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In this work, different formulations of a room-temperature silicone composite backing material (SCBM) composed of polydimethylsiloxane (PDMS), fumed silica and corn starch were investigated using different characterization techniques, i.e., differential scanning calorimetry, thermogravimetry analysis, X-ray diffraction (XRD) and small-angle X-ray scattering, as a function of controlled relative humidity. At ambient relative humidities in the range of about 20–80%, the equilibrium water content in the SCBM ranges from approximately 4–10%, which is predominantly absorbed by the corn starch. This amount of water content has been shown to have minimal effect on thermal transition temperatures (melting and glass transition) of the SCBMs. The enthalpy of melting increases with increasing relative humidity, which reflects the heterogeneous semicrystalline structure of starch granules and the role of moisture in facilitating the formation of amylopectin double helices mainly in the imperfect crystalline regions. The thermal degradation of SCBM exhibits three major mass loss steps that correspond to dehydration, decomposition of corn starch and decomposition of PDMS. The XRD patterns reveal a characteristic diffuse peak for amorphous PDMS and an A-type crystallinity for the corn starch. The XRD results show no observable changes in the crystal type and crystallinity as a function of moisture content. Results from this work help clarify the fundamental structure–property relationships in SCBMs, which are important for future development of documentary standards, especially the handling and storage specifications of next-generation ballistic witness materials for body armor testing.

Carbon nanotube (CNT) polymer nanocomposites are attractive multifunctional materials with a growing range of commercial applications. With the increasing demand for these materials, it is imperative to develop and validate methods for on-line quality control and process monitoring during production. In this work, a novel combination of characterization techniques is utilized, that facilitates the non-invasive assessment of CNT dispersion in epoxy produced by the scalable process of calendering. First, the structural parameters of these nanocomposites are evaluated across multiple length scales (10 −10 m to 10− 3 m) using scanning gallium-ion microscopy, transmission electron microscopy and small-angle neutron scattering. Then, a non-contact resonant microwave cavity perturbation (RCP) technique is employed to accurately measure the AC electrical conductivity of the nanocomposites. Quantitative correlations between the conductivity and structural parameters find the RCP measurements to be sensitive to CNT mass fraction, spatial organization and, therefore, the processing parameters. These results, and the non-contact nature and speed of RCP measurements identify this technique as being ideally suited for quality control of CNT nanocomposites in a nanomanufacturing environment. When validated by the multiscale characterization suite, RCP may be broadly applicable in the production of hybrid functional materials, such as graphene, gold nanorod, and carbon black nanocomposites.

Coaxial cables for data transmission are ubiquitous in telecommunications, aerospace, automotive, and robotics industries. Yet, the metals used to make commercial cables are unsuitably heavy and stiff. These undesirable traits are particularly problematic in aerospace applications, where weight is at a premium and flexibility is necessary to conform with the distributed layout of electronic components in satellites and aircraft. The cable outer conductor (OC) is usually the heaviest component of modern data cables; therefore, exchanging the conventional metallic OC for lower weight materials with comparable transmission characteristics is highly desirable. Carbon nanotubes (CNTs) have recently been proposed to replace the metal components in coaxial cables; however, signal attenuation was too high in prototypes produced so far. Here, we fabricate the OC of coaxial data cables by directly coating a solution of CNTs in chlorosulfonic acid (CSA) onto the cable inner dielectric. This coating has an electrical conductivity that is approximately 2 orders of magnitude greater than the best CNT OC reported in the literature to date. This high conductivity makes CNT coaxial cables an attractive alternative to commercial cables with a metal (tin-coated copper) OC, providing comparable cable attenuation and mechanical durability with a 97% lower component mass.

