Dancing with Light: Advances in Photofunctional Liquid-Crystalline Materials

272 Pages·2013·40.009 MB·\272

by  Haifeng Yu (Author)

Haifeng Yu
Liquid crystal (LC) displays dominating in the present market of flat panel
displays are generally based on interactions of light and LCs. Recent progress
in this field indicates that integrating photochromic molecules into LC materials
enables one to photomanipulate unique features such as photoinduced
phase transition, photocontrolled alignment, and phototriggered molecular
cooperative motion, giving birth to their novel applications beyond displays. For
instance, on connecting with three-dimensionally crosslinked elastomers, LCs
show photomechanical and photomobile properties, converting light energy
directly into mechanical work. Combining supramolecular cooperative motion
with microphase separation of well-defined block copolymers, they exhibit
controllable regular nanostructures on a macroscopic scale with excellent
D
reproducibility and mass production.
a
n
This book first introduces the basic knowledge on LCs in a step-by-step manner c
and then deeply discusses photoresponsive LCs in low-molecular-weight i
n
compounds or small molecules, polymers or macromolecules, elastomers, and g
block copolymers, respectively. The engrossing photoresponsive LC materials
w
offer an effective and convenient chance to adjust properties of advanced
i
materials by integrating photoresponsive molecules with LC properties, which t DANCING
h
has become one of the emerging topics in the present and future LC researches.
L
This book comprehensively compiles the nature of this type of materials and the
i
ongoing progress in this research area and uses graphs and figures extensively g
h
to enhance understanding especially of beginners. This book would be useful for
t
students and primary researchers in soft materials and self-organized materials
in both chemistry and physics. It may also serve as a reference for experienced
researchers to keep up the current research trends in photoresponsive LC
materials.
WITH LIGHT
Haifeng Yu is leading a research group that is working on liquid
crystals and micro/nano composite materials, light-responsive
soft matters, supramolecular self-assembled materials since 2012
at Peking University, China. He received his PhD from Tsinghua
University, China, in 2003, after which he went to Japan, where he
worked for four and a half years as a researcher at Tokyo Institute of
Technology, Japan, and Kyoto University, Japan. He joined Nagaoka
Y
University of Technology, Japan, as a specially appointed associate
u Advances in Photofunctional
professor in 2008. He received the 2010 Distinguished Lectureship
Award of the Asian International Symposium on Nanotechnology and
Materials Chemistry. He was also the 2011 National Thousand Young
Liquid-Crystalline Materials
Talents Program award recipient. In 2013, he obtained the NSFC
Award for Excellent Young Scholar.
V338
ISBN 978-981-4411-11-0
DANCING
WITH LIGHT
N
GHT

