New experimental methods have been developed to optimize the accuracy and precision of the measured phase angle in nanoindentation experiments on viscoelastic materials performed with a Berkovich indenter. Measurements conducted in fused silica and sapphire form the basis of a new instrument calibration. Experimental verification of the new calibration and an enhanced test method is demonstrated in polycarbonate (PC) and polymethyl methacrylate (PMMA). In comparison to the standard continuous stiffness measurement (CSM) technique, the new calibration and test method reduces the measurement error in the phase angle of PC from 1900% to 10% and from 135% to 10% in PMMA. Scatter in phase angle measured by the new test method is nearly 10 times less than the level observed using the standard CSM technique. The effect of time dependent deformation on the measured phase angle is also documented. The experimental observations and results are applicable to a variety of dynamic nanoindentation test methods.

During the advance of the nuclear fission reaction, fission products accumulate and form pores (gas bubbles) that decrease the thermal conductivity of the nuclear fuel, potentially leading to overheating of the fuel element. To investigate this important phenomenon, a finite-element method is used to simulate the effect of 3-dimensional (3D) distributions of pores on the thermal transport in a nuclear fuel element consisting of uranium oxide (UO2) nuclear fuel pellet and Zircaloy cladding. Spherical pores ranging in size from 70 to 172 µm are introduced to create up to 30 vol% total porosity. The simulations demonstrate that the centerline temperature increases with the total porosity and the increase is nonlinear. The results also show that the centerline temperature, at fixed total porosity, weakly depends on the pore size distribution. This method can provide useful information regarding the effect of high porosity levels that may occur in off-normal operation conditions.

Great research efforts to investigate the glass-forming ability (GFA) in alloys have been made, leading to an observation that a pinpoint composition produces the best glass-forming characteristics. The reason for this observation is still unknown, limiting the development of bulk metallic glasses (MGs) with a relatively large size. In this work, systematic experimental measurements coupled with calculations were performed to address this issue using the NiNb binary alloy system. It is found that the atomic-level packing efficiency and the clusters-level regularity parameters strongly contribute to their GFA. In particular, the best glass former found in a pinpoint composition possesses the local maximum of the atomic-packing efficiency and the highest degree of the cluster regularity. This work provides an understanding of GFA from atomic and cluster levels and will shed light on the development of more MGs with relatively large critical casting sizes.

The material characteristics of single-walled carbon nanotubes (SWCNTs) influence the performance of SWCNT thin-film transistors (TFTs). In this study, a density gradient ultracentrifugation method was used to sort surfactant (sodium deoxycholate)-dispersed SWCNTs by length. SWCNTs of 150 ± 33 nm and 500 ± 91 nm long were fabricated into TFTs. The results show that the performance of SWCNT-TFTs is tube length dependent. TFTs fabricated using 500-nm long tubes have maximum on/off ratio around 105 with the mobility at ∼0.15 cm2/(V s), which is much higher than that of TFTs using 150-nm long tubes. Shorter tubes need higher tube density to form semiconducting paths, leading to lower on/off ratio and high contact resistance. Surfactant-wrapped SWCNTs will bundle into ropes of different size when tube density is high. It is critical to control tube length as well as surfactant residue content to build high performance SWCNT-TFTs.

The porous Li1.2Ni0.13Co0.13Mn0.54O2 nanoplate is prepared by colloidal crystal template assembled by the poly (methyl methacrylate) (PMMA) beads. Scanning electron microscopy and transmission electron microscopy results show that the nanoplates of porous solid solution cathodes are composed of nanoparticles with a size range of 30 nm, which interweave together forming an open porous structure. Electrochemical tests show that porous Li1.2Ni0.13Co0.13Mn0.54O2 cathode could deliver higher discharge capacity than that of bulk Li1.2Ni0.13Co0.13Mn0.54O2 cathode at all C-rates. The enhanced structural stability reflected by high ratios of integrated Intensity I(003)/I(104) and lattice parameters c/a, high specific surface area, a fast reaction and ionic diffusion kinetics of the nanoplates are considered attributable to the improved electrochemical properties.

The increased use of viscous electrolytes in dye-sensitized solar cells (DSSCs) has revitalized the interest in three-dimensionally ordered macroporous (3DOM) structures as potential electrodes. The simplest approach to a 3DOM structure, such as inverse opals, is colloidal assembly followed by precursor infiltration and calcination. However, current assembly methods are often optimized for very narrow particle size ranges due to the colloidal forces specific to the method used. Using five particle sizes, ranging from 0.5 to 10 μm, we have studied the particle-size dependence of six commonly used colloidal assembly methods and its effect on the resulting inverse opal structure using scanning electron microscopy and Fast Fourier Transforms. Our results indicate a clear correlation between particle size and colloidal assembly method. The information provided by our study will enable systematic studies on inverse opal TiO2 electrodes with various pore sizes, in which the influence of the inverse opal preparation methods used is minimized.

