Molecular Liquid Crystals Research Articles

Hierarchical Assembly of a Series of Rod−Coil Block Copolymers: Supramolecular LC Phase in Nanoenviroment

A series of narrowly distributed rod−coil diblock copolymers, poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS−PMPCS), were synthesized by 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-mediated living free radical polymerization. Differential scanning calorimetry, wide-angle X-ray diffraction, small-angle X-ray scattering, polorized light microscopy, and transmission electron microscopy were used to study the phase structure of this series of rod−coil polymers. It was found that the block copolymers microphase separate into ordered structures at temperatures below ca. 240 °C. PMPCS blocks form supramolecular columnar nematic phase (φN) within the microphase-separated block copolymers. LC columnar axes were identified to be parallel to the block copolymer lamellar normal. Two layers of LC columns are confined in each LC domain, and the hierarchical structure resembles the “bilayer smectic A” phase observed in small molecular liquid crystals and rod−coil oligomers.

Preparation of photo-crosslinked films of new Chalcone-based side chain type liquid crystalline polymers and its application to alignment film

We synthesized two kinds of side chain type polymers containing chalconyl moieties to investigate the alignment's capability of photo-crosslinked polymer films. One is methacrylate type polymer having the chalconyl moiety in the side chain, and the other is imide type polymer. A smectic phase was exhibited for the methacrylate type polymers, while no mesophases were observed for the imide type polymer. These polymer films were irradiated with linearly polarized UV (LPUV) light (350 nm) under different conditions. The liquid crystalline (LC) cell was fabricated from the polymer film irradiated with LPUV light to examine the alignment properties of low molecular liquid crystal on the film. A mixture of a low molecular liquid crystal and a dichroic dye was filled in the LC cells. Alignment behavior of the low molecular liquid crystal was discussed by the dichroic ratio of the dichroic dye in the LC cell.

片側パターン電極における低分子液晶系ER流体のER効果の発現(アクチュエータの機構と制御2)

片側パターン電極における低分子液晶系ER流体のER効果の発現(アクチュエータの機構と制御2)

Growth of Polystyrene Domains in Isotropic, Nematic and Smectic Phase of 8CB Liquid Crystal

A small-angle light-scattering (SALS) technique is performed to investigate the phase separation in the films of flexible polymer (polystyrene, PS) mixed with low molecular weight thermotropic liquid crystal LC (4-cyano-4‘-n-octylbiphenyl, 8CB). The growth of isotropic (polymer) domains is studied in both isotropic and anisotropic (nematic or smectic phase) LC matrices, as a function of time, film thickness, and film composition. The size of the domains, L(t), grows algebraically with time as L(t) ∼ tβ. For 70/30 wt % of 8CB/PS, we found the diffusion growth in isotropic (β = 0.25) and smectic (β = 0.28) matrices, independent of the film thickness. In the nematic matrix, β changes from 0.33 to 0.47 as we change the thickness of the sample from 120 to 10 μm. We think that the change of β is due to the attractive forces between the polymer domains which follow from the elastic deformations of the nematic matrix caused by the glass surfaces and polymer domains. In every matrix and for different thicknesses of a sample, scaling is observed in this growth regime. At longer times, there is a crossover from the diffusion growth to the hydrodynamic fast-mode growth, characteristic for systems in which one of the components wets the confining walls. In this regime, we do not observe the scaling; i.e., there is more than one characteristic length scale in the system, and β ranges from 1 to 3/2. Considering extremely viscous systems (50/50 wt % of 8CB/PS), we also find the diffusion growth but with smaller exponent β < 0.2. In this case, we observe two peaks in the scattering intensity S(q,t). One of them is the surface and one the bulk peak. For systems with small amount of a polymer (90/10 wt % of 8CB/PS), the process of growth is very fast, and β = 0.4. In this case, the bulk peak is very quickly covered by the peak coming from the growth of the domains at the surface. To perform the measurements in anisotropic LC systems, we had to eliminate the multiple scattering of light coming from the large difference in ordinary and extraordinary refractive indexes of LC.

U.S. Court of Appeals, Fifth Circuit: Larry Thompson et al. v. Mastercard International Inc. et al.

