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High Dielectric Constant Materials Containing Liquid Crystals

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High Dielectric Constant Materials Containing Liquid Crystals HIGH DIELECTRIC CONSTANT MATERIALS CONTAINING LIQUID CRYSTALS A dissertation submitted to Kent State University in partial fulfillment of requirements for the degree of Doctor of Philosophy by Clinton Ignatius Braganza August 2009 Dissertation written by Clinton Ignatius Braganza B.A., College of Wooster, 2003 Ph.D., Kent State University, 2009 Approved by ________________________________, Chair, Doctoral Dissertation Committee Dr. L.C. Chien ________________________________, Members, Doctoral Dissertation Committee Dr. Michael Fisch ________________________________ Dr. Antal Jakli ________________________________ Dr. Dengke Yang ________________________________ Dr. Mikhail Chebotar Accepted by ______________________________, Chair, Chemical Physics Interdisciplinary Program Dr. Oleg Lavretovich ______________________________, Dean, College of Arts and Sciences Dr. Timothy Moerland ii TABLE OF CONTENTS LIST OF FIGURES .............................................................................................. V LIST OF TABLES............................................................................................. XIX ACKNOWLEDGEMENTS ...............................................................................XXV CHAPTER 1 MOTIVATION AND APPROACH....................................................1 1.1 Dielectric Materials in Electric Fields........................................................................................... 5 1.2 Dielectric Properties of Heterogeneous Systems.......................................................................... 9 1.3 Measurement Equipment ............................................................................................................ 24 1.3.1 Schlumberger 1260 Gain-Phase Analyzer ................................................................................. 24 ® 1.3.2 Solartron 1296 Dielectric Interface.......................................................................................... 28 1.4 Dielectric Measurement Analysis................................................................................................ 31 1.4.1 Equivalent Circuit Models......................................................................................................... 33 1.4.2 The Debye Equivalent Circuit ................................................................................................... 34 1.4.3 The Cole-Cole Equivalent Circuit ............................................................................................. 36 1.4.4 Distributed Circuit Elements ..................................................................................................... 38 1.4.5 Models for Diffusion ................................................................................................................. 39 1.4.6 The Constant Phase Element ..................................................................................................... 44 1.4.7 Theoretical models .................................................................................................................... 46 1.5 Curve Fitting................................................................................................................................. 60 CHAPTER 2 THE DIELECTRIC SAMPLE HOLDER.........................................64 2.1 The Apparent Dielectric Response.............................................................................................. 65 2.2 Cell Properties affecting the Apparent Dielectric Response..................................................... 67 2.3 Polyimide Thickness Measurements........................................................................................... 83 2.3.1 Theory of Ellipsometry.............................................................................................................. 84 2.3.2 Experimental Setup and Procedure............................................................................................ 88 2.3.3 Data and Analysis...................................................................................................................... 98 2.3.3.1 The SiO 2 on Glass Layer .................................................................................................. 98 2.3.3.2 The ITO Layer ............................................................................................................... 100 2.3.3.3 The Polyimide Layer on ITO Glass ............................................................................... 106 iii 2.3.4 Summary of Results................................................................................................................. 121 2.4 Discussion and Summary........................................................................................................... 123 CHAPTER 3 THE INDIVIDUAL COMPONENTS .............................................124 3.1 Liquid Crystals ........................................................................................................................... 125 3.2 Solvents........................................................................................................................................ 131 3.3 Surfactants .................................................................................................................................. 134 3.3.1 Polymeric Triblock Surfactants ............................................................................................... 138 3.4 Summary ..................................................................................................................................... 144 CHAPTER 4 BINARY MIXTURES ...................................................................145 4.1 The Effect of Ionic Dopants on the Dielectric Response ......................................................... 146 4.1.1 In Liquid Crystals .................................................................................................................... 146 4.1.2 In Surfactants........................................................................................................................... 150 4.2 The Effects of Surfactant Additives on the Dielectric Response of Liquid Crystals............. 152 4.2.1 DDAB (S7) in E31 .................................................................................................................. 156 4.3 Summary ..................................................................................................................................... 161 CHAPTER 5 HETEROGENEOUS SYSTEMS..................................................163 5.1 Ternary Systems containing Ferroelectric Liquid Crystals and Calcium Fluoride ............. 165 5.2 Ternary Systems containing Nematic Liquid Crystals ........................................................... 169 5.2.1 Replacing NMF with NMP...................................................................................................... 175 5.2.2 Other Surfactants ..................................................................................................................... 183 5.2.3 Triblock Polymeric Surfactants ............................................................................................... 188 5.2.3.1 Effects of Increased Surfactant Concentration............................................................... 194 5.2.3.2 Effects of Increased NMP Concentration....................................................................... 199 5.2.3.3 Mixing Surfactants......................................................................................................... 206 5.2.3.4 The effect of increased PEG........................................................................................... 208 5.2.4 Polymer Binders ...................................................................................................................... 214 5.3 Summary ..................................................................................................................................... 216 CHAPTER 6 CONCLUSIONS ..........................................................................219 APPENDIX .......................................................................................................223 REFERENCES .................................................................................................223 iv LIST OF FIGURES Figure 1.1: A Ragone chart showing for a particular device, the amount of energy stored (energy density) and the power density. DLC are double layer capacitors. The diagonal lines show how long it would take to discharge the device. It would be desirable to be in the top right corner................................................... 1 Figure 1.2: The two-layer lossy capacitor. The heavy dark lines are the plates of the capacitor. The lower section is dielectric 2 with the dielectric constant ε 2 and conductivity σ 2 and the upper section dielectric 1 with dielectric constant ε1 and conductivity σ1 . They are of thickness d 2 and d 1 respectively, with a total thickness d. ................................................................................................................................................... 11 Figure 1.3: The current produced through the device under test (dashed) in response to the applied voltage (solid line)..................................................................................................................................................... 24 Figure 1.4: The relationship between the resistance (R) and
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