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NASA NTRS2018

Ionic Liquids at Electrified Interfaces: from Double Layers to Decomposition

Ionic liquids are versatile electrolytes whose properties at electrified interfaces have the potential to enable technologies such as supercapacitors and Li-metal battery anodes. At electrified carbon surfaces, ionic liquids form an electric double layer that stores energy and provides the foundation for supercapacitors. At electrified lithium surfaces, ionic liquids decompose to form a solid electrolyte interphase that has the potential to stabilize Li-metal anodes in rechargable batteries. The behavior of two ionic liquids of technological importance, [pyr14][TFSI] and [EMIM][BF4], are examined at these electrified interfaces through molecular dynamics and ab initio techniques.

Haskins, Justin B.↗

NASA NTRS2018

Ionic Liquids at Electrified Interfaces: from Double Layers to Decomposition

Haskins, Justin B.↗

NASA NTRS1999

3D Structured Grid Generation Codes for Turbomachinery

This report describes the research tasks during the past year. The research was mainly in the area of computational grid generation in support of CFD analyses of turbomachinery components. In addition to the grid generation work, a numerical simulation was obtained for the flow through a centrifugal gas compressor using an unstructured Navier-Stokes solver. Other tasks involved many different turbomachinery component analyses. These analyses were performed for NASA projects or for industrial applications. The work includes both centrifugal and axial machines, single and multiple blade rows, and steady and unsteady analyses. Over the past five years, a set of structured grid generation codes were developed that allow grids to be obtained fairly quickly for the large majority of configurations we encounter. These codes do not comprise a generalized grid generation package; they are noninteractive codes specifically designed for turbomachinery blade row geometries. But because of this limited scope, the codes are small, fast, and portable, and they can be run in the batch mode on small workstations. During the past year, these programs were used to generate computational grids were modified for a wide variety of configurations. In particular, the codes or wrote supplementary codes to improve our grid generation capabilities for multiple blade row configurations. This involves generating separate grids for each blade row, and then making them match and overlap by a few grid points at their common interface so that fluid properties are communicated across the interface. Unsteady rotor/stator analyses were performed for an axial turbine, a centrifugal compressor, and a centrifugal pump. Steady-state single-blade-row analyses were made for a study of blade sweep in transonic compressors. There was also cooperation on the application of an unstructured Navier-Stokes solver for turbomachinery flow simulations. In particular, the unstructured solver was used to analyze the flow through a centriftio compressor impeller.

Loellbach, James↗

DOE OSTI2026

Amphiphilic Baskets for Supramolecular Nanoarchitectures at Interfaces: Inverted Monolayer Formation on Water

Interfacial chemistry of molecular baskets remains poorly understood despite their promise for supramolecular applications of detection and sequestration of toxic molecules including those of illicit drugs, organophosphorus compounds, and anticancer agents. We present a fundamental investigation of the interfacial behavior of three amphiphilic supramolecular baskets (ASB 4, 8, and 12), having increasingly longer yet linear alkyl chains at the top of their bowl-shaped cavity. The studies were completed at the air−water interface to elucidate surface activity, interfacial stability, self-assembly, and monolayer organization that drive inverted monolayer formation, in which the molecular arms orient toward the aqueous phase in a configuration opposite to that typically observed for lipids. Herein, surface pressure−area isotherms of ASB 4, 8, 12, deposited on a water surface, were performed in tandem with nonequilibrium relaxation experiments to quantify surface activity, thermodynamic stability, and monolayer compressibility of the baskets’ monolayer assembly. Brewster angle microscopy enabled direct visualization of morphological evolution, aggregation, and packing at the interface. We show that systematic extension of the hydrocarbon arms, from four to 12 methylene groups, progressively modifies intermolecular packing, drives distinct two-dimensional aggregation pathways, and increases number densities at the air−water interface. Atomistic molecular dynamics simulations corroborate many of these experimentally observed trends and provide mechanistic detail on the cooperative roles of basket topology and interfacial concentration in regulating the hydration structure and dynamics within the cavities generated by surface-adsorbing baskets, consistent with observed variations in surface activity and packing. Our results establish how the topology of these unique supramolecules and their concentration govern interfacial organization and offer a rational framework for designing amphiphiles with predictable behavior at soft interfaces.

