Search

Commercial off-the-shelf (COTS) electronics are generally not specifically designed to perform in extremely transient high impact scenarios. This research focused on the development of a silver-decorated carbon black-based polymeric nanocomposite with properties such as high conductivity, flexibility, and shock absorbency. Polymeric rubber materials are generally very flexible and shock absorbing, however, most polymeric materials are electrical insulators. The dispersion of the silver-decorated carbon black into the polymeric matrix could significantly improve the electrical conductivity. The processing and fabrication of Ag-CB (silver-carbon black)/Epoxy (thermosetting epoxy polymer) and Ag-CB/TPU (thermoplastic polyurethane) will be reported. Both Ag-CB/Epoxy and Ag-CB/TPU mixtures with solvents showed the shear-thinning behavior, which was an important characteristic for direct printing of traces and Additive Manufacturing (AM). The mechanical properties of the nanocomposites were measured using Dynamic Mechanical Analysis (DMA) over a wide range of temperatures. These nanocomposite materials were also successfully used to print flexible circuits using a 3D-printing machine. The electrical resistance change for the Ag-CB/Epoxy on polydimethylsiloxane (PDMS) and Ag-CB/TPU on PDMS under strain was studied, and the results will be discussed.

The erosive effect of ultraviolet radiation and atomic oxygen at the lower earth orbit space environment of the International Space Station on Epon 862 based epoxy composites with 12 and 100 nm silica particles was investigated. Although exposure to ultraviolet radiation had a small effect on surface erosion, restricted to 2 µm of the top surface, concurrent exposure to ultraviolet radiation and atomic oxygen resulted in significant erosion. Atomic oxygen erosion of nanocomposites with 1–5 wt% silica particles resulted in a carpet-like residual surface layer whose thickness and morphology were dependent on the size and concentration of the embedded silica particles. The eroded surface of the control epoxy had high surface roughness in the form of 10–40 µm long conical protrusions. With the addition of silica particles, the residual surface layer became fibrous and rich in silica particles, and its density increased with the weight fraction and size of the silica particles. The large and uneven erosion depth of samples exposed to atomic oxygen and ultraviolet radiation resulted in a surface damage layer with average thickness between 5 and 100 µm with significantly reduced mechanical properties compared to the surface of the as-fabricated nanocomposites. The erosion yield of the control epoxy due to atomic oxygen was 4.36 × 10−24 cm3/atom and the addition of silica nanoparticles reduced it significantly to 1.78 × 10−25 cm3/atom. In particular, silica nanoparticles of diameter 12 and 100 nm and weight fraction 5% reduced the erosion yield of the control epoxy by 90% and 96%, respectively.

The primary objective of the research was to evaluate the rheology and thermal properties of silylated apophyllite–filled epoxy nanocomposite. Several n-octyldimethylsiloxy-apophyllite with different grafting degrees were synthesized by controlling the ratio of the apophyllite and n-octyldimethylchlorosilane. The thermal studies of silylated apophyllite have shown that the onset decomposition temperature of silylated apophyllite far exceeds the onset temperature of conventional organoclays (~260 °C). Chemorheological measurements of 1.8 wt% silylated apophyllite–filled tetra functional epoxy (MY720) and difunctional epoxy (DER661) resin mixture showed that the addition of the silylated apophyllite does not dramatically affect the cure profile of the epoxy resin with the availability of 40 min of processing window after the addition of apophyllite. Wide angle X-ray diffraction and transmission electron microscopy results of the shear mixed and cured nanocomposite suggest that the apophyllite was well dispersed in the epoxy matrix. The thermal studies of epoxy nanocomposite showed an increase in the char yield on the addition of silylated apophyllite to the epoxy resin. In addition, an improvement in the onset decomposition temperature of the cyanopropyldimethylsiloxy-apophyllite epoxy nanocomposite was observed compared with that of pure epoxy resin. Copyright © 2011 John Wiley & Sons, Ltd.

