A soft co-crystalline solid electrolyte for lithium-ion batteries.

Alternative solid electrolytes are the next key step in advancing lithium batteries with better thermal and chemical stability. A soft solid electrolyte, (Adpn)2LiPF6 (Adpn, adiponitrile), is synthesized and characterized that exhibits high thermal and electrochemical stability and good ionic conductivity, overcoming several limitations of conventional organic and ceramic materials. The surface of the electrolyte possesses a liquid nano-layer of Adpn that links grains for a facile ionic conduction without high pressure/temperature treatments. Further, the material can quickly self-heal if fractured and provides liquid-like conduction paths via the grain boundaries. A substantially high ion conductivity (~10-4 S cm-1) and lithium-ion transference number (0.54) are obtained due to weak interactions between 'hard' (charge dense) Li+ ions and the 'soft' (electronically polarizable) -C≡N group of Adpn. Molecular simulations predict that Li+ ions migrate at the co-crystal grain boundaries with a (preferentially) lower activation energy Ea and within the interstitial regions between the co-crystals with higher Ea values, where the bulk conductivity is a smaller but extant contribution. These co-crystals establish a special concept of crystal design to increase the thermal stability of LiPF6 by separating ions in the Adpn solvent matrix, and also exhibit a unique mechanism of ion conduction via low-resistance grain boundaries, which contrasts with ceramics or gel electrolytes.

A Self-Binding, Melt-Castable, Crystalline Organic Electrolyte for Sodium Ion Conduction.

The preparation and characterization of the cocrystalline solid-organic sodium ion electrolyte NaClO4 (DMF)3 (DMF=dimethylformamide) is described. The crystal structure of NaClO4 (DMF)3 reveals parallel channels of Na+ and ClO4- ions. Pressed pellets of microcrystalline NaClO4 (DMF)3 exhibit a conductivity of 3×10-4  S cm-1 at room temperature with a low activation barrier to conduction of 25 kJ mol-1 . SEM revealed thin liquid interfacial contacts between crystalline grains, which promote conductivity. The material melts gradually between 55-65 °C, but does not decompose, and upon cooling, it resolidifies as solid NaClO4 (DMF)3 , permitting melt casting of the electrolyte into thin films and the fabrication of cells in the liquid state and ensuring penetration of the electrolyte between the electrode active particles.

Damage Resistance of Kevlar® Fabric, UHMWPE, PVB Multilayers Subjected to Concentrated Drop-Weight Impact.

The impact resistance of layered polymer structures using polyvinyl butyral (PVB) in combination with Kevlar® fabric and ultra-high molecular weight polyethylene (UHMWPE) were fabricated and tested. Methods of wet impregnation and hot-press impregnation and consolidation of fabric with PVB and UHMWPE were used to manufacture multilayer constructs. All sandwich constructs were fixed to the surface of ballistic clay and subject to a free drop-weight test with a conical impactor having a small contact area. All tests were made at the same impact energy of 9.3 J and velocity of 2.85 m/s. The change in the resistance force was recorded using a piezoelectric force sensor at the time intervals of 40 µs. Using experimental force-time history, the change in the impactor's velocity, the depth of impactor penetration, the energy transformation at various stages of impactor interaction with the sample, and other parameters were obtained. Three indicators were considered as the main criteria for the effectiveness of a sample's resistance to impact: (1) minimum deformation, bulging, of the panel backside at the moment of impact, (2) minimum absorption of impact energy per areal density, and (3) minimal or, better yet, no destruction of structural integrity. Under the tested conditions, the rigid Kevlar-PVB-Kevlar sandwich at the frontside and relatively soft but flexible UHMWPE-Kevlar-UHMWPE layers in the middle helped to localize and absorb impact energy, while the backside Kevlar-PVB-Kevlar sandwich minimized local bulging providing the best overall performance. The front layer damage area was very shallow and less than two impactor tip diameters. The backside bulging was also less than in any other tested configurations.

Preparation and characterization of graphene oxide paper.

