Emilie J. Siochi's research while affiliated with Hampton VA Medical Center and other places
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Publications (89)
A simulation technique has been developed for predicting the char yield of organic resins during high-temperature processing. In silico methods can aid in the screening of new advanced materials for a number of important properties, but no chemistry-sensitive protocol currently exists for predicting the important experimental value of char yield. T...
An expansion of the high-temperature/high-performance polymer 3D printing feedstock palette is critical for the adoption of the technology in more aerospace applications. Open-source printers are a potential platform for the insertion of new materials to the printing palette. However, as-purchased, they are not capable of printing high-temperature...
A framework using peridynamic theory is developed and demonstrated for deformation and failure analysis of carbon nanotube (CNT) yarn-based structural composites. Experimental work involved tension testing of a CNT yarn/polymer composite resulting in stress–strain response up to and including failure. The as-prepared specimen was characterized usin...
Fused filament fabrication (FFF), a form of filament-based material extrusion additive manufacturing (AM), is an extremely useful technique for the rapid production of highly customized products; however, empirical evidence is heavily relied upon for understanding of the process. Initial modeling attempts have traditionally focused on predicting he...
Large-diameter carbon nanotubes (CNTs) synthesized by floating-catalyst chemical vapor deposition (FC-CVD) assemble into bundles and subsequently into aerogel networks from which yarns and sheets are mechanically drawn. The CNT bundles exhibit unique microstructures with collapsed CNT packing, not found in other types of CNT yarns. At the same time...
Achieving high strength in fiber reinforced structural composites requires effective load transfer between the high-performance fiber reinforcement, e.g., carbon nanotube (CNT) yarn, and the matrix. Various processing approaches to enhance the interaction between CNT fiber and the matrix were investigated. The apparent interfacial shear strengths (...
Carbon nanotube aerogels are interesting platforms for manufacturing lightweight composites. To guide the development, we screen with tight-binding atomistic calculations two primary crystalline organizations of nanotubes with 1.4-4.5 nm radii and 1-3 number of walls. Calculations reveal a crossover from polygonised nanotubes with hexagonal close-p...
We report on electrical insulating materials that not only have sufficient mechanical toughness to survive use conditions, but also possess the ability to undergo thermally induced self-repair when damaged. By controlling the cross-link density, a modified ethylene-octene copolymer (EOC) is able to retain its self-healing abilities while also being...
The growing commercial availability of carbon nanotube (CNT) macro-assemblages such as sheet and yarn is making their use in structural composite components increasingly feasible. However, the mechanical properties of these materials continue to trail those of state-of-the-art carbon fiber composites due to relatively weak inter-tube load transfer....
Graphene, the first discovered and most studied two-dimensional material, has gained increasing interest in the research community due to a combination of unique optical, electronic transport, and structural properties. Single layer graphene is transparent, conductive, strong and flexible. In this work the mechanical flexibility, conductivity, and...
Quality control and repeatability of 3D printing must be enhanced to fully unlock its utility beyond prototyping and noncritical applications. Machine learning is a potential solution to improving 3D printing performance and is explored for areas including flaw identification and property prediction. However, critical problems must be resolved befo...
Molecular dynamics simulations of carbon nanotube (CNT) composites, in which the CNTs are continuous across the periodic boundary, overestimate the experimentally measured mechanical properties of CNT composites along the fiber direction. Since the CNTs in these composites are much shorter than the composite dimensions, load must be transferred eit...
Recent availability of carbon nanotubes in quantities and formats amenable to producing macroscale components invites consideration of these materials in space applications where their attractive properties can enable the realization of bold concepts for affordable space exploration. The challenge is to identify relevant systems and quantify the be...
Additive manufacturing (or 3D printing) via Fused Filament Fabrication (FFF), also known as Fused Deposition Modeling (FDM), is a process where material is placed in specific locations layer-by-layer to create a complete part. Printers designed for FFF build parts by extruding a thermoplastic filament from a nozzle in a predetermined path. Original...
Continuous carbon nanotube (CNT) yarn filaments can be employed as an inherently multifunctional feedstock for additive manufacturing (AM). With this material, it becomes possible to use a single material to impart multiple functionalities in components and take advantage of the tailorability offered by fused filament fabrication (FFF) over convent...