In this article, the biofunctionalization of 6H–SiC (0001) surfaces via self-assembled monolayers (SAMs) has been studied as a means to modify the in vitro biocompatibility of this semiconductor substrate with H4 (human neuroglioma) and PC12 (rat pheochromocytoma) cells. Silanization with aminopropyldiethoxymethylsilane (APDEMS) and aminopropyltriethoxysilane (APTES), which provided moderately hydrophilic surfaces, and alkylation with 1-octadecene that produced hydrophobic surfaces were used to control the 6H–SiC surface chemistry and evaluate changes in cell viability and morphology due to these surface modifications. The morphology of the cells was evaluated with atomic force microscopy. In addition, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays were used to quantitatively evaluate the cell viability on the SAM-modified surfaces. In all cases, the cell proliferation was observed to improve with respect to untreated 6H–SiC surfaces, with up to a 2x increase in viability on the 1-octadecene-modified surfaces, up to 6x increase with APDEMS-modified surfaces, and up to 8x increase with APTES-modified surfaces. This proves the potential of SiC as a substrate for medical devices given the possibility to tailor its surface chemistry for specific applications.

The Ag@SiO2 core–shell structure nanoparticles prepared by chemical method were dispersed into epoxy matrix. By comparing with the epoxy-based composites filled with the mixed Ag and SiO2 nanoparticles (Ag + SiO2), it is found that the Ag@SiO2 core–shell structure fillers had important effects on the improved dielectric properties of the Ag@SiO2/epoxy composites. The core–shell structure fillers introduce a duplex interfacial polarization and a small number of free charge carriers, which enhance the dielectric permittivity of the composites. At the same time, the insulating SiO2 shell layer changes the interfacial interaction between the Ag filler and the epoxy matrix, not only avoiding Ag particles to connect directly and aggregate together but also providing a rough surface to contact with the epoxy host, which enhances the compatibility between the Ag@SiO2 fillers and the epoxy matrix. As the Ag@SiO2 packing ratio increases, the permittivity of the composites straightly increases and the loss tangent decreases, reaching the maximum and minimum respectively with the filler loading up to 60%.

The hydrophobic rutile titania aerogels were successfully prepared by nonalkoxide ambient pressure drying through a modification process. The resulted materials were characterized by x-ray diffraction, scanning electronic microscope, transmission electron microscope, contact angle analyzer, Brunauer–Emmett–Teller specific surface area, and ultraviolet (UV)–visible diffuse reflection spectrum. The experimental results demonstrated that the as-prepared samples nanoparticles with rutile crystalline structure were uniformly distributed. The UV-resistant hydrophobic samples having high surface area were used as photocatalysts for dye degradation reaction.

A highly biocompatible peptide, triplet repeats of asparagine–serine–serine (3NSS) regulates mineral deposition for the reconstruction of erosive enamel. Healthy human enamel was demineralized to create lesions, then exposed to the 3NSS peptide solution, and finally immersed in artificial saliva. The degrees of nanohardness recovery were 5.02% and 16.27% for the control group and enamel treated with the 3NSS peptide, respectively. Peptides assembling at enamel interrod attracted greater quantities of ions from the solution to form nanocrystalline hydroxyapatite minerals during the reconstruction of vacant gap. This resulted in a decrease in the surface roughness, and the acidic eroded pores were filled completely. Additionally, the newly deposited hydroxyapatites remineralized with the aid of the 3NSS peptide exhibited a smaller average crystalline size, which effectively inhibited plastic deformations. Treatment with the 3NSS peptide provided great improvements in nanohardness and elastic modulus.

Indentation tests are used to determine the hardness of a material, e.g., Rockwell, Vickers, or Knoop. The indentation process is empirically observed in the laboratory during these tests; the mechanics of indentation is insufficiently understood. We have performed first molecular dynamics computer simulations of indentation resistance of polymers with a chain structure similar to that of high density polyethylene (HDPE). A coarse grain model of HDPE is used to simulate how the interconnected segments respond to an external force imposed by an indenter. Results include the time-dependent measurement of penetration depth, recovery depth, and recovery percentage, with respect to indenter force, indenter size, and indentation time parameters. The simulations provide results that are inaccessible experimentally, including continuous evolution of the pertinent tribological parameters during the entire indentation process.

Films of 3-aminopropyltriethoxysilane films (APTES) deposited from nonpolar solvents show unusual hardness and tribological properties. The morphological origin of this behavior is determined using x-ray reflectivity. The deposited APTES films are smooth, evolving from a sparse structure when less than two-molecule-thick (<1 g/cm3) to a dense structure (1.26 g/cm3) when thicker. Previously reported improvements in wear resistance and hardness are due to the unusually dense nature of the APTES film. The density of multilayered APTES film has implications for its use as an interface-coupling agent because the film density limits the reactivity of embedded amine groups. A high-temperature cure (120 °C) does not affect film density but does significantly improve hydrolytic stability. Given their high density, predictable reactivity, stability and resistance to wear, multilayered APTES films are well suited for interfacial modification designed to improve mechanical properties, provided the films are properly cured.