Engineering topics

Taylor, L. T.

Publications and source records attributed to Taylor, L. T..

At least 19 records

NASA NTRS1988

Polyimide/metal composite films via in situ decomposition of inorganic additives - Soluble polyimide versus polyimide precursor

Polyimide-metal oxide (Co3O4 or CuO) composite films have been prepared via in situ thermal decomposition of cobalt (II) chloride or bis(trifluoroacetylacetonato)copper(II). A soluble polyimide (XU-218) and its corresponding prepolymer (polyamide acid) were individually employed as the reaction matrix. The resulting composites exhibited a greater metal oxide concentration at the air interface with polyamide acid as the reaction matrix. The water of imidization that is released during the concurrent polyamide acid cure and additive decomposition is believed to promote metal migration and oxide formation. In contrast, XU-218 doped with either HAuCl4.3H2O or AgNO3 yields surface gold or silver when thermolyzed (300 C).

Rancourt, J. D.↗

NASA NTRS1988

Characterization of microcomposite polyimide films

Thermally stable microcomposite polyimide films were prepared by the homogeneous incorporation of either a soluble metal salt or a metal complex into a poly(amide-acid)/N,N-dimethylacetamide solution. The thermal processing of films solvent cast onto glass substrates and cured in an appropriate atmosphere yields films containing not only a fairly uniform dispersion of submicrometer particles, but also a new surface layer of metal or metal oxide. These polymeric systems have been characterized using X-ray photoelectron spectroscopy, Auger electron spectroscopy with depth profiling via argon ion etching, transmission electron microscopy of ultramicrotomed cross-sections, scanning electron microscopy, elemental analysis, thermal analysis, and variable temperature electrical resistivity determinations. The data from these techniques were used cooperatively to develop a model for these microcomposite polyimide films.

Rancourt, J. D.↗

NASA NTRS1988

Poly(imide-siloxane) segmented copolymer structural adhesives prepared by bulk and solution thermal imidization

The improved properties that have been demonstrated through thermal solution imidization in the case of polyimides and poly(imide-siloxane) segmented copolymers suggests significant potential for application of these new materials. Specifically, the enhancement in solubility, moisture reduction, and processability observed through this solution technique is quite dramatic. Previous work has shown that the presence of low amounts of siloxane does not detract significantly from the lap shear strength of these materials to titanium in the case of bulk thermal imidization synthesis. In addition, the siloxane incorporation results in the added advantage of resistance to hot, wet environments. This added durability is presumably due to the hydrophobic siloxane segments preventing the uptake of water at the critical interphase between the adhesive and the adherend. This paper discusses the extension of this work to the solution imidization synthesis technique recently developed in our laboratory. Results dealing with the absolute bond strengths as well as durability and failure surface analysis will be presented.

Bott, R. H.↗

NASA NTRS1988

Characterization of cobalt(II) chloride-modified condensation polyimide films

The effect of solvent extraction on the properties of cobalt(II) chloride-modified polyimide films was investigated. Solvent-cast films were prepared from solutions of cobalt chloride in poly(amide acid)/N,N-dimethylacetamide (DMAc) and were subsequently dried and cured in static air, forced air, or inert gas ovens with controlled humidity. The films were extracted by either of the three processes (1) soaking in a tray with distilled water at room temperature, (2) soxhlett extraction with distilled water, or (3) soxhell extraction with DMAc. Extraction with DMAc was found to remove both cobalt and chlorine from the films and to slightly increase bulk thermal stability and both surface resistivity and electrical resistivity.

Rancourt, J. D.↗

NASA NTRS1987

DC electrical, thermal, and spectroscopic properties of various condensation polyimides containing surface cobalt oxide

Doping polyimides with cobalt ion causes the room temperature direct current electrical resistivity to decrease relative to the polymer alone, the reduction being most pronounced for the air-side of the cobalt modified polyimides. At a constant electrical field, resistivity for the volume, air-side and glass-side modes decreases yet further with an increase in temperature as expected for semiconductors and insulators. X-ray photoelectron spectroscopy indicates the air-side of the cobalt modified polyimides is predominantly Co3O4. The bulk resistivity of the air-side and activation energy of conduction for this surface are comparable to high purity sintered Co3O4. Charging characteristics at room temperature indicate a substantial polymer matrix contribution to both the glass-side and volume mode measurements but a negligible contribution to the air-side electrical properties. Volume electrical resistivity for similar additive levels is reduced by increasing the molecular flexibility of the host polymer.

