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  • 1
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    Polyimides Containing Fluorine and Phosphorus for Potential Space Applications (2000)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: As part of an effort to develop low color, ultraviolet (UV) radiation and atomic oxygen resistant polyimides for potential space applications, a novel diamine containing fluorine and phosphorus was synthesized and used to prepare polyimides. The approach was to combine attributes from colorless, UV resistant polyimides and atomic oxygen (AO) resistant polymers into a single material. Preparation of colorless polyimides has focused on minimization of charge transfer complex formation by incorporation of bulky substituents and disrupting conjugation by using meta-catenated monomers. AO resistant polymer technology development has focused on placing phenylphosphine oxide groups into the backbone of aromatic polymers. However, polyimides prepared utilizing this approach thus far have all exhibited significant color. Thus in an attempt to combine these features in a polyimide a new diamine, bis(3-aminophenyl)-3,5-di(trifluoromethyl)phenylphosphine oxide (TFMDA) was synthesized and used to prepare polyimides. The polyimides were cast into films and characterized for physical and mechanical properties, optical transmission and AO and UV resistance.
    Keywords: Nonmetallic Materials
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  • 2
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    The Effect of Low Earth Orbit Atomic Oxygen Exposure on Phenylphosphine Oxide-Containing Polymers (2000)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: Thin films of phenylphosphine oxide-containing polymers were exposed to low Earth orbit aboard a space shuttle flight (STS-85) as part of flight experiment designated Evaluation of Space Environment and Effects on Materials (ESEM). This flight experiment was a cooperative effort between the NASA Langley Research Center (LaRC) and the National Space Development Agency of Japan (NASDA). The thin film samples described herein were part of an atomic oxygen exposure experiment (AOE) and were exposed to primarily atomic oxygen (~1 X 1019 atoms/cm2). The thin film samples consisted of three phosphine oxide containing polymers (arylene ether, benzimidazole and imide). Based on post-flight analyses using atomic force microscopy, X-ray photoelectron spectroscopy, and weight loss data, it was found that atomic oxygen exposure of these materials efficiently produces a phosphate layer at the surface of the samples. This layer provides a barrier towards further attack by AO. Consequently, these materials do not exhibit linear erosion rates which is in contrast with most organic polymers. Qualitatively, the results obtained from these analyses compare favorably with those obtained from samples exposed to atomic oxygen and or oxygen plasma in ground based exposure experiments. The results of the low Earth orbit atomic oxygen exposure on these materials will be compared with those of ground based exposure to AO.
    Keywords: Nonmetallic Materials
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  • 3
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    Space Environmentally Stable Polyimides and Copolyimides (2000)
    In:  CASI
    Details
    Publication Date: 2018-06-05
    Description: Polyimides with a unique combination of properties including low color in thin films, atomic oxygen (AO), ultra-violet (UV) radiation resistance, solubility in organic solvents in the imide form, high glass transition (T(sub g)) temperatures and high thermal stability have been prepared and characterized. The polymers were prepared by reacting a novel aromatic diamine with aromatic dianhydrides in a polar aprotic solvent. The solubility of the polymers in the imide form as well as the color density of thin films were dependent upon the chemical structure of the dianhydride. Several thin films (25-50 mm thick) prepared by solution casting of amide acid or imide solutions exhibited very low color and high optical transparency (approximately 90%) as determined by UV/visible spectroscopy. The polymers exhibited T(sub g)s 〉200 C depending upon the structure of the dianhydride and temperatures of 5% weight loss approximately 500C in air as determined by dynamic thermogravimetric analysis. Thin films coated with silver/inconel were exposed to a high fluence of AO and 1000 equivalent solar hours of UV radiation. The effects of these exposures on optical properties were minor. These space environmentally durable polymers are potentially useful in a variety of applications on spacecraft such as thin film membranes on antennas, second-surface mirrors, thermal/optical coatings and multi-layer thermal insulation (MLI) blanket materials. The chemistry, physical and mechanical properties of the polymers as well as their responses to AO and UV exposure will be discussed.
