pretilt angle effects on liquid crystal response time

113 Pages·2007·1.19 MB·English

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Electronic Theses and Dissertations, 2004-2019
2007
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Xiangyi Nie
University of Central Florida
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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
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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.
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To my parents, wife, and daughter
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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
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wife and parents’ support and sacrifice, the accomplishment of my education is impossible.
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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
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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
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CHAPTER SIX: CONCLUSION.................................................................................................88
LIST OF REFERENCES..............................................................................................................90

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