Air Force Wright Lab
Wright Patterson AFB, OH 45433-7702
Center for Optoelectronics
Univ of Rochester
COI Room 1213
Rochester, NY 14623-1212
Liquid Crystal Institute
Kent State Univ
Kent, OH 44242
Dept of Matls Physics & Chem
Fukuoka, 812-81 JAPAN
Dept of Chemistry
Science Univ of Tokyo
Tokyo, 162-8601 JAPAN
IBM T.J. Watson Research Lab
Yorktown Heights, NY 10598
Proceedings published as Volume 559
- Air Force Research Laboratory
- Everlight Chemical Industrial Corp., Taiwan
of the Materials Research Society
Symposium Proceedings Series.
* Invited paper
SESSION D1: NEW MATERIALS AND EFFECTS
8:30 AM *D1.1
JAVELINS, HOCKEY-STICKS, AND BOMERANGS; THE ROLE OF MESOGEN
SHAPE IN PHASE STABILITY AND PHASE TYPE. E.T. Samulski , University of
North Carolina, Department of Chemistry, Chapel Hill, NC.
Chairs: Liang-Chy Chien and E. Samulski
Monday Morning, April 5, 1999
In order to obtain more insight into the relation between
molecular shape and phase symmetry and stability we have synthesized thiophene
analogues of p-quinquephenyl (PPPPP). We have systematically ``moved''
2.5-thiophene from a terminal position (PPPPT) to the center of the molecule
(PPTPP, a symmetric bent molecule), and by doing so, changed the overall
molecular shape. Liquid crystal transition temperatures drop considerably
when the non-linear thiophene segment moves to the center of the molecule,
and the asymmetric molecule PPPTP exhibits a broad LC phase (289-356C)
and displays both a smectic A and nematic phase. Such systems, are particularly
suited for realistic Monte Carlo simulations and it is anticipated that
a comparison of simulation results with experiment will provides an assessment
of the influence of molecular shape and dipolar interactions on phase structure.
9:00 AM *D1.2
DIRECT STRUCTURAL CHARACTERIZATION OF FERRI- AND ANTIFERRO-ELECTRIC
CHIRAL SMECTIC-C LIQUID-CRYSTAL PHASES. Peter Mach , Dept of Physics, University
of Minnesota, Minneapolis, MN.
A great deal of effort has been directed in recent years
at determining the detailed structures of various chiral smectic-C phases
exhibiting antiferroelectric (SmCA*) or ferrielectric
(SmCFI1*, SmCFI2*, SmC*)
electrooptic responses. Along with the ferroelectric SmC*, these phases
hold great promise for future generations of high-speed optical switching
devices. By applying polarized resonant x-ray scattering at the sulfur
K edge to freely-suspended films of one thiobenzoate liquid-crystal enantiomer,
we made the first direct structural observations of superlattice periodicities
associated with the antiferro- and ferri-electric phases . Respectively,
we observed helical superlattices of four-, three-, and two-layer periodicity
in the SmCFI2*, SmCFI1*, and SmCA*
phases, and periodicity incommensurate with layer spacing in SmC*.
For x-ray energy differing from the sulfur K edge by more then 25 eV, the
diffraction peaks of superlattice origin disappear. We have also measured
the polarization states of these resonant diffraction peaks. The observed
polarizations agree with the clock model of chiral smectic-C variants,
and rule out other proposals made to date for these structures. Results
on the thiobenzoate racemic compound and a thiophene-containing liquid-crystal
will be presented as well. 1. P. Mach et al., Phys. Rev. Lett. 81, 1015
(1998). *Collaborators: R. Pindak, A.-M. Levelut, P. Barois, H. T. Nguyen,
J. Goodby, C. C. Huang, and L. Furenlid.
9:30 AM *D1.3
FERROELECTRIC AND ANTIFERROELECTRIC LIQUID CRYSTALS FROM
ACHIRAL MOLECULES. David M. Walba , Eva Korblova, Univ of Colorado, Dept
of Chemistry, Boulder, CO; Renfan Shao, Joseph E. Maclennan, Darren R.
Link, Noel A. Clark, Univ of Colorado, Dept of Physics, Boulder, CO.
In bent-core mesogenic structures and in tilted bi-layer
smectics, a class of ferro- and antiferroelectric phases composed of achiral
or racemic molecules has recently been discovered. A discussion of the
requirements for antiferroelectricity in such systems will be given, and
the directed design of new antiferroelectric and ferroelectric phases composed
of racemic molecules will be described. Achiral symmetry breaking in the
ferroelectric phase provides a unique liquid crystalline conglomerate.
10:30 AM *D1.4
ROLE OF THE CHOLESTERIC PHASE IN THE FORMATION OF TWISTED
SMECTIC STRUCTURES. S.W. Suh, Licom Technologies, Inc., State College,
PA; Angela L. Campbell, Materials and Manufacturing Directorate, AFRL/MLPJ,
Wright-Patterson AFB, OH; J.S. Patel , Department of Physics and Electrical
Engineering, The Pennsylvania State University, University Park, PA.
We have recently demonstrated a new ferroelectric liquid
crystal structure that combines the fast speed of ferroelectric and the
optical behavior of the twisted nematic structures. This ferroelectric
twisted smectic structure (FETS) allows fast switching and at the same
time allows variable transmission controlled by an externally applied field.
In the talk, we will present our recent results, which show the importance
of structure in the cholesteric phase in the formation of twisted smectic
structure. We also show that a presence of a helical inversion close to
the cholesteric to smectic C* phase transition temperature in our material
is responsible for the different structures that are obtained by using
different cooling rates.
11:00 AM *D1.5
PHOTOCONDUCTIVITY OF DISCOTIC LIQUID CRYSTALS DERIVED
FROM A LONG-CHAIN TETRAPHENYLPORPHYRIN. Yo Shimizu , Hirosato Monobe, Shoji
Mima, Taizo Higashiyama, Tomonori Fuchita, Takushi Sugino, Osaka National
Research Institute (ONRI) AIST-MITI, Dept. of Organic Materials, Ikeda,
Some tetraphenylporphyrin-based mesophase materials (C15TPP)
were synthesized and investigated on their photoconductive properties.
These all exhibit one or two lamellar mesophases with high order of molecular
alignments. All measurements of photocurrent were carried out for ITO/C15TPP/ITO
type cells. The metal-free compound showed strong dependence of photocurrent
behavior on the mesomorphic phase transitions. A drastic change of the
applied voltage characteristics was observed on the phase transition between
two lamellar mesophases and this phenomenon was interpreted in terms of
the variant mechanism of charged carrier generation depending on the phase
transition by the results of the action spectra and illumination light
intensity dependence of photocurrent.
11:30 AM *D1.6 THE EFFECT OF SIDE CHAIN SUBSTITUTION
ON THE FIELD-DEPENDENT BIREFRINGENCE IN A SERIES OF CHIRAL SMECTIC A LIQUID
CRYSTALS. J.R. Lindle , F.J. Bartoli, S.R. Flom, J.V. Selinger, R. Shashidhar
and B.R. Ratna, Naval Research Lab, Washington, DC.
The field-dependent birefringence and the electroclinic
tilt angle are measured for a homologous series of four chiral liquid crystals
in the smectic A phase. These are designated as KN125, SiKN105, DSiKN65
and TSiKN105. The aromatic core and chiral center of these molecules are
identical, and they differ only in the side-chain substituent at the end
opposite to the chiral center. The zero-field birefringence decreased significantly
and monotonically with the length of the siloxane side chain. Measurements
of the wavelength dispersion of the birefringence show that changes in
the resonant wavelength of the molecules account for only a small fraction
of the observed results. This work examines the origin of the change in
birefringence and possible roles played by changes in the polarizability
anisotropy and the molecular order parameter for this series. In all four
samples, both the electroclinic tilt angle and the birefringence increased
substantially with the application of a field. At 10 V/um, the electroclinic
tilt angle in DSiKN65 and TSiKN105 exceeded 22.5 degrees and the phase
retardation due to the change in the birefringence exceeded a quarter wave.
In all four liquid crystals, the electroclinic tilt angle and the field-induced
change in birefringence were found to follow a quadratic relationship,
and surprisingly the same quadratic coefficient could be used to fit the
data for the four samples. Moreover, this quadratic relationship persists
even at high fields where both processes undergo saturation. A model based
on a field-dependent order parameter is presented to describe the strong
coupling observed between the field-dependent birefringence and the electroclinic
effect. The mechanisms responsible for the large induced change in the
birefringence and the implications for device performance will be discussed.
SESSION D2: POLYMER/LIQUID CRYSTAL COMPOSITES
1:30 PM *D2.1
AN ANALYSIS OF THE PHOTO-POLYMERIZATION INDUCED PHASE
SEPARATION PROCESS IN LIQUID CRYSTAL/POLYMER COMPOSITE FILMS. Toru Fujisawa
, Masao Hayashi, Hideo Nakada, Siger Matumoto, Yuitiro, Tani, Masao Aizawa,
Dainippon Ink & Chemicals, Inc., Central Research Laboratories, Sakura,
Chairs: Timothy J. Bunning and Toru Fujisawa
Monday Afternoon, April 5, 1999
In the optical device that is prepared by the photo-polymerization
induced phase separation process, the molecular structures, molecular interactions
of the materials at a polymer surface, and the morphology play an important
role to determine their electro-optical properties. The morphology in the
films is strongly affected by several parameters such as UV curing conditions,
LC concentration, and a type of materials. Therefore, understanding the
relation between the phase separation process during photo-polymerization
and the parameters based on the materials is extremely important to control
of microstructure in the films. In this paper, we present the results of
analysis in the micro-phase separations during photo-polymerization based
on the system that employs mixtures of liquid crystal materials containing
alkyl cyanobiphenyl compounds and various photo-curable diacrylates having
the different alkyl main chain in order to investigate the effects of the
molecular structure, because the microstructure in the films are dependent
on what kinds of materials are used. In the phase diagram during polymerization,
the change in the phase diagram during curing depends on the type of monomers.
In the measurement of time resolved light-scattering profiles during curing,
it is confirmed that the process of phase separation during curing is affected
by the number of methylene groups in the main chain of diacrylates. Moreover,
from the scanning electron micrographs, we can observed the tendency that
the shape of surface in polymer layer in the films changes a smooth into
a interconnected spherical particles as the number of methylene groups
decreases. Consequently, it turned out that the molecular structure in
diacrylate reflects the process of phase separation during curing.
