We report a new insulation composite of aramid honeycombs filled with superflexible resorcinol–formaldehyde aerogels. Aerogels produced via a sol–gel process were dried with supercritical CO2. The aerogels exhibit a high, rubber-like flexibility, due to almost zero shrinkage and networking of nanoparticles and suitably sized macropores. The high porosity of the aerogels in the range of about 95–98% leads to a low thermal conductivity about 0.037 W/mK and low bulk density of 0.05 g/cm3. The filling of light and stiff aramid honeycombs with these flexible aerogels results in a composite with decreased thermal conductivity and modified mechanical properties.

Indentation-induced phase transformation processes were studied by in situ Raman imaging of the deformed contact region of silicon thin films, using a Raman spectroscopy-enhanced instrumented indentation technique (IIT). In situ Raman imaging was used to study the generation and evolution of the phase transformation of silicon while performing an IIT experiment analyzed to determine the average contact pressure and indentation strain. This is, to our knowledge, the first sequence of Raman images documenting the evolution of the strain fields and changes in the phase distributions of a material while conducting an indentation experiment. The reported in situ experiments provide insights into the transformation processes in silicon during indentation, confirming, and providing the experimental evidence for, some of the previous assumptions made on this subject. The developed Raman spectroscopy-enhanced IIT has shown its potential in advancing the understanding of deformation mechanisms and will provide a very useful tool in validating and refining contact models and related simulation studies.

Practical implementation of oxide thermoelectrics on an industrial or commercial scale for waste heat energy conversion requires the development of chemically stable interfaces between metal interconnects and oxide thermoelements that exhibit low electrical contact resistances. A commercially available high-chrome iron alloy (i.e., Crofer® 22 APU) serving as the interconnect metal was spray coated with LaNi0.6Fe0.4O3 (LNFO) or (Mn,Co)3O4 spinel and then interfaced with a p-type thermoelectric material—calcium cobaltate (Ca3Co4O9)—using spark plasma sintering. The interfaces have been characterized in terms of their thermal and electronic transport properties and chemical stability. With long-term exposure of the interfaced samples to 800 °C in air, the cobalt–manganese spinel acted as a diffusion barrier between the Ca3Co4O9 and the Crofer® 22 APU alloy resulting in improved interfacial stability compared to that of samples containing LNFO as a barrier layer, and especially those without any barrier. The initial area specific interfacial resistance of the Ca3Co4O9/(Mn,Co)3O4/Crofer® 22 APU interface at 800 °C was found to be ∼1 mΩ·cm2.

From the view of tissue engineering, the deficiency in porosity has impeded further application of bacterial cellulose (BC) as a super biomaterial. In this study, we used a combination method consisting of acetic acid treatment and freeze-drying operation to improve the porous profile of BC, as well as a simple and fast method to measure the thickness, density, and porosity of BC. Results have shown a significant improvement in the porosity of the inner structure of BC treated with acetic acid and freeze-drying. Microscopic observation by scanning electron microscopy exhibited explicit evidences that more orderly porous layer-by-layer structures and more pores were formed along the cross section of modified BC as compared with the control. The enhancement of mechanical properties and crystallinity of modified BC was also demonstrated due to the improvement of material porosity in the particular extent from 50.3 to 76.43%. Cell culture of human fibroblast cells exhibited good cell viability on modified BC, suggesting that a better porous profile of BC on the surface and cross section helps facilitate cells to attach, as well as potentially promotes cells to grow in. These significant results may open the possibility of producing BC nanomaterials for tissue engineering with desirable properties.

In this article, a comprehensive investigation on the thermal properties of Yb3Al5O12 is conducted, including Debye temperature, thermal expansion coefficient (TEC), thermal diffusivity, heat capacity, and thermal conductivity. The calculated Debye temperature of Yb3Al5O12 from the measured elastic properties is 625 K. The linear and volumetric thermal expansions of Yb3Al5O12 from 298 to 1273 K are (7.83 ± 0.14) × 10−6 and (23.74 ± 0.42) × 10−6 K−1, respectively. The linear TEC of the polycrystalline bulk Yb3Al5O12 determined by dilatometer is (8.22 ± 0.3) × 10−6 K−1. The measured thermal conductivities of Yb3Al5O12 are 4.67 and 2.05 W (m K)−1, respectively, at 300 and 1400 K. The estimated minimum thermal conductivity, κmin, is 1.22 W (m K)−1. The high temperature thermal conductivity is close to the evaluated κmin, which is lower than most commonly used thermal barrier coating (TBC) material such as Y2O3-stabilized-ZrO2 (YSZ). The unique combination of these properties renders Yb3Al5O12 being a very promising candidate material for TBC.

Superelasticity of shape memory alloy (SMA) results from the reversible thermoelastic martensitic transformation. Although this property has been studied extensively at the macroscale, the study of this superelastic behavior at the micro/nanoscale is relatively new. In this work, we processed TiNi-based SMAs with different compositions and different phase transformation temperatures. Nanoindentations were performed with different peak loads and at various temperatures to systematically characterize the degree of localized stress-induced martensitic transformation at the nanoscale for each SMA. Micropillar compression tests were also performed to study the global superelastic behavior at the microscale. The physics of stress-induced martensitic transformation versus the phase transformation temperature, the testing temperature, and the peak load relations was explored and the difference between the localized and the global superelastic behaviors was discussed. Our results demonstrate the potential of integrating TiNi-based SMAs into functional micro- and nanodevices.

