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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Oligomers as Triggers for Responsive Liquid Crystals

We report an investigation of the influence of aqueous solutions of amphiphilic oligomers on the ordering of micrometer-thick films of thermotropic liquid crystals (LCs), thus addressing the gap in knowledge arising from previous studies of the interactions of monomeric and polymeric amphiphiles with LCs. Specifically, we synthesized amphiphilic oligomers (with decyl hydrophobic and pentaethylene glycol hydrophilic domains) in monomer, dimer, and trimer forms, and incubated aqueous solutions of the oligomers against nematic films of 4'-pentyl-4-biphenylcarbonitrile (5CB). All amphiphilic oligomers caused sequential surface-driven orientational (planar to homeotropic) and then bulk phase transitions (nematic to isotropic) with dynamics depending strongly on the degree of oligomerization. The dynamics of the orientational transitions accelerated from monomer to trimer, consistent with the effects of an increase in adsorption free energy. The mechanism underlying the orientational transition, however, involved a decrease in anchoring energy and not change in the easy axis of the LC. In contrast, the rate of the phase transition induced by absorption of oligomers into the LC decreased from monomer to trimer, suggesting that constraints on configurational degrees of freedom influence the absorption free energies of the oligomers. Interestingly, the oligomer-induced transition from the nematic to isotropic phase of 5CB was observed to nucleate at the aqueous-5CB interface, consistent with surface-induced disorder underlying the above-reported decrease in anchoring energy caused by the oligomers. Finally, we provided proof-of-concept experiments of the triggering of LCs using a trimeric amphiphile that is photocleaved by UV illumination into monomeric fragments. Overall, our results provide insight into the rational design of oligomers that can be used as triggers to create responsive LCs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Active Thermal Extraction and Temperature Sensing of Near-field Thermal Radiation

Recently, we proposed an active thermal extraction (ATX) scheme that enables thermally populated surface phonon polaritons to escape into the far-field. The concept is based on a fluorescence upconversion process that also occurs in laser cooling of solids (LCS). Here, we present a generalized analysis of our scheme using the theoretical framework for LCS. We show that both LCS and ATX can be described with the same mathematical formalism by replacing the electron-phonon coupling parameter in LCS with the electron-photon coupling parameter in ATX. Using this framework, we compare the ideal efficiency and power extracted for the two schemes and examine the parasitic loss mechanisms. As a result, this work advances the application of ATX to manipulate near-field thermal radiation for applications such as temperature sensing and active radiative cooling.

42 ENGINEERING↗
DOE OSTI2016

Sensitizing properties of luminescence centers on the emission of Er{sup 3+} in Si-rich SiO{sub 2} film

In this paper, we report on the luminescence-center (LC)-mediated excitation of Er{sup 3+} as a function of annealing temperature in Er-doped Si-rich SiO{sub 2} (SRO) films fabricated by electron beam evaporation. It is found that the annealing temperature has significant effects on the emission of Er{sup 3+} and the specific optical-active point-defects called LCs within Er-doped SRO films. Different luminescence centers generated by the evolution of microstructures during annealing process act as efficient sensitizers for Er{sup 3+} in the films when the annealing temperature is below 1100 °C. Moreover, the temperature dependence of the energy coupling between LCs and Er{sup 3+} demonstrates the effective phonon-mediated energy transfer process. In addition, when the annealing temperature reaches 1100 °C, the decreased density of activable erbium ions induced by the aggregation of Er will bring detrimental effects on the emission of Er{sup 3+}. It is demonstrated that an appropriate annealing process can be designed to achieve efficiently enhanced emissions from Er{sup 3+} ions by optimizing the density of LCs and the coupling between Er{sup 3+} and LCs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Toluene-induced phase transitions in blue phase liquid crystals

Here, we report phase transitions in blue phase-forming liquid crystals (LCs) that are triggered by exposure to toluene vapours. Specifically, we reveal that room-temperature cholesteric phase mixtures of MLC-2142 and S-811 form blue phases (BP I, II and III) with increasing vapour pressure of toluene. To probe the mechanism underlying this observation, we investigated the phase behaviour of mixtures of BP-forming LCs containing a range of non-volatile aromatic compounds (e.g. pyrene). We interpret our observations to indicate that the principal effect of small aromatic compounds is to decrease the energy penalty associated with the formation of disclination lines in BPs. We also conclude that the absorption of toluene into the BP-forming LCs lowers the energy required for the formation of disclination cores in the BP phase, thus allowing the elastically favoured double-twist cylinders to form at lower temperatures. We further show that BP-forming LCs containing pyrene can be used to detect toluene at concentrations below 200 ppm at room temperature. Overall, these results guide the design of LC-based materials that respond to VOCs at concentrations relevant to occupational settings.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