    Keywords: Nonmetallic Materials
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  • 4
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    Measurement of Elastic Microfence Deflection for Aerodynamic Flow Sensing (2018)
    In:  CASI
    Details
    Publication Date: 2019-08-01
    Description: Bio-inspired artificial hair sensors have the potential to detect aerodynamic flow features such as stagnation point, flow separation, and flow reattachment that could be beneficial for ight control and performance enhancement of aircraft. In this work, elastic microfence structures were tested on a at-plate setup. The microfences were fabricated from a two-part silicone molded against a template patterned by laser ablation. The response of the microfences to different freestream velocities and to flow reversal at the sensor were recorded via an optical microscope.
    Keywords: Aerodynamics
    Type: NF1676L-28893 , (ISSN 0957-0233) (e-ISSN 1361-6501)
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  • 5
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    Shear Stress Sensing using Elastomer Micropillar Arrays (2013)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: The measurement of shear stress developed as a fluid moves around a solid body is difficult to measure. Stresses at the fluid-solid interface are very small and the nature of the fluid flow is easily disturbed by introducing sensor components to the interface. To address these challenges, an array of direct and indirect techniques have been investigated with various advantages and challenges. Hot wire sensors and other indirect sensors all protrude significantly into the fluid flow. Microelectromechanical systems (MEMS) devices, although facilitating very accurate measurements, are not durable, are prone to contamination, and are difficult to implement into existing model geometries. One promising approach is the use of engineered surfaces that interact with fluid flow in a detectable manner. To this end, standard lithographic techniques have been utilized to generate elastomeric micropillar arrays of various lengths and diameters. Micropillars of controlled length and width were generated in polydimethylsiloxane (PDMS) elastomer using a soft-lithography technique. The 3D mold for micropillar replication was fabricated using laser ablative micromachining and contact lithography. Micropillar dimensions and mechanical properties were characterized and compared to shear sensing requirements. The results of this characterization as well as shear stress detection techniques will be discussed.
    Keywords: Nonmetallic Materials
    Type: NF1676L-16327 , American Chemical Society National Meeting and Exposition; Sep 08, 2013 - Sep 12, 2013; Indianapolis, IN; United States
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  • 6
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    Carbon Nanotube/Conductive Additive/Space Durable Polymer Nanocomposite Films for Electrostatic Charge Dissipation (2003)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Thin film membranes of space environmentally stable polymeric materials possessing low color/solar absorptivity (alpha) are of interest for potential applications on Gossamer spacecraft. In addition to these properties, sufficient electrical conductivity is required in order to dissipate electrostatic charge (ESC) build-up brought about by the charged orbital environment. One approach to achieve sufficient electrical conductivity for ESC mitigation is the incorporation of single wall carbon nanotubes (SWNTs). However, when the SWNTs are dispersed throughout the polymer matrix, the nanocomposite films tend to be significantly darker than the pristine material resulting in a higher alpha. The incorporation of conductive additives in combination with a decreased loading level of SWNTs is one approach for improving alpha while retaining conductivity. Taken individually, the low loading level of conductive additives and SWNTs is insufficient in achieving the percolation level necessary for electrical conductivity. When added simultaneously to the film, conductivity is achieved through a synergistic effect. The chemistry, physical, and mechanical properties of the nanocomposite films will be presented.