2:00 PM *D2.2
FACTORS AFFECTING NANO-SCALE MORPHOLOGY IN PDLC BRAGG
GRATINGS. Pogue, R.T. , S.A. Siwecki, L.V. Natarajan, V.P. Tondiglia, R.L.
Sutherland, Science Applications International Corp., Beavercreek, OH and
T.J. Bunning, AFRL, WPAFB, OH.
Polymer-dispersed liquid crystal (PDLC) volume gratings
have all of the advantages and applications of traditional holographic
gratings with the additional benefit that the optical properties can be
electrically switched. The optical and electro-optical properties of these
gratings, however, are determined by the nano-scale morphologies of the
PDLC films. In order to optimize these properties it is necessary to understand
the factors which contribute to the final film morphologies and how these
factors can be controlled. In this study we have evaluated formulation
and processing changes which effect these morphologies. Such factors as
average monomer functionality, photoinitiator concentration and cure temperature
have been studied and each is shown to have a significant effect on the
resulting film morphologies. Polymerization kinetics have been investigated
using differential photo-calorimetry (DPC), and the film morphologies were
evaluated using low-voltage SEM. The results indicate that increased functionality,
altered either by a change in the primary monomer or the co-monomer concentration
leads to larger LC domains, higher diffraction efficiencies and lower switching
voltages. Increased initiator concentration also lead to larger LC droplets.
Domain size decreased, however, with increasing cure temperature. This
result was initially unexpected. Discussion in this presentation will focus
on the effects of each of these parameters on the film properties and will
briefly include some mention of the mechanisms that may drive the phase
separation process. Some relationships will be postulated based on comparison
of the polymerization kinetics with respect to real-time diffraction efficiency
measurements obtained during writing of the holographic gratings.
2:30 PM D2.3
EFFECT OF PHASE ORDERING ON PHASE SEPARATION KINETICS
IN LIQUID-CRYSTAL/POLYMER MIXTURES. A.M. Lapeñ a, Univ of California-Los
Angeles, Dept of Chemistry, Los Angeles, CA; S.A. Langer, NIST, Information
Technology Laboratory, Gaithersburg, MD; S.C. Glotzer, NIST, Polymers Division
and CTCMS, Gaithersburg, MD; A.J. Liu, Univ of California-Los Angeles,
Dept of Chemistry, Los Angeles, CA.
Materials based on mixtures of liquid crystals with a
small amount of polymer are used for a variety of electro-optical devices,
because the polymer tends to form a network that aligns the liquid crystals.
Often, making such mixtures involves the interplay of three kinetic processes:
phase separation, phase ordering, and polymerization. We focus on the interplay
of the first two processes, using a simple model.1,2 This model
allows for composition and orientation fields to evolve with time in a
coupled fashion. We conduct numerical analyses and present results for
a system quenched from a mixed isotropic phase into coexisting polymer-rich
isotropic and liquid-crystal-rich nematic phases. We find that orientational
ordering not only affects resulting domain morphologies, but also affects
the time evolution of domain growth.
1A.J. Liu and G.H. Fredrickson, Macromolecules
29, 8000, (1996)
2A.M. Lapeña, S.C. Glotzer, S.A. Langer,
and A.J. Liu. Preprint.
2:45 PM D2.4
THE EFFECT OF FLUORINE-SUBSTITUTED MONOFUNCTIONAL MONOMERS
ON POLYMER DISPERSED LIQUID CRYSTAL ELECTRO-OPTICAL AND MORPHOLOGICAL PROPERTIES.
Michael D. Schulte and Stephen J. Clarson, University of Cincinnati, Dept
MS&E, Cincinnati, OH; Lalgudi V. Natarajan and Vincent P. Tondiglia,
SAIC Inc., Dayton, OH; Timothy J. Bunning, AFRL/MLPJ WPAFB, OH.
Floodlit and holographic polymer dispersed liquid crystals
(PDLCís) with semi-fluorinated host matrices have been investigated. Films
were formed by photopolymerization-induced phase separation from an initially
isotropic solution of monomer and liquid crystal. We report the observed
electro-optical and morphological properties that result from the systematic
addition of fluorine-containing acrylates and methacrylates to a pentaacrylate-based
prepolymer solution. General increases in polymer network phase separation
were observed using low voltage scanning electron microscopy (SEM) in floodlit
specimens with additions of fluorinated monomers up to 10% by weight. Electro-optical
properties such as contrast ratio, switching voltage and relaxation time
are reported. Contrast ratio and relaxation time increased with fluorinated
monomer concentration in floodlit films. The less reactive methacrylate
monomers revealed greater relaxation times and tended to form large polymer
beads while the faster reacting acrylate monomers resulted in smaller polymer
aggregates and shorter relaxation times. Photo differential scanning calorimetry
(PDSC) was utilized to study the polymerization reaction kinetics of prepolymer
syrups. In holographic PDLC films, the inclusion of fluorine-substituted
monomers produced initially promising morphological features.
3:30 PM *D2.5
LIGHT TRANSMISSION-LIGHT SCATTERING REVERSE MODE SWITCHING
OF (LIQUID CRYSTALLINE POLYMER/LIQUID CRYSTALS) COMPOSITE SYSTEM. Hirotsugu
Kikuchi , Shigeru Kibe, Tisato Kajiyama, Kyushu University, Graduate School
of Engineering, Fukuoka, JAPAN.
Conventional (polymer/liquid crystal) composite films
exhibit the normal mode electro-optical switching, that is, the light scattering-light
transmission switching upon electric field OFF-ON states, respectively.
In this study, the ``reverse mode'' electro-optical switching, that is,
the light transmission-light scattering switching upon electric field OFF-ON
states, respectively, has been investigated for a novel type of composite
system consisting of the side chain type liquid crystalline polymer (LCP)
and the low molecular weight liquid crystals (LCs). The polarizing optical
microscopic observation and X-ray diffraction study revealed that the two
types of smectic-like short range orderings were present in the (LCP/LCs)
composite system in a nematic state. It was ascertained from the electric
capacitance measurements of the homogeneous alignment cell that these phases
with different smectic-like short range orderings exhibited each different
value of threshold voltage. Although the homogeneous alignment cell of
the (LCP/LCs) composite system was the light transmission state in the
absence of an electric field, the cell turned into the light scattering
state upon the application of electric field of 1.0-1.5 MV/m. The transmission-scattering
states were reversible in the electric field OFF-ON states, respectively.
The light scattering state of the (LCP/LCs) composite system upon the application
of electric field might be due to the appearance of optically heterogeneous
structure induced by heterogeneous reorientation behavior of the mesogenic
groups of LCP and LC molecules in an electric field ON state. A possible
origin for the field-induced heterogeneous reorientation is the different
values of the threshold voltage between the two types of smectic-like phases
with different short range orderings. These phases might be in a phase-separated
state with an optical dimension. In conclusion, the reversible ``reverse
mode'' electro-optical switching was realized for the (LCP/LCs) composite
system in a nematic state in which the two types of smectic-like short
range orderings were separately formed in optical size level.
4:00 PM *D2.6
POLYMER DISPERSED LIQUID CRYSTALS AS OPTICAL STORAGE
MATERIALS. Francesco Simoni , Sonia Di Bella, Liana Lucchetti, Dept. Scienze
dei Materiali e della Terra, Univ. Ancona, Ancona, ITALY; Gabriella Cipparrone,
Alfredo Mazzulla, Dept. Fisica, Univ. della Calabria, Cosenza, ITALY and
Istituto Nazionale per la Fisica della Materia.
In the last years several experiments have been carried
out in order to investigate memory effects in Polymer Dispersed Liquid
Crystals (PDLC). Two different approaches have been used: in the first
one the optical information is stored during the polymerization process
by fixing a specific droplets' morphology in the material, while in a second
approach the information is recorded on a PDLC sample after the curing
process, by exploiting different phenomena. We present our more recent
results obtained by the mentioned methods. In the first case UV curable
polymers have been used and a detailed investigation of the phase separation
process has been performed using both conventional UV lamp and UV laser
lines. Very different morphologies have been obtained leading to droplets
or channels formation. Under different experimental conditions either opaque
images on transparent background or transparent images on opaque background
have been obtained. Moreover all the recorded images could be switched
off by a moderate applied voltage. Using the second method of recording
optical patterns on already cured samples, it was possible to write and
erase many times holographic gratings on the same spot. Two beams interference
was used to record the grating, while single beam illumination lead to
erasure of the optical pattern. A detailed investigation of this phenomenon
has demonstrated that photorefractive effect plays a major role in this
4:30 PM D2.7
OPTICALLY SWITCHABLE GRATINGS BASED ON POLYMER-DISPERSED
LIQUID CRYSTAL FILMS DOPED WITH A GUEST-HOST DYE. Andy Ying-Guey Fuh ,
Ming-Shan Tsai, Li-Jue Huang and Tsung-Chi Liu, Department of Physics,
National Cheng Kung University, Tainan, TAIWAN.
In this work, we add a small amount of a guest-host dye
G-206 in the polymerdispersed liquid crystal (PDLC) mixtures to fabricate
holographic gratings. Following formation, the grating is irradiated by
a single Ar' laser beam while probed by a He-Ne laser. Experimental results
indicate that the first-order diffracted intensity of the probe beam significantly
increases. Such an optically switchable diffraction effect is attributed
to thermal expansion. The G-206 dye absorbs Ar+ laser subsequently
resulting in thermal expansion. The liquid crystal (LC) droplets are then
squeezed so that the LC molecules within the droplets are reoriented collectively.
Thus, the refractive index difference between the LC-rich and polymer-rich
stripes, n, increases.
4:45 PM D2.8
OPTICAL POWER LIMITING IN POLYMER-DISPERSED LIQUID CRYSTAL
FILMS DOPED WITH FULLERENES. N.V. Kamanina , L.N. Kaporskii, Vavilov State
Optical Inst, St. Petersburg, RUSSIA.
Effect of reverse saturable absorption has been investigated
in the liquid crystal composites based on polymers (polyimide and polyvinyl
alcohol) and fullerenes. With stirring, the initial mixture of polymer
and nematic liquid crystal (NLC) was prepared in the ratio of 3 polymer
to 2 NLC as long as an uniform emulsion was obtained. ZhK999, ZhK1289,
and E7 were used as NLC. A finely divided powder of fullerenes was introduced
either in NLC or in a polyimide solution in 1,1,2,2-tetrachloroethane.