Hydrocarbons↗

DOE OSTI2023

Ductile adhesive elastomers with force-triggered ultra-high adhesion strength

Elastomers play a vital role in many forthcoming advanced technologies in which their adhesive properties determine materials’ interface performance. Despite great success in improving the adhesive properties of elastomers, permanent adhesives tend to stick to the surfaces prematurely or result in poor contact depending on the installation method. Thus, elastomers with on-demand adhesion that is not limited to being triggered by UV light or heat, which may not be practical for scenarios that do not allow an additional external source, provide a solution to various challenges in conventional adhesive elastomers. Herein, we report a novel, ready-to-use, ultra high-strength, ductile adhesive elastomer with an on-demand adhesion feature that can be easily triggered by a compression force. The precursor is mainly composed of a capsule-separated, two-component curing system. After a force-trigger and curing process, the ductile adhesive elastomer exhibits a peel strength and a lap shear strength of 1.2 × 10 4 N m -1 and 7.8 × 10 3 kPa, respectively, which exceed the reported values for advanced ductile adhesive elastomers. The ultra-high adhesion force is attributed to the excellent surface contact of the liquid-like precursor and to the high elastic modulus of the cured elastomer that is reinforced by a two-phase design. In conclusion, incorporation of such on-demand adhesion into an elastomer enables a controlled delay between installation and curing so that these can take place under their individual ideal conditions, effectively reducing the energy cost, preventing failures, and improving installation processes.

36 MATERIALS SCIENCE↗

NASA NTRS1989

Transmission and reflection of compressive waves at a nonmagnetic-magnetic interface

The transmission and reflection properties of compressive waves at a plane interface between uniform nonmagnetic and magnetic regions in the absence of gravity are examined. Using stereographic polar projection, these properties are presented as functions of the two angles determining the direction of incidence. It is shown that the reflection coefficient and the direction of propagation of the transmitted wave are dependent on the direction of propagation of the incident wave for several representative parametric values. It is found that the incident, reflected, and transmitted wavenumber vectors always lie in the same plane, although the group velocity of the transmitted wave does not always lie in this plane. When the transmitted wave is a fast mode, there is generally weak reflection.

Abdelatif, Toufik E.↗

DOE OSTI2021

Design of tough adhesive from commodity thermoplastics through dynamic crosslinking

Tough adhesives provide resistance against high debonding forces, and these adhesives are difficult to design because of the simultaneous requirement of strength and ductility. Here, we report a design of tough reversible/recyclable adhesive materials enabled by incorporating dynamic covalent bonds of boronic ester into commodity triblock thermoplastic elastomers that reversibly bind with various fillers and substrates. The spectroscopic measurements and density functional theory calculations unveil versatile dynamic covalent binding of boronic ester with various hydroxy-terminated surfaces such as silica nanoparticles, aluminum, steel, and glass. The designed multiphase material exhibits exceptionally high adhesion strength and work of debonding with a rebonding capability, as well as outstanding mechanical, thermal, and chemical resistance properties. Bonding and debonding at the interfaces dictate hybrid material properties, and this revelation of tailored dynamic interactions with multiple interfaces will open up a new design of adhesives and hybrid materials.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Best practices for first-principles simulations of epitaxial inorganic interfaces

Abstract At an interface between two materials physical properties and functionalities may be achieved, which would not exist in either material alone. Epitaxial inorganic interfaces are at the heart of semiconductor, spintronic, and quantum devices. First principles simulations based on density functional theory (DFT) can help elucidate the electronic and magnetic properties of interfaces and relate them to the structure and composition at the atomistic scale. Furthermore, DFT simulations can predict the structure and properties of candidate interfaces and guide experimental efforts in promising directions. However, DFT simulations of interfaces can be technically elaborate and computationally expensive. To help researchers embarking on such simulations, this review covers best practices for first principles simulations of epitaxial inorganic interfaces, including DFT methods, interface model construction, interface structure prediction, and analysis and visualization tools.

Physics↗

DOE OSTI2020

A novel fiber-fretting test for tribological characterization of the fiber/matrix interface

Ceramic matrix composites exhibit excellent high temperature properties and are candidate materials for structural applications from jet engines to nuclear fuel cladding. The strength and deformation behavior of these composites are intrinsically tied to the properties of the fiber/matrix interface. This research introduces a novel technique to evaluate the fundamental friction and wear characteristics of these interfaces. A case study on SiC f /PyC/SiC m composites applies in situ fiber fretting to investigate the kinetic friction coefficient and cyclic wear characteristics of the interphase. The experimental methodology is presented in explicit detail to encourage other researchers to explore the capabilities of this technique. Additionally, testing was carried out as a function of fiber roughness, PyC thickness (≈10, 500, 1200 nm), cycle count (10, 100, 1000), and frequency (1, 5, and 10 Hz). The friction coefficient and wear behavior changed with cycle length due to a transition from adhesive to abrasive mechanisms. SEM fractography provided insights to tribological evolution from adhesive sliding to three-body abrasive wear. The structural disorder at the tribo-surface relating to graphitic content and dangling bond density was investigated using Raman spectroscopy. Properties are contextualized with comparison to uniaxial tensile behavior of the parent composite.