Gaming Law ReviewVol. 7, No. 1 Full Text CasesU.S. Court of Appeals, Fifth Circuit: Larry Thompson et al. v. Mastercard International Inc. et al.Published Online:6 Jul 2004https://doi.org/10.1089/109218803762871926AboutSectionsPDF/EPUB ToolsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetailsCited ByProperties of Indium Zinc Oxide Films on Various Polymer Substrates Deposited by Low-Frequency 60 Hz Magnetron Sputtering Method22 September 2010 | Molecular Crystals and Liquid Crystals, Vol. 470, No. 1Shooting the Messenger: The Ethics of Attacks on Environmental RepresentationSSRN Electronic Journal, Vol. 17 Volume 7Issue 1Feb 2003 To cite this article:U.S. Court of Appeals, Fifth Circuit: Larry Thompson et al. v. Mastercard International Inc. et al..Gaming Law Review.Feb 2003.61-67.http://doi.org/10.1089/109218803762871926Published in Volume: 7 Issue 1: July 6, 2004PDF download

Charge Carrier Transport in Polymeric Smectic Liquid Crystals

Recently the liquid crystals are being recognized to be a quality organic semiconductor, since the fast charge carrier transport was discovered in some types of liquid crystals including discotic (disk-like) and calamitic (rod-like) liquid crystals. In the present study, we have synthesized a polymeric liquid crystal exhibiting smectic (Sm) mesophases, i.e., polyacrylates having 2-phenylnaphthalene moiety as mesogenic group (PNP-acrylate) and investigated its charge carrier transport properties by time-of-flight experiments. We found that the smectic A phase of the polymer exhibited a high hole mobility of 10&#x2212;4 cm2/Vs, which was comparable to that in the smectic A phase of small molecule, 2-phenylnaphthalene derivatives. Furthermore, the fast hole transport was also observed in Sm glassy phase at ambient temperatures, when a small amount of 2-phenynaphthalene derivative was added to the polyacrylate. These facts indicate that the Sm mesophases in polymeric liquid crystals exhibit fast charge carrier transport comparable to the small molecular weight Sm liquid crystals basically.

Stationary statistical size distribution of nematic droplets in the course of the isotropic liquid-nematic phase transition

The statistical size distribution of nematic droplets in the course of the phase transition isotropic liquid-nematic has been analysed using polarizing optical microscopy and described by the model of reversible aggregation. The materials under investigation are low molecular mass nematics, polymeric nematics and polymer dispersed liquid crystals observed at their clearing temperatures in the stationary time regime.

Theory of bent-core liquid-crystal phases and phase transitions.

We study phases and phase transitions that can take place in the recently discovered bow-shaped or bent-core liquid-crystal molecules. We show that to completely characterize phases exhibited by such bent-core molecules a third-rank tensor T(ijk) order parameter is necessary in addition to the vector and the nematic (second-rank) tensor order parameters. We present an exhaustive list of possible liquid phases, characterizing them by their space-symmetry group and order parameters, and catalog the universality classes of the corresponding phase transitions that we expect to take place in such bent-core molecular liquid crystals. In addition to the conventional liquid-crystal phases such as the nematic phase, we predict the existence of other liquid phases, including the spontaneously chiral nematic (N(T)+2)(*) and chiral polar (V(T)+2)(*) phases, the orientationally ordered but optically isotropic tetrahedratic T phase, and a nematic N(T) phase with D(2d) symmetry that is neither uniaxial nor biaxial. Interestingly, the isotropic-tetrahedratic transition is continuous in mean-field theory, but is likely driven first order by thermal fluctuations. We conclude with a discussion of smectic analogs of these phases and their experimental signatures.

The external electric field effects on the morphology of phase separation in a mixture of liquid crystal/flexible polymer

In this article, the morphologies of phase separation in the mixtures of small molecular liquid crystal and flexible polymers with or without being subjected to the external electric field are preliminarily studied by polarized light microscope. It is found that the characteristic “Swiss cheese” morphology can always be observed for the case of zero field strength. For the case of 1.2 V/μm field strength, it is found that the external electric field make the binodal curves of the phase diagrams shift to higher temperature and the “Swiss cheese” morphology can never be observed. However, the domain growth rate is highly accelerated due to the fact that the electric field oriented liquid crystal phase excludes the polymer coils strongly. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 250–258, 2002

Mixed-Valence State of a One-Dimensional Platinum Complex with a Counter Ion Having Two Alkyl Chains and its Liquid Crystal Phase

We have investigated optical property and crystal structure of a one-dimensional halogen-bridged platinum complex (MX chain compound) with a counter ion having two alkyl chains, [Pt(en) 2 ][PtCl 2 (en) 2 ]{(CH 3 (CH 2 ) 7 CO 2 ) 2 CH 2 CHSO 3 } 4 2H 2 O, to elucidate influence of molecular fastener effect of the long alkyl chain on mixed-valence state of the platinum atoms. Thermal-behavior observations of the complex were also performed using a polarizing optical microscope without and with crossed nicols to examine thermal change of the mixed-valence state and appearance of the liquid crystal phase. Consequently, the complex has exhibited that the interaction between the platinum atoms is strengthened and the Pt II -Pt IV distance is shortened by doubling the number of alkyl chains around the platinum complex moieties compared with a corresponding PtCl chain complex with a single alkyl chain counter ion. We have also observed a texture of liquid crystal at about 200C. Mixed-Valence State One-Dimensional Halogen-Bridged Platinum Complex Long Alkyl Chain Molecular Fastener Effect Liquid Crystal Phase