A significant mechanical reinforcement of epoxy matrices with carbon nanotubes (CNTs) requires a very strong covalent interfacial bonding between the tube and the resin, diglycidylether of bisphenol A (DGEBA). Using classical molecular dynamics (MD) and density functional theory (DFT), various methods of improving covalent binding to CNTs are appli...
Carbon nanotubes (CNTs) are one-dimensional nanomaterials with outstanding electrical and thermal conductivities and mechanical properties. Recent advances in CNT manufacturing have made bulk forms such as yarns, tapes and sheets available in commercial quantities to permit the evaluation of these materials for aerospace use. The high tensile prope...
While the mechanical properties of highly aligned carbon nanotube (CNT) thin films and their nanocomposites have been widely studied, the load transfer mechanisms and failure modes of aligned CNT composites have not been sufficiently explored and understood. In this research, super-aligned CNT thin films with a measured alignment fraction of up to...
Carbon nanotubes (CNTs) have captured the imagination of the research community because of their many superior properties. In the nearly 25 years since their novelty was recognized, however, progress toward their utility as superlightweight structural materials, especially for aerospace applications, has been disappointing. Recent advancements have...
Mitigation of insect residue contamination on next generation aircraft is vital for the commercial exploitation of laminar flow technologies. A review of the critical entomological, meteorological and aeronautical factors affecting insect residue accumulation on aircraft leading edge surfaces is herein presented. An evaluation of a passive mitigati...
Thermoset/carbon nanotube (CNT) sheet nanocomposites were successfully fabricated by resistive heating assisted infiltration and cure (RHAIC) of the polymer matrix resin. Resistive heating takes advantage of the electrical and thermal conductivity of CNTs to rapidly and uniformly introduce heat into the CNT sheet. Heating the CNT sheet reduces the...
Large volumes of carbon nanotube (CNT) sheets and yarns are required to enable practical applications such as structural reinforcements, electrical conductors, electromagnetic interference shielding, and energy storage. Although these macroscopic assemblages of CNTs are commercially available, reports on their handling and processing have been quit...
A key, enabling element of a dielectric barrier discharge (DBD) actuator is the dielectric substrate material. While various investigators have studied the performance of different homogeneous materials, most often in the context of related DBD experiments, fundamental studies focused solely on the dielectric materials have received less attention....
Due to their unique shape memory capability, shape memory materials have been studied in numerous areas that require shape reconfiguration. This capability enables the adaptive wing structural concept. The structure prototype required enhanced interfacial strength between the shape memory polymer composite and structural metal alloys to enable the...
Recent advances in the synthesis of large-scale quantities of carbon nanotubes (CNT) have provided the opportunity to study the mechanical properties of polymer matrix composites using these novel materials as reinforcement. Nanocomp Technologies, Inc. currently supplies large sheets with dimensions up to 122 cm × 244 cm containing both single-wall...
A nanocomposite structure and method of fabricating same are provided. The nanocomposite structure is a polymer in an extruded shape with carbon nanotubes (CNTs) longitudinally disposed and dispersed in the extruded shape along a dimension thereof. The polymer is characteristically defined as having a viscosity of at least approximately 100,000 poi...
Practical approaches are needed to take advantage of the nanometer-scale mechanical properties of carbon nanotubes (CNTs) at the macroscopic scale. This study was conducted to elucidate the salient factors that can maximize the mechanical properties of nanocomposites fabricated from commercially available CNT sheets. The CNT sheets were modified by...
In this paper, the interdisciplinary energy harvesting issues on piezoelectric energy harvesting were investigated using a '33' mode (mechanical stress and/or electric field are in parallel to the polarization direction) lead zirconate titanate multilayer piezoelectric stack (PZT-Stack). Key energy harvesting characteristics including the generated...
Surface contamination from insect strikes on aircraft wing leading edges can induce localized boundary layer transition from laminar to turbulent flow, resulting in increased aerodynamic drag and reduced fuel efficiency. As aviation fuel costs continue to climb, strategies to reduce fuel burn using laminar flow have led to renewed interest in surfa...
