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Results for “nematic ordering”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Substrate-induced orientational order in the isotropic phase of liquid crystals

Nematic order induced near a solid boundary in an otherwise isotropic liquid crystal is studied theoretically, at temperatures just above the bulk nematic-isotropic phase transition. Three distinct regimes are found, depending on the strength of orientational torques at the boundary: (1) strong orientational order, (2) strong orientational order followed by a first-order transition to a state of weak orientational order as temperature is raised, and (3) a state of weak orientational order.

Mauger, A.↗
NASA NTRS1996

Synthesis and Characterization of a Chitosan Derivative for Electro-Optical Applications

Chitin is a naturally occurring polymer of alpha(1-4) poly N-acetylglucosamine found primarily in the shells of crustaceans and insects. This polymer is chemically and thermally stable and physically durable as a consequence of hydrogen bonding which causes the alignment and ordering of the polymer chains into microcrystals which aggregate into sheets with chiral nematic order. Industry has attempted to take advantage of chitin's properties and low cost (chitin is a waste product of the shellfish industry) to produce durable fibers and other products. This has been largely unsuccessful because of chitin's non reactivity and insolubility. Chitosan is the deacetylation product of chitin and retains many of the structural properties of chitin. Unlike chitin, chitosan is soluble in aqueous solution at reduced pH making it easier to be processed into fibers and films than chitin. Chitosan and its derivatives are now used in such commercial applications as wound dressings, waste water treatment, and in pharmaceuticals. In this study, we have synthesized a chitosan derivative, N-para-nitrophenyl chitosan (NPNPC), as a model material with potential applications in electro optics.

Prastofer, Thomas↗
NASA NTRSDate not supplied

The Light Microscopy Module A Facility Overview-History and Science

We will share a brief history and provide a science overview of the many accomplishments of the Light Microscopy Module (LMM), a microscope that has been operating in the microgravity environment of the International Space Station (ISS) since 2010. It will be removed in October 2021. It was initially outfitted for the Constrained Vapor Bubble – Wickless Heat Pipe experiment. It was later reconfigured and upgraded many times to support a broad portfolio of Physical science and Biological experiments including: Complex Fluids, Colloids, Macro-Molecular Biophysics, Protein Crystals, and Plant Biology. The LMM has enabled many significant studies and discoveries and has seen its fair share of pleasant surprises. These include recording order arising out of disorder, e.g., systems of colloids that were glasses on Earth crystallizing to form large defect-free crystals, nematic ordering of elliptical colloids, and colloidal-polymer systems crystallizing. The LMM science teams have also seen how to improve product stabilizers once the effects of sedimentation on Earth were removed; they were able to see which tagged genes express in plants when gravity is removed, telling them which genes are essential for growing plants in space; they’ve tested protein crystal growth models; checked models for creating bijel electrodes that turn batteries into fast-charging supercapacitors; tested many forms of colloidal self-assembly: including those using depletion attraction, magnetic fields, and critical Casimir forces; they’ve observed explosive bubble nucleation in a wickless heat pipe, and much more. This work has been supported by the NASA Biological and Physical Sciences (BPS) Division and the ISS Program Office, Johnson Space Center Code OZ and Code OB, the Center for the Advancement of Science in Space (CASIS) / ISS National Lab, EPSCoR, and ISS international partners from ESA – the Netherlands and Italy, CSA, JAXA and S. Korea, and by Space Act Agreements with Procter and Gamble (P&G).

Colloids↗
NASA NTRS1972

Electron paramagnetic resonance studies of a viscous nematic liquid crystal: Evidence counter to a second-order phase change

The ordering in a viscous, nematic, liquid crystal was studied using vanadyl acetyl acetonate and several nitroxides as paramagnetic probes. The ordering curve for VAAC at both K-band and X-band shows a slope discontinuity at a reduced temperature of 0.85. This discontinuity is caused by the tumbling time of the VAAC becoming comparable with the hyperfine splitting. The slope discontinuity is not present in the ordering curves of the nitroxides. The results are taken as evidence counter to the presence of a second-order phase transition.

