Development of techniques to improve bladder materials and test methods Final report, May 18, 1966 - May 17, 1968

Process parameters for fabricating flexible Teflon films, crystallinity determinations, and techniques for electroplating Teflon films with lea

Optical properties of carbon grains: Influence on dynamical models of AGB stars

For amorphous carbon several laboratory extinction data are available, which show quite a wide range of differences due to the structural complexity of this material. We have calculated self-consistent dynamic models of circumstellar dust-shells around carbon-rich asymptotic giant branch stars, based on a number of these data sets. The structure and the wind properties of the dynamical models are directly influenced by the different types of amorphous carbon. In our test models the mass loss is not severely dependent on the difference in the optical properties of the dust, but the influence on the degree of condensation and the final outflow velocity is considerable. Furthermore, the spectral energy distributions and colours resulting from the different data show a much wider spread than the variations within the models due to the variability of the star. Silicon carbide was also considered in the radiative transfer calculations to test its influence on the spectral energy distribution.Comment: 12 pages, 6 figures. To appear in A&

A systematic approach to the formulation of anti-onychomycotic nail patches

Nail patches have a potential role as drug carriers for the topical treatment of nail diseases such as onychomycosis, a common condition. O ur aim was therefore to develop a systematic and novel appr oach to the formulat ion of a simple drug -in-adhesive ungual patch. Twelve pressure -sensitive adhesives (PSAs), four backing membranes, two release liners and three drugs were screened for pharmaceutical and mechanical properties . From this initial screeni ng, two PSAs, two drugs, one backing membrane and one release liner were selected for further investigation. Patches were prepared by solvent -casting and characterised. The patches had good uniformity of thickness and of drug content, and showed minimal drug crystallisation during six month s of storage. Meanwhile, the d rug stability in the patch upon storage and patch adhesion to the nail was influenced by the nature of the drug, the PSA and the backing membrane . The reported methodology paves the way for a systematic formulation of ungual nail patches to add to the armamentarium of nail medicines . Further , from this work, the best patch formulation has been identified

Short- and Long-Range Mechanical and Chemical Interphases Caused by Interaction of Boehmite (γ-AlOOH) with Anhydride-Cured Epoxy Resins

Understanding the interaction between boehmite and epoxy and the formation of their interphases with different mechanical and chemical structures is crucial to predict and optimize the properties of epoxy-boehmite nanocomposites. Probing the interfacial properties with atomic force microscopy (AFM)-based methods, especially particle-matrix long-range interactions, is challenging. This is due to size limitations of various analytical methods in resolving nanoparticles and their interphases, the overlap of interphases, and the effect of buried particles that prevent the accurate interphase property measurement. Here, we develop a layered model system in which the epoxy is cured in contact with a thin layer of hydrothermally synthesized boehmite. Different microscopy methods are employed to evaluate the interfacial properties. With intermodulation atomic force microscopy (ImAFM) and amplitude dependence force spectroscopy (ADFS), which contain information about stiffness, electrostatic, and van der Waals forces, a soft interphase was detected between the epoxy and boehmite. Surface potential maps obtained by scanning Kelvin probe microscopy (SKPM) revealed another interphase about one order of magnitude larger than the mechanical interphase. The AFM-infrared spectroscopy (AFM-IR) technique reveals that the soft interphase consists of unreacted curing agent. The long-range electrical interphase is attributed to the chemical alteration of the bulk epoxy and the formation of new absorption bands.DFG, 232311024, FOR 2021: Wirkprinzipien nanoskaliger Matrixadditive für den Faserverbundleichtba

