Liquid crystals beyond displays chemistry physics and applications

LIQUID CRYSTALS
BEYOND DISPLAYS


LIQUID CRYSTALS
BEYOND DISPLAYS
CHEMISTRY, PHYSICS, AND
APPLICATIONS

Edited by

Quan Li
Liquid Crystal Institute
Kent, OH


Copyright Ó 2012 by John Wiley & Sons, Inc. All rights reserved
Published by John Wiley & Sons, Inc., Hoboken, New Jersey
Published simultaneously in Canada
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Library of Congress Cataloging-in-Publication Data:
Liquid crystals beyond displays : chemistry, physics, and applications /
edited by Quan Li, Liquid Crystal Institute, Kent, OH.
pages cm
Includes bibliographical references and index.
ISBN 978-1-118-07861-7
1. Liquid crystals–Research. 2. Optoelectronic devices–Research. I. Li,
Quan, 1965- editor of compilation.
QC173.4.L55L55 2012
530.40 29–dc23
2011052325
Printed in the United States of America
10 9 8

7 6 5 4

3 2 1


CONTENTS

Preface

vii

Contributors

ix

1. Liquid Crystal Lasers

1

Hideo Takezoe

2. Self-Organized Semiconducting Discotic Liquid Crystals for
Optoelectronic Applications

29

Chenming Xue and Quan Li

3. Magnetic Liquid Crystals

83

Rui Tamura, Yoshiaki Uchida, and Katsuaki Suzuki

4. Ferroelectric Liquid Crystals for Nonlinear Optical Applications

111

Yongqiang Zhang and Jesus Etxebarria

5. Photo-Stimulated Phase Transformations in Liquid Crystals and
Their Non-Display Applications

157

C. V. Yelamaggad, S. Krishna Prasad, and Quan Li

6. Light-Driven Chiral Molecular Switches or Motors in Liquid
Crystal Media

213

Yan Wang and Quan Li

7. Liquid Crystal-Functionalized Nano- and Microfibers Produced
by Electrospinning

251

Jan P. F. Lagerwall

8. Functional Liquid Crystalline Block Copolymers: Order Meets
Self-Assembled Nanostructures

285

Xia Tong and Yue Zhao

9. Semiconducting Applications of Polymerizable Liquid Crystals

303

Mary O’Neill and Stephen M. Kelly

v


vi

CONTENTS

10. Liquid Crystals of Carbon Nanotubes and Carbon Nanotubes in
Liquid Crystals

341

Giusy Scalia

11. Liquid Crystals in Metamaterials

379

Augustine M. Urbas and Dean P. Brown

12. Ferroelectric Colloids in Liquid Crystals

403

Yuriy Reznikov

13. Fact or Fiction: Cybotactic Groups in the Nematic Phase of Bent
Core Mesogens

427

Bharat R. Acharya and Satyendra Kumar

14. Lyotropic Chromonic Liquid Crystals: Emerging Applications

449

Heung-Shik Park and Oleg D. Lavrentovich

15. Liquid Crystal-Based Chemical Sensors

485

Jacob T. Hunter and Nicholas L. Abbott

16. Polymer Stabilized Cholesteric Liquid Crystal for Switchable
Windows

505

Deng-Ke Yang

17. Liquid Crystals for Nanophotonics

525

Timothy D. Wilkinson and R. Rajesekharan

Index

569


PREFACE

Liquid crystals (LCs) were discovered more than 100 years ago, however the
renaissance of research and development activities during the last quarter of 20th
century led to the successful commercialization of LC devices for information
displays. Currently the global market of LC displays (LCDs) stands more than $100
billion annually. Though the LCDs ubiquitous in our daily life seem mature, there is
still considerable interest in the development of 3D-displays using LCs. Nevertheless
parallel to this development, nowadays there is an unprecedented growth of interest
for non-display applications of LCs during the 1st decade of 21st century. Consequently the research and development of LCs are moving rapidly beyond displays and
evolving into entirely new scientific frontiers, opening broad avenues for versatile
applications such as lasers, photovoltaics, light-emitting diodes, field effect transistors, nonlinear optics, biosensors, switchable windows, and nanophotonics. These
fields, which gain extensive attentions of physicists, chemists, engineers, and
biologists, are of a most engaging and challenging area of contemporary research,
covering organic chemistry, materials science, bioscience, polymer science, chemical engineering, material engineering, electrical engineering, photonics, optoelectronics, nanotechnology, and renewable energy.
This book does not intend to exhaustively cover the field of LCs beyond displays,
as it is extremely difficult to do so within a single book. Instead, the book focuses on
the recent developments of most fascinating and rapidly evolving areas related to the
theme. The chapters span the following topics: LC lasers (Chapter 1), self-organized
semiconducting discotic LCs (Chapter 2), magnetic LCs (Chapter 3), ferroelectric

