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Results for “Responsive nanostructures”

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
DOE OSTI2023

Strategy for Nonenzymatic Harvesting of Cells via Decoupling of Adhesive and Disjoining Domains of Nanostructured Stimulus-Responsive Polymer Films

The nanostructured polymer film introduces a novel mechanism of nonenzymatic cell harvesting by decoupling solid cell-adhesive and soft stimulus-responsive cell-disjoining areas on the surface. The key characteristics of this architecture are the decoupling of adhesion from detachment and the impermeability to the integrin protein complex of the adhesive domains. This surface design eliminates inherent limitations of thermoresponsive coatings, namely, the necessity for the precise thickness of the coating, grafting or cross-linking density, and material of the basal substrate. The concept is demonstrated with nanostructured thermoresponsive films made of cell-adhesive epoxy photoresist domains and cell-disjoining poly(N-isopropylacrylamide) brush domains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Theoretical study on optical response in nanostructures in the Born–Markov regime: The role of spontaneous emission and dephasing

We theoretically study the linear and nonlinear optical susceptibility in a nanostructure that interacts with a classical monochromatic optical field, by means of the solution of a Born–Markov master equation in the Lindblad form, considering as environment for the system the quantum vacuum of the continuum of modes of the external electromagnetic field. The processes of spontaneous emission and dephasing between two levels of the nanostructured quantum system are studied formally, within the framework of the quantum theory of open systems. It was found that the phenomenological master equation corresponds to a Born–Markov master equation in the Lindblad form that considers only the dissipative terms of spontaneous emission and dephasing, provided that the transverse coherence time T{sub 2} is smaller than spontaneous emission time T{sub 1}. Finally, comparative results are presented between the proposed methodology and the conventional method for: optical rectification, optical absorption, generation of second harmonic and generation of third harmonic in a cylindrical quantum dot (CQD) of AsGa∕AsGaAl with a hydrogen-like impurity inside it and under the action of a uniform magnetic field.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Complex pH-Dependent Interactions between Weak Polyelectrolyte Block Copolymer Micelles and Molecular Fluorophores

Amphiphilic block copolymers with weak polyelectrolyte blocks can assemble stimulus-responsive nanostructures and interfaces. Applications of these materials in drug delivery, biomimetics, and sensing largely rely on the well-understood swelling of polyelectrolyte chains upon deprotonation, often induced by changes in pH or ionic strength. This deprotonation can also tune interfacial interactions between the polyelectrolyte blocks and surrounding solution, an effect which is less studied than morphological swelling of polyelectrolytes but can be just as critical for intended function. Here, we investigate whether the pH-driven morphological response of polyelectrolyte-bearing nanostructures also affects the interactions of these nanostructures with molecules in solution, using micelles of a short-chain polybutadiene-block-poly(acrylic acid) (pBd–pAA) as a model system. Here we introduce a Förster resonance energy transfer (FRET) approach to probe interactions between micelles and fluorescent molecular solutes as a function of solution pH. As expected, the pAA corona of these pBd–pAA micelles increases in thickness monotonically as a function of pH. However, FRET efficiency, which provides a metric of the spatial proximity of fluorescently labeled micelles and freely diffusing fluorophores, exhibits complex nonmonotonic behavior as a function of pH, indicating that the average separation of micelles and acceptor fluorophores is not strictly correlated with micelle swelling. Dialysis experiments quantify the affinity of fluorophores for micelles as a function of pH, confirming that changes in FRET are driven almost entirely by the pH-dependent affinity of the pAA block for the investigated molecular fluorophores, not simply by a shape change of the pAA corona. This study provides key insights into the interfacial interactions between weak-polyelectrolyte-bearing nanostructures and molecular solutes, of importance for the development of their stimulus-responsive applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Comparative Analysis of the Near‐ and Far‐Field Optical Response of Thin Plasmonic Nanostructures

