Molecular Orientation State Research Articles

Simple Stokes polarimeter using a liquid crystal grating with ternary orientation domains.

We propose a liquid crystal (LC) grating with a ternary orientation domain for application to optical polarization measurements. The ternary orientation domain, which generates two-dimensional diffraction properties, is the key to simultaneous acquisition of multiple of polarization parameters. The LC molecular orientation state and the polarization dependence of the diffraction efficiency were investigated experimentally, focusing on the applicability to a practical Stokes polarimeter. An experiment was conducted using the proposed LC grating as a Stokes polarimeter, and the four Stokes parameters (S0, S1, S2, and S3) were determined for linearly and circularly polarized incident light. As a result, the feasibility of the proposed LC grating Stokes polarimeter has been demonstrated experimentally. Finally, the operational performance of the proposed LC grating Stokes polarimeter is discussed using a figure of merit that is numerically derived from the measured polarization dependence of the diffracted light intensity.

Non-destructive characterisation of all-polypropylene composites using small angle X-ray scattering and polarized Raman spectroscopy

Small angle X-ray scattering (SAXS) and polarized Raman spectroscopy were used to examine the structure of unidirectional all-polypropylene composites prepared at different consolidation temperatures. Analysis of the anisotropy of the X-ray scattering pattern provided a way to quantify the disorientation of the crystallites and a direct correlation has been found between a measure of overall orientation and the Young’s modulus of the composites. In the case of the Raman spectroscopic measurements, the molecular orientation state of the reinforcing PP fibres were evaluated by classical least squares (CLS) modelling with real reference spectra. Strong correlation was evinced between the estimated relative degree of orientation of the reinforcing fibres and the Young’s modulus of the multi-layered all-polypropylene composites. Based on these results, both SAXS and Raman spectroscopy are suitable methods to predict the mechanical performance of all-polymer composites, being especially sensitive to manufacturing and application conditions, in a non-destructive way.

(Keynote) Dimensional Change of Oriented Polymers upon Heating

Molecular orientation can be incorporated to the polymeric materials through either stretching in a solid state or elongation in a molten state. When a polymer has molecular orientation in a glassy state, shrinkage may proceed when temperature is increased above its glass transition temperature. Degree of shrinkage may vary depending on the temperature reached and the degree of molecular orientation. In the case of crystalline polymers, however, shrinkage may be suppressed because of the occurrence of crystallization prior to the shrinkage. It should be noted that the crystallization rate can be accelerated significantly with the increase of molecular orientation. Accordingly, there can be a critical degree of molecular orientation; below which orientation relaxation proceeds upon heating, whereas above which spontaneous orientation enhancement caused by crystallization proceeds upon heating. In some cases, even the spontaneous elongation of materials takes place along with the progress of crystallization. On the other hand, it is well known that the dynamics of polymeric materials is characterized by the wide range of relaxation time. This means that the state of molecular orientation can be manipulated through the combination of deformation/flow history and temperature history. Dimensional change of oriented polymeric materials upon heating is mainly governed by the oriented structure of relatively long relaxation time such as network structure of molecular entanglement. Based on this concept, we could prepare fibers which showed no birefringence but exhibited significant shrinkage with the increase of temperature. This is possible because birefringence merely reflects the degree of orientation of relatively short segments, i.e. short relaxation time, in the polymer chain. Concept of manipulating the oriented structure of wide range of relaxation period leads to the idea of controlling the state of molecular entanglement. Based on this concept, we speculated that the polymeric materials of high strength and high toughness can be prepared if the material has rather homogeneous state of molecular entanglement, i.e. narrow distribution of molecular weight between adjacent entanglement points. As-spun poly(ethylene terephthalate) (PET) fibers with rather homogeneous state of molecular entanglement was prepared through the control of melt spinning process. Applying the drawing and annealing processes to such as-spun fibers, high-strength PET fibers were prepared. To verify the applicability of the concept of homogeneous state of molecular entanglement, PET fibers prepared under various processing conditions were analyzed using the laser Raman spectroscopy. It was found that the narrow distribution of internal stress field and limited widening of such distribution upon applying the tensile stress to the fibers are the key factors for realizing the high-strength and high-toughness.