LCs for nonlinear optical applications (Chapter 4), photo-stimulated phase transformations in LCs (Chapter 5), light-driven chiral molecular switches or motors in
LC media (Chapter 6), LC functionalized nano- and microfibers produced by
electrospinning (Chapter 7), functional LC block copolymers (Chapter 8), semiconducting applications of polymerizable LCs (Chapter 9), LCs of carbon nanotubes and
carbon nanotubes in LCs (Chapter 10), LCs in metamaterials (Chapter 11), ferroelectric colloids in LCs (Chapter 12), cybotactic groups in the nematic phase of bent
core mesogens (Chapter 13), lyotropic chromonic LCs: emerging applications
(Chapter 14), LC-based chemical sensors (Chapter 15), LCs for switchable windows
(Chapter 16), and LCs for nanophotonics (Chapter 17). In each chapter, the state-ofthe-art along with future potentials in the respective fields has been discussed and
highlighted by the leading experts.
I hope this book is not only to introduce fundamental knowledge, illustrative
examples, and successful applications beyond displays, but also to stimulate more
vii


viii

PREFACE

interest for further development in this realm of research, wishing the interdisciplinary actions of physicists, chemists, engineers, and biologists can bring grateful
values to push the LCs research forward in the 21st century. For graduate students,
researchers, and scientists from other fields who want to get involved in LCs, this
book is anticipated to serve as a beginners’ guide. For established researchers,
this book is expected to provide insights into knowledge beyond their expertise.
I sincerely hope this book can generate interest to readers and help researchers to
spark creative ideas.
I would like to express my gratitude to Jonathan Rose at John Wiley & Sons, Inc.
for inviting us to bring this exciting field of research to a wide audience, and to all our
distinguished contributors for their dedicated efforts. Also I am indebted to my wife
Changshu, my sons Daniel and Songqiao for their great support and encouragement.
QUAN LI
KENT, OHIO

August 2011


CONTRIBUTORS

Nicholas L. Abbott, Department of Chemical and Biological Engineering,
University of Wisconsin, Madison, WI, USA
Bharat R. Acharya, Platypus Technologies, Madison, WI, USA
Dean P. Brown, Materials and Manufacturing Directorate, Air Force Research
Laboratory WPAFB, OH, USA
Jes
us Etxebarria, Department of Condensed Matter Physics, University of the
Basque Country, Bilbao, Spain
Jacob T. Hunter, Department of Chemical and Biological Engineering, University
of Wisconsin, Madison, WI, USA
Stephen M. Kelly, Department of Physics and Chemistry, University of Hull, UK
Satyendra Kumar, Department of Physics, Kent State University, Kent, OH, USA
Jan P. F. Lagerwall, Graduate School of Convergence Science and Technology,
Seoul National University, Gyeonggi-do, Korea
Oleg D. Lavrentovich, Liquid Crystal Institute, Kent State University, Kent, OH,
USA
Quan Li, Liquid Crystal Institute, Kent State University, Kent, OH, USA
Mary O’Neill, Department of Physics and Chemistry, University of Hull, UK
Heung-Shik Park, Liquid Crystal Institute, Kent State University, Kent, OH, USA
S. Krishna Prasad, Center for Soft Matter Research, Bangalore, India
R. Rajesekharan, Electrical Engineering Division, University of Cambridge,
Cambridge, UK
Yuriy Reznikov, Institute of Physics, National Academy of Sciences of Ukraine,
Kyiv, Ukraine
Giusy Scalia, Department of Nanoscience and Technology, Seoul National

University, Gyeonggi-do, Korea
Katsuaki Suzuki, Graduate School of Human and Environmental Studies, Kyoto
University, Kyoto, Japan
ix


x

CONTRIBUTORS

Rui Tamura, Graduate School of Human and Environmental Studies, Kyoto
University, Kyoto, Japan
Hideo Takezoe, Department of Organic and Polymeric Materials, Tokyo Institute of
Technology, Tokyo, Japan
Xia Tong, Department of Chemistry, University of Sherbrooke, Que´bec, Canada
Yoshiaki Uchida, Graduate School of Human and Environmental Studies, Kyoto
University, Kyoto, Japan
Augustine M. Urbas, Materials and Manufacturing Directorate, Air Force Research
Laboratory WPAFB, OH, USA
Yan Wang, Liquid Crystal Institute, Kent State University, Kent, OH, USA
Timothy D. Wilkinson, Electrical Engineering Division, University of Cambridge,
Cambridge, UK
Chenming Xue, Liquid Crystal Institute, Kent State University, Kent, OH, USA
Deng-Ke Yang, Chemical Physics Interdisciplinary Program and Liquid Crystal
Institute, Kent State University, Kent, OH, USA
C. V. Yelamaggad, Center for Soft Matter Research, Bangalore, India
Yongqiang Zhang, Micron Technology, Inc., Longmont, CO, USA
Yue Zhao, Department of Chemistry, University of Sherbrooke, Que´bec, Canada