The emulsion was poured over a substrate with calibrated spacers followed
by drying in order to remove the solvent.
A thickness of the samples was 10m.
A size of NLC drops in the polymer matrix was 2m.
The second harmonic of a pulsed Nd-laser at wavelength of 532 nm was used
to investigate optical limiting.
Under laser radiation the samples with fullerenes in
millijoule range of powers, the attenuation of laser power was found at
least by a factor of 10-15. The effect was caused by an increase in absorption
cross-section of the fullerene molecule in excited state in comparison
with that in ground state. By contrast, transmission augmentation was observed
in the samples without fullerenes. The transmission augmentation was caused
by laser-heating NLC, resulting in the transition of NLC to isotropic phase
with refractive index close to the one of the polymer. In this case transmission
was varied by the factor 1.7-2. Moreover, a memory effect was observed
after the transmission augmentation of the samples when the laser power
SESSION D3: NEW MATERIALS AND EFFECTS
8:00 PM D3.1
COMPLEX FORMATION IN MIXTURES OF CYANOBIPHENYLS AND 4,
Mary E. Neubert , Sandra S. Keast, Erica E. Humeniuk, Margaret E. Walsh
and Kyle J. Miller, Glenn H. Brown, Liquid Crystal Institute, Kent State
Univ., Kent, OH; Rolfe G. Petschek, Physics Dept, Case Western Reserve
Univ., Cleveland, OH.
Chair: Liang-Chy Chien
Monday Evening, April 5, 1999
A variety of 1:1 mixtures of 4,4'-disubstituted-diphenyidiacetylenes
(PTTP series) with cyano containing mesogens were investigated for possible
complex formation. Complexes were formed when alkyl/alkoxycyanobiphenyls
(CB series) were mixed with alkyl/alkoxy PTTP homologs. Two types of complexes
were observed, depending on chain length and the presence of an alkoxy
group: those with a melting temperature higher than that for either component
and those with lower melting temperatures. A fluro substituent on the PTTP
gave an enhanced nematic phase and a cyclohexane ring in place of a benzene
ring yielded an enhanced smectic A phase but a cyano group produced a poor
mixture. Phase diagrams were constructed for PTTP-24/5-CB and PTTP-24/80-CB.
Both complexes formed had melting temperatures higher than those for either
component. These complexes were recrystallized and shown by X-ray studies
to be 1:1 complexes. The PTTP-24/5-CB complex showed only a monotropic
nematic phase but the PTTp-24/80-CB complex showed induced smectic A and
hexatic B phases in addition to an enantiotropic nematic phase.
*This work was supported in part by the NSF Center for
Advanced Liquid Crystalline Optical Materials (ALCOM), DMR89-20147.
8:15 PM D3.2
RELATION BETWEEN MOLECULAR AND MACROSCOPIC PROPERTIES
OF NEMATIC LIQUID CRYSTALS. Kim F. Ferris and Gregory J. Exarhos, Pacific
Northwest National Laboratories, Richland, WA; Steven M. Risser, Texas
A&M University Commerce, TX.
While many studies have focused on static structural and
electronic properties, dynamic factors such as molecular anisotropy, partial
ordering and structural fluctuations have hindered descriptions linking
liquid crystalline properties from the molecular level with the macroscopic
level (as is measured experimentally). In this paper, we examine the transition
from molecular to bulk properties for the nematogen 5-alkyl-cyanobiphenyl
(5CB), using both molecular dynamics and quantum mechanical calculations.
We perform molecular dynamics simulations of a collection of molecules
in the nematic phase, and sample the trajectory to create a representative
collection of structures of individual molecules. We also create a collection
of structures for clusters of 5CB molecules. We then perform electronic
structure calculations on the structures sampled from the trajectory. By
varying the number of molecules included in the cluster, we explore the
evolution of the electronic properties from the molecular to the macroscopic
level. We will also compare these all-molecule results to calculations
using point-charge representations of adjacent molecules to examine how
inter-molecular interactions alter the collective response. This work was
supported in part by the US Department of Energy, Office of Basic Energy
Sciences, Materials Sciences Directorate under contract DE-AC06 76 RLO
8:30 PM D3.3
THE DYNAMIC PROPERTIES OF 5CB FILLED WITH AEROSIL PARTICLES
INVESTIGATED BY PCS. F.M. Aliev a, M. Kreuzerb
and Yu.P. Panarina, aDept. of Physics,
University of Puerto Rico, San Juan, PUERTO RICO; bIAP,
Darmstadt University of Technology, Darmstadt, GERMANY.
Nematic liquid crystal filled with aerosil particles,
the prospective composite material for optoelectronic application, has
been investigated by static light scattering and Photon Correlation Spectroscopy
(PCS). The aerosil particles in filled nematics (FN) liquid crystals form
the network structure with linear size of LC domains about 250 nm with
random distribution of the director orientation of each domain. From this
point of view, the dynamical properties of filled nematics are expected
to be similar the properties of LC confined in random porous matrices.
However the flexibility of the framework of filled nematics may cause new
properties and phenomena which absent in rigid matrices. We found that
the properties of 5CB are considerably affected by the network. The N-I
phase transition in filled 5CB was found to be depressed while the nematic
phase retains even 20 K below crystallization point of bulk 5CB. PCS experiment
shows that two new relaxation processes appear in filled 5CB in addition
to the director fluctuation process in bulk. The slow relaxation process,
with a broad spectrum of relaxation times, is somewhat similar to the slow
decay, which observed in confined nematic liquid crystal. The middle frequency
process, which doesn't exist neither in bulk nor in pores, was assigned
to the director fluctuations in the surface layer formed at particle-LC
interface. The decay function describing this relaxation process is stretched
The temperature dependence of the relaxation times of the middle frequency
process was found to follow to Vogel-Fulcher low, while the temperature
dependence of the relaxation times of the bulk-like process was not. Such
a temperature dependence, accompanied by broad spectrum of relaxation times
suggests the glass-like dynamics of the director fluctuations near the
aerosil particle-LC interface.
SESSION D4: LIQUID CRYSTALLINE POLYMERS AND APPLICATIONS
8:30 AM *D4.1
DYNAMICS OF SIDE-GROUP LIQUID CRYSTALLINE POLYMERS. J.A.
Kornfield , M. Kempe, W.J. Zhou, Caltech, Pasadena, CA; C. Ober, Y.U. Kim,
Y.C.Chao, Cornell University, Ithaca, NY.
Chairs: Shaw H. Chen and Julie A. Kornfield
Tuesday Morning, April 6, 1999
Chain dynamics of side-group liquid crystalline polymers
provide a powerful tool to manipulate alignment of the liquid crystalline
phase formed from their side groups. As the length of the chains increases,
their relaxation dynamics slow down. This can be used to advantage, since
deformation of the material can then readily alter chain conformation.
Therefore we are interested in synthetic strategies to produce well-defined
SG-LCPs that are long relative to their entanglement molecular weight (
300,000 g/mol). Extending polymer analogous chemistries to produce SG-LCPs
of a few million g/mol, we can prepare polymers with narrow distributions
of chain length starting from anionically synthesized prepolymers (e.g.
1,2-polybutadiene). The dynamics of these materials in the melt and when
solvated by small-molecule liquid crystals will be described.
9:00 AM D4.2
EFFECT OF COMPOSITION ON THE MORPHOLOGY AND ELECTRO-OPTICAL
PROPERTIES OF PHYSICALLY CROSSLINKED LIQUID CRYSTALS. Steffen Geppert,
Armin Schneider, Richard Spontak , Wolfram Gronski, Heino Finkelmann, Albert
Ludwigs Universitat Freiburg, Inst fur Makromolekulare Chemie, Freiburg,
In a conventional polymer-dispersed liquid crystal (PDLC)
composite material, a small-molecule liquid crystal is uniformly dispersed
within a matrix of glassy polymer typically through either polymerization-induced
phase separation or emulsification. The liquid crystals residing in the
resultant dispersions inherently possess a random molecular director, but
can be oriented through the application of an electric field to yield a
highly transparent medium. An alternative to PDLCs, in which the liquid
crystal constitutes the minor component confined within discrete micron-size
dispersions, is the physically crosslinked liquid crystal (PCLC). A PCLC
consists of liquid crystal molecules physically bound within a linear multiblock
copolymer network. In this case, the copolymer comprises the minor component,
whereas the liquid crystal is the major component. In this work, we report
on the phase stability, morphological characteristics and electro-optical
properties of blends of E7, a commercial liquid crystal mixture exhibiting
a nematic mesophase, and novel triblock copolymers with styrenic endblocks
and side-chain liquid crystalline midblocks. Since the copolymer endblocks
are glassy at ambient temperature, they serve as physical crosslink sites,
thereby forming a thermally reversible copolymer network in which the E7
9:15 AM D4.3
DESIGN AND SYNTHESIS OF THERMOTROPIC CHIRAL-NEMATIC CONJUGATED
POLYMERS. John C. Mastrangelo , Brooke M. Conger, Philip H. Chen, Shaw
H. Chen, Andrew S. Kende, Materials Science Program, Departments of Chemical
Engineering and Chemistry, Center for Photoinduced Charge Transfer and
Laboratory for Laser Energetics, University of Rochester, Rochester, NY.
With various nematogenic and chiral pendants, thermotropic
polymers with p-phenylene, thiophene, and p-phenylenevinylene conjugated
backbones were synthesized and characterized. Spontaneous assembly of the
conjugated systems into helically stacked planes inherent to cholesteric
mesomorphism was characterized with circularly polarized fluorescence.
Unique features include: (1) ability to form macroscopically ordered solid
films; (2) both right- and left-handded circular polarization of incident
light; (3) circularly polarized photoluminescence with unpolarized, UV-excitation.
Potential applications of this novel class of materials are being explored.
9:30 AM D4.4
SYNTHESIS AND OPTO-ELECTRIC PROPERTIES OF LIQUID CRYSTALLINE
POLYMERS CONTAINING CARBAZOLYL GROUP. Naoyuki Koide , Koji Arai, Science
University of Tokyo, Department of Chemistry, Tokyo, JAPAN; Tetsuya Wada
and Hiroyuki Sasabe, The Institute of Physical and Chemical Research, Bio-polymer
Physics Laboratory, Saitama, JAPAN.
