This work presents key modeling aspects that are central to the manipulation of the decoration of metallic nanoparticles by a thin shell of a metal of different chemical nature. The concept of underpotential deposition is generalized to nanoparticles. An all-atom model, taking into account many-body interactions by means of the embedded atom potential, was used to represent nanoparticles of different sizes and atomic adsorbates on them. A full set of state-of-the-art computer simulations are performed for a model system, showing that selective decoration of facets is possible. The trends observed in the present work are in good qualitative agreement with experimental data reported very recently.

Organic–inorganic interfaces exist in many natural or synthetic materials, such as mineral–protein interfaces found in bone and epoxy–silica interfaces found in concrete construction. Here, we report a model to predict the intrinsic strength between organic and inorganic materials, based on a molecular dynamics simulation approach combined with the metadynamics method, used to reconstruct the free energy surface between attached and detached states of the bonded system and scaled up to incorporate it into a continuum model. We apply this technique to model an epoxy–silica system that primarily features nonbonded and nondirectional van der Waals and Coulombic chemical interactions. The intrinsic strength between epoxy and silica derived from the molecular level is used to predict the structural behavior of epoxy–silica interface at the macroscopic length scale by invoking a finite element approach using a cohesive zone model which shows a good agreement with existing experimental results.

This paper presents the results of a combined experimental, theoretical, and computational study of the adhesion between suspended polymeric films and a substrate in a model drug-eluting stent. Atomic force microscope is used to measure the pull-off force between the polymer and the substrate. The adhesion energy was then obtained from the measured pull-off forces and adhesion theories. Subsequently, the adhesion energy was incorporated into interfacial fracture mechanics zone model that was used to determine mode mixity dependence of the interfacial fracture toughness. The mode mixity-dependent fracture toughness conditions were then integrated into finite element models that were used to compute the critical push-out force of the suspended polymeric films. The predicted push-out forces were in good agreement with the results obtained from the experiments.

A hyperbranched epoxy resin has been synthesized by using epichlorohydrin, bisphenol-A, and hyperbranched polyether polyol by a low-temperature polycondensation technique in the presence of a base. The reaction parameters of this polycondensation reaction were optimized, and 5 N aqueous sodium hydroxide solution, (54 ± 1) °C reaction temperature and 3 h reaction time were found to be the best. The degree of branching of the resin was found to be 0.57 as determined from 13C nuclear magnetic resonance spectroscopy (Fig. 3). This hyperbranched epoxy resin was cured with poly(amido amine) hardener at 120 °C for a specified period of time. The resin exhibits very good crosscut adhesive strength (100%). The cured films showed moderate impact strength (60 cm), good scratch resistance (5.5 kg), good gloss (82 at 60°), thermostability up to 270 °C, and good chemical resistance in various chemical media. All these results indicate its suitability to be used as an advanced surface coating material.

We have created hybrids of functionalized single wall carbon nanotubes (fSWCNTs) and also multiwall CNTs (fMWCNTs) with PBT/PTMO, a block copolymer of semicrystalline poly(butyl terephthalate) (PBT) with amorphous oxytetramethylene (PTMO). For both single wall (SW) and multiwall (MW) carbon nanotubes (CNTs) tensile modulus and strain at break as a function of CNTs’ concentration (cCNT) show maxima. Elongation at break is enhanced by the nanotubes, a plasticizing effect—much stronger for SWCNTs because they have less contact points per unit area with the matrix and also are more flexible. Repetitive tensile tests were also performed; each loading cycle resulted in lowering the tensile modulus. Brittleness B(cCNT) diagrams show minima. New results for CNT hybrids fit an earlier general diagram for determination of viscoelastic recovery in sliding wear (f) as a function of brittleness (B); the original equation with unchanged parameters covers also these results. Volumetric wear was determined after abrasion on a pin-on-disk tribometer. Minima are seen on the volumetric wear versus cCNT diagrams, similar to those on the B(cCNT) diagrams.

