The paper describes a multiscale experimental investigation of the mechanical behavior of polymer nanocomposites with nanoscale fused silica inclusions with the objective to shed light into the effect of the hard nanoparticles on the quasistatic mechanical behavior of epoxy matrix and the implications of the latter to the effective composite properties. The main variable in this study was the nanofiller volume fraction while the particle size was either 15 nm or 100 nm. Local strain measurements indicated strain field localization in the vicinity of the nanofillers at strains that macroscopically fall in the linearly elastic regime. The matrix strains were as high as three times the applied far field strain at applied effective strains of ∼ 1%. At larger stresses the local strain fields evolved to maxima that were considerably higher than the applied strain, and they were affected by local particle density and distribution. In composites with the largest particle volume fraction, 5 vol.%, 100 nm fillers, neighboring particles located in small proximities behaved as single large particles and often resulted in matrix strain shielding thus decreasing the benefit of the large surface-to-volume ratio and the associated efficiency in load transfer. On the other hand the 15 nm fillers resulted in more uniformly distributed deformation compared to composites with 100 nm particles.

Poly(acrylonitrile-co-butadiene-co-styrene) (ABS) is a thermoplastic polymer that is used in numerous structural applications as a result of its excellent mechanical properties. For those applications where good electrical conductivity is also desired, carbon black is often used as the filler of choice. Most reports in the literature indicate that at least 8 wt% carbon black filler is needed in order to achieve percolation. Our group recently reported that by manual mixing of ABS pellets and carbon black to create a segregated microstructure, percolation was achieved at an unprecedented low filler fraction of less than 0.01 wt% carbon black, a value which is comparable to or even better than that obtained using single wall carbon nanotubes as the filler. While the ABS/CB composites had excellent electrical performance, with a conductivity as high as 10-1 S/m, their mechanical strength was compromised.

In this paper we report on new experiments designed to maintain high electrical conductivity while improving on the mechanical behavior of percolating ABS/CB nanocomposites. The experiments were aimed at controlling the processing parameters such as temperature, pressure and time during hot pressing of the mechanically mixed precursor materials. Using data obtained at the various temperature-pressure combinations used, it will be shown that similar volume percentages of carbon black and carbon nanotubes can be used to obtain equivalent conductivities, suitable for EMI shielding, while still maintaining good mechanical properties.

The tailoring of thin film coatings comprised of high strength constituents, such as diamond like carbon and partially stabilized zirconia and ductile constituents, such as gold and molybdenum is investigated by new microstructurally-based finite-element techniques for applications related to the wear, durability, and performance of these coatings over a broad range of temperatures and loading conditions. The effects of contact transfer films, grain-shape sizes and distributions, grain-boundary structure and sliding, texture, and strength are used to determine the optimal thin film coating compositions. Comparisons are made with experimental measurements and observations, and guidelines for optimal thin film composite coatings are proposed.