The paper reports synthesis of side-chain type liquid
crystalline polymers containing carbazolyl group and their thermal and
opto-electric properties. The polymers containing carbazolyl group at the
side of methacrylate polymer backbone via spacer length exhibited smectic
phases. One of the methacrylate type polymer( PMICZ) was turned out to
have photoconductivity, and a hole mobility of PMICZ was 4.24 x 10-5
cm2/Vs at an electric field of 3.00 x 105V/cm at room temperature
by the time-of-flight measurements. This value of PMICz was superior to
that of PVK. In general amorphous polymer, such as PVK, the mobility of
PVK becomes larger with increasing electric field. However, the mobility
of PMICZ became smaller in proportion to the applied electric field. This
tendency would be attributed by characteristic of the mesogenic state .
9:45 AM D4.5
DETERMINATION OF LOCAL FIBER TEXTURE IN LIQUID CRYSTAL
POLYMER BY ELECTRON DIFFRACTION. Jennifer Taylor , Matthew Libera, Stevens
Institute of Technology, Dept of Materials Science, Hoboken, NJ.
Liquid crystal polymers (LCP) are being increasingly used
for applications requiring light weight material with high yield strength
and high elastic modulus. High yield strength originates from crystalline
and semicrystalline LCP domains separated by poorly oriented or amorphous
LCP matrix. A ``skin-core effect'' is observed in certain LCP fibers and
moldings where an unoriented core is covered by a surface layer of variable
thickness oriented along the flow direction. By controlling the shear dynamics
during melt-forming operations, the morphology may be manipulated to maximize
crystallinity thereby improving mechanical properties. Conventional selected-area
electron diffraction is being used here to study the morphological variations
resulting from the ``skin-core effect.'' Successive thin sections from
an LCP fiber exhibit features indicating a varying degree of orientation
from the skin to the center of the fiber. A simulation of chain morphology
is also presented to understand the real-space orientations represented
by the diffraction data. The effects of electron radiation damage are qualified
by the decay of diffraction features as a function of electron dose.
10:30 AM *D4.6
NEW FERROELECTRIC LIQUID CRYSTALS FOR NON-DISPLAY APPLICATIONS.
W. Haase, D. Ganzke, T. Weyrauch, Institute of Physical Chemistry,
Darmstadt University of Technology, Darmstadt, GERMANY; E. Pozhidaev, P.N.
Lebedev Physical Institute, Moscow, RUSSIA, Institute of Physical Chemistry,
Darmstadt University of Technology, Darmstadt, GERMANY.
New Ferroelectric Liquid Crystals (FLC's) considering
mainly Deformed Helix Ferroelectric (DHF) or Electroclinic (E) effect will
be demonstrated. The feasibility of the electrooptical performance of broad
temperature range DHF FLC's from below -20C
to 90C will be shown. Such mixtures
are favorable for both low voltage light shutters (contrast ration more
than 100:1) and electrically controlled phase retarders. The birefringence
can be changed more than twice with a typical response time 0.2-10 ms under
action of 2-7 A.C. voltage in an analogous mode. Single Electroclinic light
shutters providing an electrically induced inclination more than 20
at R.T. under A.C. electric field strength of about 15V/m
Those cells provide practically the same level of light transmission as
nematic based cells but response time is 1s
at R.T. Main goal of the report is to present the state of the art overview
on the various fields of such FLC's of non-display application for shutters,
switchers, diffraction gratings, adaptive optics etc. in electrically driven
mode by special consideration of the requirements for each of the FLC-mixtures
applied. Moreover, some recent results on optically driven spatial light
modulators will be presented.
11:00 AM D4.7
HOLOGRAPHIC GRATING FORMED BY PHOTOCHEMICAL PHASE TRANSITION
OF POLYMER AZOBENZENE LIQUID CRYSTAL. Takahiro Yamamoto , Satoshi Yoneyama,
Makoto Hasegawa, Akihiko Kanazawa, Takeshi Shiono, Tomiki Ikeda, Tokyo
Inst. of Technology, Research Laboratory of Resources Utilization, Yokohama,
To establish the liquid-crystalline materials for photonics
in which properties of light are controlled by a stimulating light, we
have performed so far study on photochemical nematic (N) to isotropic (I)
phase transition behavior of polymer azobenzene liquid crystals (PALCs).
We already reported optical switching and two-dimensional image storage
by transmission-, reflection- and scattering-mode analyses. We present
here the formation of the holographic grating by diffraction-mode analysis.
When two writing beams (argon-ion laser, 488 nm, unpolarized) were interfered
on the surface of PALC film (thickness, 500
nm), multiple diffraction signals were observed immediately, resulting
from formation of the grating. Such generation of the diffraction signals
was assumed to be due to a periodic induction of photochemical phase transition
in the bright regions of the interference pattern. The grating is namely
made up of a periodic arrangement of N (dark region) and I phases. In fact,
the intensity of the diffraction signals was affected by the polarization
direction of the readout beam (He-Ne laser, 633 nm, linearly polarized).
In Raman-Nath diffraction, diffraction efficiency (D.E.) depends on the
difference in the refractive indices between the bright and the dark regions
(n). When the plane of polarization
of the beam was parallel to the director of liquid crystal in the dark
region, D.E. was highest (20).
On the other hand, D.E. was lowest when the plane of the polarization was
perpendicular to the director because the n
was smaller in this case. Observation of recorded interference pattern
under a cross-polarized optical microscope also supported our speculation
for the structure of the grating. On the basis of these results, we succeeded
in recording image hologram of photomask as an object.
11:15 AM D4.8
FORMATION OF POLYMER STABILIZED FERROELECTRIC LIQUID
CRYSTALS USING A FLUORINATED DIACRYLATE. C. Allan Guymon , University of
Southern Mississippi, Department of Polymer Science, Hattiesburg, MS; Christopher
N. Bowman, Department of Chemical Engineering, University of Colorado,
Ferroelectric liquid crystals (FLCs) have shown great
potential for use in electro-optic and display technology due to their
inherently fast switching speeds and bistability. Recently, considerable
research has been devoted to FLCs mechanically stabilized by a polymer
network. The network is formed typically by in situ polymerization of a
monomer dissolved in the FLC. Because of the inherent order in the FLC,
the polymerization behavior may be significantly different than what might
be expected in solution polymerizations. These deviations result largely
from the segregation properties of the monomer in the liquid crystal. One
class of monomers, namely fluorinated acrylates, is a likely candidate
for inducing novel segregation, polymerization and electro-optic behavior
in polymer stabilized ferroelectric liquid crystals (PSFLCs). The use of
fluorinated moieties has a significant impact on the phase and polymerization
behavior of liquid crystal systems. This study focuses on the polymerization
of a fluorinated diacrylate, octafluoro 1,6-hexanediol diacrylate (FHDDA),
to form PSFLCs and the consequent impact of the polymerization on the ultimate
performance. Interestingly, as the temperature is increased and the order
of the system decreases, a dramatic increase in the polymerization rate
is observed. This increase is especially prominent for polymerizations
in the smectic C* phase for which the rate is more than five times that
exhibited at much higher temperatures in the isotropic phase. As with other
monomer/FLC systems, the segregation of the monomer plays a role in this
polymerization behavior as the monomer segregates between the smectic layers
of the liquid crystal. The segregation properties also significantly impact
the ultimate electro-optic properties. Both ferroelectric polarization
and response time of the PSFLC change markedly with different polymerization
temperatures, and approach values very close to those of the neat FLC under
appropriate polymerization conditions. This behavior not only provides
a unique mechanism for rate acceleration in PSFLCs, but also paves the
way for new methods to optimize performance in these materials.
11:30 AM D4.9
NEW WHOLLY-AROMATIC THERMOTROPIC POLYESTERS WITH CONTROLLED
FLEXIBILITY. Devdatt S. Nagvekar, Univ. Dayton Research Inst., AFRL/MLBP,
Wright Patterson AFB, OH; Patrick T. Mather , L.-Seng Tan, AFRL/MLBP, Wright
Patterson AFB, OH; Hong G. Jeon, Systran Corp., AFRL/MLBP, Wright Patterson
Aromatic copolyesters which are para-linked are known
to feature thermotropic behavior in which heating the semicrystalline solid
results in melting to a mesomorphic phase, often nematic, giving rise to
desirable molding characteristics, mechanical properties, and solvent resistance.
Often, their high modulus and strength come at the expense of low toughness,
manifested as failure strains less than 5%. In addition, such polymers
feature nematic-isotropic transition temperatures in excess of thermal
decomposition, eliminating the potential benefit of traversing the isotropic-nematic
phase transition during processing. In this work, we present the synthesis
and characterization of a new series of wholly-aromatic copolyesters derived
from the condensation of various weight fractions of 4,4´ -(o-phenylenedioxy)
dibenzoyl chloride (OPDB) and substituted terephthaloyl chloride (BTA)
with 2-phenylhydroquinone (PHQ). The Hagashi method, involving tosyl
chloride and pyridine as solvent, was employed to yield polymer with significant
molecular weight. These polymers are intended to enable accessible clearing
transition and to control the balance of stiffness and toughness in melt-spun
fibers systematically. We report the synthetic details along with characterization
of quiescent phase behavior and morphology. Fiber orientation, microstructure,
and mechanical properties for selected samples are also presented. 
Higashi, F.; Akiyama, N.; Takahashi, I.; Koyama, T. J. Polym. Sci. A: Polym.
Chem. Ed. 1984, 22, 1653.
11:45 AM D4.10
DYNAMICS AND ALIGNMENT BEHAVIOR OF A THERMOTROPIC MAIN-CHAIN
LIQUID CRYSTALLINE POLYMER. Weijun Zhou, Julia A. Kornfield , Caltech,
Pasadena, CA; Victor M. Ugaz, Wesley R. Burghardt, Northwestern University,
The material properties of thermotropic liquid crystalline
polymers (TLCPs) are strongly influenced by the flow-history they experience
during processing because it can dramatically alter the orientation distribution
of the polymer and the texture of the liquid crystalline domains. However,
the flow behavior of TLCPs have received relatively little attention due
to experimental difficulities. Here we describe the rheology and flow-induced
orientation behavior of a model TLCP, which has good thermal stability
and an accessible isotropization temperature: DHMS-7,9, C, C, C,
where Txn is the transition temperature from an unidentified
mesophase (X) to the nematic phase. Systematic rheological studies were
carried out on DHMS-7,9 as a function of temperature and Mw
(Mw=11K to 65K g/mol). The storage modulius ()
showed a plateau at an intermediate frequency in Phase X, but no plateau
for was observed over the
whole nematic range. This TLCP exhibits qualitatively different flow-aligning
behavior in the X mesophase than in the nematic phase. Wide-angle X-ray
diffraction shows that all steady shear conditions probed in the nematic
phase induce a preferential orientation along the flow direction (``parallel),
whereas a log-rolling alignment results under steady shear conditions in
Phase X for low enough shear rates. The orientation can be flipped back
and forth by raising or lowering the shear rate or temperature across the
boundary between the parallel and log-rolling regimes.