36 MATERIALS SCIENCE↗

NASA NTRS1999

Effects of Fiber/Matrix Interface and its Composition on Mechanical Properties of Hi-Nicalon/Celsian Composites

To evaluate the effects of fiber coatings on composite mechanical properties. unidirectional celsian matrix composites reinforced with uncoated Hi-Nicalon fibers and those precoated with a dual BN/SiC layer in two separate batches (batch 1 and batch 2) were tested in three-point flexure. The uncoated-fiber reinforced composites showed catastrophic failure with strength of 210+/-35 MPa and a flat fracture surface. In contrast, composites reinforced with coated fibers exhibited graceful failure with extensive fiber pullout and showed significantly higher ultimate strengths, 904 and 759 MPa for the batch 1 and 2 coatings. respectively. Fiber push-in tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interfaces that might be responsible for fiber strength degradation. Instead, the low strength of composite with uncoated fibers was due to degradation of the fiber strength from mechanical damage during composite processing. Despite identical processing, the first matrix cracking stresses (Sigma(sub mc)) of the composites reinforced with fibers coated in batch 1 and batch 2 were quite different, 436 and 122 MPa, respectively. The large difference in Sigma(sub mc) of the coated-fiber composites was attributed to differences in fiber sliding stresses (Tau(sub friction)), 121.2+/-48.7 and 10.4+/-3.1 MPa, respectively. for the two composites as determined by the fiber push-in method. Such a large difference in Tau(sub friction). for the two composites was found to be due to the difference in the compositions of the interface coatings. Scanning Auger microprobe analysis revealed the presence of carbon layers between the fiber and BN. and also between the BN and SiC coatings in the composite showing lower Tau(sub friction). This resulted in lower Sigma(sub mc) in agreement with the ACK theory. The ultimate strengths of the two composites depended mainly on the fiber volume fraction and were not significantly effected by Tau(sub friction) values, as expected. The poor reproducibility of the fiber coating composition between the two batches was judged to be the primary source of the large differences in performance of the two composites.

Bansal, Narottam P.↗

DOE OSTI2021

Emitter Reconstruction for Cleaved CdSexTe1-x Devices with Cu vs. As Doping

CdTe absorbers have had historically low carrier densities of ~10^14 cm-3 due to the self-compensating nature of copper dopants. Recent advances in group-V (e.g., arsenic) doping have increased this to 10^16-10^17 cm-3, but modeling suggests that the front interface and emitter properties become limiting in this case. By cleaving arsenic- and copper-doped CdTe device stacks at the emitter/absorber interface, we gain the ability to reconstruct emitters with known properties, which will not change during subsequent device processing, and directly test the modeling. By doing so, we find a much larger performance drop in arsenic devices; this is attributed to insufficient electron density in the emitter and increased sensitivity to interface changes due to collapsed depletion width. This work can help guide emitter engineering for highly-doped CdTe devices in both the as-grown-superstrate- and cleaved-substrate configurations.

As-doped↗

DOE OSTI2020

Learning Coarse-Grained Potentials for Binary Fluids

Even though atomistic and CG models have been used to simulate liquid nanodroplets in vapor, very few rigorous studies of the liquid-liquid interface structure are available, and most of them are limited to planar interfaces. In this work, we evaluate several existing force fields (FF)s, including two atomistic and three CG FFs, with respect to modeling the interface structure and thermodynamic properties of the water-hexane interface. Both atomistic FFs are able to quantitatively reproduce the interfacial tension and the coexisting densities of the experimentally-observed planar interface. We use the atomistic FFs to model water droplets in hexane and use these simulations to test the CG FFs. We found that the tested CG FFs cannot reproduce the interfacial tensions of planar and/or curved interfaces. Finally, we propose a new approach for learning coarse-grained (CG) potentials within the CG SDK (Shinoda-DeVane- Klein) FF framework from atomistic simulation data. We demonstrate that the new potential significantly improves the prediction of both the interfacial tension and structure of water-hexane planar and curved interfaces.

Gao, Peiyuan↗

DOE OSTI2024

Enhancing Electrochemical Sensing through Molecular Engineering of Reduced Graphene Oxide–Solution Interfaces and Remote Floating-Gate FET Analysis

Not Available

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Dark states of electrons in a quantum system with two pairs of sublattices

A quantum state of matter that is forbidden to interact with photons and is therefore undetectable by spectroscopic means is called a dark state. This basic concept can be applied to condensed matter where it suggests that a whole band of quantum states could be undetectable across a full Brillouin zone. Here we report the discovery of such condensed-matter dark states in palladium diselenide as a model system that has two pairs of sublattices in the primitive cell. By using angle-resolved photoemission spectroscopy, we find valence bands that are practically unobservable over the whole Brillouin zone at any photon energy, polarization and scattering plane. Our model shows that two pairs of sublattices located at half-translation positions and related by multiple glide-mirror symmetries make their relative quantum phases polarized into only four kinds, three of which become dark due to double destructive interference. This mechanism is generic to other systems with two pairs of sublattices, and we show how the phenomena observed in cuprates, lead halide perovskites and density wave systems can be resolved by the mechanism of dark states. Our results suggest that the sublattice degree of freedom, which has been overlooked so far, should be considered in the study of correlated phenomena and optoelectronic characteristics.