    Keywords: Nonmetallic Materials
    Type: 35th SAMPE International Technical Conference; Sep 28, 2003 - Oct 02, 2003; Dayton OH; United States
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  • 7
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    Further Investigation Into the Use of Laser Surface Preparation of Ti-6Al-4V Alloy for Adhesive Bonding (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Adhesive bonding offers many advantages over mechanical fastening, but requires robust materials and processing methodologies before it can be incorporated in primary structures for aerospace applications. Surface preparation is widely recognized as one of the key steps to producing robust and predictable bonds. This report documents an ongoing investigation of a surface preparation technique based on Nd:YAG laser ablation as a replacement for the chemical etch and/or abrasive processes currently applied to Ti-6Al-4V alloys. Laser ablation imparts both topographical and chemical changes to a surface that can lead to increased bond durability. A laser based process provides an alternative to chemical-immersion, manual abrasion, and grit blast process steps which are expensive, hazardous, environmentally unfriendly, and less precise. In addition, laser ablation is amenable to process automation, which can improve reproducibility to meet quality standards for surface preparation. An update on work involving adhesive property testing, surface characterization, surface stability, and the effect of laser surface treatment on fatigue behavior is presented. Based on the tests conducted, laser surface treatment is a viable replacement for the immersion chemical surface treatment processes. Testing also showed that the fatigue behavior of the Ti-6Al-4V alloy is comparable for surfaces treated with either laser ablation or chemical surface treatment.
    Keywords: Nonmetallic Materials
    Type: NF1676L-18257 , Society for the Advancement of Material and Process Engineering (SAMPE TECH 2014); Jun 02, 2014 - Jun 05, 2014; Seattle, WA; United States
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  • 8
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    Synthesis and Modification of Holey Graphene for Energy Storage (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Nonmetallic Materials
    Type: NF1676L-20992 , Spring 2015 American Chemical Society National Meeting; Mar 22, 2015 - Mar 26, 2015; Denver, CO; United States
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  • 9
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    Synthesis and Modification of Holey Graphene for Energy Storage (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Porous graphene materials have recently drawn significant interest for energy storage applications due to the effective use of the graphitic surface area provided by the pores. Holey graphene is a type of porous graphene with pores in the form of physical through thickness holes. This type of porous graphene provides a unique morphology that allows for effective transport of molecular species through the graphene plane. Therefore, as we recently demonstrated, holey graphene could be advantageous in the preparation of electrodes in supercapacitors with high volumetric performance.1 We have developed methodologies to scalably prepare holey graphene materials with or without the use of catalysts (Figure 1).1,2 In this presentation, we will discuss the choice of synthetic strategies and experimental conditions on the morphology and physical properties of holey graphene (Figure 2) and the effect on their electrochemical properties. We will also present the results on the further modification of holey graphene to study their physical and chemical properties, especially with regard to the stability and chemical reactivity of carbons located around the edges of the holes.
    Keywords: Nonmetallic Materials
    Type: NF1676L-19947 , Spring 2015 American Chemical Society National Meeting; Mar 22, 2015 - Mar 26, 2015; Denver, CO; United States
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  • 10
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    Shear Stress Sensing with Elastic Microfence Structures (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: In this work, elastic microfences were generated for the purpose of measuring shear forces acting on a wind tunnel model. The microfences were fabricated in a two part process involving laser ablation patterning to generate a template in a polymer film followed by soft lithography with a two-part silicone. Incorporation of a fluorescent dye was demonstrated as a method to enhance contrast between the sensing elements and the substrate. Sensing elements consisted of multiple microfences prepared at different orientations to enable determination of both shear force and directionality. Microfence arrays were integrated into an optical microscope with sub-micrometer resolution. Initial experiments were conducted on a flat plate wind tunnel model. Both image stabilization algorithms and digital image correlation were utilized to determine the amount of fence deflection as a result of airflow. Initial free jet experiments indicated that the microfences could be readily displaced and this displacement was recorded through the microscope.
    Keywords: Aerodynamics
    Type: NF1676L-19956 , AIAA Aviation 2015; Jun 22, 2015 - Jun 25, 2015; Dallas, TX; United States|AIAA Aviation 2015 Aerodynamic Measurement Technology and Ground Testing Conference; Jun 22, 2015 - Jun 25, 2015; Dallas, TX; United States
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