A1 Signature pattern and phylogenetic analysis of full-length env genes in 20 hemophiliacs infected with Korean subclade of HIV-1 subtype B

Twenty patients with hemophilia (HP) were diagnosed with HIV-1, one to two years after exposure to domestic clotting factor IX (DCF), in 1989–90. Previous analysis of pol and vif genes confirmed that HIV-1 transmission to 20 HPs occurred through infusion of DCF. In this study, we determined full-length env gene sequences (about 2,550 bp) in 21 HPs, three plasma donors whose plasma were used in DCF production, and 45 local controls. The env gene from frozen stored sera obtained 1–3 years after diagnosis as well as from samples collected years after infection, was amplified by RT-PCR, and subjected to direct sequencing. Phylogenetic analysis revealed that all sequences were subtype B, with 109 sequences from 64 patients (20 HPs, 3 serum donors, 41 local controls, LCs) belonging to the Korean subclade (KSB) and 13 sequences from 5 patients (1HP infected outside Korea, 4 LCs) not in the KSB. Sequences of the env gene from donors O and P plus the 20 HPs comprised two subclusters within KSB. In addition, signature pattern analysis revealed signature nucleotides at 45 positions between the HPs and LCs (P < 0.05). Surprisingly, specific signature nucleotides positions were conserved 100% in clusters O and P only (at 4 and 1 positions, respectively) with none in LCs. Within both clusters, sequence identity was high. These results are consistent with our previous conclusion that these 20 HPs were infected with viruses in the DCF used for treatment. In addition, we found that there are 25 signature pattern residues in amino acids in env gene of KSB distinct from subtype B.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Analysis of the Feasibility of UAS-Based EMI Sensing for Underground Utilities Detection and Mapping

This paper investigates the feasibility of using a linear current sensing (LCS) technique integrated on an unmanned aerial system (UAS) for detecting and mapping underground infrastructure rapidly and cost-effectively. The LCS technique is based on data from a wide band of electromagnetic induction frequencies (50 kHz to 2 MHz) using a vector magnetic field gradiometer. This technique takes advantage of a slowly decaying secondary magnetic field in order to achieve greater standoff detection distance ($\frac{1}{R^2}$ vs. $\frac{1}{R^6}$ for compact metallic targets during EMI sensing, where R is the distance from a target to the sensor). These secondary magnetic fields are produced by the excite current on long conductors, allowing detection at a distance of 10 meters or more. The system operates between tens of kHz to a few MHz and uses either an active EMI source or existing EM fields to excite this linear current on a long metallic subsurface target. Once excited, these linear currents produce a secondary magnetic field that is detected with an above ground triaxial magnetic field gradiometer. By moving and tracking its geolocation, the system outputs rich datasets sufficient to support high-fidelity forward and inverse EMI models for estimating the depth and orientation of deep underground long linear metallic infrastructure. The system’s hardware and its integration to a UAS system are outlined, along with the formulation of LCS theory, and numerical and experimental data are presented. The results illustrate that the LCS technique offers large standoff detection, is adaptable to UAS, and could be used effectively for detecting deep underground infrastructure such as wires and pipes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Evaluating the Consistency of Cosmological Distances Using Supernova Siblings in the Near-infrared

Abstract The study of supernova (SN) siblings, supernovae with the same host galaxy, is an important avenue for understanding and measuring the properties of Type Ia SN Ia light curves (LCs). Thus far, sibling analyses have mainly focused on optical LC data. Considering that LCs in the near-infrared (NIR) are expected to be better standard candles than those in the optical, we carry out the first analysis compiling SN siblings with only NIR data. We perform an extensive literature search of all SN siblings and find six sets of siblings with published NIR photometry. We calibrate each set of siblings ensuring they are on homogeneous photometric systems, fit the LCs with the SALT3-NIR and SNooPy models, and find median absolute differences inμvalues between siblings of 0.248 and 0.186 mag, respectively. To evaluate the significance of these differences beyond measurement noise, we run simulations that mimic these LCs and provide an estimate for uncertainty on these median absolute differences of ∼0.052 mag, and we find that, statistically, our analysis rules out the nonexistence of intrinsic scatter in the NIR at the 99% level. When comparing the same sets of SN siblings, we observe a median absolute difference inμvalues between siblings of 0.177 mag when using optical data alone as compared to 0.186 mag when using NIR data alone. It is unclear if these results may be due to limited statistics or poor quality NIR data, all of which will be improved with the Nancy Grace Roman Space Telescope.