Joints held by polymeric adhesives are commonplace in many engineered products, but normal service can require exposure to environmental conditions that present a significant challenge for maintaining the structural integrity of the interface. In particular, aqueous environments can wreak havoc on the joint strength. Here, a mechanistic approach is used to understand the difference in the debonding behavior of an epoxy/aluminum (oxide) interface when exposed to deionized (DI) water and aqueous sodium chloride by correlating macroscopic failure with the sorption of salt and water into the adhesive and its nanoscale distribution. For the epoxy-aluminum system examined here, the presence of sodium chloride increases the resistance to crack growth in comparison to DI water. The debonding appears to be controlled by water near the buried interface. Salt water decreases the solubility of water in the epoxy and decreases the concentration of water near the buried interface, but the concentration of salt that enters the epoxy is below the detection limit. Thus, even if ions cannot penetrate or sorb into the adhesive, the presence of salt can significantly alter the water distribution within the adhesive and ultimately the strength of the joint. POLYM. ENG. SCI., 2015. © 2015 Society of Plastics Engineers

A combined computational/experimental technique was developed to analyze the compressive elastic properties of a rigid organic foam. This technique combines X-ray computed tomography, image analysis, and large-scale finite element computations utilizing a new numerical technique. Predictions of Young’s modulus were validated with uniaxial compression testing. Good agreement was obtained between imaging/finite element computations and experimental mechanical measurements within experimental error, and the limited knowledge existing on the solid material comprising the backbone of the foam. Using the new combined experimental/theoretical procedures, it was found that the predicted Young’s modulus of the solid backbone differed by more than a factor of 100 % between two different grades of the foam, in accordance with the findings of other researchers. A significant variability of the backbone modulus was also found within the same grade. Density measurements identified the variability between different grades of foam and different as-received sample thicknesses within the same grade of foam.

Carbon nanotube (CNT) hierarchical composites are increasingly identified as next-generation aerospace materials, so it is vital to evaluate their long-term structural performance under aging environments. In this work, the durability of hierarchical CNT grafted aluminoborosilicate microfiber-epoxy composites (CNT composites) are compared against aluminoborosilicate composites (baseline composites), before and after immersion in water at 25 °C (hydro) and 60 °C (hydrothermal), for extended durations (90 d and 180 d). The addition of CNTs is found to reduce water diffusivities by approximately 1.5 times. The mechanical properties (bending strength and modulus) and the damage sensing capabilities (DC conductivity) of the CNT composites remain intact regardless of exposure conditions. The baseline composites show significant loss of strength (44%) after only 15 d of hydrothermal aging. This loss of mechanical strength is attributed to fiber-polymer interfacial debonding caused by accumulation of water at elevated temperatures. In situ acoustic and DC electrical measurements of hydrothermally aged CNT composites identify extensive stress-relieving micro-cracking and crack deflections that are absent in the aged baseline composites. SEM images of the failed composite cross-sections highlight secondary matrix toughening mechanisms in the form of CNT pullouts and fractures that enhance the service life of composites., Airbus Group, Boeing Company, EMBRAER, Lockheed Martin, Saab (Firm), ANSYS, Inc., Toho Tenax

Roma Plastilina No. 1 (RP1), an artist modeling clay that has been used as a ballistic clay, is essential for evaluation and certification in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM) behind the armor, where the magnitude of the plastic deformation in the clay after a ballistic impact is the figure of merit (known as &ldquo, backface signature&rdquo, ). RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and frequent performance-based evaluations to verify that its deformation response satisfies requirements. A less complex BWM formulation that allows for room-temperature storage and use as well as a more consistent thermomechanical behavior than RP1 is desired, but a validation based only on ballistic performance would be extensive and expensive to accommodate the different ballistic threats. A framework of lab-scale metrologies for measuring the effects of strain, strain rate, and temperature dependence on mechanical properties are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM, i.e., silicone composite backing material (SCBM), to understand the fundamental structure&ndash, property relationships in comparison to those of RP1. Small-amplitude oscillatory shear frequency sweep experiments were performed at temperatures that ranged from 20 &deg, C to 50 &deg, C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and the material response was analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported to identify the degree of plasticity. The results show that the SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence than RP1. Both SCBM and RP1 are identified as elastoviscoplastic materials, which is particularly important for accurate determination of backface signature in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological properties of SCBM, at small and large strains, are similar to RP1 with substantial improvements in BWM performance requirements in terms of temperature sensitivity and thixotropy.