Optical surfaces for mid-infrared sensing

The mid-infrared (mid-IR) spectral region, with wavelengths between 3 and 15 µm, is known for a wide range of applications ranging from spectroscopic sensing to thermal imaging. However, despite the strong technological interest, optoelectronic devices in the mid-IR are expensive and often inferior in performance compared to their visible and near-IR counterparts. In this thesis, we combine ultrathin materials, e.g. graphene, and novel substrates to develop optical surfaces for applications in the mid-IR.First, we demonstrate a novel uncooled photodetector, combining graphene with a ferroelectric (pyroelectric) substrate. More specifically, we develop a graphene on z-cut lithium niobate (LiNbO3) pyro-resistive platform that supports dynamic tunablity of the responsivity. We also develop a model to identify the key parameters that influence the performance of such detectors and can therefore provide guidelines to improve their performance. Second, we introduce ultra-thin yttria-stabilized zirconia (YSZ), a ceramic material, as a novel platform for IR nano-optics. In particular, we combine YSZ substrates with metallic nanostructures and graphene to demonstrate plasmonic, polarizing and transparent heating devices, which enable high temperature processing and can withstand harsh environments thanks to the high thermal and chemical stabilities of YSZ. Additionally, the mechanical flexibility of YSZ substrates also makes them ideally suited for manufacturing foldable or bendable devices and for low cost large-scale roll-to-roll fabrication processes. Finally, we investigate for the first time electrostatically tunable graphene nano-hole array surfaces by performing a detailed experimental study of structures with periods as low as 100 nm. We obtain a clear plasmonic response from these surfaces in the range 1300-1600 cm-1. We also demonstrated for the first time that these tunable nanostructures can be fabricated by scalable nano-imprint technique. Such large area plasmonic nanostructures are suitable for industrial applications, for example, surface-enhanced infrared absorption (SEIRA) sensing. This is because they combine an easy design, extreme field confinement and the possibility to excite multiple plasmon modes for multiband sensing, a feature not readily available in nanoribbons or other localized resonant geometries. The results contained in this thesis are particularly relevant with regard to extending the use of materials, such as graphene combined with specific substrates (LiNbO3 or zirconia), to mid-IR photodetection, enhanced absorption and molecular sensing.La región espectral del infrarrojo medio (mid-IR), de longitudes de onda entre los 3 y los 15µm, se conoce por su vasto número de aplicaciones: desde la detecciónespectroscópica hasta la imagen térmica. No obstante, a pesar de su gran interéstecnológico, los dispositivos optoelectrónicos en el mid-IR son caros y, a menudo,con rendimientos inferiores al compararlos con sus homólogos en la región visibley en el infrarrojo cercano. En esta tesis, combinamos materiales ultrafinos(e.g. grafeno) con nuevos substratos para desarrollar superficies ópticas conaplicaciones en el mid-IR.Primero, mostramos los resultados de un fotodetector innovador, que nonecesita ser enfriado, fabricado combinando grafeno con un substrato ferroeléc-trico (piroeléctrico). Más específicamente, desarrollamos un artefacto de grafenodispuesto sobre niobato de litio (LiNbO3) cortado en la dirección z, que admiteuna modulación dinámica de su capacidad de respuesta. También desarrollamosun modelo matemático con el propósito de identificar los parámetros claves queinfluyen en el rendimiento de estos fotodetectores y, en consecuencia, propor-cionar una serie de pautas para mejorarlo. En segundo lugar, introducimos la circonita estabilizada con óxido de itrioultrafina (YSZ) como material cerámico vanguardista en el campo de la nanoóp-tica en el IR. En particular, combinamos substratos de YSZ con nanoestructurasmetálicas y grafeno para demostrar la idoneidad de dispositivos plasmónicos,transparentes y polarizadores, que posibilitan el procesamiento a alta temper-atura y que pueden soportar condiciones ambientales más duras gracias a laexcelente estabilidad térmica y química de la YSZ. Además, la flexibilidad delos substratos de YSZ hace de éstas, unas estructuras ideales para la manufactura de dispositivos flexibles y plegables, cuyo proceso rollo-a-rollo de fabricacióna gran escala es de bajo coste. Finalmente, investigamos por vez primera las superficies de grafeno modu-ladas electrostáticamente con patrones de nano-orificios, cuyos periodos llegana distancias tan pequeñas como los 100 nm, por medio de un exhaustivo estudioexperimental. A través del mismo, obtenemos una respuesta plasmónica claraen el rango de los 1300-1600cm-1. También demostramos por primera vez, queestas nanoestrucutras modulables pueden ser fabricadas mediante técnicas es-calables de nanoimpresión. Las grandes dimensiones de dichas nanoestructurasplasmónicas, las hacen plenamente apropiadas para aplicaciones industrialescomo, por ejemplo, la detección por absorción infrarroja amplificada de super-ficie (SEIRA, por sus siglas en inglés). Esto ocurre debido a que combinan undiseño simple, con un confinamiento extremo del campo y con la posibilidad deexcitar diferentes modos plasmónicos, lo que es de gran utilidad para la detec-ción multi-banda, una característica difícil de conseguir con cintas de grafeno uotras geometrías localizadas resonantes. Los resultados integrados en esta tesisson particularmente relevantes con respecto a la extensión de la utilización demateriales como el grafeno en combinación con substratos específicos (LiNbO3o circonita) para la fotodetección en el mir-IR, la absorción amplificada y ladetección molecular.Postprint (published version

Design of a Polymer-Based Hollow-Core Bandgap Fiber for Low-Loss Terahertz Transmission

We use numerical simulations to design a hollowcore microstructured polymer optical fiber (HC-mPOF) suitable for broadband, terahertz (THz) pulse transmission with relatively low losses and small dispersion. The HC-mPOF consists of a central large air-core surrounded by periodically arranged wavelength-scale circular air holes in a hexagonal pattern, embedded in a uniform Teflon matrix. The THz guidance in this fiber is achieved by exploiting the photonic bandgap (PBG) effect. In our low index contrast Teflon-air (1.44:1) hexagonal periodic lattice, the PBG appears only for a certain range of non-zero values of the longitudinal wavevector. We have achieved PBG over a broad spectral range (bandwidth ~400 GHz) ranging from 1.65 to 2.05 THz in the proposed HC-mPOF. The achievable loss coefficient in our designed HC-mPOF is <;4 m-1 and the group velocity dispersion parameter is <;±5 ps/THz·cm over a 300-GHz bandwidth (1.65~1.95 THz)

Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics

D’Angelo F, Mics Z, Bonn M, Turchinovich D. Ultra-broadband THz time-domain spectroscopy of common polymers using THz air photonics. Optics Express. 2014;22(10): 12475

Index to NASA Tech Briefs, 1975

This index contains abstracts and four indexes--subject, personal author, originating Center, and Tech Brief number--for 1975 Tech Briefs