Mitigation of insect residue adhesion on leading edges of future aircraft to reduce fuel burn through sustenance of laminar flow is being investigated under NASA's Environmentally Responsible Aviation Program. Depending on air speed, temperature, and wing design, the critical residue height for laminar flow disruption can be as low as 10 μm near th...
Research at NASA Langley Research Center (NASA LaRC) has identified several commercially available thermoplastic polymers that self-heal after ballistic impact and through-penetration. One of these resins, polybutadiene graft copolymer (PBg), was processed with unsized IM7 carbon fibers to fabricate reinforced composite material for further evaluat...
To understand the mechanical properties of amorphous carbon (a-C)/boron nitride nanotube (BNNT) nanostructures, in situ mechanical tests are conducted inside a transmission electron microscope equipped with an integrated atomic force microscope system. The nanotube structure is modified with amorphous carbon deposited by controlled electron beam ir...
Microwave irradiation was shown to be an effective energy source for the rapid decomposition of organic metal salts (such as silver acetate) in a solid mixture with various carbon and noncarbon substrates under completely solvent-free conditions. The rapid and local Joule heating of microwave absorbing substrates (i.e., carbon-based) resulted in th...
Polymer-single wall carbon nanotube (SWNT) composite films were prepared and characterized as part of an effort to develop polymeric materials with improved combinations of properties for potential use on future spacecraft. Next generation spacecraft will require ultra-lightweight materials that possess specific and unique combinations of propertie...
In this paper, we report the study of a “33” longitudinal mode, piezoelectric PZT ceramic multilayer stack (PZT-Stack) with high effective piezoelectric coefficient for broader bandwidth high-performance piezoelectric energy harvesting transducers (PEHTs). The PZT-Stack is composed of 300 layers of 0.1 mm thick PZT plates, with overall dimensions o...
Several commercially available polymeric materials that display puncture self-healing functionality at different temperature ranges have been identified. The puncture healing mechanism in these materials is a function of the synergistic combination of viscoelastic properties. Temperatures at the site of impact were measured to be as high as 130 o C...
Ground-based hypervelocity impact testing was conducted on IM7/977-3 quasi-isotropic flat panels at normal incidence using micron-sized particles (i.e. ≤ 100 μm) of soda lime glass and olivine. Testing was performed at room temperature (RT) and 175°C with results from the 175°C test compared to those obtained at RT. Between 10 and 30 particles with...
For co-polyimides (PIs) of mellitic acid dianhydride, 1,3-aminophenoxybenzene and 4,4′-oxydiphthalic anhydride, Zr-pendent group content could be increased to 50% (mol) improving atomic oxygen (AO) resistance while retaining good film properties. Spectral data are consistent with expected structures. Intrinsic viscosities of 0.54—0.60 dL g—1 and av...
Methyl, methoxy, and nitrile (cyano) functional groups were incorporated into the metal–organic pendent group of a co-polyamic acid, co-PAA[(3,4′-ODA/ODPA)0.9(3,4′-ODA/{MADA-p-Zr(adsp)(Rdsp)})0.1], in various locations to investigate their effects on polymer chain interactions and film quality. Proton nuclear magnetic resonance and gel permeation c...
Control of electrospun fiber placement and distribution was investigated by examining the effect of electric field parameters on the electrospinning of fibers. The experimental set-up used in this study eliminated the bending instability and whipping, allowing the jet to be modeled as a stable trajectory. Coupling of experimental and computational...
Highly aligned electrospun micro- and nanoscale fibers and pseudowoven mats were produced via electrospinning by incorporating an auxiliary counter electrode to create an electric field of controlled geometry and magnitude. Two polymers were examined using this technique: a polyimide (CP2) and a biodegradable polymer, poly(glycolic acid) (PGA). Hig...
Using mellitic acid dianhydride to prepare Zr-containing pendent copolyimides (co-PIs) is currently being evaluated as a means of further increasing Zr concentration and atomic oxygen resistance while retaining other desirable film properties. The immediate objectives en route to this ultimate goal are: (1) to address the increased tendency of copo...