SESSION D5: DISPLAY TECHNOLOGIES AND MODELING
1:30 PM *D5.1
POLYMER STABILIZED FLCD. H. Furue, T. Takahashi, T. Miyama,
M. Shikada, R. Kurihara and S. Kobayashi , Liquid Crystal Institute, Science
University of Tokyo in Yamaguchi, Onoda, Yamaguchi, JAPAN.
Chairs: Shui-Chih Alan Lien and Shunsuke Kobayashi
Tuesday Afternoon, April 6, 1999
We present electrooptical performance of polymer-stabilized
(PS) FLCDs and their applications to active matrix LCD and field sequential
full color LCD. The PS-FLCD, which is fabricated by UV photocuring doped
mesogenic sidechain polymer, exhibits high contrast ratio (230:1) with
thresholdless monostability and fast response speed (40micro seconds).
We confirmed that our PS-FLCD is addressable using switching FETs with
the gate pulse condition for SXGA specifications having 1024 strobing lines.
We also demonstrate a field sequential fullcolor LCD using PS-FLCD.
2:00 PM *D5.2
COLORLESS HIGH DIELECTRIC COMPOUNDS FOR LOW VOLTAGE LIQUID
CRYSTAL APPLICATION. Shin-Tson Wu , Robert N. Schwartz, HRL Laboratories,
Malibu, CA; Qing T. Zhang, Seth Marder, Beckman Institute, California Institute
of Technology, Pasadena, CA.
Several colorless compounds with high dielectric anisotropy
were designed and synthesized. Their physical properties, such as phase
transition temperature, heat fusion enthalpy, absorption spectra, dielectric
constants and visco-elastic coefficient were measured. Confirming molecular
modelings on the structures and dipole moments of these compounds are developed.
These compounds are useful for lowering the operation voltage of liquid
2:30 PM *D5.3
ELECTRIC PROPERTIES OF LIQUID-CRYSTAL MATERIALS FOR DISPLAY
APPLICATIONS. Shohei Naemura , Merck Japan Ltd., Atsugi Technical Center,
High image quality is an essential requirement for displays,
and, especially for mobile applications, low power consumption is another
key issue. In order to lower the power consumption of liquid crystal displays
(LCDs), an anisotropy of the dielectric property is required to be sufficiently
large for LC materials and, at the same time, the dielectric constant value
is required to be kept low enough. Electrical conduction is also important
not only for the dielectric loss but also for the image quality. In practical
LCD panels driven by AC voltage, the electrical conduction is governed
by a long-range movement of ions in a LC slab. Mobile ions also act as
a space charge and affect the dielectric property in a very low frequency
range. Moreover, when localized at an interface of dielectric layers, they
can cause an internal electric-potential and affect the effective field
across the LC slab. The electric properties of LC materials such as dielectric
and conductive properties are essentially important for LCDs, as far as
they are addressed electrically. In order to understand these electric
properties of LC materials, behavior of ions in LC materials are indispensable,
and will be focused in the presentation.
3:30 PM *D5.4
COMPUTER SIMULATION OF THE OPTICAL PERFORMANCE OF LIQUID
CRYSTAL DEVICES. Jack R. Kelly and Weimin Liu, Liquid Crystal Institute,
Kent State University, Kent, OH.
We present various approaches for simulating the optical
performance of liquid crystal devices in more than one dimension. Two ray
optics approaches based on the extended Jones matrix method and geometrical
optics are appealing because of their simplicity. These approaches are
expected to break down when the wavefronts develop significant curvature,
as occurs in the neighborhood of a defect or a shadow edge. Near defects
where the wavefronts distort smoothly, a modified Jones matrix approach
can yield useful results, while for shadows, the geometrical theory of
diffraction can be generalized to birefringent media. We compare the simulations
with experimental transmission measurements of a liquid crystal device:
an in-plane switching device with homeotropic boundary conditions.
4:00 PM *D5.5
REFLECTIVE FULL COLOUR LIQUIED-CRYSTAL DISPLAY: ACTIVITIES
IN ASET. Yoshiharu Nakajima , Association of Super-Advanced Electronics
Technologies (ASET), Tokyo, JAPAN.
In February 1996, ASET was established and made the contract
with NEDO (New Energy Development Organization) to promote this Government
research project ``Super-Advanced Electronic Technology Development Promotion
Project'' formed by Ministry of International Trade and Industry (MITI).
Main research subjects conducting in ASET are next generation silicon semiconductors,
Ultrahigh density magnetic storage and low power liquid crystal display.
Reflective full colour liquid crystal display project is one of major subject
in this government research project. Five materials and four devices companies
are participating. The research aim is to make technological breakthrough
with the objective of creating full colour displays that can provide high
resolution and high quality images with very low power consumption. To
meet this aim, we are now doing the research and development in the following
sub-fields: 1) forming the fine composite structures creating new display
mode such as stacked holographic one, 2) to create high gain effective
light reflecting characteristics, 3) retentive memories mode by using ferroelectric
properties, in addition to these devise related research, 4) development
of new liquid crystal, optical and alignment film materials which have
large anisotoropy, high scattering efficiency, pure and high reliable and
to show new alignment mode, respectively. We have just passed intermediate
stage of our first five years project term, the results obtained so far
will be discussed as well as project outline. This work was performed under
the management of ASET in the MITIÕs R & A program supported
4:30 PM D5.6
12.1 SVGA WIDE VIEWING ANGLE TFT-LCDS BASED ON RIDGE
AND FRINGE-FIELD STRUCTURES. A. Lien , C. Caiü, R.A. John, E. Galligan,
R. Nunes, J. Wilson, H. Ifill, IBM T. J. Watson Research Center, Yorktown
Heights, NY; Department of Chemical Engineering, Chemistry and Material
Science, Potytechnic University, Brooklyn, NY.
Compared with cathode ray tube (CRT) displays, it is well
known that liquid crystal displays (LCDs) have a much narrower viewing
angle . To solve this problem, the in-plane switching (IPS) mode [2,3,4]
is a popular approach. However, because of the low optical transmission
compared to the conventional twisted nematic (TN) mode, the IPS mode is
restricted to desktop applications and not suitable for notebook applications.
We have recently proposed a ridge and fringe-field multi-domain homeotropic
(RFFMH) mode  as another approach to achieve wide viewing angle for
LCDs. The operation of this new structure is based on the combined effect
of the ridge structure and the pixel fringe electric field to control the
tilt direction of LC molecules inside each pixel. We have also demonstrated
that RFFMD structure is suitable for the desktop application . In this
paper we investigated whether the RFFMH mode is suitable for the notebook
application. To do that, several RFFMH structures were built on the 12.1
SVGA panels. The result shows that RFFMH method is suitable for the high-end
large-area notebook application since it provides a wide viewing angle
with a reasonably high transmission. The ridge structure is constructed
only on top of the indium tin oxide (ITO) layer of the color filter (CF)
substrate, and can be fabricated during color filter manufacture. This
process is thus compatible with the conventional TFT-LCD process, and quires
only one extra photolithographic step, but without rubbing treatment. References:
 A. Lien, H. Takano, S. Suzuki and H. Uchida, The Symmetry Property
of a 90 degree Nematic Liquid Crystal Cell, Mol. Cryst. Liq. Cryst. 198,
37 (1991).  R. A. Soref, Field Effects in Nematic Liquid Crystal Obtained
with Interdigital Electrodes, Jour. of Appl. Phys, 45, 5466 (1974). 
R. Kiefer, B. Weber, F. Windscheid and G. Baur, In-Plane Switching of Nematic
Liquid Crystals, Japan Display'92, 547 (1992).  M. Ohta, M. Oh-e and
K. Kondo, Development of Super-TFT-LCDs with In-Plane Switching Display
Mode, Asia Display'95, 707 (1995).  A. Lien, C. Cai, R. Nunes, R. A.
John, A. E. Colgan, J. Wilson, Ridge and Fringe Field Multi-Domain Homeotropic
Liquid Crystal Display, submitted to SID'98.  A. Lien, C. Cai, R. Nunes,
S. L. Wright, R. A. John, E. A. Galligan, W. S. Wilson,Wide Viewing Angle
TFT-LCD Based on Ridge and Fringe Field Multi-Domain Homeotropic Structure,
Asia Display 98, p 375 (1998).
4:45 PM D5.7
SIMULATION OF REORIENTATION DYNAMICS IN BIPOLAR NEMATIC
DROPLETS. Philip K. Chan , Ryerson Polytechnic Univ, School of Chemical
Engineering, Toronto, Ontario, CANADA; Alejandro D. Rey, McGill Univ, Dept
of Chemical Engineering, Montreal, Quebec, CANADA.
A two-dimensional model composed of a synthesis of the
Leslie-Erickson continuum theory of nematics and the Euler-Lagrange equation
for surface director motion is used to study the magnetic-induced director
reorientation dynamics confined in spherical bipolar droplets with viscoelastic
surfaces. The magnetic field is restricted to the droplet axis of symmetry
direction. The numerical results indicate that the surface viscosity and
anchoring strength must be taken into account to describe accurately director
reorientation dynamics in droplets. In addition, the numerical results
replicate frequently reported experimental observations on the performance
of polymer dispersed liquid crystal films. These observations include the
familiar exponential increase followed by saturation in light transmittance
as the external applied field increases, and the exponential increase (decrease)
followed by saturation as time increases in the on (off) state. Furthermore,
this model is able to predict precisely the relationships between the rise
and decay times and the external applied field strength, and the fact that
the switching field strength is inversely proportional to droplet size.
SESSION D6: POSTER SESSION:
ELECTRO-OPTICAL RESPONSE OF UNIAXIALLY ORIENTED PDCHLC
FILMS WITH VARIOUS DROPLETS ANISOMETRY AND CONCENTRATION OF THE CHIRAL
ADDITIVE. Vladimir V. Presnyakov , Sergei A. Vetoshkin, Victor Ya. Zyryanov,
Vasily F. Shabanov, L.V. Kirensky Institute of Physics, Krasnoyarsk, RUSSIA.
