Besides biological and chemical cues, cellular behavior has been found to be affected by mechanical cues such as traction forces, surface topology, and in particular the mechanical properties of the substrate. The present study focuses on completely characterizing the bulk linear mechanical properties of such soft substrates, a good example of which are hydrogels. The complete characterization involves the measurement of Young's modulus, shear modulus, and Poisson's ratio of these hydrogels, which is achieved by manipulating nonspherical magnetic microneedles embedded inside them. Translating and rotating these microneedles under the influence of a known force or torque, respectively, allows us to determine the local mechanical properties of the hydrogels. Two specific hydrogels, namely bis-cross-linked polyacrylamide gels and DNA cross-linked polyacrylamide gels were used, and their properties were measured as a function of gel concentration. The bis-cross-linked gels were found to have a Poisson's ratio that varied between 0.38 and 0.49, while for the DNA-cross-linked gels, Poisson's ratio varied between 0.36 and 0.49. The local shear moduli, measured on the 10 μm scale, of these gels were in good agreement with the global shear modulus obtained from a rheology study. Also the local Young's modulus of the hydrogels was compared with the global modulus obtained using bead experiments, and it was observed that the inhomogeneities in the hydrogel increases with increasing cross-linker concentration. This study helps us fully characterize the properties of the substrate, which helps us to better understand the behavior of cells on these substrates.

We report the quasistatic tensile and impact penetration properties (falling dart test) of injection-molded polycarbonate samples, as a function of multiwall carbon nanotube (MWNT) concentration (0.0–2.5%). The MWNT were incorporated by dilution of a commercial MWNT/polycarbonate masterbatch. The stiffness and quasistatic yield strength of the composites increased approximately linearly with MWNT concentration in all measurements. The energy absorbed in fracture was, however, a negative function of the MWNT concentration, and exhibited different dependencies in quasistatic and impact tests. Small-angle x-ray scattering (SAXS) showed that the dispersion of the MWNT was similar at all concentrations. The negative effects on energy absorption are attributed to agglomerates remaining in the samples, which were observed in optical microscopy and SAXS. Overall, there was a good correspondence between static and dynamic energy absorption.

The effects of variable conversion parameters on the microstructure and critical currents of TFA-derived YBa2Cu3O7 (YBCO) films annealed under low-pressure conditions were investigated, accompanied by the analysis of their relationship with the nucleation process and the growth rate. It is found that non-c-axis oriented YBCO grains are formed under high supersaturation conditions, i.e., by increasing oxygen pressure, water pressure, or temperature. The optimal PH2O–PO2 window for preparation of completely c-axis oriented YBCO films expands as the total pressure rises from 50 to 100 mbar due to the decrease of supersaturation at enhanced total pressure; the corresponding maximum growth rate is only slightly increased up to 0.6 nm/s. Additionally, it is shown that the gas flow needs to be high enough to avoid random nucleation of YBCO grains. A single gas-flow–water-pressure diagram, showing simultaneously the film-growth rate, allows visualizing the cross-linked influence of processing parameters to achieve c-axis oriented YBCO films with Jc above 1 MA/cm2 in one single growth step.

Several binary intermetallic compounds—each containing a rare-earth (RE) element paired with a transition metal (TM)—were prepared by self-propagating, high-temperature synthesis (SHS). Thin multilayers, composed of alternating Sc or Y (RE element) and Ag, Cu, or Au (TM), were first deposited by direct current magnetron sputtering. Once the initially distinct layers were stimulated and caused to mix, exothermic reactions propagated to completion. X-ray diffraction revealed that Sc/Au, Sc/Cu, Y/Au, and Y/Cu multilayers react in vacuum to form single-phase, cubic B2 structures. Multilayers containing Ag and a RE metal formed cubic B2 (RE)Ag and a minority (RE)Ag2 phase. The influence of an oxygen-containing environment on the reaction dynamics and the formation of phase were investigated, providing evidence for the participation of secondary combustion reactions during metal-metal SHS. High-speed photography demonstrated reaction propagation speeds that ranged from 0.1–40.0 m/s (dependent on material system and foil design). Both steady and spin-like reaction modes were observed.