Multi‐wall carbon nanotubes were synthesized from sucrose by a pyrolytic technique using mesopourous MCM‐41 silicate templates without transition metal catalysts. The nanotubes were examined in the carbon/silicate composite and after dissolution of the silicate. High‐resolution transmission electron microscopy study of the multi‐wall nanotubes show...
For the purpose of incorporating multifunctionality into advanced composites, blends of PETI-330 and multi-walled carbon nanotubes (MWCNTs) were prepared, characterized and fabricated into moldings. PETI-330/MWCNT mixtures were prepared at concentrations ranging from 3 to 25wt% by dry mixing the components in a ball mill. The resulting powders were...
The goal of this research is to increase the metal-organic concentration in Kapton-like polyimides (PIs) to achieve increased atomic oxygen (AO) resistance while retaining desirable film properties. Co-polyamic acid (PAA) precursors were prepared using a novel polymer building block, mellitic acid dianhydride (MADA), to provide sites for pendent gr...
Multifunctional composites present a route to structural weight reduction. Nanoparticles such as carbon nanofibers (CNF) provide a compromise as a lower cost nanosize reinforcement that yields a desirable combination of properties. Blends of PETI-330 and CNFs were prepared and characterized to investigate the potential of CNF composites as a high-p...
As part of an ongoing effort to develop multi-functional advanced composites, blends of PETI-330 and multi-walled carbon nanotubes (MWNTs) were prepared and characterized. Dry mixing techniques were employed and the maximum loading level of the MWNT chosen was based primarily on its effect on melt viscosity. The PETI-330/MWNT mixtures were prepared...
The equations needed to correctly interpret both AC and DC conductivity results of single wall carbon nanotube (SWNT) polymer composites and the scaling of these results onto a single master curve are presented. Brief discussions on the factors that determine the critical volume fraction (ϕc) and the percolation exponent (t) are also given. The res...
A hybrid-clay nanocomposite was prepared by dispersing organically modified layered silicates (organoclay) into an organic–inorganic hybrid matrix. Layered silicates were dispersed in a hybrid matrix consisting of an alkoxysilane terminated amide acid oligomer and tetraethoxysilane. Transmission electron microscopy (TEM) and wide angle X-ray diffra...
As part of an ongoing effort to incorporate multi-functionality into advanced composites, blends of PETI-330 and multi-walled carbon nanotubes (MWCNTs) were prepared, characterized and fabricated into moldings. The PETI-330/MWCNT mixtures were prepared at concentrations ranging from 3 to 25 weight percent by dry mixing the components in a ball mill...
As part of an ongoing effort to incorporate multifunctionality into advanced composites, blends of PETI-330 and multi-walled carbon nanotubes (MWCNTs) were prepared, characterized and fabricated into moldings. The PETI-330/MWCNT mixtures were prepared at concentrations ranging from 3 to 25 weight percent by dry mixing the components in a ball mill....
As part of an ongoing effort to incorporate multifunctionality into advanced composites, blends of PETI-330 and multi-walled carbon nanotubes (MWCNTs) were prepared, characterized and fabricated into moldings. The PETI-330/MWCNT mixtures were prepared at concentrations ranging from 3 to 25 weight percent by dry mixing the components in a ball mill....
High performance polymeric foams have experienced a growing demand in aerospace applications such as cryogenic insulation, flame-retardant panels and structural sub-components. The Next Generation Launch Technology (NGLT) program requires foams capable of retaining their structural integrity while providing insulating capabilities in a liquid hydro...
A method of stepwise assembling thin polymer/single-walled carbon nanotube (SWCNT) films using donor−acceptor interactions is demonstrated. When the affinity that amine groups have for nanotubes were utilized, films were formed by the sequential adsorption of polyethylenimine and polyallylamine followed by SWCNTs onto silicon substrates. In an effo...
Melt processing of SWCNT/Ultem nanocomposite fibers was demonstrated for fibers containing up to 1 wt% SWCNTs. High-resolution electron microscopy and Raman spectroscopy were used to evaluate the quality of SWCNT dispersion. SWCNT alignment in the fiber direction was induced by shear forces present during the melt extrusion and fiber drawing proces...