Free-standing paper-like or foil-like materials are an integral part of our technological society. Their uses include protective layers, chemical filters, components of electrical batteries or supercapacitors, adhesive layers, electronic or optoelectronic components, and molecular storage. Inorganic 'paper-like' materials based on nanoscale components such as exfoliated vermiculite or mica platelets have been intensively studied and commercialized as protective coatings, high-temperature binders, dielectric barriers and gas-impermeable membranes. Carbon-based flexible graphite foils composed of stacked platelets of expanded graphite have long been used in packing and gasketing applications because of their chemical resistivity against most media, superior sealability over a wide temperature range, and impermeability to fluids. The discovery of carbon nanotubes brought about bucky paper, which displays excellent mechanical and electrical properties that make it potentially suitable for fuel cell and structural composite applications. Here we report the preparation and characterization of graphene oxide paper, a free-standing carbon-based membrane material made by flow-directed assembly of individual graphene oxide sheets. This new material outperforms many other paper-like materials in stiffness and strength. Its combination of macroscopic flexibility and stiffness is a result of a unique interlocking-tile arrangement of the nanoscale graphene oxide sheets.

Anti-Ballistic Performance of PPTA/UHMWPE Laminates.

Poly(p-phenylene terephthalamide) (PPTA) and ultra-high-molecular-weight polyethylene (UHMWPE) are high-performance polymer materials largely used for body armor applications. Although composite structures from a combination of PPTA and UHMWPE have been created and described in the literature, the manufacture of layered composites from PPTA fabrics and UHMWPE films with UHMWPE film as an adhesive layer has not been reported. Such a new design can provide the obvious advantage of simple manufacturing technology. In this study, for the first time, we prepared PPTA fabrics/UHMWPE films laminate panels using plasma treatment and hot-pressing and examined their ballistic performance. Ballistic testing results indicated that samples with moderate interlayer adhesion between PPTA and UHMWPE layers exhibited enhanced performance. A further increase in interlayer adhesion showed a reverse effect. This finding implies that optimization of interface adhesion is essential to achieve maximum impact energy absorption through the delamination process. In addition, it was found that the stacking sequence of the PPTA and UHMWPE layers affected ballistic performance. Samples with PPTA as the outermost layer performed better than those with UHMWPE as the outermost layer. Furthermore, microscopy of the tested laminate samples showed that PPTA fibers exhibited shear cutting failure on the entrance side and tensile failure on the exit side of the panel. UHMWPE films exhibited brittle failure and thermal damage at high compression strain rate on the entrance side and tensile fracture on the exit side. For the first time, findings from this study reported in-field bullet testing results of PPTA/UHMWPE composite panels, which can provide important insights for designing, fabricating, and failure analysis of such composite structures for body armors.

Graphene-based composite materials.

Graphene sheets--one-atom-thick two-dimensional layers of sp2-bonded carbon--are predicted to have a range of unusual properties. Their thermal conductivity and mechanical stiffness may rival the remarkable in-plane values for graphite (approximately 3,000 W m(-1) K(-1) and 1,060 GPa, respectively); their fracture strength should be comparable to that of carbon nanotubes for similar types of defects; and recent studies have shown that individual graphene sheets have extraordinary electronic transport properties. One possible route to harnessing these properties for applications would be to incorporate graphene sheets in a composite material. The manufacturing of such composites requires not only that graphene sheets be produced on a sufficient scale but that they also be incorporated, and homogeneously distributed, into various matrices. Graphite, inexpensive and available in large quantity, unfortunately does not readily exfoliate to yield individual graphene sheets. Here we present a general approach for the preparation of graphene-polymer composites via complete exfoliation of graphite and molecular-level dispersion of individual, chemically modified graphene sheets within polymer hosts. A polystyrene-graphene composite formed by this route exhibits a percolation threshold of approximately 0.1 volume per cent for room-temperature electrical conductivity, the lowest reported value for any carbon-based composite except for those involving carbon nanotubes; at only 1 volume per cent, this composite has a conductivity of approximately 0.1 S m(-1), sufficient for many electrical applications. Our bottom-up chemical approach of tuning the graphene sheet properties provides a path to a broad new class of graphene-based materials and their use in a variety of applications.

Improving Interlayer Adhesion of Poly(p-phenylene terephthalamide) (PPTA)/Ultra-high-molecular-weight Polyethylene (UHMWPE) Laminates Prepared by Plasma Treatment and Hot Pressing Technique.

