In-Plane Deformation Mechanics for Highly Stretchable Electronics.

Scissoring in thick bars suppresses buckling behavior in serpentine traces that have thicknesses greater than their widths, as detailed in a systematic set of analytical and experimental studies. Scissoring in thick copper traces enables elastic stretchability as large as ≈350%, corresponding to a sixfold improvement over previously reported values for thin geometries (≈60%).

Large-deformation and high-strength amorphous porous carbon nanospheres.

Carbon is one of the most important materials extensively used in industry and our daily life. Crystalline carbon materials such as carbon nanotubes and graphene possess ultrahigh strength and toughness. In contrast, amorphous carbon is known to be very brittle and can sustain little compressive deformation. Inspired by biological shells and honeycomb-like cellular structures in nature, we introduce a class of hybrid structural designs and demonstrate that amorphous porous carbon nanospheres with a thin outer shell can simultaneously achieve high strength and sustain large deformation. The amorphous carbon nanospheres were synthesized via a low-cost, scalable and structure-controllable ultrasonic spray pyrolysis approach using energetic carbon precursors. In situ compression experiments on individual nanospheres show that the amorphous carbon nanospheres with an optimized structure can sustain beyond 50% compressive strain. Both experiments and finite element analyses reveal that the buckling deformation of the outer spherical shell dominates the improvement of strength while the collapse of inner nanoscale pores driven by twisting, rotation, buckling and bending of pore walls contributes to the large deformation.

Epidermal radio frequency electronics for wireless power transfer.

Epidermal electronic systems feature physical properties that approximate those of the skin, to enable intimate, long-lived skin interfaces for physiological measurements, human-machine interfaces and other applications that cannot be addressed by wearable hardware that is commercially available today. A primary challenge is power supply; the physical bulk, large mass and high mechanical modulus associated with conventional battery technologies can hinder efforts to achieve epidermal characteristics, and near-field power transfer schemes offer only a limited operating distance. Here we introduce an epidermal, far-field radio frequency (RF) power harvester built using a modularized collection of ultrathin antennas, rectifiers and voltage doublers. These components, separately fabricated and tested, can be integrated together via methods involving soft contact lamination. Systematic studies of the individual components and the overall performance in various dielectric environments highlight the key operational features of these systems and strategies for their optimization. The results suggest robust capabilities for battery-free RF power, with relevance to many emerging epidermal technologies.

Mechanical Properties of Molybdenum Disulfide and the Effect of Doping: An in Situ TEM Study.

Direct observations on nanopillars composed of molybdenum disulfide (MoS2) and chromium-doped MoS2 and their response to compressive stress have been made. Time-resolved transmission electron microscopy (TEM) during compression of the submicrometer diameter pillars of MoS2- and Cr-doped MoS2 (Cr: 0, 10, and 50 at %) allow the deformation process of the material to be observed and can be directly correlated with mechanical response to applied load. The addition of chromium to the MoS2 changed the failure mode from plastic deformation to catastrophic brittle fracture, an effect that was more pronounced as chromium content increased.

Compression-induced deformation of individual metal-organic framework microcrystals.

The deformation and mechanical behavior of individual zeolitic-imidazolate framework (ZIF-8) micro- and sub-microcrystals were observed under compression. Young's modulus and volume changes as a function of applied pressure were determined on individual single crystals, offering insights in the relationship among structure, morphology, and mechanical properties. Dramatic volume decreases and amorphization were detected during compression over a pressure range of 0-4 GPa for individual 1.2 µm ZIF-8 microcrystals, and the deformed microcrystals partially recovered after pressure release. The orientation and size effects on the mechanical behavior of ZIF-8 nano- and microcrystals were also investigated. The presence of solvates within the pores of the ZIF-8 has a dramatic effect on the mechanical properties of the single crystals. Methanol-solvated ZIF-8 microcrystals are much less deformable than the desolvated microcrystals and shatter completely at very low applied force.

Chromatographic resolution and isotherm determination of (R,S)-mandelic acid on Chiralcel-OD column.

Resolution of racemic mandelic acid ((R,S)-MA) and numerical determination of binary competitive isotherm of (R,S)-MA on Chiralcel-OD column have been investigated in this study. The effects of the alcohol modifier and acidic additive in the mobile phase on the retention and enantioseparation of (R,S)-MA were studied at first. The inverse method was then used to determine the competitive isotherm parameters of (R,S)-MA by minimizing the sum of square deviations of the model predictions from the measured elution profiles. The results indicate that the mobile phase with 85% hexane/15% isopropanol/0.3% trifluoroacetic acid mixture gives the best resolution of (R,S)-MA and competitive-modified Langmuir isotherm provides the more accurate sorption mechanism of (R,S)-MA on the cellulose tris(3,5-dimethylphenylcarbamate) chiral stationary phase.