Analysis of Preload-Dependent Reversible Mechanical Interlocking Using Beetle-Inspired Wing Locking Device

We report an analysis of preload-dependent reversible interlocking between regularly arrayed, high aspect ratio (AR) polymer micro- and nanofibers. Such a reversible interlocking is inspired from the wing-locking device of a beetle where densely populated microhairs (termed microtrichia) on the cuticular surface form numerous hair-to-hair contacts to maximize lateral shear adhesion. To mimic this, we fabricate various high AR, vertical micro- and nanopillars on a flexible substrate and investigate the shear locking force with different preloads (0.1–10 N/cm²). A simple theoretical model is developed based on the competition between van der Waals (VdW) attraction and deflection forces of pillars, which can explain the preload-dependent maximum deflection, tilting angle, and total shear adhesion force

Beetle-Inspired Bidirectional, Asymmetric Interlocking Using Geometry-Tunable Nanohairs

We present bidirectional, asymmetric interlocking behaviors between tilted micro- and nanohair arrays inspired from the actual wing locking device of beetles. The measured shear adhesion force between two identical tilted microhair arrays (1.5 μm radius, 30 μm height) turned out to be higher in the reverse direction than that in the angled direction, suggesting that the directionality of beetle’s microtrichia may play a critical role in preventing the elytra from shifting along the middle of insect body. Furthermore, we observed dramatic enhancement of shear adhesion using asymmetric interlocking of various nanohair arrays (tilting angle, δ < 40°). A maximum shear locking force of ∼60 N/cm² was measured for the nanohair arrays of 50 nm radius and 1 μm height with a hysteresis as high as ∼3. A simple theoretical model was developed to describe the measured asymmetric adhesion forces and hysteresis, in good agreement with the experimental data

Robust Microzip Fastener: Repeatable Interlocking Using Polymeric Rectangular Parallelepiped Arrays

We report a highly repeatable and robust microzip fastener based on the van der Waals force-assisted interlocking between rectangular parallelepiped arrays. To investigate zipperlike interlocking behaviors, various line arrays were fabricated with three different spacing ratios (1, 3, and 5 of 800 nm in width) and width of parallelepipeds (400 nm, 800 nm, and 5 μm with the spacing ratio of 1). In addition, the different rigidity of line arrays was inspected for a repeatable microzip fastener. The normal and shear locking forces were measured with variation of the material rigidity as well as geometry of the array, in good agreement with a proposed theory based on the contact area and force balance. The maximum adhesion forces as high as ∼8.5 N cm^–2 in the normal direction and ∼29.6 N cm^–2 in the shear direction were obtained with high stability up to 1000 cycles. High stability of our fastening system was confirmed for preventing critical failures such as buckling and fracture in practical applications

Combined Steam and CO₂ Reforming of CH₄ on LaSrNiO_<i>x</i> Mixed Oxides Supported on Al₂O₃‑Modified SiC Support

The combined steam and CO₂ reforming reaction of CH₄ was investigated using LaSrNiO_<i>x</i> mixed oxides supported on Al₂O₃-modified β-SiC to elucidate the largely enhanced CO₂ conversion at an optimal concentration of Al₂O₃ modifier. The dispersion of Al₂O₃ on the SiC support simultaneously altered the dispersion of LaSrNiO_<i>x</i> crystallites increasing their strength when combined with the Al₂O₃-modified SiC. Although all tested catalysts showed similar activation energies, the increased Al₂O₃ dispersion on SiC at around 10 wt % Al₂O₃ modifier was well-correlated with the increased dispersion of active perovskite-like La₂NiO₄ crystallites which resulted in an enhanced catalytic activity. The formation of smaller NiO and La₂NiO₄ crystallites through an intimate contact with Al₂O₃ particles seems to be responsible for the suppressed aggregation of nickel crystallites during higher temperature reforming reactions. The higher amounts of CO₂ adsorption on the well-dispersed basic lanthanum and strontium oxides contained in the LaSrNiO_<i>x</i> mixed oxides are also responsible for the enhanced CO₂ conversion. Observed surface properties including the crystallite size of active components, the reducibility of NiO, and the CO₂ adsorption property are explained in terms of the results obtained from X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, CO₂ temperature-programmed desorption (CO₂-TPD), and NH₃-TPD analyses

High-Performance Hybrid Catalyst with Selectively Functionalized Carbon by Temperature-Directed Switchable Polymer

Carbon-supported Pt (Pt/C) catalyst was selectively functionalized with thermally responsive poly­(<i>N</i>-isopropylacrylamide) (PNIPAM) to improve water transport in the cathode of proton exchange membrane fuel cell (PEMFC). Amine-terminated PNIPAM selectively reacted with the functional group of −COOH on carbon surfaces of Pt/C via the amide reaction by 1-ethyl-3-(3-dimethylaminopropyl)­carbodiimide (EDC) as a catalyst. Pt surfaces of Pt/C were intact throughout the carbon surface functionalization, and the carbon surface property could be thermally changed. The PNIPAM-functionalized Pt/C was well-dispersed, because of its hydrophilic surface property at room temperature during the catalyst ink preparation. In sharp contrast, when PEMFC was operated at 70 °C, PNIPAM-coated carbon surface of Pt/C became hydrophobic, which resulted in a decrease in water flooding in the cathode electrode. Because of the switched wetting property of the carbon surface, PEMFC with PNIPAM-functionalized Pt/C catalyst in the cathode showed high performance in the high current density region. To explain the enhanced water transport, we proposed a simple index as the ratio of systematic pressure (driving force) and retention force. The synthetic method presented here will provide a new insight into various energy device applications using organic and inorganic composite materials and functional polymers