Carbon nanofibers of diameter 200 nm may be used as an additive to thermoplastics for applications requiring electrical conductivity and enhanced mechanical properties. The electrical properties of nanofiber in thermoplastics such as nylon and polypropylene and are very attractive compared with those provided by other conventional conducting additives. Because of the low diameter of the nanofibers used, the onset of electrical conductivity (percolation threshold) can be below 1 volume %. Because of the highly conductive nature of the fibers, particularly after a graphitization step, the composites can reach resistivities as low as 0.15 Ohm cm. These conducting composites may be used for applications such as radio frequency interference shielding, primerless electrostatic painting, and static discharge. In order to make composites having excellent mechanical properties, good adhesion between fiber and matrix is essential. Carbon nanofiber-matrix adhesion was studied after surface treating the fibers using a variety of methods. Among as-grown fibers, those produced with longer gas phase feedstock residence times in the fiber growth reactor were less graphitic but adhered to a polypropylene matrix better, giving improved tensile strength and modulus Two chemical treatments were found to be somewhat effective in increasing tensile strength, but both decreased the modulus.. A modest degree of oxidation was also found to increase adhesion to the matrix and increase composite tensile strength, while extended oxidation attacked the fibers sufficiently to decrease composite properties.

Magnetic nanocomposites formed by metal oxide nanoparticles and organic polymers can be produced from a polymer-metal ion complex material by a soft thermal treatment. With only slight variations in the preparation procedure it is possible to obtain: 1) different iron oxide phases, e.g., hematite (antiferromagnetic), goethite and akaganeite (both canted antiferromagnets), and maghemite (ferrimagnetic); 2) nanocomposites with a different particle size, in a range from 2 nm to 20 nm; and 3) different particle density. In this contribution the preparation and properties of maghemite nanoparticles in polyvinyl pyridine composites are reported.

Using a novel electrostatic self-assembly (ESA) method to incorporate CdSe quantum dots into polymer we have successfully synthesized ultrathin films. This method allows the molecular-level thickness control and layer-by-layer formation of multilayer thin and thick films using alternative anionic and cationic molecular solution dipping. From ellipsometric measurements, we obtained that the thickness of per bilayer is around 3.7 nm. UV-vis absorption spectra versus the number of bilayers have also been obtained using an Hitachi 2001 spectrometer. The size of CdSe quantum dots has been measured using transmission electron microscopy before the CdSe quantum dots are incorporated and confirmed using atomic force microscopy after the formation of the film, respectively. Both measurements indicate that the diameter of the CdSe quantum dots is 2-3 nm. Xray photoelectron spectroscopy indicates that the concentration of the CdSe quantum dots in the film is 2.14%.

Selected MPEG-b-PDLLA block copolymers have been synthesized with systematic variation of the chain lengths of the resident hydrophilic and hydrophobic blocks. The size and shape of the micelles that spontaneously form in solution are then controlled by the characteristics of the copolymer template. Formation of nanoporous silica at room temperature with short-preparation time is demonstrated and silica-containing materials evolve with uniform pore shape and wall structure. The formation mechanism of these nanoporous structures obtained by controlling the micelle size has been confirmed using both liquid and solid state 13C and 29Si NMR techniques.

Polyhedral Oligomeric Silsequioxane molecules have been incorporated into a commercial polyurethane formulation to produce nanocomposite polyurethane foam. This tiny POSS silica molecule has been used successfully to enhance the performance of polymer systems using co-polymerization and blend strategies. In our investigation, we chose a high-temperature MDI Polyurethane resin foam currently used in military development projects. For the nanofiller, or “blend”, Cp7T7(OH)3 POSS was chosen. Structural characterization was accomplished by TEM and SEM to determine POSS dispersion and cell morphology, respectively. Thermal behavior was investigated by TGA. Two methods of TEM sample preparation were employed, Focused Ion Beam and Ultramicrotomy (room temperature).