Pan Stanford Series on Renewable Energy — Volume 2
DANCING
WITH LIGHT
Advances in Photofunctional
Liquid-Crystalline Materials
editors
Preben Maegaard
Anna Krenz
Wolfgang Palz
Haifeng Yu
The Rise of Modern Wind Energy
Wind Power
for the World
CRC Press
Taylor & Francis Group
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© 2013 by Taylor & Francis Group, LLC
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Version Date: 20150206
International Standard Book Number-13: 978-981-4411-12-7 (eBook - PDF)
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Contents
Preface
1. In troduc tion x1i
1.1 What is a Liquid Crystal? 1
1.2 Brief History 4
1.3 LC Classifications 12
1.4 LC Phases 16
1.5 Characterization Methods 21
1.5.1 Differential Scanning Calorimetry (DSC) 22
1.5.2 Polarizing Optical Microscopy 24
1.5.3 X-Ray Diffraction 25
1.5.4 Heating Glass Tubes 26
1.5.5 Miscible with an LC Sample 27
2. Structur1e.s5 a.6n d POrtohpeerr tMieest hods 2371
2.1 Basic Structures 31
2.1.1 Mesogenic Core Ring 31
2.1.2 Central Linking Groups 33
2.1.3 End Groups 34
2.1.4 Lateral Substituents 35
2.2 Some Physical Parameters 36
2.2.1 Order Parameter 36
2.2.2 Mechanical Properties (Elastic Constant) 36
2.2.3 Electrical Properties (Dielectric
Anisotropy) 38
2.2.4 Magnetic Anisotropy (Diamagnetism) 38
2.2.5 Optical Anisotropy (Birefringence) 39
2.2.6 Fréedericksz Transition 40
2.3 LC Alignment 41
2.3.1 Rubbing Technique 42
2.3.2 Microgroove Method 44
2.3.3 Electric and Magnetic Fields 45
2.3.4 Surfactant Dipping and LB Membrane 45
2.3.5 Supramolecular Self-Assembly 47
vi Contents
2.3.6 Oblique Evaporation 47
2.3.7 Ionic and Plasma Beams 50
2.4 Photoalignment 50
2.4.1 Photoisomerization (Command Surface) 51
2.4.2 Photocrosslinking (or Linearly
Photodimerized) Reaction 53
2.4.3 Photodegradation (Photoactive
3. Light and LiquidP Corlyysitmalisd e) 5663
3.1 Photochemical Reactions 64
3.2 Photoinduced Alignment and Reorientation
of LCs 68
3.2.1 Photoresponse to Linearly Polarized
Light 68
3.2.2 Thermal Effect on Photoalignment 71
3.2.3 Thermal Enhancement of
Photoalignment in Photocrosslinkable
LCs 75
3.2.4 Photoresponse to Unpolarized Light 79
4. 3Lo.3w -MoPlehcoutloamr-Wodeuiglahtti oLniq oufid L CCrsy stals 8931
4.1 Photoinduced Phase Transition 91
4.1.1 Photoinduced Phase Transition in Pure
Photochromic LMWLCs 92
4.1.2 Photoinduced Phase Transition in
Azobenzene-Doped LCs 93
4.1.3 Photoinduced Phase Transition in
LCs Doped with other Dyes 98
4.1.4 Photoinduced Phase Transition in
LMWLCs–Polymer Composites 100
4.2 Phototunning of Cholesteric LCs 103
4.2.1 General Principles 103
4.2.2 Phototuning CLCs with
Photoisomerization 104
4.2.3 Phototuning with other Chromophores 106
4.2.4 Possible Applications 107
4.3 Photochemical Flip of Polarization of
Ferroelectric LCs 110
Contents vii
4.4 Phototriggered Sol–Gel Transition in LMWLC
Organogels 114
4.5 Photocontrolled Orientation by Photophysical
Processes 118
5. 4Li.q6u id CPryhsotatol dProilvyemne Mrso tion of LMWLCs 112353
5.1 Photochemical Phase Transition 133
5.1.1 Copolymers and Polymer Composites 133
5.1.2 Homopolymers 136
5.2 Photoinduced Cooperative Motion 143
5.3 Photoinduced Large Change in Birefringence 145
5.4 Polarized Electroluminescence (EL) 149
5.5 Holographic Applications 151
5.5.1 Holographic Recording 151
5.5.2 Recording Gratings with LC Alignment
Changes 152
5.5.3 Recording Gratings with
Photoinduced Phase Transition 155
5.5.4 Subwavelength Gratings 156
5.5.5 Mechanically Tunable Gratings 157
5.5.6 Bragg-Type Gratings 158
5.6 Other Applications 160
5.6.1 Photocontrol of Functional Materials 160
5.6.2 Photocontrolled Nanostructures 161
5.6.3 Photorewritable Paper 161
5.6.4 Photoswitching of Gas Permeation 163
6. Liquid Cr5y.6st.5al ElPashtootmoderrsiv en Motions 116735
6.1 Preparation of LCEs 176
6.1.1 Two-Step Method 177
6.1.2 One-Step Method of Direct
Crosslinking of Linear LCPs 177
6.1.3 Polymerization of LC Mixture of
Monomers and Crosslinkers 178
6.1.4 Physical Crosslinking Method 179
6.2 Photochemical Phase Transition 180
6.3 Photoinduced Contraction and Expansion 181
6.3 Photoinduced 3D Motions 184
viii Contents
6.3.1 Photoinduced Bending 184
6.3.2 Precise Control of Photoinduced
Bending 187
6.3.3 Effect of Order of Mesogen on
Photoinduced Bending 190
6.3.4 Effect of Light Polarization on
Photoinduced Bending 192
6.3.5 Effect of LCE Structures on
Photoinduced Bending 192
6.4 Microscale LCE Actuator 194
6.4.1 LCE Fibers 194
6.4.2 LCEs for Artificial Cilia 196
6.4.3 LCEs with Micromolding 196
6.4.4 Photocontrol of Surface-Relief
Formation 197
6.5 Novel LCE Materials and Photomechanical
Ways 198
6.5.1 Recyclable Hydrogen-Bonded LCEs 198
6.5.2 Dye-Doped LCEs 199
6.5.3 Twisted LCEs 200
6.5.4 Hummingbird Movement 201
7. 6Li.q6u id-CLryCsEt-aLllainmei nBaloteckd CFoilpmosly mers 220111
7.1 Synthesis of Well-Defined LCBCs 212
7.1.1 Direct Polymerization 213
7.1.2 Post-Functionalization 216
7.1.3 Supramolecular Self-Assembly 217
7.1.4 Special Reactions 217
7.2 Phase Diagram of LCBCs 218
7.3 Structures and Properties of LCBCs 222
7.3.1 Effect of Microphase Separation
on LC Phases 223
7.3.2 Effect of Non-LC Blocks 225
7.3.3 Effect of LC Blocks 228
7.4 Control of Microphase Separation 230
7.4.1 Thermal Annealing 232
7.4.2 Mechanical Rubbing 234
7.4.3 Photoalignment 236
7.4.4 Electric and Magnetic Fields 240
Contents ix
7.4.5 Other Methods 243
7.5 Applications 245
7.5.1 Enhancement of Surface-Relief
Gratings 245
7.5.2 Enhancement of Refractive-Index
Modulation 246
7.5.3 Nanotemplates 247
7.5.4 Microporous Structures 251
Index
7.6 Outlooks 252
259