Astronomy & Astrophysics↗
NASA NTRS1993

Genetic learning in rule-based and neural systems

The design of neural networks and fuzzy systems can involve complex, nonlinear, and ill-conditioned optimization problems. Often, traditional optimization schemes are inadequate or inapplicable for such tasks. Genetic Algorithms (GA's) are a class of optimization procedures whose mechanics are based on those of natural genetics. Mathematical arguments show how GAs bring substantial computational leverage to search problems, without requiring the mathematical characteristics often necessary for traditional optimization schemes (e.g., modality, continuity, availability of derivative information, etc.). GA's have proven effective in a variety of search tasks that arise in neural networks and fuzzy systems. This presentation begins by introducing the mechanism and theoretical underpinnings of GA's. GA's are then related to a class of rule-based machine learning systems called learning classifier systems (LCS's). An LCS implements a low-level production-system that uses a GA as its primary rule discovery mechanism. This presentation illustrates how, despite its rule-based framework, an LCS can be thought of as a competitive neural network. Neural network simulator code for an LCS is presented. In this context, the GA is doing more than optimizing and objective function. It is searching for an ecology of hidden nodes with limited connectivity. The GA attempts to evolve this ecology such that effective neural network performance results. The GA is particularly well adapted to this task, given its naturally-inspired basis. The LCS/neural network analogy extends itself to other, more traditional neural networks. Conclusions to the presentation discuss the implications of using GA's in ecological search problems that arise in neural and fuzzy systems.

Smith, Robert E.↗
NASA NTRS1999

Transport of Passive Tracers in Baroclinic Wave Life Cycles

The transport of passive tracers in idealized baroclinic wave life cycles is studied using output from the National Center for Atmospheric Research Community Climate Model (CCM2). Two life cycles, LCn and LCs, are simulated, starting with baroclinically unstable initial conditions similar to those used by Thorncroft et al. in their study of two life cycle paradigms. The two life cycles LCn and LCs have different initial horizontal wind shear structures that result in distinctive nonlinear development. In terms of potential vorticity-potential temperature (PV-theta) diagnostics, the LCn case is characterized by thinning troughs that are advected anti-cyclonically and equatorward, while the LCs case has broadening troughs that wrap up cyclonically and poleward. Four idealized passive tracers are included in the model to be advected by the semi-Lagrangian transport scheme of the CCM2, and their evolutions are investigated throughout the life cycles. Tracer budgets are analyzed in terms of the transformed Eulerian mean constituent transport formalism in pressure coordinates and also in isentropic coordinates. Results for both LCn and LCs show transport that is downgradient with respect to the background structure of the tracer field, but with a characteristic spatial structure that maximizes in the middle to high latitudes. For the idealized tropospheric tracers in this study, this represents a net upward and poleward transport that enhances concentrations at high latitudes. These results vary little with the initial distribution of the constituent field. The time tendency of the tracer is influenced most strongly by the eddy flux term. with the largest transport occurring during the nonlinear growth stage of the life cycle. The authors also study the transport of a lower-stratospheric tracer, to examine stratosphere-troposphere exchange for baroclinic waves.