Shutt, W. E.↗
NASA NTRS1973

Kerr response of nematic liquids.

Description of the results of recent observations of the Kerr effect in nematic liquid crystals in a temperature range just above their nematic-isotropic transition. These results indicate that the intermolecular ordering forces in a nematic substance can enhance the Kerr effect just above the nematic transition in their isotropic state. It is felt that existing theory provides a useful approximation for relating molecular size to response time.

Johnston, A. R.↗
NASA NTRS1993

Application of multigrid methods to the solution of liquid crystal equations on a SIMD computer

We will describe a finite difference code for computing the equilibrium configurations of the order-parameter tensor field for nematic liquid crystals in rectangular regions by minimization of the Landau-de Gennes Free Energy functional. The implementation of the free energy functional described here includes magnetic fields, quadratic gradient terms, and scalar bulk terms through the fourth order. Boundary conditions include the effects of strong surface anchoring. The target architectures for our implementation are SIMD machines, with interconnection networks which can be configured as 2 or 3 dimensional grids, such as the Wavetracer DTC. We also discuss the relative efficiency of a number of iterative methods for the solution of the linear systems arising from this discretization on such architectures.

Farrell, Paul A.↗
NASA NTRS1972

Electron paramagnetic resonance study of alinement induced by magnetic fields in two smectic-A liquid crystals not exhibiting nematic phases

Using vanadyl acetylacetonate (VAAC) as a paramagnetic probe, the molecular ordering in two smectic-A liquid crystals that do not display nematic phases were studied. Reproducible alinement was attained by slow cooling throughout the isotropic smectic-A transition in dc magnetic fields of 1.1 and 2.15 teslas. The degree of order attained is small for a smectic-A liquid crystal. Measurements were made of the variation of the average hyperfine splitting of the alined samples as a function of orientation relative to the dc magnetic field of the spectrometer. This functional dependence is in agreement with the theoretical prediction except where the viscosity of the liquid crystal becomes large enough to slow the tumbling of the VAAC, as indicated by asymmetry in the end lines of the spectrum.

Fryburg, G. C.↗
NASA NTRS1978

Electron paramagnetic resonance studies of slowly tumbling vanadyl spin probes in nematic liquid crystals

An analysis of EPR line shapes by the method of Polnaszek, Bruno, and Freed is made for slowly tumbling vanadyl spin probes in viscous nematic liquid crystals. The use of typical vanadyl complexes as spin probes for nematic liquid crystals is shown to simplify the theoretical analysis and the subsequent interpretation. Rotational correlation times tau and orientational ordering parameters S sub Z where slow tumbling effects are expected to be observed in vanadyl EPR spectra are indicated in a plot. Analysis of the inertial effects on the probe reorientation, which are induced by slowly fluctuating torque components of the local solvent structure, yield quantitative values for tau and S sub Z. The weakly ordered probe VOAA is in the slow tumbling region and displays these inertial effects throughout the nematic range of BEPC and Phase V. VOAA exhibits different reorientation behavior near the isotropic-nematic transition temperature than that displayed far below this transition temperature.

Bruno, G. V.↗
NASA NTRS1978

Electron paramagnetic resonance studies of slowly tumbling vanadyl spin probes in nematic liquid crystals

The purposes of this vanadyl spin probe study are threefold: (1) to establish when the breakdown of motionally narrowed formulas occurs; (2) to analyze the experimental vanadyl EPR line shapes by the stochastic Lioville method as developed by Polnaszek et al. (1973) for slow tumbling in an anisotropic liquid; and (3) to compare the vanadyl probe study results with those of Polnaszek and Freed (1975). Spectral EPR line shapes are simulated for experimental spectra of vanadyl acetylacetonate (VOAA) in nematic liquid crystal butyl p-(p-ethoxyphenoxycarbonyl) phenyl carbonate (BEPC) and Phase V of EM laboratories. It is shown that the use of typical vanadyl complexes as spin probes for nematic liquid crystals simplifies the theoretical analysis and the subsequent interpretation. Guidelines for the breakdown of motionally narrowed formulas are established. Both the slow tumbling aspects and the effects of non-Brownian rotation should be resolved in order to extract quantitative information about molecular ordering and rotational mobility.