Nanocomposites were made using deionized gelatin filled with well-dispersed nanoscale alumina particles. Scratch tests on the nanocomposite films showed substantially improved scratch resistance. Tensile tests revealed increases in both modulus and tensile strength of the nano-filled gelatin films accompanied by a decrease in strain-to-failure. The increase in modulus and strength reduced the degree of plastic deformation during scratch testing, but the onset of periodic cracking in the scratch track was unaffected. Optical transmittance measurements of the gelatin composite showed that the films retained transparency in the visible light range.

The dielectric and electrical behaviors of a NafionTM membrane, a NafionTM/7SiO2-2P2O5-ZrO2 gel composite, and a NafionTM/ZrP particle composite were investigated using ac impedance spectroscopy at different relative humidities and temperatures. Only NafionTM/7SiO2-2P2O5-ZrO2 showed a slightly higher conductivity than NafionTM at high temperature. For NafionTM/ZrP, proton mobility was significantly lower, particularly at high relative humidity. The results suggest that improvement in fuel cell performance, previously measured on composite membranes, does not merely result from increased hydrophilic properties.

Molecular dynamics (MD) simulations of carbon nanotube (NT) pull-out from a polymer matrix are carried out. As the NT pull-out develops in the simulation, variations in the displacement and velocities of the NT are monitored. The existence of a carbon-ring-based period in NT sliding during pull-out is identified. Linear trends in the NT velocity-force relation are observed and used to estimate an effective viscosity coefficient for interfacial sliding at the NT/polymer interface. As a result, the entire process of NT pull-out is characterized by an interfacial friction model that is based on a critical pull-out force, and an analog of Newton's friction law used to describe the NT/polymer interfacial sliding.

Polystyrene (PS) clay nanocomposites were synthesized and used to prepare foams in both batch and continuous extrusion process. It was found that the addition of a small amount of clay could greatly reduce cell size and increase cell density. Once exfoliated, the nanocomposite foam exhibits the highest cell density and the smallest cell size at the same particle concentration. Exfoliated microcellular nanocomposite foams with good surface quality was successfully produced using supercritical carbon dioxide.

Molecular dynamics simulations were used to study the interlayer structure and dynamics of polystyrene (PS) and polystyrene-polyisoprene (PS-PI) block copolymers intercalated in organically modified layered silicates. In the case of PS the polymer chains displace the aliphatic surfactant chains and reside adjacent to the silicate layers. The electrostatic interactions between the aromatic rings on the PS chains and the silicate surface drive the intercalation of the polymer into the host galleries. PI, which lacks such electrostatic interactions, is immiscible (does not intercalate) with the host. There appears to be a minimum number of PS mers for intercalation of PS-PI copolymers to take place. The intercalated copolymer appears to structure inside the host galleries with the PS mers adjacent to the silicate layers and the corresponding PI away from the surface and towards the middle of the gallery. Using the mean square displacements we find that PS is the least mobile species in the galleries with the surfactant chains been the most mobile of all.

Furan-resin-derived carbon structures have attracted interest as a component in carbon based composite materials. We have investigated the microstructures of furan-resin-derived carbon by transmission electron microscopy after high-temperature heat treatments. We observed that graphitization occurred at the surface even although furan-resin-derived carbon is believed to be a non-graphitizable carbon. On the other hand the interior of the specimens exhibited a cage-like structure. Specimens heat-treated at higher temperatures exhibited a well-developed cage structure, as evidenced by the number of stacked layers and their periodicity. Post-column type EELS was utilized to study the chemical state of the interior of the specimens. All of the EELS spectra had a characteristic edge structure showing the existence of π bonding. There were not significant differences between the spectra of early-stage and well-developed cage structures.