Previous research has shown that the inclusion of the spherical silica (SiO 2 ) nanoparticles into epoxy resin can achieve simultaneous improvement of fracture toughness and modulus. However, the glass transition temperature of the nanocomposite was significantly decreased when loading the nanosilica was higher than 5 wt.%. This perhaps was caused by utilization of the ultrasonication probe in the processing of these materials. In this paper, milder processing procedures were applied to make spherical silica epoxy nanocomposites while investigating if the homogeneous dispersion and morphology of the individual silica nanoparticle dispersed in the epoxy matrix could still be achieved. The results show that even at high loading of the silica nanoparticle, such as 30 wt.% silica, the perfect morphology of the nanocomposite could still be achieved with these milder processing conditions which indicates that ultrasonication is not needed. With the use of milder processing conditions, the glass transition temperature of the nanocomposite of 5 wt.% silica loading did not change, and the drop in the T g was minimal for silica loading up to 15%, but some effects of self-polymerization of the epoxy were noted on T g up to 30 wt.% loading of silica. Thermal analysis and flammability testing of the resulting materials suggest that nanosilica has only an inert filler effect (dilution of fuel) on flammability reduction and char yield increase, not a synergistic decrease in heat release as is often observed for clays and carbon nanotubes/nanofibers. So the mild and easy processing procedure only achieved uniform nanoscale morphology with excellent dispersion in the final nanocomposite, but also the effect on the change in the T g can be minimized as nanosilica loading was increased.

Epoxy–nanocomposite resins filled with 12-nm spherical silica particles were investigated for their thermal and mechanical properties as a function of silica loading. The nanoparticles were easily dispersed with minimal aggregation for loadings up to 25 wt% as determined using transmission electron microscopy (TEM) and ultra-small-angle X-ray scattering (USAXS). A proportional decrease in cure temperatures and glass transition temperature (for loadings of 10 wt% and above) was observed with increased silica loading. The morphology determined by USAXS is consistent with a zone around the silica particles from which neighboring particles are excluded. The “exclusion zone” extends to 10× the particle diameter. For samples with loadings less than 10 wt%, increases of 25% in tensile modulus and 30% in fracture toughness were obtained. More highly loaded samples continued to increase in modulus, but decreased in strength and fracture toughness. Overall, the addition of nanosilica is shown as a promising method for property enhancement of aerospace epoxy composite resins.

Polymer/layered-silicate nanocomposites have unique and hierarchical structures that can provide improvements to the properties of polymeric materials. Controlling the dispersion of the nanomaterials through processing greatly influences the resulting morphology and the resulting properties of the nanocomposite. In this article, the dispersion behavior of organic layered silicates (OLS) as a function of the processing procedure is reported. The behavior of the OLS in all stages of processing—in the solvent, the epoxy prepolymer, and in the epoxy through cure—is discussed. On the basis of understanding of the dispersion behavior of the OLS in the epoxy resin at each stage of processing, a different processing procedure can be designed and used so that the morphology of the epoxy/layered-silicate nanocomposite can be regulated. Mild low-shear processing resulted in an intercalated nanocomposite with large-size aggregates (> 10 μm), and high-shear processing resulted in an intercalated nanocomposite with relatively small-size aggregates (0.5–3 μm), whereas the high-shear and ultrasonication processing procedures gave rise to an exfoliated nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

This research demonstrates that an epoxy nanocomposite can be made through electron beam (e-beam) curing. The nanofillers can be two-dimensional (layered-silicate) and zero-dimensional (spherical silica). Both the spherical silica epoxy nanocomposite and the layered-silicate epoxy nanocomposite can be cured to a high degree of curing. The transmission electron microscopy (TEM) and small-angle X-ray scattering of the e-beam-cured layered-silicate epoxy nanocomposites demonstrate the intercalated nanostructure or combination of exfoliated and intercalated nanostructure. The TEM images show that the spherical silica epoxy nanocomposite has the morphology of homogeneous dispersion of aggregates of silica nanoparticles. The aggregate size is ∼ 100 nm. The dynamic mechanical analysis shows that the storage modulus of the spherical silica nanocomposite has been improved, and the glass transition temperature can be very high (∼ 175°C). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Fully exfoliated layered silicate epoxy nanocomposites are reported in this article. The processing route that resulted in these fully exfoliated layered silicate epoxies is based on a combination of high-shear mixing in the presence of acetone and ultrasonication. Homomogeneous and random dispersion of the individual silicate nanolayers in the epoxy is confirmed through transmission electron microscopy images spanning low to high magnification as well as by X-ray diffraction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3981–3986, 2004