Single wall carbon nanotubes (SWNTs) have been dispersed in a nitrile functionalized polyimide matrix and the resulting composite shows excellent stability with respect to reaggregation of the nanotubes. This contrasts with the behaviour of structurally similar polyimides in which the dispersion is only stable for short periods of time. Shifts in c...
High-resolution electron microscopy and energy-filtered imaging methods were used to examine single-wall carbon nanotubes and nanotube reinforced polyimide composites. The nanotubes were studied alone, in a polyimide matrix composite, and after deposition of composite material previously dissolved in a solvent. Energy-filtered images based on nitro...
Electrical properties of single wall carbon nanotube (SWNT) reinforced polyimide composites were investigated as a function of SWNT concentration. AC and DC conductivities were measured, and the frequency behavior of the specific admittance was investigated. The experimental conductivity was found to obey a percolation-like power law with a relativ...
For centuries, biology has provided fertile ground for hypothesis, discovery, and inspiration. Time-tested methods used in nature are being used as a basis for several research studies conducted at the NASA Langley Research Center as a part of Morphing Project, which develops and assesses breakthrough vehicle technologies. These studies range from...
Revolutionary design concepts in future aerospace vehicles will depend on extraordinary material properties to permit significant reduction of mass and size of components, while imparting intelligence. Due to their combination of remarkable electrical and mechanical properties, carbon nanotubes (CNT) are expected to enable this paradigm shift in de...
For centuries, biology has provided fertile ground for hypothesis,
discovery, and inspiration. Time-tested methods used in nature are being
used as a basis for several research studies conducted at the NASA
Langley Research Center as a part of Morphing Project, which develops
and assesses breakthrough vehicle technologies. These studies range from...
Application of carbon nanotubes as reinforcement in structural composites is dependent on the efficient dispersion of the nanotubes in a high performance polymer matrix. The characterization of such dispersion is limited by the lack of available tools to visualize the quality of the matrix/carbon nanotube interaction. The work reported herein demon...
Single wall carbon nanotube (SWNT) reinforced polymer nanocomposites were prepared. Uniform dispersion of thin bundles of SWNTs in the polymer matrix was evidenced by high-resolution electron microscopy. Electrical and dielectric properties of the nanocomposites were measured as a function of SWNT concentration, temperature, and frequency. The nano...
A key impediment to the widespread application of carbon nanotubes as reinforcing fillers in nanocomposite applications is the lack of a general method for uniformly dispersing individual tubes in the polymer matrix and stabilizing the resulting composite. In an effort to address the latter challenge, this contribution examines the stability of the...
Electrospinning was utilized to create lightweight, electrically responsive wing skins for micro-air vehicle (MAV) wing frame designs. Various compositions of an electroactive polymer were investigated to determine the appropriate electrospinning conditions for these materials. Electrospun mats of these materials were characterized via optical micr...
For centuries, biology has provided fertile ground for hypothesis, discovery, and inspiration. Time-tested methods used in nature are being used as a basis for several research studies conducted at the NASA Langley Research Center as a part of Morphing Project, which develops and assesses breakthrough vehicle technologies. These studies range from...
Single wall nanotube reinforced polyimide nanocomposites were synthesized by in situ polymerization of monomers of interest in the presence of sonication. This process enabled uniform dispersion of single wall carbon nanotube (SWNT) bundles in the polymer matrix. The resultant SWNT–polyimide nanocomposite films were electrically conductive (antista...
An EFTEM Study of Polyimide Adhesion to Single-Walled Carbon Nanotube Bundles - Volume 8 Issue S02 - N.D. Evans, C. Park, R. Crooks, E.J. Siochi, E.A. Kenik
The NASA Morphing Project seeks to develop and assess advanced technologies and integrated component concepts to enable efficient, multi-point adaptability in air and space vehicles. In the context of the project, the world 'morphing' is defined as 'efficient, multi-point adaptability' and may include macro, micro, structural and/or fluidic approac...
The NASA Morphing Project seeks to develop and assess advanced technologies and integrated component concepts to enable efficient, multi-point adaptability in air and space vehicles. In the context of the project, the world 'morphing' is defined as 'efficient, multi-point adaptability' and may include macro, micro, structural and/or fluidic approac...