Synclinic–anticlinic phase transition in tilted organosiloxane liquid crystals

In this paper, we considered the case of low molecular weight bimesogenic liquid crystals containing a siloxane moiety as the central part of their molecular architecture. For some of these compounds, both ferro- and antiferroelectric mesophases are present. Two distinct smectic structures can develop as a function of temperature, the first one at high temperature corresponding to a synclinic molecular arrangement with elongated molecules, and the second one at lower temperature corresponding to an anticlinic organisation with V-shaped molecules. Numerical calculations of the energy of different conformations of these bimesogenic molecules presented here indicate that there is no difference in energy between V-shaped and linear conformations regardless of the number of silicon atoms in the siloxane moiety. Thus a microscopic model of the synclinic–anticlinic phase transition is developed where the driving force is indeed a free energy difference between the two phases, and not a difference of energy between the V-shaped and linear conformations. The model explains why the anticlinic SmCA phase is more stable than the synclinic SmC one, why the synclinic SmC phase is generally the higher temperature one, and why in some organosiloxane materials the anticlinic SmCA phase is not present.

Rational Design of Lipid Molecular Structure: A Case Study Involving the C19:1c10 Monoacylglycerol

The phase properties of lipids have far-reaching consequences in membrane biology. Their influence ranges from domain formation in intact biomembranes to membrane protein reconstitution and crystallization. To exploit phase behavior in the spirit of rational design, it is imperative that the rules relating lipid molecular structure and liquid crystal or mesophase behavior be established. Phase behavior is quantitatively and concisely represented in the form of temperature-composition phase diagrams. A somewhat limited number of phase diagrams exists for the monoacylglycerols. The objective of the current study was to determine the quality of phase behavior prediction for a specific monoacylglycerol based on an analysis of the existing phase diagrams for related chain homologs. To this end, a phase diagram for the monononadecenoin (19:1c10)/water system was predicted in the temperature range from −15°C to 120°C and from 0% to 80% (w/w) water. The prediction was tested by constructing the corresponding phase diagram using low- and wide-angle x-ray diffraction, differential scanning calorimetry, and polarized light microscopy. The results show that the predicted and experimental phase diagrams agree remarkably well. They also highlight the need for additional phase studies of the type described to enlarge the data bank of phase diagrams and to strengthen the foundations of the rational design approach.

Photoinduced anisotropy and photoalignment of nematic liquid crystals by a novel polymer liquid crystal with a coumarin-containing side group

A new type of photo-crosslinkable methacrylate polymer liquid crystal (PLC) with a coumarincontaining mesogenic side group was synthesized and applied as the photoalignment layer for low molecular mass nematic liquid crystals. Linearly polarized ultraviolet light was directed onto a thin film of PLC under various exposure conditions. When a film was irradiated at room temperature, a small negative optical anisotropy was generated due to angular-selective photo-crosslinking. In contrast, when the film was exposed near the clearing temperature of the PLC, the induced anisotropy was positive due to thermally enhanced photoinduced reorientation of the side groups. The aggregation of the mesogenic groups was also observed when the irradiation was carried out in the liquid crystalline temperature range of the PLC. The LC alignment on the photoreacted film was greatly dependent on these irradiation conditions. It was made clear that the LC alignment was regulated by the interaction among the LC, the photo-crosslinked side groups and the remaining mesogenic side groups, and that the aggregated mesogenic groups inhibited the LC alignment.

Equilibrium Phase Properties of Polymer/Liquid Crystal Blends: Theory and Experiments

A theoretical formalism to calculate the phase diagrams of polymer/liquid crystal mixtures is presented. Mixtures involving linear and crosslinked polymers together with low molecular weight nematic and smectic-A liquid crystals are considered. The generalization to binary mixtures of nematogens is briefly shown. The method of calculating model phase diagrams of side chain liquid crystal linear and crosslinked polymers in either isotropic or nematic solvents is presented. In nematogen mixtures, the coupling parameter induces tremendous changes in the miscibility of both linear and crosslinked polymers with low molecular weight analogous or different liquid crystals. Applications of the theoretical formalism are given.

