UUnniivveerrssiittyy ooff CCeennttrraall FFlloorriiddaa SSTTAARRSS Electronic Theses and Dissertations, 2004-2019 2007 AAnncchhoorriinngg EEnneerrggyy AAnndd PPrreettiilltt AAnnggllee EEffffeeccttss OOnn LLiiqquuiidd CCrryyssttaall RReessppoonnssee TTiimmee Xiangyi Nie University of Central Florida Part of the Electrical and Electronics Commons Find similar works at: https://stars.library.ucf.edu/etd University of Central Florida Libraries http://library.ucf.edu This Doctoral Dissertation (Open Access) is brought to you for free and open access by STARS. It has been accepted for inclusion in Electronic Theses and Dissertations, 2004-2019 by an authorized administrator of STARS. For more information, please contact [email protected]. SSTTAARRSS CCiittaattiioonn Nie, Xiangyi, "Anchoring Energy And Pretilt Angle Effects On Liquid Crystal Response Time" (2007). Electronic Theses and Dissertations, 2004-2019. 3281. https://stars.library.ucf.edu/etd/3281 ANCHORING ENERGY AND PRETILT ANGLE EFFECTS ON LIQUID CRYSTAL RESPONSE TIME by XIANGYI NIE B.S. Nanjing University, P.R. China, 1999 M.S. Nanjing University, P.R. China, 2002 M.S. University of Central Florida, USA, 2004 A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the School of Electrical Engineering and Computer Science in the College of Engineering and Computer Science at the University of Central Florida Orlando, Florida Fall Term 2007 Major Professors: Shin-Tson Wu Thomas X. Wu ABSTRACT This dissertation covers some important topics on the liquid crystal-substrate surface effects, including theoretical derivations and confirming experimental results. The research work is expected to make important impacts on liquid crystal device designs and to open new doors for further research along these topics. In this dissertation, a novel high-electric-field technique is developed to characterize the anchoring energy of vertically-aligned liquid crystal cells. Both theoretical analyses and confirming experimental results are presented. Vertically-aligned liquid crystal cells with buffed polyimide alignment layers are used to validate the measurement techniques. Based on the voltage-dependent transmittance of the liquid crystal cells, a linear fitting can be obtained, which leads to a precise determination of the anchoring energy. If some specific liquid crystal material parameters are known, then the traditional cell capacitance measurements can be avoided. Anchoring energy and cell gap effects on liquid crystal response time is theoretically analyzed and experimentally investigated. A novel theory on the liquid crystal dynamics is developed. In this part, two different theoretical approaches are discussed: one is surface dynamic equation method and the other is effective cell gap method. These two different approaches lead to consistent results, which are also confirmed by our experimental results. This work opens a new door for LCD industry to optimize liquid crystal response time, and it is especially critical for liquid crystal cells with thin cell gap, which is a promising approach for fast response time liquid crystal display. Pretilt angle effects on liquid crystal dynamics are analyzed theoretically and validated experimentally. Analytical expressions are derived to describe liquid crystal response time under nonzero pretilt angle conditions. The theoretical analysis is confirmed experimentally ii using vertically-aligned liquid crystal cells. These results quantitatively correlate pretilt angles with liquid crystal response time, which is important for optimizing liquid crystal response time. iii To my parents, wife, and daughter iv ACKNOWLEDGMENTS I would like to thank those who contributed and supported my efforts throughout my graduate studies at the University of Central Florida. First of all, I would like to sincerely thank my advisor, Dr. Shin-Tson Wu, for his constant and precious help, motivation, and guidance. Without his valuable advises and instructions, it is impossible for me to accomplish these research works. I also would like to thank him for his kind instructions and patience to improve my oral English in presentations and written English in publications. I am truly indebted to my advisor, Dr. Thomas X. Wu for his enlightening discussion and advice. I would like to thank him for his patience and time to teach me the numerical simulation techniques and electromagnetics, which are critical throughout my research work. His kind help for my life in the United States is also truly appreciated. I would also like to thank my dissertation committee members, Dr. Jiann S. Yuan, Dr. Parveen F. Wahid, and Dr. John Shen, for their help and valuable suggestions about my dissertation. I gratefully acknowledge all the postdoctoral fellows in the Photonics and Display group for their stimulating discussions and technical assistance, particularly Dr. Yanqing Lu, Dr. Xinyu Zhu, Dr. Ruibo Lu, and Dr. Haiqing Xianyu. I am grateful to all the students in the Photonics and Display group and High-Speed Electronic System group; I would like to thank them for their help and encouragement. Finally, I would like to give special thanks to my wife, Ying Lou. She gave up her career in China and came to the United States with me. She has always been supporting me wholeheartedly. I am also very appreciated to my parents for their full support. Without my v wife and parents’ support and sacrifice, the accomplishment of my education is impossible. vi TABLE OF CONTENTS LIST OF FIGURES........................................................................................................................x LIST OF TABLES.......................................................................................................................xiv LIST OF