Bruno, G. V.↗
NASA NTRS2015

Rheological Properties of Quasi-2D Fluids in Microgravity

In recent years, research on complex fluids and fluids in restricted geometries has attracted much attention in the scientific community. This can be attributed not only to the development of novel materials based on complex fluids but also to a variety of important physical phenomena which have barely been explored. One example is the behavior of membranes and thin fluid films, which can be described by two-dimensional (2D) rheology behavior that is quite different from 3D fluids. In this study, we have investigated the rheological properties of freely suspended films of a thermotropic liquid crystal in microgravity experiments. This model system mimics isotropic and anisotropic quasi 2D fluids [46]. We use inkjet printing technology to dispense small droplets (inclusions) onto the film surface. The motion of these inclusions provides information on the rheological properties of the films and allows the study of a variety of flow instabilities. Flat films have been investigated on a sub-orbital rocket flight and curved films (bubbles) have been studied in the ISS project OASIS. Microgravity is essential when the films are curved in order to avoid sedimentation. The experiments yield the mobility of the droplets in the films as well as the mutual mobility of pairs of particles. Experimental results will be presented for 2D-isotropic (smectic-A) and 2D-nematic (smectic-C) phases.

microgravity↗
NASA NTRS2022

Liquid crystals of neat boron nitride nanotubes and their assembly into ordered macroscopic materials

Boron nitride nanotubes (BNNTs) have attracted attention for their predicted extraordinary properties; yet, challenges in synthesis and processing have stifled progress on macroscopic materials. Recent advances have led to the production of highly pure BNNTs. Here we report that neat BNNTs dissolve in chlorosulfonic acid (CSA) and form birefringent liquid crystal domains at concentrations above 170 ppmw. These tactoidal domains merge into millimeter- sized regions upon light sonication in capillaries. Cryogenic electron microscopy directly shows nematic alignment of BNNTs in solution. BNNT liquid crystals can be processed into aligned films and extruded into neat BNNT fibers. This study of nematic liquid crystals of BNNTs demonstrates their ability to form macroscopic materials to be used in high- performance applications.

Cedric J. Simonsen Ginestra↗
NASA NTRS2004

Liquid-Crystal Thermosets, a New Generation of High-Performance Liquid-Crystal Polymers

One of the major challenges for NASA's next-generation reusable-launch-vehicle (RLV) program is the design of a cryogenic lightweight composite fuel tank. Potential matrix resin systems need to exhibit a low coefficient of thermal expansion (CTE), good mechanical strength, and excellent barrier properties at cryogenic temperatures under load. In addition, the resin system needs to be processable by a variety of non-autoclavable techniques, such as vacuum-bag curing, resin-transfer molding (RTM), vacuum-assisted resin-transfer molding (VaRTM), resin-film infusion (RFI), pultrusion, and advanced tow placement (ATP). To meet these requirements, the Advanced Materials and Processing Branch (AMPB) at NASA Langley Research Center developed a new family of wholly aromatic liquid-crystal oligomers that can be processed and thermally cross-linked while maintaining their liquid-crystal order. All the monomers were polymerized in the presence of a cross-linkable unit by use of an environmentally benign melt-condensation technique. This method does not require hazardous solvents, and the only side product is acetic acid. The final product can be obtained as a powder or granulate and has an infinite shelf life. The obtained oligomers melt into a nematic phase and do not exhibit isotropization temperatures greater than the temperatures of decomposition (Ti > T(sub dec)). Three aromatic formulations were designed and tested and included esters, ester-amides, and ester-imides. One of the major advantages of this invention, named LaRC-LCR or Langley Research Center-Liquid Crystal Resin, is the ability to control a variety of resin characteristics, such as melting temperature, viscosity, and the cross-link density of the final part. Depending on the formulation, oligomers can be prepared with melt viscosities in the range of 10-10,000 poise (100 rad/s), which can easily be melt-processed using a variety of composite-processing techniques. This capability provides NASA with custom-made matrix resins that meet the required processing conditions for the fabrication of textile composites. Once the resin is in place, the temperature is raised to 375 C and the oligomers are cross-linked into a high-glass-transition-temperature (Tg) nematic network without releasing volatiles. The mechanical properties of the fully crosslinked, composite articles are comparable to typical composites based on commercially available epoxy resins.