FIGURE 1.21 Helical structure in a CLC microdroplet. Image of microdroplet in a lasing
condition is also shown [76].

FIGURE 2.20 Top: Synchrotron XRD patterns from homeotropic monodomain of material
35 (a) and the blend of 35 (b) with PC61BM in an 8-mm-thick glass cell. Bottom: Calculated
geometric dimensions of porphyrin 35 and 3D ChemDraw spacing-filling model of fullerene
derivative PC61BM and the schematic representations of homeotropically aligned architecture
of the blend of 35 and PC61BM. Reproduced with permission from ref. 110.
Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications, Edited by Quan Li.
Ó 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.


FIGURE 2.32 Formation of homeotropic texture on a macroscopic scale via slow cooling of
the 1.8 mm cell with 33. Slow cooling induces selective nucleation and growth of homeotropic
domain (parts (a) and (b) at 121.0 C) and hence yields uniform homeotropic columnar
orientation at lower temperatures ((c) 113.0 C and (d) 75.0 C), confirmed by both (e) optical
texture under crossed polarizers and (f) conoscopic image at 75.0 C. Optical images were
taken at (a–d) 70 and (e) 90 angles between polarizers. The scale bar corresponds to 50 mm.
(g) X-ray 2D pattern for the Colh phase at 75.0 C of 33. (h) The azimuthal scan of the peak in
(g) shows equally spaced six peaks with uniform intensity distribution. Reproduced with
permission from ref. 77(a).


FIGURE 4.8 Schematic illustration of (a) a homeotropically aligned FLC cell with the
spontaneous polarization P parallel to the polar axis which is the Y-axis in the XYZ coordinate
system and the y-axis in the xyz molecular coordinate system, (b) SHG experiments using phase
matching method, and (c) SHG experiments using Maker fringe method at normal incidence.
In (b), the phase matching is achieved by rotating the cell around the polar axis, y is the tilt
angle, si is the incident angle, and s is the angle between the optical propagation direction and
the FLC molecule director ^n.

FIGURE 4.15 Switching by molecular rotation around the long axis (left) changes both
chirality and polarity, while switching on the tilt cone (more common, right) only changes
polarity with retention of chirality.

FIGURE 5.30 (a) Demonstration of photocontraction of a
cross-linked polymer liquid crystal containing azobenzene, in
which the bending direction of
the film is manipulated by the
orientation of linearly polarized
light in the UV region (inducing
contraction) and visible light
(recovery of the original shape).
Reprinted with permission from
ref. 100, Copyright 2003, Nature
publishing group. (b) Schematic
to illustrate the proposed mechanism governing the photocontraction. Reprinted with permission from ref. 90, Copyright
2006, John Wiley & Sons.


FIGURE 6.1 A schematic mechanism of the reflective wavelength of light-driven chiral
molecular switch or motors in achiral nematic LC media reversibly and dynamically tuned by
light.

FIGURE 6.9 Changes in the reflection color of the CLC consisting of chiral azobenzene 9
and non-photoresponsive chiral dopant 10 in E44 by varying UV irradiation time: 0 s (left), 4 s
(middle), and 10 s (right) (top); (a) gray mask and (b) red–green–blue (RGB) patterning of the
CLC obtained by UV irradiation for 10 s through the gray mask at 25 C. Used with permission
from Ref. [43].

FIGURE 6.11 A flexible optically addressed photochiral display (A); a conventional display
attached bulky and costly electronics compared with an optically addressed display with the
same image without the added electronics (B). Used with permission from Ref. [47].

FIGURE 6.14 Reflection color images of 6.5 wt% chiral switch 2 in commercially available
achiral LC host E7 in 5 mm thick planar cell. A: upon UV light at 365 nm (5.0 mW/cm2) with
different time; B: reversible back across the entire visible spectrum upon visible light at 520 nm
(1.5 mW/cm2) with different time. The colors were taken from a polarized reflective mode
microscope. Reflective spectra of 6.5 wt% chiral switch 2 in LC E7 in a 5 mm thick planar cell at
room temperature. C: under UV light at 365 nm wavelength (5.0 mW/cm2) with different time
(3 s, 8 s, 16 s, 25 s, 40 s, and 47 s, from left to right). D: under visible light at 520 nm wavelength
(1.5 mW/cm2) with different time (2 s, 5 s, 9 s, 12 s, and 20 s, from right to left). Used with
permission from Ref. [39].