In this study, nanoindentation was utilized to measure the local, three-dimensional properties of Kevlar 49 and Kevlar KM2 on the length scales of the fiber microstructure. First, atomic force microscopy-based methods were used to explore the extent of property changes with respect to radial position in the fibers’ axial and hoop planes. From these measurements, no significant change in response was found for Kevlar 49 fibers, consistent with transverse isotropy. However, a reduced stiffness “shell” region (up to ∼300–350 nm thick) was observed for KM2 fibers. Instrumented indentation was then used to evaluate fiber response with respect to orientation and contact size and establish a critical contact size above which the response is independent of indenter size (i.e., “homogeneous” behavior). A previously proposed analytical method for indentation of a transversely isotropic material was used to estimate the local material properties of the Kevlar fibers from the measured homogeneous response.

The piezoelectric β-phase of poly(vinylidene fluoride) (PVDF) has been synthesized through solution route in presence of varying percentage of silicon carbide (SiC). Various measurements were conducted to analyze the effect of SiC addition on structural, mechanical, and dielectric properties, as also the properties affecting hydrophilicity and morphology of PVDF. The x-ray diffraction, Fourier transform infrared spectroscopic and differential scanning calorimetry analyses confirm the presence of β-phase of PVDF on addition of SiC. The Young’s modulus of the composites increases as compared with pristine PVDF. The hydrophilic nature of the composites improves with increasing SiC content. Dielectric constant increases in composites, especially at lower frequency range and the relaxation pattern in the crystalline phase changes significantly causing reduction of relaxation frequency with increasing SiC concentration.

In this study, we have developed and characterized two previously unstudied alkoxysilane surface chemistries for use with superparamagnetic iron oxide (SPIO) nanoparticles as a magnetic resonance imaging contrast agent. We modified superparamagnetic iron oxide nanoparticles (SPIO) using aminopropyl triethoxysilane and two analogous alkoxysilanes, aminopropyl dimethylethoxysilane and aminopropyl methyldiethoxysilane, to compare a mono- and dialkoxysilane, respectively, to a more commonly used trialkoxysilane as two new SPIO surface chemistries capable of forming ultrathin functional surface coatings. The ligand densities of the mono- and dialkoxysilane-modified SPIO produced in this study are consistent with near monolayers of ligands on the SPIO surface. We studied the chemical stability of the mono-, di-, and trialkoxysilane-modified SPIO in neutral and acidic media to evaluate the viability of these surface chemistries for use in long-term intracellular applications. The mono- and dialkoxysilane-modified SPIO demonstrate comparable chemical stability to the trialkoxysilane-modified SPIO, indicating that the mono- and dialkoxysilane are both viable new SPIO surface chemistries for future applications requiring minimally thick alkoxysilane surface coatings.

Electrical conductivity and magnetic properties of core-shell silver-coated magnetite composite nanoparticles prepared by electroless deposition of silver on magnetite nanopowder are found to be affected mainly by the pressure used when preparing the nanoparticles sample cylinder and the Ag content in the nanoparticles. The electrical conductivity can be enhanced by increases of both the pressure and the Ag content. Direct current volume electrical resistivity of the nanoparticles with 40 wt% silver content is close to the order of 10−4 Ω cm when the pressure is larger than 1 × 106 Pa. The saturation magnetization of the nanoparticles almost reduces linearly with increasing the silver content. According to the rule of mixtures, the resistivity of the nanoparticles is calculated. But it shows that the calculated values have a large deviation with the corresponding measured ones. As a comparison, resistivity and saturation magnetization of the mixtures consisting of silver and magnetite nanopowder are also measured. It will be an effective method to adjust the electromagnetic properties of the nanoparticles by changing the silver content.