Dingemans, Theo↗
NASA NTRS1995

Report on twisted nematic and supertwisted nematic device characterization program

In this study we measured the optical characteristics of normally white twisted nematic (NWTN) and super twisted nematic (STN ) cells. Though no dynamic computer model was available, the static observations were compared with computer simulated behavior. The measurements were taken as a function of both viewing angle and applied voltage and included in the static case not only luminance but also contrast ratio and chromaticity . We employed the computer model Twist Cell Optics, developed at Kent State in conjunction with this study, and whose optical modeling foundation, Iike the ViDEOS program, is the 4 x 4 matrix method of Berreman. In order to resolve discrepancies between the experimental and modeled data the optical parameters of the individual cell components, where not known, were determined using refractometry, profilometry, and various forms of ellipsometry. The resulting agreement between experiment and model is quite good due primarily to a better understanding of the structure and optics of dichroic sheet polarizers. A description of the model and test cells employed are given in section 2. Section 3 contains the experimental data gathered and section 4 gives examples of the fit between model and experiment. Also included with this report are a pair of papers which resulted from the research and which detail the polarizer properties and some of the cell characterization methods.

Source record↗
NASA NTRS1973

Optical-to-optical interface device

Studies were conducted on the performance of a photoactivated dc liquid crystal light valve. The dc light valve is a thin film device that consists of two transparent electrodes, deposited on glass substrates, that enclose a thin film photoconductor (cadmium sulfide) and a thin layer of a nematic liquid crystal that operates in the dynamic scattering mode. The work was directed toward application of the light valve to high resolution non-coherent light to coherent light image conversion. The goal of these studies was to improve the performance and quality of the already existing dc light valve device and to evaluate quantitatively the properties and performance of the device as they relate to the coherent optical data processing application. As a result of these efforts, device sensitivity was improved by a factor of ten, device resolution was improved by a factor of three, device lifetime was improved by two-orders of magnitude, undesirable secondary liquid crystal scattering effects were eliminated, the scattering characteristics of the liquid crystal were thoroughly documented, the cosmetic quality of the devices was dramatically improved, and the performance of the device was fully documented.

Jacobson, A. D.↗
NASA NTRS1984

Finite elastic-plastic deformation of polycrystalline metals

Applying Hill's self-consistent method to finite elastic-plastic deformations, the overall moduli of polycrystalline solids are estimated. The model predicts a Bauschinger effect, hardening, and formation of vertex or corner on the yield surface for both microscopically non-hardening and hardening crystals. The changes in the instantaneous moduli with deformation are examined, and their asymptotic behavior, especially in relation to possible localization of deformations, is discussed. An interesting conclusion is that small second-order quantities, such as shape changes of grains and residual stresses (measured relative to the crystal elastic moduli), have a first-order effect on the overall response, as they lead to a loss of the overall stability by localized deformation. The predicted incipience of localization for a uniaxial deformation in two dimensions depends on the initial yield strain, but the orientation of localization is slightly less than 45 deg with respect to the tensile direction, although the numerical instability makes it very difficult to estimate this direction accurately.

Iwakuma, T.↗