LIQUID CRYSTAL MATERIALS AND DEVICES
Chair: Naoyuki Koide
Tuesday Evening, April 6, 1999
Metropolitan Ballroom (A)
Uniaxially oriented films of polymer dispersed cholesteric
liquid crystals (PDChLC) is a new perspective material for multifunctional
optoelectronic elements. The material presents a polymer film with an ensemble
of elongated cholesteric droplets dispersed therein. Long axes of the droplets
are oriented preferably uniaxially in the film plane. These films reveal
a great anisotropy of the polarized light transparency, which depends strongly
on the applied electric field, concentration of the chiral additive and
shape of the droplets. We have found the optimal composition and droplets
anisometry to produce the films, which can be switched by applied voltage
between three different optical states: scattering light of any polarization,
transmitting the one linear-polarized component only and transparency for
light any polarization. A device employing these films may be used as a
modulator of the whole of the light, as a modulator of one linearly polarized
component only and as a light polarizer .
 V.V. Presnyakov, S.L. Smorgon, V.Ya. Zyryanov, V.F.
Shabanov, Polyfunctional optoelectronic elements based on oriented PDCLC
films, SPIE Proceedings, 1998, V.3348, pp.98-102.
VOLTAGE CREEP IN HOLOGRAPHIC PDLC GRATINGS. A.M. Klostermann
, S. Lakhia and T.J. Bunning, AFRL/MLPJ, Materials and Manufacturing Directorate,
WPAFB, OH; R.T. Pogue, L.V. Natarajan, V.P. Tondiglia, SAIC, Dayton, OH.
It is well known that with conventional polymer dispersed
liquid crystals (PDLCs) a minimum voltage is necessary in order to switch
the cell between a scattering and a transparent state. In holographic gratings
formed using anisotropic photopolymerization of free-radical monomers,
a particular voltage is also necessary to switch the grating between a
diffracting and a transmitting state. In this work we report on the gradual
increase of this switching voltage with time after initial fabrication.
We explore the magnitude of the effect in a pentaacrylate/E7 material systems
and compare to the effect observed for a diacrylate/E7 material system.
This latter material combination crept considerably more. There was however
no change in the measured contrast ratios which suggest little increase
in the microphase separation as a function of time. We also report on processing
issues examined in an attempt to mitigate the increase in voltage. These
include the application of heat after the initial polymerization and extended
laser curing exposure time.
EFFECTS OF MOLECULAR ARCHITECTURE ON PHYSICAL AND LIQUID
CRYSTALLINE TRANSFORMATIONS IN LIQUID CRYSTALLINE THERMOSETS (LCT'S). Arthur
J. Gavrin , Elliot P. Douglas, University of Florida, Dept of Materials
Science and Engineering, Gainesville, FL.
Two homologous series of bis-acetylene LCT's have been
synthesized. Our goal is to investigate how changes in molecular architecture
affect liquid crystalline transitions and physical transformations. These
thermosets are thermotropic liquid crystalline monomers with flexible alkyl
``wings''. The flexible segments range in size from three to eight carbons.
Differential scanning calorimetry and optical microscopy were used to determine
the liquid crystalline transitions for the various monomers. The monomers
with longer flexible units had both lower melting temperatures and more
stable smectic phases. Preliminary studies on the liquid crystalline phase
transformations show that these materials progress from more ordered to
less ordered phases during isothermal cure. These results are contrary
to the trends typically seen in other LCT's.
ELECTRICALLY SWITCHABLE HOLOGRAPHIC REFLECTION GRATINGS
IN POLYMER DISPERSED LIQUID CRYSTALS. L.V. Natarajan , R.L. Sutherland,
V.P. Tondiglia, S. Siweeki, R. Pogue, M. Schmitt, D. Brandelik, B. Epling,
G. Berman, C. Wendel, M. Ritter and M. Stallings, Science Applications
International Corporation, Dayton, OH; and T.J. Bunning, Materials Directorate,
Air Force Research Laboratory, Wright-Patterson Air Force Base, OH.
Electrically switchable reflection holograms were recorded
in polymer dispersed liquid crystals using a prepolymer syrup containing
multifunctional monomers, a photosensitizing dye, a coinitiator and a nematic
liquid crystal. Using Argon ion laser wavelengths 476 and 514nm, blue,
green and red reflection holograms were made with high efficiency. The
holograms were switched electrically with contrast ratios >100. Real time
study of the holograms indicated that the hologram formation was completed
in 20 seconds. Shrinkage of the
polymer during writing blue shifted the reflection notch. Low voltage high
resolution SEM studies showed the presence of discrete phase separated
nematic droplets of 30-70 nm size.
DIELECTRIC RELAXATION IN FILLED NEMATIC LIQUID CRYSTALS.
G.P. Sinha a, M. Kreuzerb and F.M.
Alieva, aDept. of Physics, University
of Puerto Rico, San Juan, PUERTO RICO; bIAP, Darmstadt
University of Technology, Darmstadt, GERMANY.
Nematic liquid crystals (LCs) filled with aerosil particles
are new heterogenous materials important for different optoelectronic applications.
These materials are suspensions of small silica particles, about 10-17
nm in diameter, filling liquid crystals. The particles are known to form
into network structure dividing liquid crystal into domains with linear
size of about 250 nm. This material has very developed liquid crystals-solid
particle interface that makes the role of the surface layers of LC extremely
important in the determination of the properties of the material. We used
particles, both with hydrophilic and hydrophobic surfaces, filling nematic
liquid crystal-5CB. Broad band dielectric spectroscopy (0.1 mHz - 1.5 GHz)
was applied for the investigations of the dielectric properties of these
materials. Two bulk-like modes due to the rotation of molecules around
short axes and the tumbling motion were observed in filled 5CB. Additionally,
a low frequency relaxation process and the dispersion of dielectric permittivity
due to conductivity were also observed. The modification of the surface
of filling particles has strongest influence on the properties of the slow
process and it is less important for molecular modes. The characteristic
frequencies of the slow process are lower for hydrophilic particles and
in this sample the contribution of this process to the total polarization
was greater than in the case of hydrophobic particles. These facts suggest
that low frequency relaxation is aerosil particle-liquid crystal interface
related phenomena and the origin of this process maybe explained on the
basis of the surface induced polarization. Both materials show up nematic-like
behavior up to 20 degrees below bulk crystallization temperature. Deviations
from the Debye type behavior were observed and were more pronounced at
THE DYNAMIC PROPERTIES OF CONFINED ANTIFERROELECTRIC
LIQUID CRYSTAL INVESTIGATED BY PCS. Yu.P. Panarin a,
C. Rosenblattb and F.M. Alieva, aDept.
of Physics, University of Puerto Rico, San Juan, PUERTO RICO; bDepartment
of Physics, Case Western Reserve University, Cleveland, OH.
Since the discovery Antiferroelectric Liquid Crystals
(AFLCs) - materials important in display technology -various novel liquid
crystalline phases were found in the temperature range between the antiferroelectric
SmCA and ferroelectric SmC* phases. These phases were found to be ferrielectric-like.
The appearance of these phases seems to be due to the competition between
the antiferro- and ferroelectric interactions in adjacent smectic layers
that stabilize SmCA and SmC* phases. In the present work we report on the
influence of confinement on the dynamic properties and the appearance of
ferrielectric phases as determined by photon correlation spectroscopy.
The bulk AFLC under investigation (AS573) possesses various ferrielectric
and antiferroelectric phases between SmCA and SmC* phases. Dynamic light
scattering of the sample was measured in the bulk and in cylindrical pores
of two different diameters: 200 Å and 2000 Å. The intensity/intensity
autocorrelation function of the bulk sample consists of three relaxation
processes, while in the confined liquid crystal the fastest relaxation
process (50-250 msec) does not exist. The analysis of the autocorrelation
functions and the temperature dependencies of the relaxation times show
that the ferrielectric phases (SmCg, AF, FiLC) are not formed in the pores.
It was shown that in the smallest pores the electrostatic interactions
between the spontaneous polarization of neighboring smectic layers are
weaker than in the larger pores and in bulk. This fact stresses the importance
of long-range electrostatic interactions for the existence of ferrielectricity.
The SmC* - SmA phase transition temperature in the pores is about 4 C
lower than in the bulk sample, while the SmCA - SmC* transition in pores
and the SmCA- SmCg transition in bulk are of the same value of temperature.
These facts have been explained by the structural aspects of AFLCs in a
IN-SITU OBSERVATION OF THERMAL AMPLIFICATION OF PHOTOGENERATED
OPTICAL ANISOTROPY OF FILMS OF AZOBENZENE POLYMERS. Masatoshi Kidowaki
, Takenori Fujiwara, Shin'ya Morino, Kunihiro Ichimura, Tokyo Institute
of Technology, Research Laboratory and Resources Utilization, Yokohama,
JAPAN; Joachim Stumpe, Institute for Thin Film Technology and Microsensorics,
Erieseering, Berlin, GERMANY.
Photo-induced optical anisotropy in polymeric films has
been extensively studied for optical data storage and processing. Polymers
containing azobenzene derivatives are one of the promising materials for
this purpose since irradiation with linearly polarized light (LPL) to polymer
films generates dichroism and birefringence due to the axis-selective photoisomerization
and the reorientation of azobenzene moieties. We demonstrated that azimuthal
alignment of nematic liquid crystals (LCs) is regulated by LPL-irradiation
of thin films of polymers substituted with azobenzenes in their side-chains,
leading to the fabrication of rubbing-free LC-aligning films. This work
aims at revealing photochemical and thermal characteristics of photoaligned
film of polymethacrylates with azobenzene moieties to be applied to LC
aligning films. We followed the generation of optical anisotropy of LPL-irradiated
films of three types of polymethacrylates with azobenzene side-chains exhibiting
amorphous, crystalline and liquid-crystalline natures during heat treatment
by mean of elipsometry and polarized UV-visible spectroscopy. Whereas photogenerated
optical anisotropy of amorphous polymer films was disappeared above glass
transition temperature, the photo-induced anisotropy of films of liquid
crystalline and crystalline polymer films was significantly amplified by
heat treatment. In case of crystalline film it was maintained even at 573
K. Homogeneous LC alignment induced by this polymer film showed extraordinary
stability because of the generally stable anisotropy.