Abstract Nanostructures made of metallic materials support collective oscillations of their conduction electrons, commonly known as surface plasmons. These modes, whose characteristics are determined by the material and morphology of the nanostructure, couple strongly to light and confine it into subwavelength volumes. Of particular interest are metallic nanostructures for which the size along one dimension approaches the nanometer or even the subnanometer scale, since such morphologies can lead to stronger light–matter interactions and higher degrees of confinement than regular three‐dimensional nanostructures. Here, the plasmonic response of metallic nanodisks of varying thicknesses and aspect ratios is investigated under far‐ and near‐field excitation conditions. It is found that, for far‐field excitation, the strength of the plasmonic response of the nanodisk increases with its thickness, as expected from the increase in the number of conduction electrons in the system. However, for near‐field excitation, the plasmonic response becomes stronger as the thickness of the nanodisk is reduced. This behavior is attributed to the higher efficiency with which a near‐field source couples to the plasmons supported by thinner nanodisks. The results of this work advance the understanding of the plasmonic response of thin metallic nanostructures, thus increasing their potential for the development of novel applications.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of tube processing methods on microstructure, mechanical properties and irradiation response of 14YWT nanostructured ferritic alloys

In this research, innovative thermal spray deposition (Process I) and conventional hot extrusion processing (Process II) methods have been used to produce thin walled tubing (~0.5 mm wall thickness) out of 14YWT, a nanostructured ferritic alloy. The effects of processing methods on the microstructure, mechanical properties and irradiation response have been investigated by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and, micro- and nano-hardness techniques. It has been found that these two processes have a significant effect on the microstructure and mechanical properties of the as-fabricated 14YWT tubes. Even though both processing methods yield the formation of various size Y-Ti-O particles, the conventional hot extrusion method results in a microstructure with smaller, homogenously distributed nano-oxides (NOs, Y-Ti-O particles < 5 nm) with higher density. Therefore, Process II tubes exhibit twice the hardness of Process I tubes. It has also been found that these two tremendously different initial microstructures strongly affect irradiation response in these tubes under extremely high dose ion irradiations up to 1100 peak dpa at 450 °C. The finer, denser and homogenously distributed NOs in the Process II tube result in a reduction in swelling by two orders of magnitude. On the other hand, inhomogeneity of the initial microstructure in the Process I tube leads to large variations in both swelling and irradiation induced hardening. Moreover, hardening mechanisms before and after irradiation were measured and compared with detailed calculations. In conclusion, this study clearly indicates the crucial effect of initial microstructure on radiation response of 14YWT alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Liquid interfaces with pH-switchable nanoparticle arrays

Stimuli-responsive 2D nanoscale systems offer intriguing opportunities for creating switchable interfaces. At liquid interfaces, such systems can provide control over interfacial energies, surface structure, and rheological and transport characteristics, which is relevant, for example, to bio- and chemical reactors, microfluidic devices, and soft robotics. We explore the formation of a pH-responsive membrane formed from gold nanoparticles grafted with DNA (DNA–NPs) at a liquid–vapor interface. A DNA–NP 2D hexagonal lattice can be reversibly switched by pH modulation between an expanded state of non-connected nanoparticles at neutral pH and a contracted state of linked nanoparticles at acidic pH due to the AH + –H + A base pairing between A-motifs. Our in situ surface X-ray scattering studies reveal that the reversible lattice contraction can be tuned by the length of pH-activated linkers, with up to ~71% change in surface area.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Nanoscale probing of resonant photonic modes in dielectric nanoparticles with focused electron beams

We report that understanding the optical responses of nanostructures with high spatial resolution is paramount in photonic engineering. The excitation of resonant optical-frequency geometric modes in oxide nanoparticles is explored using monochromated electron energy-loss spectroscopy in a scanning transmission electron microscope. These geometric or cavity modes are found to produce a progression of resonance peaks within the bandgap regions of the electron energy-loss spectra of CeO 2 , TiO 2 , and MgO nanoparticles. Complementary simulations of the electron probe combined with analytic Mie analysis are performed to interpret the complex spectral features and to understand their underlying physical origins. The factors that influence the energies, shapes, and strengths of these modes are also investigated and their dependence upon nanoparticle size, geometry, refractive index, aggregation, impact parameter, and electron kinetic energy are elucidated. Taken together, this work demonstrates the unique ability of fast electron spectroscopy to determine the photonic density of states in individual and complex assemblies of dielectric nanoparticles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Better Radiation Response and Accident Tolerance of Nanostructured Ceramic Fuel Materials?

