Experimental results and discussions .................................................................... 101 6.2.1 Cell fabrication ............................................................................................ 101 6.2.2 Polarizing optical microscopy ..................................................................... 102 v 6.2.3 Pretilt angle measurement ........................................................................... 105 6.2.4 Electro-optical properties ............................................................................ 107 6.3 Theoretical analysis ............................................................................................... 110 6.4 Conclusion ............................................................................................................. 113 THERMALLY SWITCHABLE LIQUID CRYSTAL LIGHT WINDOW .......................................................................................................... 115 7.1 Introduction ........................................................................................................... 116 7.2 Experimental results and discussion ..................................................................... 119 7.2.1 Cell fabrication ............................................................................................ 119 7.2.2 Transmittance at varied temperatures ......................................................... 119 7.2.3 Polarizing optical microscopy ..................................................................... 123 7.2.4 Effect of dimer concentration ...................................................................... 125 7.2.5 Electro-optical properties ............................................................................ 127 7.2.6 Demo 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