Controllable degradation of scaffolds plays an important role in tissue engineering applications. Here, we describe a biomimetic approach to control chitosan scaffold degradation by incorporating lysozyme-loaded poly(D,L-lactic-co-glycolic acid) microspheres in 3D chitosan scaffolds. In vitro degradation tests reveal that the degradation rate increased when the mass ratio of microspheres-to-chitosan increased whereas the contrast group showed a visible turning point at 28d. In vivo degradation rate was much faster than that in vitro, and the relationship between in vitro degradation and in vivo degradation was correlative. Finally, for determining the primary biocompatibility of the combined scaffolds, studies such as cytotoxicity assay, cell attachment study and histological evaluation were carried out. It is concluded that the combination method of enzyme and scaffold is suitable for chitosan scaffold degradation; it also demonstrates an alternative strategy for other biomaterials used in tissue engineering.

We prepared hybrid aluminum oxide (Al2O3)/polymethyl methacrylate (PMMA) composites with tunable lamellae, produced through a two-step synthetic method: fabrication of inorganic scaffolds via ice-templating, followed by organic infiltration polymerization as a substitute for the sublimed ice. The final lamellar hybrid products show anisotropic physical properties. The thermal conductivity in both principal directions was determined for three different samples as a function of temperature (∼3 K–300 K). Typical room temperature thermal conductivities are in the range of 0.5–2.5 W/(m K), depending on the composition and direction. Across the lamellae, the thermal conductivity is well modeled by a linear series of thermal resistors, and along the lamellae it is well represented by parallel thermal resistors of continuous slabs of PMMA and ∼200-μm long slabs of Al2O3, joined by PMMA. From the thermal conductivity perspective, the Al2O3/PMMA composite is a nacre mimic.

To enhance the reliability of Pb-free solders in high temperature and high humidity conditions, the minor alloying elements of Be and Co are investigated in terms of the growth of Sn whiskers and various properties of Sn-based Pb-free solders. Sn whisker growth is suppressed by adding up to 0.02 wt% Be to Sn-based solders. Adding Be and Co can effectively reduce the undercooling of Sn–1.0Ag–0.5Cu (wt%) solders. And the microstructures of Sn–1.0Ag–0.5Cu–0.02Be solders are similar to those of Sn–1.0Ag–0.5Cu. Furthermore, adding Co to solders increases the microhardness number as a result of the solid solution hardening. Adding Be causes no changes in the morphology or thickness of Cu6Sn5 at the Cu/OSP (organic solderability preservative) under bump metallurgy interface. However, the scallop-like Cu6Sn5 microstructure changes to a flat (Cu,Co)6Sn5 microstructure when 0.05 wt% of Co is added to Sn–1.0Ag–0.5Cu–0.02Be solders.

In spite of previous reports documented that many beneficial effects can be obtained by adding rare earth (RE) elements to Pb-free solders, this paper presents the risk of Sn whisker growth in the Sn–9Zn–0.5Ga Pb-free solders due to the addition of RE Pr. Results showed that solder microstructures are refined with the addition of trace amount of Pr. However, excessive Pr addition led to the formation of Pr–Sn intermetallic compounds (IMCs) and spontaneous growth of Sn whiskers on the IMC surfaces. It was found that the IMC size has a dramatic impact on whisker growth. Sn whiskers grew in slow-cooled solder with larger IMC particles are much longer and more prolific than that in fast-cooled solder with smaller IMC size. It was proposed that the driving force for whisker growth is originated from the oxidation of the RE-rich Pr–Sn IMCs. Our results indicated that the effects of RE on Pb-free solders should be reevaluated.

The whiskers spontaneously grown in Cd–Mg–Yb alloy containing icosahedral quasicrystal as dominant phase have been investigated by electron microscopy. It is found that: (i) the whiskers are mainly composed of Cd with growth direction along . CdO particles are frequently observed on surfaces of whiskers and the alloy, indicating the importance of the oxidation process during the whisker growth; (ii) there exist four types of orientation relationship between Cd and CdO. The interfaces between them are shown to accommodate large lattice misfit, which is well explained by near coincidence site lattice model; (iii) nanosized Cd particles are observed to aggregate around the whisker root, providing a convincing experimental evidence for the long-range atomic diffusion. Our study offers a unique opportunity to unveil the relationship between unstability of quasicrystal structure and whisker formation and may have some implications for oxidation process of metals.