Acceleratory and inhibitory effects of uniaxial tensile stress on the photo-oxidation of polyethylene: Dependence of stress, time duration and temperature

The photo-oxidation behavior of high density polyethylene (HDPE) subjected to uniaxial tensile stress is investigated at various temperatures, tensile stress levels and time durations. The effect of stress on the photo-oxidation rate of HDPE is found to be non-monotonous. Tensile stress is found to play distinctly different roles, namely showing acceleratory or inhibitory effect, with the elapse of aging time and at different temperatures. Stress-induced aging inhibition is prone to occur at low temperatures and high stresses within an appropriate aging duration. With elevating temperature, however, this inhibition effect disappears gradually and the stress is found to accelerate the aging process. Microstructural analysis reveals that the effect of stress is closely related to the interplay between the changes in the surface morphology as well as amorphous aggregation structure of materials and the photochemical degradation during aging, which is induced by the variation of molecular orientation and packing state in amorphous region, stress transfer efficiency, thermodynamic and kinetic aspects of photochemical reaction process.

Nuclear Magnetic Resonance Spectroscopy

n/a

Room-temperature magnetoelectric effect in a chiral smectic liquid crystal

A direct magnetoelectric effect, an induction of electric polarization by a magnetic field, was observed at room temperature in a chiral smectic liquid crystal without magnetic metals or radicals. Our detailed measurements of the magnetoelectric effect and the magnetodielectric effect suggest a unique origin of the magnetoelectric coupling in the liquid crystal, that is, a magnetic-field manipulation of the molecular orientation state, which is closely coupled with a local electric dipole moment due to the chirality-induced symmetry breaking. This unconventional strategy based on the softness of liquid crystals provides one of the promising directions towards the achievement of room-temperature metal-free magnetoelectrics.

Orientational Glasses: NMR and Electric Susceptibility Studies

We review the results of a wide range of nuclear magnetic resonance (NMR)measurements of the local order parameters and the molecular dynamics of solid ortho-para hydrogen mixtures and solid nitrogen-argon mixtures that form novel molecular orientational glass states at low temperatures. From the NMR measurements, the distribution of the order parameters can be deduced and, in terms of simple models, used to analyze the thermodynamic measurements of the heat capacities of these systems. In addition, studies of the dielectric susceptibilities of the nitrogen-argon mixtures are reviewed in terms of replica symmetry breaking analogous to that observed for spin glass states. It is shown that this wide set of experimental results is consistent with orientation or quadrupolar glass ordering of the orientational degrees of freedom.

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets.

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90° between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90° between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Azobenzene-containing polymers for photonic crystal materials

By interaction between light and structural periodicity, structural coloration is caused. The artificially periodic materials are called photonic crystals and it has attracted great attention for optical applications. Recently, we prepared one-dimensional photonic crystal with multibilayered films consisting of azobenzene-containing polymers and polyvinyl alcohol and reported the on–off switching controlled by refractive index change depended on the molecular orientation states. In addition, we studied the birefringence properties of azobenzene-containing polymers based on their molecular design for the improvement of the switching speed and reflection intensity of photonic crystals.

Driving voltage properties sensitive to microscale liquid crystal orientation pattern in twisted nematic liquid crystal cells

We investigated the micropattern-sensitive driving voltage properties of twisted nematic liquid crystal (LC) cells and found that the threshold voltage for inducing the Fréedericksz transition strongly depends on the micropatterned LC molecular orientation state. We discuss the effects of various cell parameters such as the period of the micropattern Λ, the LC layer thickness d, and the twist angle Φ on the threshold voltage. By a computer simulation of the LC molecular orientation, we found that the threshold voltage Vth varies in response to the deformation factor Δ (= d2/Λ2 + Φ2/π2) of the spatially distributed LC molecular orientation. We confirm that is proportional to 1 − Δ from both theoretical and experimental standpoints.