Polymer layered-silicate nanocomposites have attracted a lot of attention because of impressive enhancements of polymeric properties. In this research, both commercially available and synthesized organolayered silicates, which are compatible with the epoxy resins, were used to make epoxy nanocomposites. The epoxy resin used in this research includes Epon 862/curing agent W (the aerospace epoxy resin), the Epon 828/Epi-Cure curing agent 8290-Y-60 (used as the primer layer for corrosion prevention in aircraft coating), and Epon 828/Jeffamine D400. The morphology of the nanocomposites was characterized using wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The morphology development for the aerospace epoxy-organoclay nanocomposite was monitored through in situ SAXS and analyzed. The solvent absorption of the exfoliated aerospace epoxy-organoclay nanocomposite in acetone was examined, and the diffusion coefficients of solvent in the nanocomposites were reduced. The organoclay/Epon 828/Y-60 and organoclay/Epon 828/D400 nanocomposite were used to make coatings on an Al surface. The anticorrosion properties of the nanocomposite coating were evaluated and discussed.

Research on nanocomposites attracted a lot of attention because of their unique nanostructure and interesting properties. Layered-Silicate epoxy nanocomposites cured by traditional thermal cure processing were prepared, and the morphology was confirmed by the wide-angle x-ray diffraction, small-angle x-ray scattering and transmission electron microscopy. Layered-Silicate epoxy nanocomposites could also be cured through e-beam curing. The small-angle x-ray scattering and transmission electron microscopy indicated that the e-beam-cured nanocomposites showed intercalated nanostructure. Dynamic mechanical analysis showed some improvement of the Storage modulus for the nanocomposites with high Tg.

Epoxy nanocomposites were prepared from the different organoclays with aerospace epoxy resin. A series of organoclays treated with alkylammonium chloride with different alkyl groups of different carbon chains were prepared, including SC4, SC6, SC8, SC10, SC12, SC16, SC18, and NC8, NC12, NC18. All of these organoclays, except for SC4, are very compatible with the aerospace Epon 862/curing agent W. The characterization from wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), and transmission electron microscopy (TEM) confirms the exfoliated nanostructure. The six-carbon chain length of the ammonium cation is enough to wet the surface of the clay gallery to make the organoclay compatible with epoxy resin. The clay with lower cation exchange capacity is more favorable for the polymer penetration inside the gallery and is dispersed better in the polymer matrix. The structural evolution of the aerospace epoxy nanocomposite was monitored by in situ SAXS. The 3% SC18/Epon 862/W, 3 and 6% SC8/Epon 862/W showed exfoliated nanostructure, while there is no exfoliation taking place for 3% S30B/Epon 862/W and 3%S25A/Epon 862/W up to 200°C. The acidity from the pendent group in SC18 and SC8 has a catalytic effect for the polymerization inside the gallery, while the organic pendent group of S30B and S25A does not. The faster reaction of the intragallery epoxy resin produced extra thermal heat inside the gallery to expand the gallery and is favorable for the migration of epoxy resin outside the gallery into the gallery where exfoliation took place. The exothermal heat of curing inside the gallery is an important factor for nanosheets exfoliation. Although exfoliation took place for both 3% SC18/Epon 862/W and 3% SC8/Epon 862/W, the detailed morphology development during the curing is different. For 3% SC8/Epon 862/W, the interplanar spacing between the layers is increased gradually, while 3% SC18/Epon 862/W experienced the disappearance of the ordered structure of the layered silicate in the beginning of the curing process and reappearance of the ordered structure of the silicate later. The glassy and rubbery moduli of the polymer-silicate nanocomposites were found to be greater than the unmodified resin because of the high aspect ratio and high stiffness of the layered silicate filler. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2276–2287, 2003