Rancourt, J. D.↗

NASA NTRS1987

Structure property behavior of polyimide siloxane segmented copolymers

Procedures were developed for preparing soluble fully imidized polyimide-polydimethyl siloxane segmented copolymers of wide ranging compositions. At low siloxane levels, the materails behave as modified polyimides. At higher concentrations, the materials are analogous to thermoplastic elastomers. Characterization by dynamic mechanical and thermal analysis methods will be reported along with an assesment of the bulk mechanical properties and the surface behavior. The surface behavior is particularly interesting since the materials can be tailored to have siloxane surfaces even at rather low siloxane contents. This influences a number of properties such as the coefficient of friction and, importanly, the degradation of these materials under aggressive oxygen environments (e.g., atomic oxygen, oxygen plasma).

Arnold, C. A.↗

NASA NTRS1987

Synthesis and solution imidization studies of soluble poly(imide siloxane) segmented copolymers

Soluble metalinked poly(imide siloxane) segmented copolymers were synthesized utilizing a THF/NMP cosolvent system. The presence of dual solvent makes it possibled to reach high molecular weight in the amid acid stage. Incorporation of siloxanes at about 10 weight percent or higher enables the materials to be fully soluble in a range of polar solvents even after imidization. Imidization may be achieved either by conventional thermal methods on cast amic acid films or in appropriate solvent/azeotroping-agent systems employing moderate temperatures. The imidization procedure has been followed by FT-IR and NMR studies. FT-IR studies show the solution imidization follows first order kinetics and proceeds to about 96 percent completion. NMR studies of the isolated products show residual amic acid may be present after solution imidization, but only at very low levels. Properties of the solution imidized materials compared well with those obtained from samples imidized as thin films.

Summers, J. D.↗

NASA NTRS1987

In situ deposits of copper and copper oxide containing condensation polyimide films

Novel copper-polyimide composites have been synthesized via simultaneous thermal decomposition of solid solutions of bis (trifluoroacetylacetonato) copper (II) and thermal cyclodehydration of polyimide acid. In contrast to conventional filled polymer composites which are prepared by dispersion of particles or fibers in a polymer matrix this study has yielded in general uniform Cu or CuO dispersions of very small particle size that reside near the film surface that was exposed to the atmosphere during curing. The nature of the copper deposit, the thickness of the copper deposit, and the polyimide overlayer which bonds the copper to the polymer substrate depend on the curing atmosphere used. A variety of analytical surface methods along with thermogravimetric analysis and variable temperature (surface and volume) electrical resistivity measurements have been used to characterize these thin, flexible copper doped polyimide films.

Porta, G. M.↗

NASA NTRS1987

Electrical properties of polyimides containing a near-surface deposit of silver

Films containing a surface or near-surface deposit of palladium, gold or copper metal as well as tin, cobalt, copper, or lithium oxides have been prepared by dissolving appropriate metal salts into poly(amide-acid)/N,N-dimethylacetamide solutions and curing the solvent cast films to temperatures up to 300 C. This preparation technique has been extended to evaluate the thermal, spectroscopic, and electrical characteristics of condensation polyimide films modified with silver nitrate. A near-surface deposit of metallic silver results but the reflective surface has high electrical resistivity (sheet resistivity) due to a polymer coating or overlayer above the metal. Details pertaining to the silver nitrate modified condensation polyimides are presented. Also, the applicability of the structural model and electrical model previously proposed for the cobalt oxide system are assessed.

Rancourt, J. D.↗

NASA NTRS1984

Synthesis of tin-containing polyimide films

A series of tin-containing polyimide films derived from either 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride or pyromellitic dianhydride and 4,4'-oxydianiline have been synthesized and their electrical properties examined. Highest quality materials (i.e., homogeneous, smooth surface, flexible) with the best electrical properties were doped with either SnCl2.2H2O or (n-Bu)2SnCl2. In all cases, extensive reactivity of the tin dopant with water, air or polyamic acid during imidization is observed. Lowered electrical surface resistivities appear to be correlatable with the presence of surface tin oxide on the film surface.

Ezzell, S. A.↗

NASA NTRS1984

Electrical properties of metal-doped pyridine-derived polyimide films

A series of polyimide films containing pyridine coordinating groups doped with cobalt or nickel ions has been examined. Using 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, films were prepared in combination with 4,4'-oxydianiline, 4,4'-dianiline sulfide, 3,3'-bis(aminopyridine) sulfide and 2,2'-dioxyphenelenebis (5,5'-aminopyridine). Room temperature volume resistivities have been found to decrease slightly with sulfur and pyridine containing diamines relative to diamines which do not contain these functionalities. Doping with cobalt and nickel additives results in further lowering of room temperature volume resistivity. Preliminary temperature profiling experiments have shown that volume resistivity decreases as T(g) is approached.