The objective of this research is to study structural stability and fission product behavior in nanostructured ZrO 2 and CeO 2 at temperatures and irradiation conditions relevant to operation and accidental scenarios. The fundamental understanding will support the development of innovative fuel forms. Specifically, the proposed work employs novel ion irradiation approaches, complementary characterization techniques, and advanced simulation methods to perform separate and integrated effect studies that expand the fundamental understanding of: Task (1) damage evolution in ceramic fuel materials in a controlled irradiation environment with focus in the transition energy regime where simultaneous energy deposition to both atomic and electronic structures is significant; Task (2) phase and structural stability in nanostructured fuel materials to high-temperature high-dose irradiation; and Task (3) role of the grain boundaries, surface/interface properties on migration and segregation of fission products.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Magnetically Charged Superdomain Walls In Square Artificial Spin Ice

We report direct evidence that magnetically charged superdomain walls form spontaneously in two dimensional square artificial spin ice nanostructures in response to external magnetic fields. These extended magnetic defects were revealed by the development of internal structure, which varies as a function of applied magnetic field, within the Bragg peaks of resonant soft x-ray magnetic scattering patterns. Magnetically charged superdomain walls extend over tens of lattice sites and do not necessarily align with the applied field. Our results illustrate a novel approach to detect hierarchical magnetic structures within spin textures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Toward white light emission from plasmonic-luminescent hybrid nanostructures

We study the light emission of plasmonic-luminescent hybrid nanostructures consisting of Ag nanoparticles (NPs) embedded in europium oxide (EuO X ). The Ag NPs present a bidimensional organization in the nanostructures and they optically behave as oblate spheroids. The photoluminescence (PL) spectral response of the nanostructures evolves from a narrow red emission characteristic of Eu 3+ ions in absence of Ag NPs to a broad blue-green emission band associated with Eu 2+ ions when the layer of Ag NPs is present. This behavior is not related to a change in the Eu 2+ /Eu 3+ ratio, which is verified by compositional analysis. Instead, a detailed investigation of the PL emission of the nanostructures suggests that the coupling of the Ag NPs to the Eu 2+ ions present in the EuO X layer, which manifests itself in an efficient sensitization of these ions, enhances their broad visible emission. In particular, the longitudinal mode of the Ag NPs surface plasmon is considered to be responsible for the efficient energy transfer for the non-normal incidence excitation PL configuration used. Finally, the use of a capping amorphous Al 2 O 3 layer allows improving the robustness of hybrid nanostructures and further enhances their PL emission. These findings provide a new path to actively control the selective excitation of Eu 2+ and Eu 3+ ions via a controlled coupling with the surface plasmon resonance modes of the Ag NPs and points to these nanostructures as promising building blocks for the development of integrable white light sources.

36 MATERIALS SCIENCE↗
DOE OSTI2024

De novo design of pH-responsive self-assembling helical protein filaments

Abstract Biological evolution has led to precise and dynamic nanostructures that reconfigure in response to pH and other environmental conditions. However, designing micrometre-scale protein nanostructures that are environmentally responsive remains a challenge. Here we describe the de novo design of pH-responsive protein filaments built from subunits containing six or nine buried histidine residues that assemble into micrometre-scale, well-ordered fibres at neutral pH. The cryogenic electron microscopy structure of an optimized design is nearly identical to the computational design model for both the subunit internal geometry and the subunit packing into the fibre. Electron, fluorescent and atomic force microscopy characterization reveal a sharp and reversible transition from assembled to disassembled fibres over 0.3 pH units, and rapid fibre disassembly in less than 1 s following a drop in pH. The midpoint of the transition can be tuned by modulating buried histidine-containing hydrogen bond networks. Computational protein design thus provides a route to creating unbound nanomaterials that rapidly respond to small pH changes.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Enhancing hyperspectral EELS analysis of complex plasmonic nanostructures with pan-sharpening

Nanoscale hyperspectral techniques—such as electron energy loss spectroscopy (EELS)—are critical to understand the optical response in plasmonic nanostructures, but as systems become increasingly complex, the required sampling density and acquisition times become prohibitive for instrumental and specimen stability. As a result, there has been a recent push for new experimental methodologies that can provide comprehensive information about a complex system, while significantly reducing the duration of the experiment. In this work, we present a pan-sharpening approach to hyperspectral EELS analysis, where we acquire two datasets from the same region (one with high spatial resolution and one with high spectral fidelity) and combine them to achieve a single dataset with the beneficial properties of both. This work outlines a straightforward, reproducible pathway to reduced experiment times and higher signal-to-noise ratios, while retaining the relevant physical parameters of the plasmonic response, and is generally applicable to a wide range of spectroscopy modalities.

36 MATERIALS SCIENCE↗