Synergistic Effect of Hybrid Carbon Nanotube–Graphene Oxide as Nanoadditive Enhancing the Frictional Properties of Ionic Liquids in High Vacuum

A remarkable synergetic effect between the graphene oxide (GO) layers and multiwalled carbon nanotubes (MWCNTs) in improving friction and wear on sliding diamond-like carbon (DLC) surfaces under high vacuum condition (10^–5 Pa) and low or high applied load is demonstrated. In tests with sliding DLC surfaces, ionic liquid solution that contains small amounts of GO and MWCNTs exhibited the lowest specific friction coefficient and wear rate under all of the sliding conditions. Optical microscope images of the wear scar of a steel ball showed that GO/MWCNT composites exhibited higher antiwear capability than individual MWCNTs and GO did. Transmission electron microscopy images of nanoadditives after friction testing showed that MWCNTs support the GO layers like pillars and prevent assembly between the GO layers. Their synergistic effect considerably enhances IL-GO/MWCNT composites

Self-Healing Surface Hydrophobicity by Consecutive Release of Hydrophobic Molecules from Mesoporous Silica

The paper reports a novel approach to achieve self-healing surface hydrophobicity. Mesoporous silica is used as the reservoir for hydrophobic molecules, i.e., octadecylamine (ODA), that can release and refresh the surface hydrophobicity consecutively. A polymdopamine layer is used to further encapsulate silica–ODA, providing a reactive layer, governing release of the underlying ODA, and improving the dispersivity of silica nanoparticles in bulk resin. The approach arrives at self-healing (super)­hydrophobicity without using any fluoro-containing compounds

Free-Standing Three-Dimensional Graphene/Manganese Oxide Hybrids As Binder-Free Electrode Materials for Energy Storage Applications

Novel three-dimensional (3D) hybrid materials, i.e., free-standing 3D graphene-supported MnO₂ nanosheets, are prepared by a simple and controllable solution-phase assembly process. Characterization results show that MnO₂ nanosheets are uniformly anchored on a 3D graphene framework with strong adhesion and the integral hybrids show desirable mechanical strength. Such unique structure of 3D graphene/MnO₂ hybrids thus provides the right characteristics of binder-free electrode materials and could enable the design of different kinds of high-performance energy storage devices. Especially, an advanced asymmetric supercapacitor is built by using a 3D graphene/MnO₂ hybrid and a 3D graphene as two electrodes, and it is able to work reversibly in a full operation voltage region of 0–3.5 V in an ionic liquid electrolyte and thus exhibits a high energy density of 68.4 Wh/kg. As the cathode materials for Li–O₂ and Li–MnO₂ batteries, the 3D graphene/MnO₂ hybrids exhibit outstanding performances, including good catalytic capability, high reversible capacity and desirable cycling stability. The results presented here may pave a way for new promising applications of such 3D graphene/MnO₂ hybrids in advanced electrochemical energy storage devices

Contribution of Surface Chemistry to the Shear Thickening of Silica Nanoparticle Suspensions

Shear thickening is a general process crucial for many processed products ranging from food and personal care to pharmaceuticals. Theoretical calculations and mathematical simulations of hydrodynamic interactions and granular-like contacts have proved that contact forces between suspended particles dominate the rheological characteristic of colloidal suspensions. However, relevant experimental studies are very rare. This study was conducted to reveal the influence of nanoparticle (NP) interactions on the rheological behavior of shear-thickening fluids (STFs) by changing the colloidal surface chemistries. Silica NPs with various surface chemical compositions are fabricated and used to prepare dense suspensions. Rheological experiments are conducted to determine the influence of NP interactions on corresponding dense suspension systems. The results suggest that the surface chemistries of silica NPs determine the rheological behavior of dense suspensions, including shear-thickening behavior, onset stress, critical volume fraction, and jamming volume fraction. This study provides useful reference for designing effective STFs and regulating their characteristics

Patterned Ni–P Alloy Films Prepared by “Reducing–Discharging” Process and the Hydrophobic Property

Patterned hydrophobic Ni–P alloy films consisting of orderly and regular micro-nanoscale particles were fabricated through the synergistic effect of electrochemical deposition and chemical deposition. Ni–P alloy films were deposited for different times and characterized by scanning electron microscope (SEM). It was confirmed that the addition of reducing agent induced the formation of nanoscale particles, in contrast with pure Ni film deposited by single electrochemical deposition. As “point-discharge effect”, the current density was higher at the edge of the nanoscale particles, and Ni ions would be deposited at the particles through the “point-discharge effect”. Then the Ni–P alloy films grew by “reducing–discharging” process. The X-ray photoelectron spectroscopy (XPS) was used to detect the composition and valence states of these alloy films. The existence of oxidation state of element P in these films corresponding to that in H₂PO₃^–, also gave direct evidence for the occurrence of chemical deposition, during the electrochemical deposition process. The prolongation of deposition time could provide more time for the patterned morphology to grow up. The surface roughness, evaluated by surface profilometer, increased as the deposition time extension. And these films showed gradually increased hydrophobic properties with the increase in deposition time

Promising Porous Carbon Derived from Celtuce Leaves with Outstanding Supercapacitance and CO₂ Capture Performance

Business costs and energy/environmental concerns have increased interested in biomass materials for production of activated carbons, especially as electrode materials for supercapacitors or as solid-state adsorbents in CO₂ adsorption area. In this paper, waste celtuce leaves were used to prepare porous carbon by air-drying, pyrolysis at 600 °C in argon, followed by KOH activation. The as-prepared porous carbon have a very high specific surface area of 3404 m²/g and a large pore volume of 1.88 cm³/g. As an electroactive material, the porous carbon exhibits good capacitive performance in KOH aqueous electrolyte, with the specific capacitances of 421 and 273 F/g in three and two-electrode systems, respectively. As a solid-state adsorbent, the porous carbon has an excellent CO₂ adsorption capacity at ambient pressures of up to 6.04 and 4.36 mmol/g at 0 and 25 °C, respectively. With simple production process, excellent recyclability and regeneration stability, the porous carbon that was derived from celtuce leaves is among the most promising materials for high-performance supercapacitors and CO₂ capture

Superlubricity Enabled by Pressure-Induced Friction Collapse

From daily intuitions to sophisticated atomic-scale experiments, friction is usually found to increase with normal load. Using first-principle calculations, here we show that the sliding friction of a graphene/graphene system can decrease with increasing normal load and collapse to nearly zero at a critical point. The unusual collapse of friction is attributed to an abnormal transition of the sliding potential energy surface from corrugated, to substantially flattened, and eventually to counter-corrugated states. The energy dissipation during the mutual sliding is thus suppressed sufficiently under the critical pressure. The friction collapse behavior is reproducible for other sliding systems, such as Xe/Cu, Pd/graphite, and MoS₂/MoS₂, suggesting its universality. The proposed mechanism for diminishing energy corrugation under critical normal load, added to the traditional structural lubricity, enriches our fundamental understanding about superlubricity and isostructural phase transitions and offers a novel means of achieving nearly frictionless sliding interfaces