The effect of layered-silicates on the mechanical response of intercalated polycarbonate (PC) nanocomposites subjected to quasi-static tensile, compressive and ballistic impact testing conditions has been investigated. These nanocomposites were melt-processed, in which good dispersion of nanoclays and adequate adhesive bonding between the nanoclay and PC matrix are achieved. However, their ductility upon tensile loading is significantly affected; a transition from ductile to brittle deformation occurs at clay loading of about 3 wt.%. Stress whitening is evident in the tensile- and ballistic-tested 1.5, 2.5, and 3.5 wt.% clay nanocomposites, and is attributed to the light scattering by microvoids, which are presumably formed from either crazing of PC or debonding of the nanoclay tactoids upon mechanical deformation. The effect of clay loading on the ballistic impact strength of the monolithic PC nanocomposites and layered PC/PC-nano/PC composites is determined. Compressive yield strength measurements are obtained at strain rate of 0.001/s for the monolithic PC nanocomposites and are utilized to correlate with the ballistic impact strength of the layered PC/PC-nano/PC composites. Thermal degradation is noted in these PC nanocomposites, and its effect on the mechanical deformation is briefly discussed.

Low color, space environmentally stable, polymeric materials with sufficient electrical conductivity for static charge dissipation are of interest for potential applications on Gossamer spacecraft. One method of imparting electrical conductivity while maintaining optical clarity is through the use of single wall carbon nanotubes (SWNTs). Both theory and research on SWNTs have shown them to be conductive. However, SWNTs are very difficult to uniformly disperse in a polymer. The approach described herein was to use oligomers endcapped with functional groups that could condense with functionalities present on purified, laser ablated SWNTs. Low color, radiation resistant amide acid oligomers endcapped with trialkoxysilane groups were combined with SWNTs. Since the SWNTs were purified by an oxidative process (nitric/sulfuric acid treatment), they have functionalities such as hydroxyl and carboxylic acid groups that can condense with the terminal alkoxysilane groups. After mixing at room temperature, the mixtures were used to cast films that were subsequently stage-cured up to 300°C for 1 hour in air. During this thermal treatment, imidization and condensation occurred. The chemistry, physical, and mechanical properties of the resulting nancomposite films will be presented.

A study of the polymer structure in the vicinity of an interface with a rigid, curved wall is presented. The study is performed by means of lattice Monte Carlo simulations in melts of low and high density. Both purely entropic and energetic systems are considered. The configurational entropy of the chains as well as the cohesive interactions in the bulk polymer lead to the formation of a low-density layer in the close neighborhood of the wall. This layer is about one monomer thick in the purely entropic case, and has a thickness of about three radii of gyration in presence of energetic interactions. Increasing the wall curvature leads to an increase in density in the depleted layer, the effect being more pronounced in the energetic system. Chain end segregation at the wall is observed in all cases. This effect increases with increasing chain length and decreases with increasing wall curvature. The bonds are preferentially oriented in the direction tangential to the wall. The degree of orientation decreases with increasing wall curvature and is independent of chain length. Finally, the evolution of the density, of the segregation effect and of the bond preferential orientation with temperature is investigated. The density at the wall decreases with decreasing temperature in the melt state, while the segregation becomes more pronounced. The volume of polymer in which the structure is affected by the presence of the wall increases with decreasing temperature.

The knowledge of elastic properties of the various types of rubber is significant for many commercial and academic applications. A sample set consisting of generic elastomeric compounds was studied using non-destructive non-contact ultrasonic techniques. The longitudinal sound wave velocities in the sample and wave amplitude attenuation in the sample were measured using the Second Wave Inc. Non-Contact Analyzer 1000 (NCA1000). The Contact method was then used to corroborate the results obtained. A rule-of-mixture model was used to compare the velocity values obtained by the non-contact technique. The preliminary results suggest that the differences in attenuation are driven by polymer type and also to a lesser extent by the loading level of carbon black fillers.

InMat LLC has developed aqueous, non-hazardous nanocomposite dispersions with a unique combination of barrier properties and flexibility. Using butyl rubber as the matrix, and very high aspect ratio vermiculite filler, flexible coatings with gas permeability 30-300 times lower than butyl rubber have been produced.[1,2] These coatings have been shown to be undamaged by strains up to 20%. The first commercial application of this technology (sold under InMat's trademark Air D-FenseTM) is in Wilson's new, longer life, Double CoreTM tennis ball.