A general approach to composites containing nonmetallic fillers and liquid gallium

We report a versatile method to make liquid metal composites by vigorously mixing gallium (Ga) with non-metallic particles of graphene oxide (G-O), graphite, diamond, and silicon carbide that display either paste or putty-like behavior depending on the volume fraction. Unlike Ga, the putty-like mixtures can be kneaded and rolled on any surface without leaving residue. By changing temperature, these materials can be stiffened, softened, and, for the G-O-containing composite, even made porous. The gallium putty (GalP) containing reduced G-O (rG-O) has excellent electromagnetic interference shielding effectiveness. GalP with diamond filler has excellent thermal conductivity and heat transfer superior to a commercial liquid metal-based thermal paste. Composites can also be formed from eutectic alloys of Ga including Ga-In (EGaIn), Ga-Sn (EGaSn), and Ga-In-Sn (EGaInSn or Galinstan). The versatility of our approach allows a variety of fillers to be incorporated in liquid metals, potentially allowing filler-specific "fit for purpose" materials

Towards determining the interaction of fluids with nanostructured carbons

Development of efficient approaches for modeling of nanostructures and nanofluidics is a major goal of theoretical and computational scientists. Here we focus on developing a scheme to accurately and efficiently predict the interactions of fluid molecules with nanostructured carbons where the interactions are weak and relatively short-range. As a model of these systems we consider the interaction of neon with simple polyaromatic hydrocarbons, and demonstrate that the use of basis sets of high local quality can provide a very useful approach

Different approaches for evaluating exponentially weighted nonequilibrium relations

The Kawasaki identity (KI) and the Jarzynski equality (JE) are important nonequilibrium relations. Both of these relations take the form of an ensemble average of an exponential function and can exhibit convergence problems when the average of the exponent differs greatly from the log of the average of the exponential function. In this work, we re-express these relations so that only selected regions need to be evaluated in an attempt to avoid these convergence issues. In the context of measuring free energies, we compare our method to the JE and the literature standard approach, the maximum likelihood estimator (MLE), and show that in a system with asymmetric work distributions it can perform as well as the MLE. For the KI, we derive an analog to the MLE to compare with our relation and show that these two new relations improve on the KI and are complimentary to each other

Filling the gap between transient and steady shear rheology of aqueous graphene oxide dispersions

Even though the rheological behavior of aqueous graphene oxide (G-O) dispersions has been shown to be strongly time-dependent, only few transient measurements have been reported in the literature. In this work, we attempt to fill the gap between transient and steady shear rheological characterizations of aqueous G-O dispersions in the concentration range of 0.004 < I center dot < 3.5 wt%, by conducting comprehensive rheological measurements, including oscillatory shear flow, transient shear flow, and steady shear flow. Steady shear measurements have been performed after the evaluation of transient properties of the G-O dispersions, to assure steady-state conditions. We identify the critical concentration I center dot (c) = 0.08 wt% (where G-O sheets start to interact) from oscillatory shear experiments. We find that the rheology of G-O dispersions strongly depends on the G-O concentration I center dot. Transient measurements of shear viscosity and first normal stress difference suggest that G-O dispersions behave like nematic polymeric liquid crystals at I center dot/I center dot (c) = 25, in agreement with other work reported in the literature. G-O dispersions also display a transition from negative to positive values of the first normal stress difference with increasing shear rates. Experimental findings of aqueous graphene oxide dispersions are compared and discussed with models and experiments reported for nematic polymeric liquid crystals, laponite, and organoclay dispersions

Graphitized silicon carbide microbeams: wafer-level, self-aligned graphene on silicon wafers

Currently proven methods that are used to obtain devices with high-quality graphene on silicon wafers involve the transfer of graphene flakes from a growth substrate, resulting in fundamental limitations for large-scale device fabrication. Moreover, the complex three-dimensional structures of interest for microelectromechanical and nanoelectromechanical systems are hardly compatible with such transfer processes. Here, we introduce a methodology for obtaining thousands of microbeams, made of graphitized silicon carbide on silicon, through a site-selective and wafer-scale approach. A Ni-Cu alloy catalyst mediates a self-aligned graphitization on prepatterned SiC microstructures at a temperature that is compatible with silicon technologies. The graphene nanocoating leads to a dramatically enhanced electrical conductivity, which elevates this approach to an ideal method for the replacement of conductive metal films in silicon carbide-based MEMS and NEMS devices

Nitrogen-Doped Carbon Foam as a Highly Durable Metal-Free Electrocatalyst for the Oxygen Reduction Reaction in Alkaline Solution

Nitrogen-doped carbon foam (CFN) with large surface area is synthesized via a template-free, scalable combustion technique using diethanolamine as a nitrogen source. The resulting macroporous, open-cell foam has micron-scale hollow cells, surrounded by thin, graphene-like walls. This material is applied as a metal-free electrocatalyst for the oxygen reduction reaction (ORR) in alkaline KOH solution. The activity of this metal-free electrocatalyst at the half-wave potential is just 43 mV lower than that of platinum-decorated carbon (Pt/CB), but 87 mV lower than a commercially available Fe-containing non-precious electrocatalyst (Pajarito Powder, PP), suggesting that iron is important in achieving the highest activities. In durability tests measured over 60,000 potential cycles, Pt/CB and PP undergo significant degradation, whilst the non-precious CFN electrocatalyst shows negligible change, indicating high stability of the electrochemical active sites compared with platinum or iron. Such metal-free catalysts therefore show great promise as electrocatalysts for specific alkaline ion exchange membrane fuel cell (AEMFC) applications where long lifetimes are most important.clos

Graphene Coatings as Barrier Layers to Prevent the Water-Induced Corrosion of Silicate Glass

Corrosion-protective coatings for silicate glass based on the transfer of one or two layers of graphene grown on copper by chemical vapor deposition have been demonstrated. The effectiveness of graphene to act as a glass corrosion inhibitor was evaluated by water immersion testing. After 120 days of immersion in water, bare glass samples had a significant increase in surface roughness and defects, which resulted in a marked reduction in fracture strength. In contrast, the single- and double-layer graphene-coated glasses experienced negligible changes in both fracture strength and surface roughness. The anticorrosion mechanism was also studied.close0

Efficient Metal-Free Electrocatalysts from N-Doped Carbon Nanomaterials: Mono-Doping and Co-Doping

N???doped carbon nanomaterials have rapidly grown as the most important metal???free catalysts in a wide range of chemical and electrochemical reactions. This current report summarizes the latest advances in N???doped carbon electrocatalysts prepared by N mono???doping and co???doping with other heteroatoms. The structure???performance relationship of these materials is subsequently rationalized and perspectives on developing more efficient and sustainable electrocatalysts from carbon nanomaterials are also suggested