The relationship between atomic force microscopy probe-sample adhesion force and relative humidity (RH) at five different levels of surface free energy (γs) of an organic self-assembled monolayer (SAM) has been investigated. Different γs levels were achieved by exposing a patterned SiO2/CH3-terminated octyldimethylchlorosilane SAM sample to an ultraviolet (UV)/ozone atmosphere. A model consisting of the Laplace-Kelvin theory for capillary condensation for nanosized probe and probe-sample molecular interaction was derived to describe the adhesion force as a function of RH from 25 to 90% for different SAM γs values. The equations were solved analytically by using an equivalent curvature of the probe tip shape. Experimental results show that the adhesion force increases slightly with RH for nonpolar SAM. However, for polar SAM surfaces, it increases at first, reaches a maximum, and then decreases. Both the rate of increase and the maximum of the adhesion force with humidity are γs-dependent, which is in good agreement with theoretical prediction. The large rise in the adhesion force in this RH range is due to the capillary force.

The structural, transport, and magnetotransport properties of single-phase, homogeneous nanostructured La0.7Sr0.3MnO3 (LSMO) manganites synthesized by the coprecipitation route were investigated and the effect of sintering temperature on the microstructure of LSMO compounds was studied. A strong dependence of transport and magnetotransport behavior on the microstructure and nature of grain boundaries has been observed in the single-phase LSMO sintered at various temperatures. High-field magnetoresistance (HFMR) at room temperature is found to increase [13% (LS6) to 25% (LS9)] while low temperature (5 K) magnetoresistance decreases [75% (LS6) to 46% (LS9)] under 9 T field with increase in sintering temperature, which has been attributed to the spin-polarized tunneling and spin-dependent scattering of charge carriers.

The Young’s modulus of single crystalline rutile TiO2 nanoribbons was investigated using nanoindentation. During the experiments, the nanoribbons were laid on three different substrates, including 1 μm thick SiO2 layer on silicon (SiO2/Si), Si(100), and sapphire(0001). Experimental results show the substrates have significant effects on load-indenter displacement curves. To further understand the experimental findings, three-dimensional finite element modeling was carried out to simulate the indentation of nanoribbon-on-substrate systems using ABAQUS. The results show that the receding contact mechanics is a good approximation when describing the contact between the nanoribbon and the substrate. The results also demonstrate that the substrate effect must be carefully considered when performing nanoindentation on one-dimensional nanostructures. Otherwise, the Young’s modulus of the nanostructures could either be overestimated or underestimated. The Young’s modulus is about 360 GPa, comparable to that of bulk TiO2.

The dynamics of track development due to the passage of relativistic heavy ions through solids is a long-standing issue relevant to nuclear materials, age dating of minerals, space exploration, and nanoscale fabrication of novel devices. We have integrated experimental and simulation approaches to investigate nanoscale phase transitions under the extreme conditions created within single tracks of relativistic ions in Gd2O3(TiO2)x and Gd2Zr2–xTixO7. Track size and internal structure depend on energy density deposition, irradiation temperature, and material composition. Based on the inelastic thermal spike model, molecular dynamics simulations follow the time evolution of individual tracks and reveal the phase transition pathways to the concentric track structures observed experimentally. Individual ion tracks have nanoscale core-shell structures that provide a unique record of the phase transition pathways under extreme conditions.

The reversible hydrogen adsorption site in Ni-nanoparticle-dispersed amorphous silica (Si-O) was identified by analyzing the hydrogen adsorption behavior and the microstructure. The total amount of reversibly adsorbed hydrogen was evaluated from the total surface area of Ni and the Ni concentration in the composite. The total surface area of the Ni nanoparticles in each sample powder was calculated from the mean particle size of the Ni nanoparticles in the Si-O matrix using dark field images taken by transmission electron microscopy and high-angle annular dark-field images by scanning transmission electron microscopy. The estimated amount of reversibly adsorbed hydrogen was highly consistent with that obtained experimentally by hydrogen adsorption analysis, which suggested that reversible hydrogen adsorption occurred at the Ni/Si-O interface.