Poly(p-phenylene terephthalamide) (PPTA) is a high-performance polymer that has been utilized in a range of applications. Although PPTA fibers are widely used in various composite materials, laminar structures consisting of PPTA and ultra-high-molecular-weight polyethylene (UHMWPE), are less reported. The difficulty in making such composite structures is in part due to the weakness of the interface formed between these two polymers. In this study, a layered structure was produced from PPTA fabrics and UHMWPE films via hot pressing. To improve the interlayer adhesion, oxygen plasma was used to treat the PPTA and the UHMWPE surfaces prior to lamination. It has been found that while plasma treatment on the UHMWPE surface brought about a moderate increase in interlayer adhesion (up to 14%), significant enhancement was achieved on the samples fabricated with plasma treated PPTA (up to 91%). It has been assumed that both surface roughening and the introduction of functional groups contributed to this improvement.

Author Correction: Structure-Mechanical Property Relations of Skin-Core Regions of Poly(p-phenylene terephthalamide) Single Fiber.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Structure-Mechanical Property Relations of Skin-Core Regions of Poly(p-phenylene terephthalamide) Single Fiber.

This study aims to elucidate the relationship between the mechanical properties and microstructures of poly(p-phenylene terephthalamide) (PPTA) single fibers at the micro/nano scale. The skin-core structure of Kevlar® 29 fiber was revealed through a focused electron beam experiment inside a scanning electron microscope (SEM) chamber. Cross sectional SEM images of the broken fiber showed that the thickness of the skin ranged from 300 to 800 nm and that the core region consisted of highly packed layers of fibrils. The skin and the core regions showed different mechanical behaviour and structural changes during nanoindentation and micro-tensile tests, indicating that the core region possessed higher stiffness, whereas the skin region could undergo more plastic deformation. Furthermore, micro-tensile testing results showed that the ultimate tensile strength, the elongation at failure, and the tensile toughness of single fibers could be significantly enhanced by cyclic loading. Such findings are important to understand the contribution of different microstructures of Kevlar® fibers to their mechanical performance, which in turn can be utilized to design high-performance fibers that are not limited by the trade-off between toughness and stiffness.

Pilot study on biocompatibility of fluorescent nanodiamond-(NV)-Z~800 particles in rats: safety, pharmacokinetics, and bio-distribution (part III).

INTRODUCTION: We hereby report on studies aimed to characterize safety, pharmacokinetics, and bio-distribution of fluorescent nanodiamond particles (NV)-Z~800 (FNDP-(NV)) administered to rats by intravenous infusion in a single high dose. METHODS: Broad scale biological variables were monitored following acute (90 minutes) and subacute (5 or 14 days) exposure to FNDP-(NV). Primary endpoints included morbidity and mortality, while secondary endpoints focused on hematology and clinical biochemistry biomarkers. Particle distribution (liver, spleen, lung, heart, and kidney) was assessed by whole organ near infrared imaging using an in vivo imaging system. This was validated by the quantification of particles extracted from the same organs and visualized by fluorescent and scanning electron microscopy. FNDP-(NV)-treated rats showed no change in morbidity or mortality and preserved normal motor and sensory function, as assessed by six different tests. RESULTS: Blood cell counts and plasma biochemistry remained normal. The particles were principally distributed in the liver and spleen. The liver particle load accounted for 51%, 24%, and 18% at 90 minutes, 5 days, and 14 days, respectively. A pilot study of particle clearance from blood indicated 50% clearance 33 minutes following the end of particle infusion. CONCLUSION: We concluded that systemic exposure of rats to a single high dose of FDNP-(NV)-Z~800 (60 mg/kg) appeared to be safe and well tolerated over at least 2 weeks. These data suggest that FNDP-(NV) should proceed to preclinical development in the near future.

Spontaneous Periodic Delamination of Thin Films To Form Crack-Free Metal and Silicon Ribbons with High Stretchability.