Stone, Elizabeth M.↗
NASA NTRS2008

Generating Safety-Critical PLC Code From a High-Level Application Software Specification

The benefits of automatic-application code generation are widely accepted within the software engineering community. These benefits include raised abstraction level of application programming, shorter product development time, lower maintenance costs, and increased code quality and consistency. Surprisingly, code generation concepts have not yet found wide acceptance and use in the field of programmable logic controller (PLC) software development. Software engineers at Kennedy Space Center recognized the need for PLC code generation while developing the new ground checkout and launch processing system, called the Launch Control System (LCS). Engineers developed a process and a prototype software tool that automatically translates a high-level representation or specification of application software into ladder logic that executes on a PLC. All the computer hardware in the LCS is planned to be commercial off the shelf (COTS), including industrial controllers or PLCs that are connected to the sensors and end items out in the field. Most of the software in LCS is also planned to be COTS, with only small adapter software modules that must be developed in order to interface between the various COTS software products. A domain-specific language (DSL) is a programming language designed to perform tasks and to solve problems in a particular domain, such as ground processing of launch vehicles. The LCS engineers created a DSL for developing test sequences of ground checkout and launch operations of future launch vehicle and spacecraft elements, and they are developing a tabular specification format that uses the DSL keywords and functions familiar to the ground and flight system users. The tabular specification format, or tabular spec, allows most ground and flight system users to document how the application software is intended to function and requires little or no software programming knowledge or experience. A small sample from a prototype tabular spec application is shown.

Source record↗
NASA NTRS2012

Modeling Phase-Aligned Gamma-Ray and Radio Millisecond Pulsar Light Curves

Since the discovery of the first eight gamma-ray millisecond pulsars (MSPs) by the Fermi Large Area Telescope, this population has been steadily expanding. Four of the more recent detections, PSR J00340534, PSR J1939+2134 (B1937+21; the first MSP ever discovered), PSR J1959+2048 (B1957+20; the first discovery of a black widow system), and PSR J2214+3000, exhibit a phenomenon not present in the original discoveries: nearly phase-aligned radio and gamma-ray light curves (LCs). To account for the phase alignment, we explore models where both the radio and gamma-ray emission originate either in the outer magnetosphere near the light cylinder or near the polar caps. Using a Markov Chain Monte Carlo technique to search for best-fit model parameters, we obtain reasonable LC fits for the first three of these MSPs in the context of altitude-limited outer gap (alOG) and two-pole caustic (alTPC) geometries (for both gamma-ray and radio emission). These models differ from the standard outer gap (OG)/two-pole caustic (TPC) models in two respects: the radio emission originates in caustics at relatively high altitudes compared to the usual conal radio beams, and we allow both the minimum and maximum altitudes of the gamma-ray and radio emission regions to vary within a limited range (excluding the minimum gamma-ray altitude of the alTPC model, which is kept constant at the stellar radius, and that of the alOG model, which is set to the position-dependent null charge surface altitude). Alternatively, phase-aligned solutions also exist for emission originating near the stellar surface in a slot gap scenario (low-altitude slot gap (laSG) models). We find that the alTPC models provide slightly better LC fits than the alOG models, and both of these give better fits than the laSG models (for the limited range of parameters considered in the case of the laSG models). Thus, our fits imply that the phase-aligned LCs are likely of caustic origin, produced in the outer magnetosphere, and that the radio emission for these pulsars may come from close to the light cylinder. In addition, we were able to constrain the minimum and maximum emission altitudes with typical uncertainties of 30% of the light cylinder radius. Our results therefore describe a third gamma-ray MSP subclass, in addition to the two previously found by Venter et al.: those with LCs fit by standard OG/TPC models and those with LCs fit by pair-starved polar cap models.

Venter, C.↗
NASA NTRS2019

Summary of the NASA Large Constellations Parametric Study

In recent years, several commercial companies have proposed telecommunications constellations consisting of hundreds to thousands of 100-to-300-kg class spacecraft in low Earth orbit (LEO, the region below 2000-km altitude). If deployed, such large constellations (LCs) will dramatically change the landscape of satellite operations in LEO. From the large number of spacecraft and large amount of mass involved, it is clear that the deployment, operations, and frequent de-orbit and replenishment of the proposed LCs could significantly contribute to the existing orbital debris problem. To better understand the nature of the problem, the NASA Orbital Debris Program Office (ODPO) recently completed a parametric study on LCs. The objective was to quantify the potential negative debris-generation effects from LCs to the LEO environment and provide recommendations for mitigation measures. The tool used for the LC study was the ODPO’s LEO-to-GEO Environment Debris (LEGEND) numerical simulation model, which has been used for various mitigation and remediation studies in the past. For the LC study, more than 300 scenarios based on different user-specified assumptions and parameters were defined. Selected results from key scenarios are summarized in this paper.