Application of carbon nanotubes as reinforcement in structural composites is dependent on the efficient dispersion of the nanotubes in a high performance polymer matrix. The characterization of such dispersion is limited by the lack of available tools to visualize the quality of the matrix/carbon nanotube interaction. The work reported herein demon...
As part of an effort to develop a low-volatile, essentially dry, carbon fiber tape from a phenylethynyl-terminated imide for use in heated head automated tow placement, a 70:30 blend of LaRCTM PETI-5 and LaRCTM PETI-IAX was prepared in N-methyl-2-pyrrolidinone by mixing the phenylethynylterminated amide acid solutions together. Solutions of the ami...
This report represents an attempt to see if some of the techniques biological systems use to maximize their efficiency can be applied to the problems NASA faces in aeronautics and space exploration. It includes an internal survey of resources available at NASA Langley Research Center for biomimetics research efforts, an external survey of state of...
In this study, a technique is presented for developing constitutive models for polymer composite systems reinforced with single-walled carbon nanotubes (SWNT). Because the polymer molecules are on the same size scale as the nanotubes, the interaction at the polymer/nanotube interface is highly dependent on the local molecular structure and bonding....
Unoriented thin films of phenylphosphine oxide-containing poly(arylene ether)s were exposed to low Earth orbit aboard the space shuttle Atlantis (STS-51) as part of a flight experiment designated Limited Duration Candidate Exposure (LDCE 4–5). The samples were exposed to primarily atomic oxygen (!10,\7×1019 atoms/cm2). Based on post-flight analyses...
Unoriented thin films Of phenylphosphine oxine-containing poly(arylene ether)s were exposed to low Earth orbit aboard the space shuttle Atlantis (STS-51) as part of a flight experiment designated Limited Duration Candidate Exposure (LDCE 4-5). The samples were exposed to primarily atomic oxygen (similar to 7 x 10(19) atoms/cm(2)). Based on post-fli...
A controlled-molecular-weight LARCr'-CPI 2 poly(amide acid) was synthesized to investigate solution property changes that result from aging'Both dilute and concentrated solutions were aged at five temperatures and periodically analysed over a 33 d period. Various molecular weight parameters were obtained by gel permeation chromatography in combinat...
A series of controlled molecular weight poly(arylene ether benzimidazole)s (PAEBIs) endcapped with either benzimidazole, ethynyl or phenylethynyl groups was prepared and characterized. PAEBIs endcapped with either ethynyl or phenylethynyl groups were thermally cured to provide polymers with improved moisture and solvent resistance and higher glass...
Thin films of four experimental poly(arylene ether)s of similar chemical structure were exposed to 1 MeV electrons while under high vacuum. The films received total exposures of 5 x 10 exp 7 and 1 x 10 exp 9 rads at a dose rate of 5 x 10 exp 7 rads/h and a pressure of 2 x 10 exp -7 torr. Films exposed to 5 x 10 exp 7 rads showed dramatic changes in...
Citations
... Unlike the MsM, these NsM, at proper replacement of fiber-bridging effect with nanoscale bridging, do not compromise in-plane properties and, depending on the modification type, show improvement in fracture toughness. Additionally, these NsM adds multiscale hierarchical toughening mechanisms [24,25] which is not noted in case of MsM. Compared to MsM, a NsM offers a higher surface-tovolume ratio, which presents the possibility of increasing the amount of energy dissipated during fracture. ...
... Purse et al. 24 modeled phenolic resin polymerization and pyrolysis with gas removal to find char yield, Young's modulus, reaction mechanics, and thermal conductivity for different pyrolysis temperatures, but the mass densities of the model lack experimental validation. Gissinger et al. 25 recently found that MD simulations could be used to predict the char yield of a variety of different precursors via an implementation of a novel MD in silico volatile removal algorithm. ...
... One of the most popular AM methods, based on the principle of material extrusion, is called fused filament fabrication (FFF), or fused deposition modelling (FDM). This process makes use of thermoplastics to manufacture products by depositing melted material layer-by-layer [1][2][3][4][5][6]. The systems working on the principle of FFF/FDM are termed as 3D printers [7,8]. ...
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