Design of electronic materials with high stretchability is of great importance for realizing soft and conformal electronics. One strategy of realizing stretchable metals and semiconductors is to exploit the buckling of materials bonded to elastomers. However, the level of stretchability is often limited by the cracking and fragmentation of the materials that occurs when constrained buckling occurs while bonded to the substrate. Here, we exploit a failure mechanism, spontaneous buckling-driven periodic delamination, to achieve high stretchability in metal and silicon films that are deposited on prestrained elastomer substrates. We find that both globally periodic buckle-delaminated pattern and ordered cracking patterns over large areas are observed in the spontaneously buckle-delaminated thin films. The geometry of periodic delaminated buckles and cracking periodicity can be predicted by theoretical models. By patterning the films into ribbons with widths smaller than the predicted cracking periodicity, we demonstrate the design of crack-free and spontaneous delaminated ribbons on highly prestrained elastomer substrates, which provides a high stretchability of about 120% and 400% in Si and Au ribbons, respectively. We find that the high stretchability is mainly attributed to the largely relaxed strain in the ribbons via spontaneous buckling-driven delamination, as made evident by the small maximum tensile strain in both ribbons, which is measured to be over 100 times smaller than that of the substrate prestrain.

Structure Evolution and Thermoelectric Properties of Carbonized Polydopamine Thin Films.

Carbonization of nature-inspired polydopamine can yield thin films with high electrical conductivity. Understanding of the structure of carbonized PDA (cPDA) is therefore highly desired. In this study, neutron diffraction, Raman spectroscopy, and other techniques indicate that cPDA samples are mainly amorphous with some short-range ordering and graphite-like structure that emerges with increasing heat treatment temperature. The electrical conductivity and the Seebeck coefficient show different trends with heat treatment temperature, while the thermal conductivity remains insensitive. The largest room-temperature ZT of 2 × 10-4 was obtained on samples heat-treated at 800 °C, which is higher than that of reduced graphene oxide.

High Conductivity, High Strength Solid Electrolytes Formed by in Situ Encapsulation of Ionic Liquids in Nanofibrillar Methyl Cellulose Networks.

Strong, solid polymer electrolyte ion gels, with moduli in the MPa range, a capacitance of 2 µF/cm(2), and high ambient ionic conductivities (>1 × 10(-3) S/cm), all at room temperature, have been prepared from butyl-N-methyl pyrrolidinium bis(trifluoromethylsulfonyl) imide (PYR14TFSI) and methyl cellulose (MC). These properties are particularly attractive for supercapacitor applications. The ion gels are prepared by codissolution of PYR14TFSI and MC in N,N-dimethylformamide (DMF), which after heating and subsequent cooling form a gel. Evaporation of DMF leave thin, flexible, self-standing ion gels with up to 97 wt % PYR14TFSI, which have the highest combined moduli and ionic conductivity of ion gels to date, with an excellent electrochemical stability window (5.6 V). These favorable properties are attributed to the immiscibility of PYR14TFSI in MC, which permits the ionic conductivity to be independent of the MC at low MC content, and the in situ formation of a volume spanning network of semicrystalline MC nanofibers, which have a high glass transition temperature (Tg = 190 °C) and remain crystalline until they degrade at 300 °C.

Lamellar, micro-phase separated blends of methyl cellulose and dendritic polyethylene glycol, POSS-PEG.

Blends of methyl cellulose (MC) and liquid pegylated polyoctahedralsilsesquioxane (POSS-PEG) were prepared from non-gelled, aqueous solutions at room temperature (RT), which was below their gel temperatures (Tm). Lamellar, fibrillated films (pure MC) and increasingly micro-porous morphologies with increasing POSS-PEG content were formed, which had RT moduli between 1 and 5GPa. Evidence of distinct micro-phase separated MC and POSS-PEG domains was indicated by the persistence of the MC and POSS-PEG (at 77K) crystal structures in the X-ray diffraction data, and scanning transmission electron images. Mixing of MC and POSS-PEG in the interface region was indicated by suppression of crystallinity in the POSS-PEG, and increases/decreases in the glass transition temperatures (Tg) of POSS-PEG/MC in the blends compared with the pure components. These interface interactions may serve as cross-link sites between the micro-phase separated domains that permit incorporation of high amounts of POSS-PEG in the blends, prevent macro-phase separation and result in rubbery material properties (at high POSS-PEG content). Above Tg/Tm of POSS-PEG, the moduli of the blends increase with MC content as expected. However, below Tg/Tm of POSS-PEG, the moduli are greater for blends with high POSS-PEG content, suggesting that it behaves like semi-crystalline polyethylene oxide reinforced with silica (SiO1.5).