Vavrin, Andrew↗
DOE OSTI2016

Reliability Assessment of Safety-Critical Network Communication in a Digitalized Nuclear Power Plant

In analog instrumentation and control (I and C) systems for nuclear power plants (NPPs), most connections are comprised of hardwired point-to-point types. Since they are based on analog technologies, they are fragile to noise and require analog-to-digital conversion time. Therefore, many NPPs have adopted communication network for the exchange of safety-critical data between programmable logic controllers (PLCs) in digital I and C systems to effectively accommodate a huge number of field controllers. However, the primary issue of digital network communication in a safety-critical system involves potential hazards, such as partial or total loss of communication between PLCs, which may result in a failure of safety critical signal generation when it is needed. Therefore, the probability that a safety-critical system in digitalized NPP becomes unsafe due to a network failure must be evaluated to quantify the risk of digital I and C system. In Korea, the Engineered Safety Feature-Component Control System (ESF-CCS) was developed as one of the digital safety-critical system in Advanced Power Reactor- 1400 (APR-1400). The function of a digital engineered safety feature (ESF) actuation system and field actuator controllers of conventional NPPs are performed by the ESF-CCS. In this system, safety-critical network, High Reliable- Safety Data Network (HR-SDN), was employed for the safety-critical data transmission from group controllers (GCs) to loop controllers (LCs). In this study, a framework for assessing the reliability of a HR-SDN network communication between GCs and LCs in the ESF-CCS in addition to a fault-tree model for ESF components considering network failure between GCs and LCs were developed to assess the plant risk effect of a newly developed digitalized ESF-CCS. Based on the case studies and cut set analysis, the risk effect of network failure on plant risk and the important risk contributors of network failure were quantitatively addressed. A framework for identifying the potential hazardous states of network communication in the ESFCCS was proposed. In addition, a fault-tree model for network communication failure was developed to estimate the risk effects of network failure between the GCs and LCs on ESF-CCS signal failure. The developed fault-tree model was then applied to several case studies. The fault-tree model of ESF-CCS signal failure for ESF components required for various mitigation actions regarding NPP DBAs was designed by considering the identified hazardous states of network failure that would result in a failure to provide input signals to the corresponding LC. As a sensitivity study, three case studies were performed based on the periodic test methods for hardware components in HR-SDN module and their test intervals in this study. The quantitative results for three case studies demonstrated that the probability of overall network communication failure, which was calculated as the sum of the failure probability associated with each failure cause, contributed up to 1.58% on the Small-LOCA CD frequency. The results also revealed the important basic events related to network failure in the case studies which included CCF of hardware and software in HR-SDN module. This study is expected to provide insight into the development of the fault-tree model for the network failure in digital I and C system and into the quantification of the risk effect of network failure for safety-critical data transmission in NPPs. As a further study, the risk effects of network failure in the ESF-CCS on the plant risk can be estimated in a more detailed manner by analyzing the failure modes and causes in a sub-component level and the fault detection coverage of the fault tolerance techniques for network failure implemented in ESF-CCS after the detailed configuration of ESF-CCS is decided. In terms of the failure of manual ESF actuation, the relationship among the human action failures must be investigated to consider multiple human error condition since ESF-CCS provides multiple manual actuation to assure the diversity of the system. Since the conventional HEP method cannot accommodate the multiple conditions in a fault tree, condition-based human reliability assessment (CBHRA) method or the dynamic human reliability modeling approach can be applied to include a complex relationship among the automated safety signal generation and the human operator's manual actuation, avoiding the optimistic estimation of HEP of the human action failure.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2020

Using FLAC{sup R} Modeling Software to Analyze the Stability of a LLRW Disposal Facility - 20031

Waste Control Specialists (WCS) wished to amend its existing LLRW disposal license such that it might use gravel aggregate instead of concrete as backfill around large component (LC) parts from decommissioned nuclear reactors. A classical mechanics evaluation of the strength of the LCs was presented to the Texas Commission on Environmental Quality (TCEQ), demonstrating that the LCs had adequate capacity to withstand the loads within the facilities, and that concrete was unnecessary for structural support. TCEQ requested that additional analyses of the LCs within the facilities be performed using FLAC{sup R} finite difference modeling software. Because FLAC{sup R} has the capability of modeling the support provided by the lateral earth pressures, the factors of safety against failure for the LCs increased. TCEQ found the FLAC{sup R} analyses presented in this report to be satisfactory, and granted WCS' license amendment request. This work demonstrates that FLAC{sup R} may be used advantageously to more accurately represent the complexities of the physical situation being modeled. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS2020