Tunable Mirrorless Lasing in Cholesteric Liquid Crystalline Elastomers

Cholesteric liquid crystals are chiral nematics, where the handedness of the constituent molecules causes the orientation of the local nematic director to vary in space. In the helical cholesteric structure, the director is perpendicular to the helix axis, and its orientation varies linearly with position along the helix axis. The spatial period of the structure is the pitch, which is determined by the concentration and the helical twisting power of the chiral constituents. As a consequence of the periodicity of the helical cholesteric structure and the birefringence of the liquid crystal, for a range of wavelengths, light propagation along the helix axis is forbidden for one of the normal modes. Since propagation is forbidden, incident light with a wavelength in this band and with the same helicity as the cholesteric is strongly reflected. The edges of this reflection band are at wavelengths that are equal to the refractive indices times the pitch. [1] Because of the existence of the selective reflection band, cholesteric liquid crystals are 1D photonic bandgap materials. The bandgap structure of cholesteric liquid crystals allows for the possibility of lasing without external mirrors that usually form a laser cavity. When a fluorescent dye is dissolved in the cholesteric host so that the peak of the fluorescent emission of the dye is in the selective reflection band of the cholesteric, propagation of one normal mode of the emitted light is forbidden. As a consequence, at low pump intensities, the fluorescence spectrum of the dye is modified, [2] showing suppression of emission in the reflection band, and enhanced emission near the band edge. As the pump intensity is increased, the linewidth of the enhanced fluorescence at the band edge narrows, and, above a pump threshold, lasing occurs. [2] Thin samples, typically 15‐30 lm in thickness, of low molecular weight cholesteric liquid crystals incorporating a variety of dyes [3] have been shown to lase. The primary role of the cholesteric liquid crystal in these systems is to act as a distributed cavity. Lasing occurs at the band edges, [2‐4] as pre

Materials Based on Glycoluril

Glycoluril, a bisurea compound known for 125 years, has during the past two decades established an impressive career as building block for supramolecular chemistry. The recent literature shows that glycoluril derivatives have a strong potential for applications in the materials sector, ranging from nanoporous materials via molecular switches, tailor-made polymers, synthetic receptors, liquid crystals, and molecular capsules to supramolecular gels.

Viscoelastic director rotation of a low molecular mass liquid crystal

We show evidence for a viscoelastic rotation of the spontaneous polarization in a low molecular mass chiral ferroelectric smectic liquid crystal (SmC*). A weak elastic modulusw of ~102 Pa is sufficient to cause a unique effect: the polarization turns perpendicular to sufficiently strong a.c. electric fields. Viscoelasticity is unusual for low molecular mass materials. We suggest that it is connected to the anisotropy of the positional order. This is an inherent property of liquid crystals, but has never been taken into account in macroscopic descriptions.

Photoelectrical Processes Near Interface of Molecular Crystals and Liquid Crystals

Photoelectric properties of heterostructures consisting of deposited films of an inorganic semiconductor (IS) - CdSSe or molecular crystals (MC) with different molecular structure (phthalocyanines of Pb, ClAlCl) and nematic liquid crystal BL055 have been studied. The main attention was given to the effect of MC molecular structure on the creation of potential barriers at MC/LC interface in heterostructures and effect of them on processes of polarization by strong absorbed light excitation and external constant electric field of different polarity.

Optical data recording by laser pulses in liquid-crystal cells with an azo-modified surface

The effect of trans-cis photoisomerisation of azofragments of a polymer film on the molecular reorientation ofa liquid crystal is studied. It is shown that, using nanosecondlaser pulses, one can perform both the reversible and staticdata recording in liquid-crystal cells with an azo-modified surface. The rise time of the reorientation is measured by themethods of dynamic holography to be about ~ 30 μs, and thegrating efficiency achieves 15 %.

Dipole Dynamics and Macroscopic Alignment in Molecular and Polymeric Liquid Crystals by Broad-Band Dielectric Relaxation Spectroscopy

A liquid crystal monomer (LCM) was synthesized and attached as a side chain to a siloxane polymer (SCLCP). The molecular dynamics of LCM and SCLCP were investigated by broad-band dielectric relaxation spectroscopy (DRS) over 10 decades of frequency. The surface treatment of the electrodes was found to have a pronounced effect on the macroscopic alignment and dynamics. In the isotropic state the relaxations in LCM and SCLCP are well-described by the Kohlrausch−Williams−Watts (KWW) functional form. In the LC state, the overall dielectric response is a weighted sum of two dispersions that depend on the macroscopic alignment. The hometropic (H) alignment is dominated by the (slower) δ process, while the planar (P) alignment is dominated by the (faster) αm process. Both processes are symmetric and can be described by Cole−Cole (CC) or Fuoss−Kirkwood (FK) functional forms. The δ process governs the dynamics in the SCLCP near the glass transition, similar to the segmental α process in non-LC glass formers. Excellent agreement was observed with the various aspects of the seminal work by Attard and Williams.