Khor, E.↗

NASA NTRS1984

Mechanical and spectroscopic properties of metal containing polyimides

The incorporation of specific metal ions into polyimides is described. Detailed studies have included various compounds of copper, lithium, and palladium as dopants. Addition of the metal during polymermzation or after formation of the polyamic acid precedes the thermal imidization step. With many dianhydride-diamine-dopant combinations high quality variously colored films are produced. Many metal doped films exhibit (1) improved high temperature adhesive properties, (2) increased electrical conductivity, (3) excellent thermal stability, (4) improved acid/base resistance, (5) increased modulus in flexible films and (6) excellent high temperature tensile strength. X-ray photo-electron spectroscopic study of these films suggests that many of the additives undergo chemical modification during thermal imidization. Palladium dopants appear to be partially reduced to the metallic state, while lithium and copper dopants are probably converted to their oxides. Ion etching experiments with Auger electron spectroscopy monitoring are discussed.

Taylor, L. T.↗

NASA NTRS1984

Novel metal-filled polyimide electrodes

Palladium-coated polyimide films are evaluated as electrochemical electrodes. The film electrodes exhibit essentially identical behavior compared to bulk palladium electrodes. In aqueous 0.5M H2SO4, current peaks due to oxide formation, oxide stripping, hydrogen adsorption, and H2 oxidation are observed. The ferri/ferrocyanide redox couple is grossly irreversible in the same electrolyte. Reversible electrochemical behavior is obtained for Fe(EDTA)(1-/2-) in 1M KCl/H2O, and for ferrocene/ferricenium in 0.1M TEAP/dimethylacetamide.

Furtsch, T. A.↗

NASA NTRS1983

Mechanical and spectroscopic properties of metal-containing polyimides

The incorporation of specific metal ions into polyimides is described. Detailed studies have included various compounds of copper, lithium, and palladium as dopants. Addition of the metal during polymerization or after formation of the polyamic acid precedes the thermal imidization step. With many dianhydride-diamine-dopant combinations high quality variously colored films are produced. Many metal doped films exhibit (1) improved high temperature adhesive properties, (2) increased electrical conductivity, (3) excellent thermal stability, (4) improved acid/base resistance, (5) increased modulus in flexible films and (6) excellent high temperature tensile strength. X-ray photo-electron spectroscopic study of these films suggests that many of the additives undergo chemical modification during thermal imidization. Palladium dopants appear to be partially reduced to the metallic state, while lithium and copper dopants are probably converted to their oxides. Ion etching experiments with Auger electron spectroscopy monitoring are discussed.

Taylor, L. T.↗

NASA NTRS1982

Electrically conductive palladium containing polyimide films

Lightweight, high temperature resistant, electrically conductive, palladium containing polyimide films and methods for their preparation are described. A palladium (II) ion-containing polyamic acid solution is prepared by reacting an aromatic dianhydride with an equimolar quantity of a palladium II ion-containing salt or complex and the reactant product is cast as a thin film onto a surface and cured at approximately 300 C to produce a flexible electrically conductive cyclic palladium containing polyimide. The source of palladium ions is selected from the group of palladium II compounds consisting of LiPdCl4, PdS(CH3)2Cl2Na2PdCl4, and PdCl2. The films have application to aerodynamic and space structures and in particular to the relieving of space charging effects.

Taylor, L. T.↗

NASA NTRS1981

Aluminum ion-containing polyimide adhesives

A meta-oriented aromatic diamine is reacted with an aromatic dianhydride and an aluminum compound in the presence of a water or lower alkanol miscible ether solvent to produce an intermediate polyamic acid. The polyamic acid is then converted to the thermally stable, metal ion-filled polyimide by heating in the temperature range of 300 C to produce a flexible, high temperature adhesive.

St.clair, A. K.↗

NASA NTRS1981

Electrically conductive palladium-containing polyimide films

Palladium addition makes light, flexible film with low resistivity to relieve space charging. Polyimide film is prepared in four steps: preparation of polyamic acid in polar solvent; addition of soluable palladium complex salt; fabrication of film of "palladium polyamic acid" solution; and thermal imidization of film to palladium-containing polyimide by 300 C heating. Lowered resistivities were achieved without loss in film flexibility or increase in film weight.

St.clair, A. K.↗

NASA NTRS1981

Aluminum ions enhance polyimide adhesive

Adding complexed aluminum ions raises useful temperature of polyimide adhesive without embrittling it or reducing long term stability. Adhesives may be applied to prepared substrate surface without supports. Possible substrates are metal, composite, or polymeric film. Adhesive is excellent where bond flexibility is required.

St.clair, A. K.↗