Indentation experiments on thin films are analyzed by using a rigorous solution to model elastic substrate effects. Two cases are discussed: elastic indentations where film and substrate are anisotropic and elastoplastic indentations where significant material pileup occurs. We demonstrate that the elastic modulus of a thin film can be accurately measured in both cases, even if there is significant elastic mismatch between film and substrate.

In our previous study, we modeled the indentation performed on an elastic–plastic solid with a rigid conical indenter by using finite element analysis, and established a relationship between a nominal hardness/reduced Young’s modulus (Hn/Er) and unloading work/total indentation work (We/Wt). The elasticity of the indenter was absorbed in Er ≡ 1/[(1 − ν2)/E + (1 − νi2)/Ei], where Ei and νi are the Young’s modulus and Poisson’s ratio of the indenter, and E and ν are those of the indented material. However, recalculation by directly introducing the elasticity of the indenter show that the use of Er alone cannot accurately reflect the combined elastic effect of the indenter and indented material, but the ratio η = [E/(1 − ν2)]/[Ei/(1 − νi2)] would influence the Hn/Er–We/Wt relationship. Thereby, we replaced Er with a combined Young’s modulus Ec ≡ 1/[(1 − ν2)/E + 1.32(1 − νi2)/Ei] = Er/[1 + 0.32η/(1 + η)], and found that the approximate Hn/Ec–We/Wt relationship is almost independent of selected η values over 0–0.3834, which can be used to give good estimates of E as verified by experimental results.

The effect of BaCu(B2O5) (BCB) on the sintering temperature and microwave dielectric properties of Ba(Nd0.8Bi0.2)2Ti4O12 (BNBT) ceramics was investigated. The sintering temperature of the BNBT ceramics was significantly reduced from 1300 to 900 °C. Due to adding BCB into Ba(Nd1–xBix)2Ti4O12, the temperature coefficient of resonant frequency can be adjusted to zero with BCB content increasing. Good microwave dielectric properties of quality factor (Q×f) = 2600 GHz, εr = 75, and τf = 5 ppm/°C were obtained for BNBT with 7 wt% BCB sintered at 925 °C for 2 h, which make it a potential candidate for low temperature cofired ceramics applications.

Because of the lack of universal contact models for nonlinear strain problems, indentation analysis on rubberlike materials is confined to small deformation in which Hertz's solution is applied. Recognizing that deep indentation may provide more material information, in this paper we propose a nonlinear elastic model for large spherical indentation of rubberlike materials based on the higher-order approximation of spherical function and Sneddon's solution. The effect of limiting network stretch is studied on the initial elastic modulus for lightly cross-linked rubbers. With the comparisons of the finite-element simulation and the experimental result, the proposed model is verified to predict the large indentation of rubberlike materials over the indentation depth of 0.8 times the indenter radius.

Understanding the interaction between atomic hydrogen and solid tungsten is important for the development of fusion reactors in which proposed tungsten walls would be bombarded with high energy particles including hydrogen isotopes. Here, we report results from periodic density-functional theory calculations for three crucial aspects of this interaction: surface-to-subsurface diffusion of H into W, trapping of H at vacancies, and H-enhanced decohesion, with a view to assess the likely extent of hydrogen isotope incorporation into tungsten reactor walls. We find energy barriers of (at least) 2.08 eV and 1.77 eV for H uptake (inward diffusion) into W(001) and W(110) surfaces, respectively, along with very small barriers for the reverse process (outward diffusion). Although H dissolution in defect-free bulk W is predicted to be endothermic, vacancies in bulk W are predicted to exothermically trap multiple H atoms. Furthermore, adsorbed hydrogen is predicted to greatly stabilize W surfaces such that decohesion (fracture) may result from high local H concentrations.