electronic properties and materials↗

NASA NTRS2000

Effects of Interface Coating and Nitride Enhancing Additive on Properties of Hi-Nicalon SiC Fiber Reinforced Reaction-Bonded Silicon Nitride Composites

Strong and tough Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride matrix composites (SiC/ RBSN) have been fabricated by the fiber lay-up approach. Commercially available uncoated and PBN, PBN/Si-rich PBN, and BN/SiC coated SiC Hi-Nicalon fiber tows were used as reinforcement. The composites contained approximately 24 vol % of aligned 14 micron diameter SiC fibers in a porous RBSN matrix. Both one- and two-dimensional composites were characterized. The effects of interface coating composition, and the nitridation enhancing additive, NiO, on the room temperature physical, tensile, and interfacial shear strength properties of SiC/RBSN matrix composites were evaluated. Results indicate that for all three coated fibers, the thickness of the coatings decreased from the outer periphery to the interior of the tows, and that from 10 to 30 percent of the fibers were not covered with the interface coating. In the uncoated regions, chemical reaction between the NiO additive and the SiC fiber occurs causing degradation of tensile properties of the composites. Among the three interface coating combinations investigated, the BN/SiC coated Hi-Nicalon SiC fiber reinforced RBSN matrix composite showed the least amount of uncoated regions and reasonably uniform interface coating thickness. The matrix cracking stress in SiC/RBSN composites was predicted using a fracture mechanics based crack bridging model.

Bhatt, Ramakrishana T.↗

DOE OSTI2025

A-Cation-Dependent Structure–Optical Property Relationships of Halide Perovskite Heterostructures with Complex Interfaces

Halide perovskite heterostructures offer promising interfacial interactions for energy conversion, yet challenges in synthesizing structurally well-defined systems limit detailed investigations into structure–property relationships. In this article, we report the synthesis of compositionally controlled 3D/3D and 3D/2D halide perovskite heterostructures using evaporation crystallization-polymer pen lithography (EC-PPL) and a single-particle analysis of their properties. By systematically varying A-site cation combinations and crystal dimensions, we show that heterointerfaces induce local lattice distortions that modulate vibrational dynamics and electron-phonon coupling. These interfacial effects result in significantly extended carrier lifetimes compared to compositionally similar pure phases. Raman spectroscopy, temperature-dependent photoluminescence, and power-dependent emission analysis reveal that localized structural modulations at the interface govern exciton-phonon interactions. These effects are magnified in smaller crystals due to increased interfacial contributions. Our findings highlight the critical role of interface-driven lattice control in tuning the optoelectronic properties of halide perovskites and provide design principles for engineering heterostructures in next-generation optoelectronic devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Thermodynamic Analysis of Silk Fibroin–Graphite Hybrid Materials and Their Morphology

Silk fibroin (SF) is a β-sheet-rich protein that is responsible for the remarkable tensile strength of silk. In addition to its mechanical properties, SF is biocompatible and biodegradable, making it an attractive candidate for use in biotic/abiotic hybrid materials. A pairing of particular interest is the use of SF with graphene-based nanomaterials (GBNs). The properties of this interface drive the formation of well-ordered nanostructures and can improve the electronic properties of the resulting hybrid. It was previously demonstrated that SF can form lamellar nanostructures in the presence of graphite; however, the equilibrium morphology and associated driving interactions are not fully understood. Here, in this study, we characterize these interactions between SF and SF lamellar with graphite using molecular dynamics (MD) simulations and umbrella sampling (US). We find that SF lamellar nanostructures have strong orientational and spatial preferences on graphite that are driven by the hydrophobic effect, destabilizing solvent–protein interactions and stabilizing protein–protein and protein–graphite interactions. Finally, we show how careful consideration of these underlying interactions can be applied to rationally modify the nanostructure morphology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Universality of effective central charge in interface CFTs

When an interface connects two CFTs, the entanglement entropy between the two CFTs is determined by a quantity called the effective central charge. The effective central charge does not have a simple form in terms of the central charges of the two CFTs, but intricately depends on the transmissive properties of the interface. In this article, we examine universal properties of the effective central charge. We first clarify how the effective central charge appears when considering general subsystems of the interface CFT. Then using this result and ideas used in the proof of the c-theorem, we provide a universal upper bound on the effective central charge. In past studies, the effective central charge was defined only in two dimensions. We propose an analogue of the effective central charge in general dimensions possessing similar universal properties as in two dimensions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