The conjugated polymer poly(2,5-dihexyl-1,4-phenylene-alt-2-amino-4,6-pyrimidine) was synthesized and used in the supramolecular functionalization of single-walled carbon nanotubes (SWNTs). It was found that this polymer can form strong supramolecular polymer–nanotube assembly and produce a stable composite in solution. The resulting polymerized nanotubes were analyzed by UV–Vis absorption and emission spectroscopy, thermogravimetry, transmission electron microscopy and scanning electron microscopy. It was found that the noncovalent functionalization did not damage the nanotube structure. The polymer content in the polymer–nanotube composite could be calculated to be 41% by thermogravimetry analysis. The composite exhibited certain solubility in dimethylacetamide (DMAc), where the solubility in the absence of excess free polymer solution is 78.7 mg L−1. The composite exhibited a conductivity of 0.005 S cm−1 and the anodic and cathodic peaks were observed at 0.47 and 0.37 V. Galvanostatical charge/discharge tests give good cycling behavior of maintaining a stable capacitance value of 66.7 F g−1 over 1000 cycles at a current load of 1 mA cm−2 without distinct drop.

The mechanical properties of nanoscale free-standing polymer thin films exhibit size dependence due to surface effects. However, it remains a challenge to determine the length scales at which differences are exhibited between film and bulk polymer properties. Here we use molecular dynamics simulations to uncover the dependence of elastic modulus (E) of free-standing films on film thickness and bulk properties. Comparison of the glass transition temperature (T g) and E indicates that T g converges to the bulk value slightly faster as the film thickness increases. The free-surface effects that give rise to a depression in E and T g are observed to be stronger for polymers with weaker intermolecular interactions. The most intriguing aspect of our study is the finding that despite the observed decrease in the modulus of the film up to a thickness of over 100 nm, the local stress distribution reveals that the preserved length scale of perturbation of the free surface is only several nanometers.

Designing materials for application as electrodes in sodium-ion batteries may require the use of unconventional materials to realize acceptable reversible sodium insertion/extraction capabilities. To design new materials simple electrochemical methods need to be coupled with other techniques such as in situ x-ray diffraction (XRD) to correlate the influence of electrochemical performance on a parameter that can be modified, e.g., the crystal structure of the material. Here we use in situ synchrotron XRD data on Gd2TiO5-containing cells to show the minor changes in reflection positions during discharge/charge that illustrates minimal volume expansion and contraction due to insertion/extraction reactions. These small changes correlate to the Gd2TiO5 anode material in both lithium- and sodium-ion batteries showing reversible capacities of ∼45 and ∼23 mA h/g after 20 cycles, respectively. Analysis of sodium location in the crystal structure shows a preference for sodium in the smaller channels along the c axis direction during the first discharge before moving to the larger channels at the charged state. Therefore, in this work, in situ studies highlight minimal structural changes with respect to volume expansion during electrochemical cycling and illustrate where sodium ions locate within the Gd2TiO5 structure.

Pristine multiwalled carbon nanotubes (P-MWCNTs) were functionalized with carboxylic groups (MWCNT-COOH) through oxidation reactions and then reduced to produce hydroxyl groups (MWCNT-OH). Pristine and functionalized MWCNTs were used to produce poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposites with 0.5 wt% of MWCNTs. MWCNT functionalization was verified by visual stability in water, infrared and Raman spectroscopy, and zeta potential measurements. Pristine and functionalized MWCNTs acted as the nucleating agent in a PHBV matrix, as verified by differential scanning calorimetry (DSC). However, the dispersion of filler into the matrix, thermal stability, and direct current (DC) conductivity were affected by MWCNT functionalization. Scanning electron microscopy (SEM) showed that filler dispersion into the PHBV matrix was improved with MWCNT functionalization. The surface roughness was reduced with the addition and functionalization of MWCNT. The thermal stability of PHBV/MWCNT-COOH, PHBV/P-MWCNT, and PHBV/MWCNT-OH nanocomposites were 20, 30, and 30 °C higher than neat PHBV, respectively, as verified by thermogravimetry analysis (TGA). Addition of pristine and functionalized MWCNTs provided electrical conductivity in nanocomposite, which was higher for PHBV/P-MWCNTs (1.2 × 10−5 S cm−1).

The effect of electric-current pulses on the evolution of microstructure and texture in cryogenically rolled copper was determined. The pulsed material was found to be completely recrystallized, and the recrystallization mechanism was deduced to be similar to that operating during conventional static annealing. The microstructural changes were explained simply in terms of Joule heating. A significant portion of the recrystallization process was concluded to have occurred after pulsing; i.e., during cooling to ambient temperature. The grain structure and microhardness were shown to vary noticeably in the heat-affected zone (HAZ); these observations mirrored variations of temper colors. Accordingly, the revealed microstructure heterogeneity was attributed to the inhomogeneous temperature distribution developed during pulsing. In the central part of the HAZ, the mean grain size increased with current density and this effect was associated with the temperature rise per se. This grain size was slightly smaller than that in statically recrystallized specimens.