ACRONYMS/ABBREVIATIONS...............................................................................xv CHAPTER ONE: INTRODUCTION.............................................................................................1 1.1 Motivation.............................................................................................................................1 1.2 Liquid Crystal Materials.......................................................................................................2 1.3 Basic Physical Properties of Liquid Crystals........................................................................4 1.3.1 Birefringence..................................................................................................................5 1.3.2 Dielectric Anisotropy.....................................................................................................5 1.3.3 Visco-elastic Properties.................................................................................................8 1.3.3.1 Elastic Constants.....................................................................................................8 1.3.3.2 Rotational Viscosity..............................................................................................10 1.3.3.3 Figure of Merit......................................................................................................10 1.4 Introduction to Liquid Crystal Alignment..........................................................................12 1.4.1 Rubbing method...........................................................................................................12 1.4.2 Photoalignment............................................................................................................13 1.4.3 Pretilt Angle.................................................................................................................14 1.5 Anchoring Energy...............................................................................................................15 1.6 Thesis Overview.................................................................................................................18 CHAPTER TWO: NUMERICAL SIMULATION METHODOLOGIES...................................19 2.1 Simulation of LC Director Distribution..............................................................................19 2.1.1 Static State Simulation.................................................................................................20 2.1.2 Dynamic Process Simulation.......................................................................................21 vii 2.2 Optical Simulation..............................................................................................................23 2.3 Static Simulation of Anchoring Energy Effects on Electro-optic Response of LC Cells...24 2.4 Dynamic Simulation of Dual-Frequency Liquid Crystal Device.......................................26 2.5 Simulation of Phase Retardation Dependent Liquid Crystal Electro-optic Modulation.....29 CHAPTER THREE: POLAR ANCHORING ENERGY MEASUREMENT.............................39 3.1 Introduction.........................................................................................................................39 3.2 Theory of Anchoring Energy Measurement by Freedericksz Transition...........................41 3.3 Theory of Anchoring Energy Measurement by High-Electric-Field Method....................42 3.4 Experiment..........................................................................................................................48 3.5 Discussion...........................................................................................................................54 CHAPTER FOUR: ANCHORING ENERGY AND CELL GAP EFFCTS ON LIQUID CRYSTAL RESPONSE TIME.....................................................................................................56 4.1 Introduction.........................................................................................................................56 4.2. Theory................................................................................................................................57 4.2.1 Effective Cell Gap Method..........................................................................................57 4.2.2 Surface Dynamic Equation Method.............................................................................62 4.2.3 Results and Discussion................................................................................................64 4.3 Experiment..........................................................................................................................68 4.4 Discussion of Thin Cell Gap Effect....................................................................................71 4.5 Summary.............................................................................................................................74 CHAPTER FIVE: PRETILT ANGLE EFFECTS ON LIQUID CRYSTAL RESPONSE TIME.............................................................................................................................................76 5.1 Introduction.........................................................................................................................76 5.2 Theory.................................................................................................................................76 5.3 Experiment..........................................................................................................................81 viii CHAPTER SIX: CONCLUSION.................................................................................................88 LIST OF REFERENCES..............................................................................................................90 ix