Dynamic IT Security Database and Analytics for Launch Control Systems Software

During the Summer 2020 session, I worked with intern Destani S. Van Arsdalen of EGS Software. Together, we co-created a tool to aid the dynamic investigation, updated over time,of the security compliance of LCS COTS and open source software. We originally planned touse spreadsheet software for management and analysis, but through this exploratoryproject, chose to use Python and JSON after receiving feedback on our project’s current anddesired capabilities at that time.At first, the project was solely designed to help on-board new COTS software, based on aquestionnaire that could be filled out for each software package. This, combined with usingthe spreadsheet application’s web-query capabilities to fetch information from the NVD,allowed presentation and analytics cells to automatically populate as elements of themanually-filled questionnaire changed. While this system was promising, we decided tochange technologies for a few reasons. In the spreadsheet, single cells could not hold complexdata like arrays and objects. The automatic population of cells and dynamic updates made itdifficult to manage and add new features. And finally, it had limited extensibility sinceadding new software required significant understanding of how both the spreadsheet wasconstructed, and the more obscure, proprietary scripting languages packaged with it.The pivot to a standard computer science database language of JSON, aided by thescripting capabilities of Python, greatly helped to improve the project’s functionality. First,and most importantly, the script’s import and analysis of database data is easilyreproducible. Additional data analysis can be modularly added without requiringmodification of the script and is capable of routine scheduling. The revised process can besplit into three parts. First, the conversion of LCS asset and software documentation into theJSON hierarchical database format. Second, the merging of this database with the NVD,forming a new data structure, using CPEs of the CVE object as a linking element betweenthem. And third, the automatically performed analytics and analysis of the combined data,in a modular and extensible format, to produce better informed business decisions. The outputted graphs, for example, are automatically generated by the Python script inconnection with the combined database. This allows updated graphs and any analytics to be re-rendered automatically following updates to the LCS’s initial asset documentation. Afinal report can then be programmatically and easily constructed from these sources to allow fully reproducible metrics for heavily evidenced risk management decisions.

it↗
DOE OSTI2023

Dynamic Motions of Topological Defects in Nematic Liquid Crystals under Spatial Confinement

Abstract Topological defects (TDs) have become a sensational topic due to their significant influence on the unusual optical and physiochemical characteristics of the material. To facilitate their application across a wide range of disciplines it is desirable to analyze and gain fundamental understanding of TDs in both equilibrium and nonequilibrium systems. Liquid crystals (LCs) are considered an ideal system for study given the direct visualization of TDs and a straightforward analyzation process. In addition to the equilibrium morphology of LC TDs, it is also of great interest to track and control the formation and annihilation of defects during thermodynamic processes. However, controlling the dynamic behavior of formed defects remains a challenge. Here, nematic LCs confined in a cell exhibiting surfaces with periodic anchoring conditions containing surface topography are relied on. The effects of patterned surface characteristics such as width, periodicity, and degree of curvature on defects dynamic motion, stabilization, and annihilation are explored. The computational experiments recapitulate the TDs transition path and provide free energy‐based predictions of critical distances for defect annihilation. Taken together, this simple approach offers a promising opportunity to control the dynamics of TDs in LCs through chemical patterned surfaces with topography.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Redox-Triggered Orientational Responses of Liquid Crystals to Chlorine Gas

Surface-supported liquid crystals (LCs) that exhibit orientational and thus optical responses upon exposure to ppb concentrations of Cl 2 gas are reported. Computations identified Mn cations as candidate surface binding sites that undergo redox-triggered changes in the strength of binding to nitrogen-based LCs upon exposure to Cl 2 gas. Guided by these predictions, μm-thick films of nitrile- or pyridine-containing LCs were prepared on surfaces decorated with Mn 2+ binding sites as perchlorate salts. Following exposure to Cl 2 , formation of Mn 4+ (in the form of MnO 2 microparticles) was confirmed and an accompanying change in the orientation and optical appearance of the supported LC films was measured. In unoptimized systems, the LC orientational transitions provided the sensitivity and response times needed for monitoring human exposure to Cl 2 gas. Finally, the response was also selective to Cl 2 over other oxidizing agents such as air or NO 2 and other chemical targets such as organophosphonates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