LIGHT ABSORPTION PROPERTIES OF ANTHRAQUINONE DYES FOR
GUEST-HOST LIQUID CRYSTAL DISPLAYS. Shuangxi Wang , Sugat Abeygunaratne
and Liang-Chy Chien, Department of Chemical Physics, Liquid Crystal Institute
and NSF ALCOM Center, Kent State University, Kent, OH.
Substitution of the anthraquinone systems has provided
dyes suitable for guest-host liquid crystal display applications. In general,
we seek to elongate the anthraquinonic system through the synthesis of
The light absorption properties of anthraquinone dye in different hosts
are compared in order to demonstrate the influence of the dye-liquid crystal
interactions on dye order parameter. Surprisingly, the anthraquinone dye
have a higher order parameter in liquid crystalline mixtures of positive
dielectric anisotropy as well as in a liquid crystalline mixture of negative
dielectric anisotropy (S = 0.71-0.82). As we mentioned, many types of liquid
crystal displays have taken advantages of dichroic dye additives. Such
displays include Heilmeier displays may be made to operate transmissively,
reflectively, or transflectively. The most common use is in the transmissive
mode with a backlight. We studied the Heilmeier displays use homogeneous
alignment. The display is operated at the reverse mode, transparent at
zero field. The switching voltage between the bright and dark states for
these displays is about 2-3 volts.
THREE-DIMENSIONAL PHOTOREORIENTATION OF SELF-ORGANIZED
AZOBENZENE CHROMOPHORES IN LIQUID-CRYSTALLINE POLYMER FILMS. Mina Han ,
Shin'ya Morino, and Kunihiro Ichimura, Tokyo Institute of Technology, Research
Laboratory of Resources Utilization, Yokohama, JAPAN.
Recently many efforts have been focused on developing
photoresponsive systems which demonstrate optical anisotropy changes upon
irradiation of azobenzene containing photochromic materials with linearly
polarized light as a result of the photoreorientation of azobenzene moieties
via reversible trans-cis-trans isomerization. Our recent work has revealed
that three-dimensional control of the orientational direction of azobenzene
moieties is in fact attained by slantwise photoirradiation of polymer films
containing azobenzene moieties with non-polarized light. Upon slantwise
irradiation of polymer thin films with non-polarized visible light, photodichroism
was generated in a thin film of an amorphous polymer even though the level
of the optical anisotropy was small compared to that induced by linearly
polarized light irradiation. In other words, the orientational direction
of azobenzene chromophores can be controlled by the propagation direction
of actinic light as a result of physical reorientation of the chromophores.
The main purpose of this report is to investigate the photocontrol of three-dimensional
orientation of a liquid-crystalline polymer with azobenzene side chains.
The extent of the three-dimensionally photoaligned orientational order
of azobenzene residues was considerably enhanced and stabilized by the
formation of aggregates owing to the liquid crystallinity, which was revealed
by measurement of polarized absorption spectra. The optical anisotropy
generated by non-polarized light irradiation was much increased by annealing
at temperature close to glass transition temperature.
MICROSTRUCTURE AND MORPHOLOGY OF SELF-ASSEMBLED LIQUID
CRYSTALLINE MATERIALS. Hee-Tae Jung , Dept. of Chemical Engineering, University
of California, Santa Barbara, CA; Steven D. Hudson, Virgil Percec, Department
of Macromolecular Science and Engineering, Case Western Reserve University,
We present new examples of hexagonal columnar and cubic
thermotropic liquid crystalline phases by transmission electron microscopy.
The phase symmety, dimension and local structure of the amphiphilic molecules
have been determined by controlling the orientation of the mesophase by
surface anchoring and thermal treatment. Low surface energy planes were
revealed by the faceting of discontinuous films. For polymeric materials,
in which the backbone is contained within the cylinder core, homeotropic
alignment was possible only when the film thickness was significantly larger
than the mininum size of the polymeric cylinders. The stiffness and microstructure
of the mesophase are also discussed.
LIQUID CRYSTALLINE ZINC CHLORIDE. James D. Martin , Todd
A. Thornton, Department of Chemistry, North Carolina State University,
The templated syntheses of our zeolite-type copper zinc
chloride frameworks frequently result in the formation of glassy phases
or viscous liquids that might be described as ambient temperature molten
salts. Having discovered that certain of these materials exhibit remarkable
birefringence, we have investigated the structure of both the glass and
liquid forms of alkylammonium templated zinc chloride materials by neutron
and X-ray diffraction, as well as by DSC and polarizing microscopy techniques.
Further template control using alkylammonium surfactants as directors has
yielded an entire family of liquid crystalline materials with up to 90%
inorganic content. For certain phases, liquid crystallinity has been observed
from between 275 C to below room temperature. The phase characteristics
of this unique family of anionic, inorganic liquid crystals willl be described
in terms of the relation between the structure of glassy and liquid zinc
chloride and a lamellar structure commonly found for surfactant based metallomesogens.
STUDY ON THE BULGE OF TN ELECTRO-OPTICAL PERFORMANCE
CURVE. Xinyu Zhu , Xibin Shao, Tao Yu, Zhihua Ling, Kai Ma, Ximin Huang,
Changchun Institute of Physics, Chinese Academy of Sciences, Changchun,
P.R.CHINA; North LCDs Research and Development Center, Changchun, P.R.CHINA.
There exists a bulge in TN Electro-Optical performance
Curve. Here we measure the TN EO curve for visible Light and some monochromatic
light: 450nm, 500nm, 550nm, 600nm, 650nm and 700nm. In the experiment,
we keep the polarizer and analyzer vertical to each other and change the
angle between polarizer and rubbing direction. We make comparison among
them. Based on the comparison, we get the following three important results.
First, with increase of wavelength of monochromatic light, the voltage
where occurs the bulge will decrease. This is because the phase retardation
of light is inversely proportional to the wavelength of light and the light
distance of two waves will decrease with the increase of operating voltage
near the threshold voltage. While for visible light the place where occurs
the bulge is close to that of 550nm, this is because the measurement of
electro-optical curve for visible light is corrected by the visible spectrum
sensitive function. Second, with increase of the angle between polarizer
and rubbing direction from 0 degree to 45 degrees, the transmission of
light in the place of bulge will decrease. While the angle increase from
45 degrees to 90 degrees, the transmission will increase evidently. This
is because that if the angle between polarizer and rubbing direction is
not equal to 0 degree of 90 degrees, the light in the liquid crystal layers
is far from linear polarization. This leads to the polarized state of output
light also in the nonlinear polarized state, hence reduce the transmission.
Three, when the angle between polarizer and rubbing direction is 90 degrees,
the contrast ratio is higher than in the condition of 0 degree. This is
because the effect of pretilt angle. This explains the reason that for
conventional commercial TN LCDs, the polarizer is often vertical to the
STUDY OF LC MATERIAL'S ELASTIC CONSTANTS IN MAGNETIC
FIELD. Yan Shi , Zhu Xinyu, Yu Tao, Ma Kai, Huang Ximin, Changchun Inst.
of Physics, Chinese Academy of Science, CHINA; North LC R&D Center,
By using the magnetic field measurement of LC elastic
constants, we got the ratio of splay elastic constant and bend elastic
constant (k3/k1), and the ratio of twist elastic constant and bend elastic
constant (k2/k1), then got the value of k1, k2, k3 through calculation.
The devlation brought while measuring elastic constant by using electric
field measurement is greatly diminished by using magnetic field measurement.
The magnetic field measurement of LC elastic constants is both in favor
of studying the aligning mechanism and the anchoring energy of the LC molecule
surfaces, and in favor of optimizing the apparatus parameter of LCD implement.
SESSION D7: NEW EMERGING TECHNOLOGIES
8:30 AM *D7.1
TWO-DIMENSIONAL SUPERLATTICE SELF-FORMED BY NOVEL IONIC
LIQUID CRYSTALS AND ITS PHOTOFUNCTIONAL PROPERTY. Akihiko Kanazawa , Tomiki
Ikeda, Tokyo Inst. of Technology, Research Laboratory of Resources Utilization,
Chairs: Tisato Kajiyama and Patrick J. Hood
Wednesday Morning, April 7, 1999
The ability to control structure of organizations at the
molecular or atomic levels is very important in development of new functionalized
materials. In crystalline materials, it is usually difficult to control
the crystalline structure and the molecular arrangement in the bulk. Practical
applications in magnetic, optical, or electrical materials are therefore
limited by the ease with which single crystals of a given material can
be grown. Liquid crystals have self-assembly characteristics and provide
additional features such as an ability to respond to applied external fields.
Such self-assembled materials may be one of the most potential groups for
applications in high-performance devices. In this study, we present a new
concept ``in-plane ferroelectrics'' as a two-dimensional acentric superlattice.
Its existence was revealed through the evaluation of second-order nonlinear
optical property of the multilamellar assembly organized by the phosphonium
liquid crystals which are novel thermotropic liquid crystal composed of
non-metal ions and long alkyl segments. In a two-dimensional ionic layer
within the phosphonium assembly, it was found that spontaneous polarization
(Ps) occurs because of the spontaneous displacement of ions. The Ps directions
in each in-plane ferroelectrics could be controlled by application of an
electric field. Through the theoretical calculations, such unusual ferroelectric
feature was found to originate from the variety of bonding manner (i.e.,
the characteristic electronic structure) of phosphorus atom. Furthermore,
it was found that introduction of bivalent metal ions into the amphiphiles
leads to enhancement of the thermal properties. The metal-containing ammonium
complexes showed a stable liquid-crystalline phase in the expanded temperature
range in comparison with the parent compounds. These ionic metallomesogens
formed organizations with layered structure based on two-dimensional arrangement
of the metal ions, i.e., ``sheet metal complex'' which was separated by
the insulating alkyl segments.
9:00 AM D7.2
ORIENTED PEARL-NECKLACE ARRAYS OF METALLIC NANOPARTICLES
IN POLYMERS: A NEW ROUTE TOWARDS POLARIZATION DEPENDENT COLOR FILTERS.
Yvo Dirix , Cees Bastiaansen, Walter Caseri, Paul Smith, ETH Zurich, Dept.
of Materials, Zurich, SWITZERLAND.