FIGURE 6.15 Images of 5 mm thick homeotropic alignment cell with 4 wt% chiral switch 2
in LC host E7. (See text for full caption.)

FIGURE 6.16 Top: Molecular structures of chiral cyclic azobenzenes (R)-17 and (R)-18 (A).
Middle (B–D): Schematic mechanism of reflection wavelength tuning and handedness
inversion of light-driven chiral molecular switch or motor in achiral nematic LC media
reversibly and dynamically tuned by light. Bottom: Polarized optical photomicrographs of a
planar aligned NÃ film containing 10 wt% (R)-17 in ZLI-1132 at room temperature, showing
reversible phase transitions occurring by light irradiation of the sample inside a 5 mm cell:
(a) oily streak texture of the NÃ phase before irradiation; (b) N phase obtained by exposure of
the sample to UV irradiation; (c) extinguishing orientation of the N cell by rotation between
crossed polarizers; (d) regeneration of the oily streak texture of the NÃ phase upon continued
irradiation (bottom–right). Used with permission from Ref. [56].

FIGURE 6.27 Features of a light-driven molecular motor: (a) Molecular structure of chiral
motor 47. (b) Polygonal texture of a LC film doped with 1 wt% chiral motor 47. (c) Glass rod
rotating on the LC during irradiation with ultraviolet light. (See text for full caption.)

FIGURE 7.13 The confinement of the cholesteric liquid crystal mixture 1 inside thin
cylindrical fibers forces the director helix to expand or compress from its natural pitch, leading
to a reflection color l that depends on the inner fiber diameter d, as illustrated in the center
diagram (black curve). (See text for full caption.)


FIGURE 8.1 (a) Chemical structure and phase transition temperatures of the LC diblock
copolymer. (See text for full caption.)

FIGURE 8.4 (a) Chemical structure and phase transition temperatures of the LC diblock
copolymer. (See text for full caption.)


FIGURE 9.16 Photolithographic process to produce a red, green, and blue pixellated OLED.
After patterned irradiation with ultraviolet light, the sample is washed with the solvent used for
deposition, so that the unexposed regions are removed.

FIGURE 9.18 A prototype OLED with a red, green, and blue pixel on the same substrate
fabricated by sequential spin-coating and polymerization of the materials 20, 5 blend, 5 and 19
onto a PEDOT:PSS film covering a patterned indium tin oxide (ITO) substrate. (See text for
full caption.)


FIGURE 13.4 Two dimensional X-ray diffraction pattern from (a) isotropic and (b) nematic
phases of 4-cyano-40 -pentylbiphenyl (5CB) and (c) cybotactic smectic C phase of nematic

phase of bis-(40 -n-octyloxybenzal)-2-chlor1o,4-phenylenediamine. (See text for full caption.)

FIGURE 14.19 Schematic diagram illustrating the formation of vertically aligned graphene
layer arrays (a). HR-TEM image showing the full fringe field in Z-axis projection, indicating
vertical grapheme layer orientation (b). (See text for full caption.)

FIGURE 14.20 The scheme of the LCLC biosensor for the detection of immune complexs.
(Redrawn from Shiyanovskii et al. [37].)


FIGURE 15.11 (A) and (B) Interference color of a film of nematic 5CB supported on a SAM
formed from HOOC(CH2)10SH before (A) and after (B) exposure to n-H2N(CH2)5CH3. (C)
Schematic illustration of the orientation of the LC in contact with a carboxylic acid monolayer
that is consistent with interference colors shown in panel (A). The bold arrow indicates the
direction of deposition of gold onto the substrate. (D) Schematic illustration of the orientation
of the LC in contact with the hexylamine-reacted carboxylic acid monolayer that is consistent
with the interference colors shown in panel (B). Reprinted with permission from Shah and
Abbott [28]). Copyright 2003 American Chemical Society.

FIGURE 16.3 Photographs of green house with liquid crystal switchable window in
Cleveland Botanic Garden. Photo courtesy of Cleveland Botanic Garden.


FIGURE 17.37 The 3D vision sensor camera stage developed.

FIGURE 17.39 The reconstructed 3D image in the developed 3D display from all the
elemental images viewed from top and bottom.