Nanoscale dispersion of only a few weight percentage of layered silicate (montmorillonite) in nylon 6 and epoxy results in the formation of a uniform passivating and self-healing inorganic surface region upon exposure to oxygen plasma. The enrichment of inorganic is compositionally graded with respect to the surface and is due to the preferential oxidation of the polymer from the nanocomposite and the corresponding enhancement of the nanoscale layered silicate on the surface. The structure of the inorganic region is turbostratic, with an average distance between layered silicates of 1−4 nm. This ceramic-like silicate layer provides an overcoat to the nanocomposite and can significantly retard the penetration of oxygen plasma. Thus, layered silicate containing nanocomposites may enhance the survivability of polymeric materials in aggressive oxidative environments, such as atomic oxygen in low earth orbit (LEO). The formed inorganic region was characterized chemically and morphologically by X-ray photoelect...

Polymer nanocomposites draw great interest due to their unique nanostructures and improved properties [1–2]. Epoxy is a widely-used thermosetting material. The research on the epoxy layered-silicate epoxy nanocomposite has exploded in the last decade [3–9]. The morphology of nanocomposites is the key to making high-performance nanocomposites. In this presentation, the factors influencing the morphology development behavior of epoxy nanocomposites will be discussed. The factors to be investigated include organoclay, epoxide, and curing agent. In this study, the aliphatic diamine (Jeffamines) with different molecular weights and aromatic diamine were selected as the curing agents, S30B (quaternary onium-montmorillonite) and SC18 (primary oniummont-morillonite) as the organoclays, and Epon 862 and Epon 828 as epoxides. In situ small-angle x-ray scattering (SAXS) was utilized to study the morphology development of the epoxy nanocomposite.

Polymer layered-silicate nanocomposites have attracted great attention due to their unique nanostructure and properties. The property of the nanocomposite is determined by the morphology of the nanocomposite. The typical morphologies of the nanocomposite are the intercalated and exfoliated nanostructures. In this study, the layered-silicate epoxy nanocomposite with different morphology can be controlled and achieved. The different morphology could include the intercalated nanostructure with the 15 Å increase of the interplanar spacing, the intercalated one with ∼150 Å increase of the gallery and fully exfoliated nanostructure.

Epoxy nanocomposites were prepared from the montmorillonite after organic treatment with a high Tg epoxy resin (Shell Epon 862 and curing agent W). Investigation of the rheological characteristics showed that the addition of clay to the resin did not significantly alter the viscosity or cure kinetics and that the modified resin would still be suitable for liquid composite molding techniques such as resin transfer molding. DSC was performed to study the kinetics of the curing reactions in the modified resin. An in situ small-angle x-ray scattering (SAXS) experiment was used to try to understand the structural development during cure. Based on the in situ SAXS data, structural changes were monitored in real time during cure and analyzed. Results from wide-angle x-ray diffraction, SAXS, and transmission electron microscopy of the polymer-silicate nanocomposites were used to characterize the morphology of the layered silicate in the epoxy resin matrix. The glassy and rubbery moduli of the polymer-silicate nanocomposites were found to be greater than the unmodified resin due to the high aspect ratio and high stiffness of the layered silicate filler. The solvent absorption in methanol was also slower for the polymer-silicate nanocomposites.

Spherical nanoscale particles were incorporated into an aerospace epoxy resin. When properly dispersed with a combination of mechanical and ultrasonic mixing, the fracture toughness could be made twice that of the control resin. Spherical nanoparticles were added as a suspension which tended to agglomerate, dry fumed powders which were easiest to disperse and were formed in situ from silanes. The spherical particles had little effect on the flexural properties of the resin. Layered silicates were not observed to change the fracture toughness of the resin but did double the flexural properties in some formulations.