Nanocomposites of high-density polyethylene containing
surface-coated silver or gold nanoparticles were prepared by melt-extrusion
or solution-casting techniques. The nanocomposites were subsequently oriented
by drawing in the solid state at temperatures close to, but below the melting
temperature of the polyethylene. It was found that the absorption spectrum
in the visible wavelength range of the drawn nanocomposites strongly depends
on the polarization direction of the incident light. For instance, the
polyethylene/silver nanocomposites appear bright yellow and bright red
in linearly polarized light with its vibration direction, respectively,
perpendicular or parallel to the drawing axis. The optical anisotropy of
the drawn nanocomposites originates from uniaxially oriented, pearl-necklace
type of arrays of nanoparticles possessing high aspect ratios. The color
of the composites in polarized light can be tuned either by using different
metals (silver versus gold), or by varying the size of the nanoparticles.
For example, annealing of the polyethylene/silver nanocomposite prior to
drawing results in an increase of the particle size, due to Ostwald ripening,
and consequently a range of polarization dependent colors can be generated
in the drawn films. These polarization dependent color filters are potentially
useful in LCD applications. A conventional color LCD switches between a
colored (off) state and a dark (on) state, were no light is transmitted.
In a new display set-up, a single polymer/metal nanocomposite film with
a polarization dependent color replaces both the polarizer (analyzer) and
color filter. The latter transmits colored light in both the on and off
state, which in principle raises the brightness and light efficiency of
9:15 AM D7.3
POLYMER ULTRATHIN FILMS VIA ALTERNATE SELF-ASSEMBLY ADSORPTION
OF POLYELECTROLYTE AND AZO-DYE MOLECULES: PHOTO-INDUCED ALIGNMENT AND LC
DISPLAY PROPERTIES. Rigoberto C. Advincula , Department of Chemistry, University
of Alabama at Birmingham, AL; Akira Baba and Futao Kaneko, Department of
Electrical Engineering, Niigata University, Niigata, JAPAN.
The fabrication and characterization of ultrathin polymer
films containing photoisomerizable azo dyes is described. These films are
fabricated using the alternate-polyelectrolyte self-assembly adsorption
technique of polyions originally described by Decher and co-workers. While
most materials reported involves oppositely charged polyelectrolytes, we
report the use of a small molecule dye/ polymer combination. Surface sensitive
spectroscopic and microscopic investigations were made to elucidate the
formation of the thin film on a layer-by-layer basis. We used these dyes
to influence the packing arrangement and ordering in these ultrathin films.
We investigated their photoisomerization characteristics in polarized light
and compared them with similarly investigated spin-coated films. The substrates
were subsequently used to investigate LC alignment properties for the so-called
command layer effect. A rearrangement of the dye long-axis perpendicular
to the direction of polarization was observed. This dramatically affected
the layer ordering and orientational properties of the substrate.
9:30 AM *D7.4 OPTICAL PROPERTIES AND APPLICATIONS
OF NEMATIC GLASSY LIQUID CRYSTALS. Patrick J. Hood , Cornerstone Research
Group, Inc., Dayton, OH; John C. Mastrangelo and Shaw H. Chen, Center for
Optoelectronics and Imaging, University of Rochester, Rochester, NY.
Glassy liquid crystal (GLC) materials are a relatively
new class of organic material which possess the properties of conventional
nematic low-molar-mass liquid crystals at temperature above the glass transition
temperature (Tg) and the properties of a hard plastic
at temperatures below Tg. Originally, this class of material
was developed for passive optical devices, however, recent research offers
the promise of novel active devices. In this paper, we review the structural
and physical properties of GLC materials, the temperature- and wavelength-dependence
of the GLC films, as well as device applications for this new class of
materials. The performance of passive devices as well as novel active devices
will be discussed in relation to the unique properties of the materials.
Finally, a discussion of the future directions being pursued and improvements
necessary in materials performance required to commercialize devices based
on this technology are presented.
10:30 AM *D7.5
ADVANCES IN REFLECTIVE HOLOGRAPHIC POLYMER DISPERSED
LIQUID CRYSTAL TECHNOLOGY. Chris C. Bowley , Gregory P. Crawford, Department
of Physics and Division of Engineering, Brown University, Providence, RI.
Holographically-formed polymer dispersed liquid crystals
(H-PDLCs) have been demonstrated in both reflection and transmission mode.
These materials are a natural evolutionary step from regular polymer dispersed
liquid crystals (PDLCs), discovered in the mid-1980's. Their formation
in an interference fringe pattern, instead of a blanket-exposure, results
in a spatial modulation in the density of liquid crystal droplets through
the polymer binder. In regular PDLCs, LC droplets are randomly scattered
through the binder. In the off-state, the random orientation of the droplet
directors throughout the sample results in a net refractive index mismatch
between the polymer-rich and LC droplet-rich planes. In this state the
H-PDLC behaves as a regular holographic grating. The application of an
electric field causes the directors to align and the refractive index modulation
is cancelled out. The material no longer behaves as a grating and transmits
all incident radiation. H-PDLCs show great promise for various applications,
including reflective displays, diffractive optics, fiber optics and as
filters for remote sensing. For display applications, the reflection efficiency
of volume H-PDLCs cannot, for practical purposes, be increased by making
the cell arbitrarily thick because of the implications on driving voltage.
It is important, therefore, to maximise the separation of LC and polymer
into Bragg planes thereby maximising the intrinsic effciciency of these
holograms. We report on improved reflection efficiency of volume H-PDLCs
formed using commercially available, high-functionality acrylate monomers.
We compare the performance of these H-PDLCs to those formed from similar
monomers of lower functionality. We also report on novel H-PDLCís exhibiting
two distinct reflection peaks. A simple phenomenological model is presented
to describe this effect.
11:00 AM D7.6
PHOTOLUMINESCENCE FROM THE RESONANCE REGION OF VITRIFIED
CHIRAL-NEMATIC FILMS. Dimitris Katsis , Richard Jin, Ansgar W. Schmid,
Shaw H. Chen, Materials Science Program and Chemical Engineering Department,
NSF Center for Photoinduced Charge Transfer and Laboratory for Laser Energetics,
University of Rochester, Rochester, NY; Tetsuo Tsutsui, Department of Materials
Science and Technology, Kyushu University, JAPAN; Thomas N. Blanton, Analytical
Technology Division, Eastman Kodak Company, Rochester, NY.
Luminophores such as Exalite 428 and Eu-complexes were
placed in vitrifiable chiral-nematic liquid crystalline films via doping
and functionalization. The polarization state of photoluminescence (PL)
with UV-excitation from the selective reflection region of the host was
analyzed. Novel features were observed: (1) nearly pure circularly polarized
emission; and (2) handedness reversal of emitted light in a single-handed
host. New insights into PL from periodically structured films will be presented.
11:15 AM D7.7
MID-WAVELENGTH IR (MWIR) POLARIZERS FROM GLASSY CHOLESTERIC
LIQUID CRYSTALS. P.T. Mather , W. Barnes, T.J. Bunning, AFRL/MLBP and MLPJ,
Materials and Manufacturing Directorate, WPAFB, OH; P.J. Hood, Cornerstone
Research Co., Dayton, OH.
The investigation of glass forming liquid crystalline
materials for mid-wave infrared polarization applications is driven by
their low melt viscosity and ability to vitrify order and thus functionality
into films with a wide range of thicknesses. Commercially available polarizers
which function in the mid-wave infrared region suffer from poor polarization
contrast, high cost, and limited size. In this work, we explore the feasibility
of using cyclic siloxane-based LCs with chiral mesogens to form circular
polarizers in the mid-wave infrared spectrum (3-5 mm). Specifically, we
have designed a cholesteric molecular blend to possess the proper helical
twisting power to exhibit a selective reflection notch in the 4.0-4.5 micron
region. We have fabricated circular polarizers using shear under a number
of processing conditions and explored their performance as measured by
polarization contrast. Processed films with reflection notches at the proper
wavelength and near theoretical reflection performance have been prepared.
The use of simple alignment layers was demonstrated to yield consistent
formation of Grandjean monodomains by reducing the tendency of the large
pitch blends to spontaneously form a fingerprint molecular orientation
observed in cells with untreated surfaces. The measured polarization contrast
of >70:1 exceeds the values obtained from state-of-the art commercial polarizers
in this wavelength regime.
11:30 AM D7.8
EFFECT OF NETWORK ELASTICITY ON NEMATIC LIQUID CRYSTAL/CROSSLINKED
POLYMER PHASE DIAGRAM. Domasius Nwabunma, Thein Kyu , Institute of Polymer
Engineering, The University of Akron, OH; Robert T. Pogue, SAIC, OH; Timothy
J. Bunning, AFRL/MLPJ, Materials and Manufacturing Directorate, WPAFB,
The influence of elasticity on the phase behavior of a
mixture of nematic liquid crystal (LC) and crosslinked polymer has been
investigated. The LC used is the low molar mass eutectic mixture E7, while
the polymer network was made in-situ from crosslinking photopolymerization
of a mixture of two monomers: dipentaerythrol hydroxylpentaacrylate (DPHPA)
and N-vinylpyrrollidone (NVP) using a mixture of two photoinitiators: Rose
Bengal (RB) and N-phenylglycine (NPG). Of particular significance is that
the experimental phase diagram supported by theoretical calculation showed
no critical point.Instead, the binodal curve exhibits an upward asymptotic
behavior as E7 concentration approaches unity due to domination arising
from network elasticity. An examination of the effect of average repeat
units between cross-links and network functionality on the theoretical
phase diagram of E7/crosslinked polymer showed that, although both parameters
exert similar effect, the former parameter exerts a greater influence.
11:45 AM D7.9
EFFECT OF PROCESSING VARIABLES ON THE MAGNETIC FIELD
ORIENTATION OF LIQUID CRYSTALLINE THERMOSETS. Derek M. Lincoln and Elliot
P. Douglas , Department of Materials Science and Engineering, University
of Florida, Gainesville, FL.
We have determined the effect of magnetic field processing
on the orientation and properties of the 4,4-bis(2,3-epoxypropoxy)- -methylstilbene
(EPAMS)/sulfanilamide (SAA) epoxy system. A statistical experimental design
was generated and analyzed to determine the effects of the time in the
magnetic field, field strength, and the amount of B-staging. A regression
model with a coefficient of determination of 0.8577 was calculated to predict
the orientation parameter for the input variables. An optimization study
was also conducted to check the prediction of the orientation parameters
by the model. The model can predict the experimentally measured orientation
in regions where the model predicts physically realistic values for the
orientation. Physical properties of the oriented material have also been
measured. The tensile modulus increases with increasing field strength,
and fits a simple model for the modulus of anisotropic materials.