CHAPTER 1

Liquid Crystal Lasers
HIDEO TAKEZOE
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, Tokyo, Japan

1.1

INTRODUCTION

Liquid crystals (LCs) have fluidity and a long-range orientational order. These
properties enable us to use LCs as display materials. Another important property is a
positional order. The periodicity is in the range not only of the molecular length
periodicity like in smectic LCs but also of visible light wavelength. The latter
generally arises from chirality, and in many cases results in helical structures. The
most well-known example is cholesteric LCs (CLCs), in which the local structure is
nematic and the director rotates to form a helical structure with the helical axis
perpendicular to the director. The media that have periodic structures in the optical
wavelength are called photonic crystals. Hence, we can call CLC a one-dimensional
(1D) photonic crystal. Like an energy gap for electrons propagating in periodic
crystal structures, a stop band emerges at the edges of the first Brillouin zone in CLCs.
Within the stop band, light dampens and cannot propagate. When the light propagation is limited along any direction, we call it the photonic bandgap (PBG) [1, 2].
In this chapter, the stop band is called PBG in a broad sense.
The dispersion relation between angular frequency o and wavenumber k in vacuo
is given by o ¼ ck, where c is the velocity of light (Figure 1.1a). In CLCs, the
refractive index changes periodically, so the incoming light to the helix undergoes
reflection if the light wavelength coincides with the optical pitch (structural pitch
multiplied by an average refractive index), that is, Bragg reflection. Helical periodic
structure makes the reflection very unique; that is, only a circularly polarized light
(CPL) with the same handedness as the helix is reflected and another CPL with
opposite handedness just passes through. This is called selective reflection. Such light

propagation characteristics along the helical axis are rigorously solved, giving an
analytical solution [3]. The dispersion relation thus obtained is shown in Figure 1.1b.
Another unique feature compared with the other periodic structure is the sinusoidal
Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications, Edited by Quan Li.
Ó 2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.

1


2

LIQUID CRYSTAL LASERS

FIGURE 1.1 Dispersion relation (a) in vacuo, (b) in CLC at normal incidence, and (c) in
CLC at oblique incidence. At oblique incidence, higher order reflection and total reflection
regions are recognized.

change of the refractive index. Because of this, only the first-order Bragg reflection
takes place (Figure 1.1b). For oblique incidence of light with respect to the helical
axis, the periodic structure is no more than sinusoidal, so higher order reflections
occur [4]. In addition, total reflection band(s) emerges, where light with any
polarization states is reflected [5]. The dispersion relation (Figure 1.1c) calculated
by the 4 Â 4 matrix method [6] clearly reveals such behaviors. The emergence of
higher order reflections and total reflection can be brought about by deforming the
sinusoidal helical structure, for example, by applying an electric field. Such optical
properties are similarly observable in other helical LC phases such as chiral smectic
CÃ (SmCÃ ) and twist grain boundary (TGB) phases.
Because of the selective reflection in visible wavelength regions, it is a natural
question how the emission from dye molecules existing inside the helical structure is
affected by the Bragg condition. Actually, Kogelnik and Shank [7] studied possible

distributed feedback (DFB) lasers. Namely, lasing may occur if emitted light is
confined in a DFB cavity made of CLC. The lifetime of the luminescence from dyes
embedded in CLCs was also examined [8, 9]. The first observation of lasing from
CLC was reported by Il’chishin et al. in 1980 [10]. They even showed the lasing
wavelength tuning by temperature. However, it took almost two decades to be paid


TYPES OF LASERS

3

much attention from other groups until Kopp et al. [11] reported a CLC microlaser.
For historical details, please refer to an article by Bartolino and Blinov [12].
Let us consider efficient lasing conditions. In an isotropic medium, the rate R of
photon emitted from an excited molecule is described by Fermi’s golden rule:
Riso $ Miso jE Á mj2

ð1:1Þ

where Miso is the density of state (DOS), m is the transition dipole moment, and E
is the electric field. In isotropic media, M is independent of the polarization and
the radiation direction. In anisotropic media, the emission depends on the
orientation of transition dipole moment m with respect to the polarization of light,
that is, E. When emission occurs from the excited CLC molecules, light propagates as
one of the two eigenmodes E1 and E2. Then, emission rate for eigenmode Ei (Ri) is
described as
Ri $ Mi jEi Á mj2

ð1:2Þ

where Mi is the DOS associated with the eigenmode Ei. The fluorescent molecules
embedded in CLCs have a certain degree of the nematic order, resulting in an
anisotropic orientation distribution of the transition dipole moment. Hence to have
large Ri, it is profitable that m is parallel to the polarization of the eigenmode Ei. Now
the other factor to have large Ri is DOS M, which is defined as