The vanadium (V)-doped titania (Ti0.95V0.05O2) was impregnated in the host matrix of the pre-synthesized siliceous mesoporous material MCM-41 in a single pot synthesis step, by the wet impregnation route. The samples were characterized by x-ray diffraction, transmission electron microscopy (TEM), N2 adsorption, diffuse reflectance ultraviolet–visible spectroscopy (DRUVS). As compared to Ti0.95V0.05O2, the DRUV spectra of the impregnated catalysts showed a blue shift; still the absorption lies in the visible region. Presence of nano-sized (∼2–12 nm) V-doped titania particles in V-TiO2/MCM-41 was revealed by TEM and the particle size was found to increase with the loading of the V-doped titania in the host matrix. All impregnated samples were found to be more active than either the bulk V-doped titania or titania for photocatalytic oxidation of ethylene in air at ambient conditions under both UV and visible irradiation.

Transmission electron microscopy (TEM) and spectroscopy have been evolved to a stage such that they can be routinely used to probe the structure and composition of the materials with the resolution of a single atomic column. However, a direct in situ TEM observation of structural evolution of the materials in a lithium ion battery during dynamic operation of the battery has never been reported. In this paper, we report the results of exploring the in situ TEM techniques for observation of interfaces in the lithium ion battery during the operation of the battery. A miniature battery was fabricated using a single nanowire and an ionic liquid electrolyte. The structure and composition of the interface across the anode and the electrolyte was studied using TEM imaging, electron diffraction, and electron energy-loss spectroscopy. In addition, we also explored the possibilities of carrying out in situ TEM studies of lithium ion batteries with a solid state electrolyte.

Polyimide (PI)-matrix composite films containing inorganic nanoparticles (nano-Al2O3 and nano-TiO2) have been fabricated. A proposed model is used to explain different structures of the (Al2O3–TiO2)/PI (ATP) films synthesized by employing in situ polymerization. Dependences of dielectric permittivities of the ATP films on frequency and temperature were studied. Results show the breakdown strength of the films decreases with prolonging the corona aging time. The incorporation of the nano-Al2O3 and nano-TiO2 particles significantly improves the corona resistance of the films. The corona aging also influences the infrared absorbance, the glass transition temperature (Tg), and loss factor (tanδ) of the ATP films.

Ni0.8Zn0.2Fe2O4/Ba0.6Sr0.4TiO3 (NZO/BST) composites with high permittivity and low loss were synthesized via the hybrid processing route. The composites possess very dense and homogenous microstructure. The NZO/BST composites show good dielectric properties and magnetic properties with low loss in high frequency range. This indicates that this kind of magnetodielectric composites can be used in high-frequency communications for the capacitor-inductor integrating devices such as electromagnetic interference filters and antennas. The permittivities of the composites were also fitted using the combination of Maxwell–Wagner polarization and modified Curie–Weiss law.

A new function that describes the shape of three-sided pyramidal indenters is introduced. This function differs from the polynomial tip shape function conventionally used in nanoindentation tip shape calibration in that the new function includes fewer fitting parameters with clearer physical meaning. Specifically, two of the fitting parameters integrated into the new function are the indenter’s tip radius and the slope of the indenter’s equivalent cone. Tip shape calibration data were collected with four different diamond indenter tips, and both the new function and the standard polynomial function were fit to the data. It is found that the new function can fit calibration data nearly as well as the standard polynomial function and better than existing physically based functions. Although the tip radius parameter obtained by fitting the new model to data deviates from the tip radius determined from Hertzian elastic contact, the two values are correlated.

Niobium and tantalum doped anatase were prepared by thermal hydrolysis of peroxotitanium complex aqueous solutions containing of niobium or tantalum peroxo-complexes at 100 °C for 3 days. Niobium-doping increased the unit cell constants of anatase and changed the morphology of TiO2 from spindle-like to rectangular or square cross section. Nb and Ta doping in the TiO2 nanostructure increases the anatase to rutile transformation temperature to >1000 °C. In the visible region, the photocatalytic activity is directly proportional to the concentration and increases with increasing of Nb concentration. The niobium addition enhances the photocatalytic activity of titania in the visible light region.