The incorporation of carbon nanofiber (CNF) into glass fiber (GF) composites is a potential route to extend polymer composite service-life and enhance mechanical properties. Under nonstatic conditions, only limited information concerning water uptake and contaminant release properties of nanocomposite materials is currently available. Polyester composites containing GF and oxidized CNF were immersed in water for 30 days under nominal pressure at 23 °C, below the polymer's glass-transition temperature. Water was analyzed and changed every three days to simulate water chemistry regeneration similar to exposures in flowing systems. Composites with oxidized CNF had greater water sorption capacity and leaching rates than CNF-free composites. The total mass of organic contaminant released correlated with the amount of water sorbed by each composite (r2 = 0.91), although CNF dispersion was found to vary greatly within composites. The greatest and least contaminant release rates were found for the polyester-CNF and the polyester-GF composites, respectively. While volatile aromatic resin solvents and stabilizer compounds were detected, their concentrations declined over the 30 day exposure period. We hypothesize that the hydrophilic nature of the oxidized CNF increased the water sorption capacity of the polyester composites. Additional studies are warranted that examine the impact of this phenomenon on composite mechanical and long-term durability properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43724.

Thermoviscoelastic properties and creep response of two commercial ambient temperature cure epoxy structural adhesives were analyzed and compared. The adhesives were formulated by the same manufacturer and appeared to be chemically similar; however, one system contained accelerators to shorten its cure time. In the laboratory, dynamic mechanical temperature/frequency sweeps were performed on both systems to generate dynamic mechanical and creep compliance master curves using time-temperature superposition principles. Differences were observed in the dynamic mechanical properties of the two adhesive systems as well as in their calculated creep compliance, which have been attributed to differences in their curing agent(s) and accelerator(s). Full-scale creep tests were carried out on anchors installed in concrete slabs and subjected to sustained loads for 82 days. These results were in good agreement with the creep compliance estimated using time-temperature superposition, suggesting that dynamic mechanical...

Incorporating metal-oxide nanoparticles such as nano-alumina and nano-silica into polymer coatings to enhance mechanical durability is widely utilized in the current antiscratch and mar technologies. In this article, a quantitative study of the effect of a nano-alumina additive on the surface mechanical properties and scratch behavior of a two-part polyurethane coating is reported. An instrumented indenter with a conical diamond tip is used to measure surface mechanical properties (modulus and hardness) and to perform scratch tests, over a wide range of scratch loads. The scratch behavior in terms of the onset of elastic–plastic transition and scratch morphology were characterized by laser scanning confocal microscopy. The scratch results were correlated to the surface mechanical properties and relevant bulk material properties to understand the overall scratch behavior of the coatings. The results show that the scratch behavior of the coatings depends strongly on the concentration of nano-alumina.

Optical lithography deep in the UV spectrum is the predominate route for high-resolution, high-volume nanoscale pattering. However, state-of-the-art optical lithography tools are exceedingly expensive and this places serious limitations on the applications, technical sectors, and markets where highresolution patterning can be implemented. To date the only substantial market for high-end optical lithography tools has been semiconductor fabrication. Nanoimprint lithography (NIL) has recently emerged as an alternative to optical lithography and combines the potential of sub-fi ve-nanometer patterning resolution with the low cost and simplicity of a stamping process. [ 1–4 ] This has led to signifi cant efforts to implement NIL methods, not only for semiconductor logic devices, but also in fi elds as diverse as the direct patterning of interlayer dielectrics (ILDs) for back-end-of-line (BEOL) interconnect structures, [ 5–7 ] bitpatterned magnetic media for data storage, [ 8 , 9 ] and high-brightness light-emitting diodes (LEDs). [ 10 ] Some of these are new areas where nanoscale patterning has previously not been considered, and are made possible here by the low cost and simplicity of the NIL stamping processes.

Multicomponent formulations coupled with complex processing conditions govern the final properties of photopolymerizable dental composites. In this study, a single test substrate was fabricated to support multiple formulations with a gradient in degree of conversion (DC), allowing the evaluation of multiple processing conditions and formulations on one specimen. Mechanical properties and damage response were evaluated as a function of filler type/content and irradiation. DC, surface roughness, modulus, hardness, scratch deformation and cytotoxicity were quantified using techniques including near-infrared spectroscopy, laser confocal scanning microscopy, depth-sensing indentation, scratch testing and cell viability. Scratch parameters (depth, width, percent recovery) were correlated to composite modulus and hardness. Total filler content, nanofiller and irradiation time/intensity all affected the final properties, with the dominant factor for improved properties being a higher DC. This combinatorial platform accelerates the screening of dental composites through the direct comparison of properties and processing conditions across the same sample.