Oxidized Lipids in Model Membranes: Atomistic Details from Solid-State NMR Experiments and MD Simulations

The unavoidable presence of reactive oxygen species (ROS) causes oxidation of lipids in the human body. In the last years, several studies have been published showing evidence for a high increase of the concentration of peroxidized lipids in tissues under different pathological conditions e.g. in Parkinson's disease, multiple sclerosis, kidney damage, preclampsia, cataracts and others. However, the effect of peroxidized lipids on lipid model membranes is still rather unknown at the molecular level. We present an atomistic description of the effect of the peroxidized lipid 1-palmitoyl-2-azelaoyl-sn-glycero-3-phosphocholine (PazePC) on different model membranes. By combining solid-state NMR measurements of 1H-13C dipolar couplings in multilamellar vesicles with molecular dynamics (MD) simulations of small bilayer patches (128 lipids), we interpret the molecular structure, orientation and protonation state of PazePC and its effect on two different model membranes (POPC and DPPC). A striking observation is that the protonation state and orientation of the oxidized chain is sensitive to the bilayer environment, namely that saturated or unsaturated environments influence the pKa of the carboxylic acid and therefore the interfacial charge of the bilayer.

Computing of the Molecular Orientation State of the Lubrication Layer

The algorithm and software for computing the order parameter value describing structural sequence in the molecular model of the boundary lubrication layer have been created. It has been shown that computer estimation of a supramolecular self-organization together with a new method of polarization tribometry can enhance the efficiency of new lubrication composition creation.

Autonomous bottom-up fabrication of three-dimensional nano/microcellulose honeycomb structures, directed by bacterial nanobuilder

We investigated the autonomous bottom-up fabrication of three-dimensional honeycomb cellulose structures, using Gluconacetobacter xylinus as a bacterial nanoengine, on cellulose honeycomb templates prepared by casting water-in-oil emulsions on glass substrates (Kasai and Kondo, Macromol. Biosci., 4, 17-21, 2004). The template film had a unique molecular orientation state along the honeycomb frames, but was non-crystalline. When G.xylinus, used as a nanofiber-producing bacterium, was incubated on the honeycomb scaffold in a culture medium, it secreted cellulose nanofibers only on the upper surface of the honeycomb frame. The movement was regulated by a selective interaction between the synthesized nanofiber and the surface of the honeycomb frames of the template. The relationship between directed deposition of synthesized nanofibers and ordered fabrication from the nano- to the micro-scale could provide a novel bottom-up methodology, using bacteria, for the design of three-dimensional honeycomb structures as functional materials with nano/micro hierarchical structures, with low energy consumption.

Molecular Orientation and Electronic States of Vanadyl Phthalocyanine on Si(111) and Ag(111) Surfaces

We have investigated the molecular orientation and electronic structures of nonplanar vanadyl phthalocyanine (VOPc) on the Si(111)-(7 × 7) and Ag(111) surfaces by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. The VOPc molecule adsorbs on Ag(111) in a parallel orientation to the surface with an oxygen-up configuration. A strong interaction between the N and C atoms of VOPc and surface Ag atoms is observed at the interface, although no marked change in the electronic state is observed for the V atom, similarly to the case for VOPc in a multilayer. On the other hand, the chemical interaction of the O atom of VOPc with the surface Si atoms favors the oxygen-down configuration. This chemical interaction causes the cleavage of the V═O π bond and facilitates electron charge transfer to the V–N–C molecular orbitals. Such intermediation of the oxygen atom between the V atom and Si surface suppresses the direct interaction between them, and the spin magnetic moment of V remains the same as that of bulk VOPc molecules.

Controlling Molecular Packing for Charge Transport in Organic Thin Films

Tuning of the packing mode, including the film morphology, molecular orientation, and phase state of chloroaluminum phthalocyanine (ClAlPc), is demonstrated, and yields optimal parallel and vertical channels for charge transport. On a pure SiO2 surface, the ClAlPc molecules lie flat and grow in the Volmer–Weber mode, resulting in a cone-array structure that is highly desirable for heterojunction organic solar cells and organic field emission. On an OTS-modified surface, the ClAlPc molecules stand obliquely and Stranski–Krastanov growth of a continuous and flat film occurs, which is suitable for organic transistors.

