Ab initio design of polymer nanocomposite materials for high breakdown strength requires prediction of localized trap states at the polymer–filler interface. Systematic first-principles calculations of realistic interfaces can be challenging, particularly for amorphous polymers and fillers that necessitate the calculation of ensembles of large unit cells with hundreds of atoms. We present a computational approach for automatically generating reasonable structures for amorphous polymer–filler interfaces, combining classical molecular dynamics and Monte Carlo simulations. We identify trap states by analyzing the localization of electronic eigenstates calculated using density functional theory on ensembles of interface structures, clearly distinguishing shallow trap states from delocalized band-edge states. Applying this approach to silica–polyethylene interfaces as an initial example, we find under-coordination and distorted coordination structures at amorphous silica surfaces contribute a combination of deep and shallow traps at these interfaces, whereas polyethylene does not generate localized interfacial states.

The addition of high refractive index (RI) inorganic nanoparticles (NPs) to LED encapsulation materials can lead to higher light extraction efficiency. In addition, the NPs can be carriers for additional functionality such as color conversion. Using a simple “grafting-to” approach, bimodal polydimethylsiloxane (PDMS) brushes were grafted onto high-RI ZrO2 NPs. Subsequently, an organic phosphor, 6-[fluorescein-5(6)-carboxamido]hexanoic acid (FCHA), was attached onto the PDMS-grafted ZrO2 NPs via a facile ligand exchange process. The bimodal polymer brush design enables homogenous dispersion of the surface functionalized NPs within the silicone matrix. The functionalized NPs with ∼53 wt% ZrO2 core have a ∼0.08 higher RI than neat silicone, and the NP-filled silicone nanocomposites exhibit a transparency of ∼ 90% in the 550-800 nm wavelength range. In addition, the nanocomposites could be excited at a wavelength around 455 nm by a blue LED and undergo secondary yellow emission at around 571 nm. It is expected that the prepared nanocomposites can be used as high-efficiency, non-scattering, color-tuned materials for advanced LED encapsulation.

Polymer nanocomposites (PNC) are complex material systems in which the dominant length scales converge. Our approach to understanding nanocomposite tradespace uses Materials Quantitative Structure-Property Relationships (MQSPRs) to relate molecular structures to the polar and dispersive components of corresponding surface tensions. If the polar and dispersive components of surface tensions in the nanofiller and polymer could be determined a priori, then the propensity to aggregate and the change in polymer mobility near the particle could be predicted. Derived energetic parameters such as work of adhesion, work of spreading and the equilibrium wetting angle may then used as input to continuum mechanics approaches that have been shown able to predict the thermomechanical response of nanocomposites and that have been validated by experiment. The informatics approach developed in this work thus enables future in silico nanocomposite design by enabling virtual experiments to be performed on proposed nanocomposite compositions prior to fabrication and testing.

Transparent polymer nanocomposites with high refractive index were prepared by grafting polymer chains onto TiO2 nanoparticles. Reversible addition-fragmentation chain transfer (RAFT) polymerization was used to prepare poly(methyl methacrylate) (PMMA) polymer brushes grafted from TiO2 nanoparticles. The refractive index of the hybrid material increased from 1.49 for neat PMMA to 1.6 by increasing the loading of TiO2 to 40 weight percent. UV-vis spectra showed that grafted particles had a transparency of more than 90% in the visible light range. The hybrid particles can be processed into transparent, high refractive index coatings and self-standing films. The grafted TiO2 nanoparticles can also be easily dispersed into a polymer matrix forming thick, robust transparent polymer nanocomposites.

Using nanocomposites in design-critical applications requires an understanding of their structure–property–function relationships. Despite many reports of highly favorable properties, the behavior of polymer nanocomposites is not generally predictable. The ability to tailor the filler/matrix interaction and an understanding of the impact of the inter face on macroscopic properties are key to designing their properties. Tailoring can be achieved by grafting short mole cules or polymer chains from the surface with precise control over their chain length (1–1000 mers), graft density (0.01–1 chains/nm2), and chemical architecture. The challenge is understanding the impact of the modified surfaces on the properties of the interfacial polymer, which can be more than 50% of the volume of the polymer matrix and, hence, can exert significant control over the macroscopic behavior of the nanocomposite. This ar ticle highlights the fundamental technical challenges that need to be overcome before spherical nanopar ticle or nanotube composites can be designed. In particular, we discuss results from the recent literature that have significantly advanced our ability to predict and control nanocomposite properties through the use of designed interfaces.

The electrical breakdown strength of TiO2 nanoparticle-filled low-density polyethylene (LDPE) nanocomposites was investigated. It was found that the surface water on the nanoparticles played a very important role in determining the breakdown strength. The breakdown strength at 63.2% cumulative failure probability (E0) for the composites filled with dried nanoscale TiO2 was similar to that of neat LDPE and 50% higher than that for the samples filled with as-received nanoscale TiO2. This increase was due to a better dispersion, a better interface, and a morphology change of the matrix. It was also found that surface modification of nanoscale TiO2 had a significant influence on the breakdown strength. N-(2-aminoethyl) 3-aminopropyl-trimethoxysilane (AEAPS)-coated TiO2-filled samples showed about 40% higher E0 than that of uncoated, as-received TiO2-filled samples. This was mainly due to enhanced electron scattering because of the presence of polar groups in AEAPS.

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.

Polymethylmethacrylate (PMMA) nanocomposites were synthesized by free radical polymerization in the presence of various weight percentages of alumina (Al2O3) nanoparticles. The resulting nanocomposites show an average increase of 600% in strain-to-failure and the appearance of a well-defined yield point. Concurrently, the glass transition temperature (Tg) of the composites decreased 20°C, while the ultimate strength and the Young's modulus decreased by 20% and 15%, respectively.

Toray M40 graphite fiber / Epon 828 epoxy resin single fiber composites with both sized and unsized fibers were exposed to distilled water at 50°C and 100°C, 10% NaOH and HCl aqueous solutions at 50°C, and air at 100°C. Micro Raman spectroscopy was used to measure the strain and interfacial shear stress profiles as a function of environmental exposure. It was found that the degradation mechanism is primarily a mechanical failure of the fiber/matrix interface.

Macroscopic properties of fiber reinforced composites are dependent on the micromechanics of the filament-matrix interphase. We present here some preliminary results of our studies aimed at understanding the behavior of the interphase when the composite is subjected to cyclic tensile loading. We have used carbon/polycarbonate mono-filament composites as a model system for studying the effects of loading direction (axial and transverse), frequency, and amplitude. The interphase was varied by etching the filament surface. Damage was characterized by fiber matrix debonding, reduction in interphase stress transfer efficiency, and changes in the locus of failure as determined by SEM fractography.

The effect of fiber surface treatments on the relationship between the tensile strength of a filament and the shear strength of its interphase is one of the central issues facing composite materials technologists today. We demonstrate here that analysis of fragmentation phenomena in monofilament composites can simultaneously yield information about these two parameters. Characterization of shear stress transfer zones in non-critical fragments has led us to the determination of interphase strength.

A phenomenological treatment that highlights the role of the matrix in the fragmentation process is presented here. This analysis considers issues such as the strain energy exchange between a failing fiber and the matrix, as well as interphase relaxation due to the viscoelastic nature of the matrix. Our observations of the fragmentation phenomena in AU4/polycarbonate monofilament composites indicate that the fiber/matrix interaction in this system is governed by micromechanical locking.