Graphene oxide windows for in situ environmental cell photoelectron spectroscopy.

The performance of new materials and devices often depends on processes taking place at the interface between an active solid element and the environment (such as air, water or other fluids). Understanding and controlling such interfacial processes require surface-specific spectroscopic information acquired under real-world operating conditions, which can be challenging because standard approaches such as X-ray photoelectron spectroscopy generally require high-vacuum conditions. The state-of-the-art approach to this problem relies on unique and expensive apparatus including electron analysers coupled with sophisticated differentially pumped lenses. Here, we develop a simple environmental cell with graphene oxide windows that are transparent to low-energy electrons (down to 400 eV), and demonstrate the feasibility of X-ray photoelectron spectroscopy measurements on model samples such as gold nanoparticles and aqueous salt solution placed on the back side of a window. These proof-of-principle results show the potential of using graphene oxide, graphene and other emerging ultrathin membrane windows for the fabrication of low-cost, single-use environmental cells compatible with commercial X-ray and Auger microprobes as well as scanning or transmission electron microscopes.

Drop-casted self-assembling graphene oxide membranes for scanning electron microscopy on wet and dense gaseous samples.

Graphene oxide sheets dispersed in water and many other solvents can spontaneously assemble into a surface film covering an evaporating droplet due to their amphiphilicity. Thus, graphene oxide membranes with controllable thickness suspended over an orifice have been directly fabricated using a simple drop-cast approach. Mechanical properties and electron transparency tests of these membranes show their use as electron transparent, but molecularly impenetrable, windows for environmental electron microscopy in liquids and dense gaseous media. The foreseeable, broader application of this drop-cast window methodology is the creation of access spots for electron probes to study isolated microsamples in their natural, undisrupted state within the interior of prefabricated devices (such as microfluidic chips or sealed containers of biological, chemically reactive, toxic, or forensic materials).

Chemically active reduced graphene oxide with tunable C/O ratios.

Organic dispersions of graphene oxide can be thermally reduced in polar organic solvents under reflux conditions to afford electrically conductive, chemically active reduced graphene oxide (CARGO) with tunable C/O ratios, dependent on the boiling point of the solvent. The reductions are achieved after only 1 h of reflux, and the corresponding C/O ratios do not change upon further thermal treatment. Hydroxyl and carboxyl groups can be removed when the reflux is carried out above 155 °C, while epoxides are removable only when the temperature is higher than 200 °C. The increasing hydrophobic nature of CARGO, as its C/O ratio increases, improves the dispersibility of the nanosheets in a polystyrene matrix, in contrast to the aggregates formed with CARGO having lower C/O ratios. The excellent processability of the obtained CARGO dispersions is demonstrated via free-standing CARGO papers that exhibit tunable electrical conductivity/chemical activity and can be used as lithium-ion battery anodes with enhanced Coulombic efficiency.

Tunable electrical conductivity of individual graphene oxide sheets reduced at "low" temperatures.

Step-by-step controllable thermal reduction of individual graphene oxide sheets, incorporated into multiterminal field effect devices, was carried out at low temperatures (125-240 degrees C) with simultaneous electrical measurements. Symmetric hysteresis-free ambipolar (electron- and hole-type) gate dependences were observed as soon as the first measurable resistance was reached. The conductivity of each of the fabricated devices depended on the level of reduction (was increased more than 10(6) times as reduction progressed), strength of the external electrical field, density of the transport current, and temperature.

Graphene-silica composite thin films as transparent conductors.

Transparent and electrically conductive composite silica films were fabricated on glass and hydrophilic SiOx/silicon substrates by incorporation of individual graphene oxide sheets into silica sols followed by spin-coating, chemical reduction, and thermal curing. The resulting films were characterized by SEM, AFM, TEM, low-angle X-ray reflectivity, XPS, UV-vis spectroscopy, and electrical conductivity measurements. The electrical conductivity of the films compared favorably to those of composite thin films of carbon nanotubes in silica.