Evaluation of Alignment of Nematic Liquid Crystal Thin Film by Spectroscopic Ellipsometry

Generally, macroscopic molecular orientation state in liquid crystal layer can be described by Ossen and Frank's continuum theory. However, the validity of applying the continuum theory to nematic liquid crystal thin film (NLCF) has not been confirmed yet. In this study, we experimentally examined NLCF by employing spectroscopic ellipsometer. As a result, theoretical and experimental result represent a good agreement when NLCF thickness is from 60 to 250 nm. Furthermore, the influence of surface roughness on alignment film surface and glass substrate was also examined.

Bulk and surface molecular orientation distribution in injection‐molded liquid crystalline polymers: Experiment and simulation

AbstractBulk and surface distributions of molecular orientation in injection‐molded plaques of thermotropic liquid crystalline polymers (TLCPs) have been studied using a combination of techniques, coordinated with process simulations using the Larson‐Doi “polydomain” model. Wide‐angle X‐ray scattering was used to map out the bulk orientation distribution. Fourier Transform Infrared Attenuated Total Reflectance (FTIR‐ATR) and Near‐Edge X‐ray Absorption Fine Structure (NEXAFS) were utilized to probe the molecular orientation states to within about ∼5 μm and ∼2 nm, respectively, of the sample surface. These noninvasive, surface‐sensitive techniques yield reasonable self‐consistency, providing complementary validation of the robustness of these methods. An analogy between Larson‐Doi and fiber orientation models has allowed the first simulations of TLCP injection molding. The simulations capture many fine details in the bulk orientation distribution across the sample plaque. Direct simulation of surface orientation at the level probed by FTIR‐ATR and NEXAFS was not possible due to the limited spatial resolution of the simulations. However, simulation results extracted from the shear‐dominant skin region are found to provide a qualitatively accurate indicator of surface orientation. Finally, simulations capture the relation between bulk and surface orientation states across the different regions of the sample plaque. POLYM. ENG. SCI., 50:1864–1877, 2010. © 2010 Society of Plastics Engineers

On complex formation in equimolar chloroform–benzene solution: A revisit by molecular dynamics simulation and orientational correlation states superposition

We present molecular dynamics simulations of the seventeen-atom system of chloroform equimolar in benzene on the basis of a previously proven Fortran code, Lennard–Jones potential parameters, fractional atomic charges, and complete molecular structure data between 248 and 498 K at a common density. Specifically, the generated l = 1 orientational auto-correlation functions of the tumbling and spinning–tumbling motions of chloroform in its benzene solution are combined, by established group-theoretical principles, to three linear combinations that quantitatively characterize for the benzene-dissolved chloroform molecules the time evolution of the average direction of their average rotation axis as well as that of the mean rotation angle around it. Based on these findings we conclude, first, that the probability density function of the average rotational motion of the dissolved chloroform molecules follows a memory-less process (Markoffian), second, that a previously proposed 1:1 chloroform–benzene complex, with the H atom of the C–H bond of its chloroform moiety pointing to the center of the plane of an adjacent benzene species, has a near-vanishing probability to prevail in the solution.

Numerical Analysis of Photoinduced Chirality in Azobenzene Polymer and Its Application as Photoaddressable Polarization Altering Elements

Optical performances of a unique photoinduced chiral material were investigated. The material employed in our study is an azobenzene-based copolymer (PCDY50) that exhibits a very large photoinduced birefringence and a superior stability of photoinduced molecular orientation state. The photoinduced chirality of the PCDY50 thin film was analyzed in detail by elliptical analysis on the basis of either circular or linear polarization. The validity of the processes is demonstrated by comparing experimental results and calculations. Consequently, the formulation based on circular polarization is appropriate for analyzing the relationship between the polarization state of incident and transmitting beams accurately. Furthermore, photoaddressable polarization-altering functions, for example, as an optical rotator, an ellipticity modificator and a circular polarization generator were examined by applying the invariant ellipticity (or azimuth) state condition to an 800-nm-thick PCDY50 film. Some possible applications of the photoinduced chiral thin film are also suggested.