[en] We have used recent advances in nanotube dispersion technology to prepare composites based on polyurethane, with mass fractions of up to 80% polyethylene glycol functionalized nanotubes. Mechanical testing shows increases in Young's modulus compared to polyurethane films by up to 800 x. While the composite strength did not vary significantly with nanotube content, the ductility and so the toughness fell by a factor of 240 x on addition of ∼40 wt% nanotubes. Depending on the nanotube content we can produce films ranging from the stiff and brittle at high nanotube loading to the compliant and ductile at low nanotube volume fraction

[en] We have dispersed graphene in water, stabilized by a range of 12 ionic and non-ionic surfactants. In all cases, the degree of exfoliation, as characterized by flake length and thickness, was similar. The dispersed flakes were typically 750 nm long and, on average, four layers thick. However, the dispersed concentration varied from solvent to solvent. For the ionic surfactants, the concentration scaled with the square of the zeta potential of the surfactant-coated flakes. This suggests that the concentration is proportional to the magnitude of the electrostatic potential barrier, which stabilizes surfactant-coated flakes against aggregation. For the non-ionic surfactants, the dispersed graphene concentration scaled linearly with the magnitude of the steric potential barrier stabilizing the flakes. However, the data suggested that other contributions are also important.

[en] The surface energy of graphene nanosheets is surprisingly poorly known, probably due to size effects and energetic heterogeneities. Here we use finite-dilution inverse gas chromatography to measure the surface energy of liquid-exfoliated, few-layer graphene nanosheets of different sizes as a function of probe coverage. In all cases, the surface energy falls with probe coverage from a defect-controlled, low-coverage value to a value that approaches the basal plane surface energy at high coverage. We find an intrinsic basal plane dispersive surface energy of 61 ± 4 mJ m⁻², close to the value of 63 mJ m⁻² found for graphite. By comparison with similar data measured on graphite and using simple models, we can use the length dependence of the low coverage surface energy to differentiate between the effects of edge and basal plane defects, finding these to contribute ∼130 and 180 mJ m⁻² to the surface energy respectively. From this data, we estimate a basal plane defect content of ∼6 × 10¹⁴ defects m^–2 for both graphite and graphene in reasonable agreement with Raman data. This work shows that, in terms of surface energetics, few-layer graphene nanosheets behave exactly like graphite with the only differences associated with platelet dimensions. (paper)

[en] Recent advances in the liquid-phase exfoliation (LPE) of layered materials have facilitated significant progress in the creation of functional inks. While ethanol/water blends have been shown to yield reasonable nanosheet dispersions with the potential for refinement into printable inks, the exfoliated mass is typically too low for practical use. Here, we show that Irish whiskey can be used as a dispersant for nanosheets of graphene, BN and WS₂, yielding stable dispersions at reasonably high concentrations. We see some benefits compared to exfoliation in simple ethanol/water mixtures which we attribute to the presence of organic compounds in the whiskey. Size selection yields nanosheets which are relatively thin, with photoluminescence spectroscopy confirming the presence of monolayer tungsten disulfide (WS₂). We also show that whiskey-dispersed nanosheets of graphene and WS₂ can be printed into networks. These can be combined in heterostructures to produce thin-film transistors whose current can be modulated using ionic liquid (IL) gating. These devices show on:off ratios up to 340 and mobilities up to 1.5  ×  10⁻³ cm² V⁻¹ s⁻¹. The fact that these networks can be gated at all demonstrates the robustness of nanosheet networks against external additives while the mobility reported here should represent a performance-floor for future devices. (paper)

[en] While it has been demonstrated that large scale liquid exfoliation of graphene is possible using high-shear exfoliation, it has not yet been shown to be applicable to a broader range of layered materials. In addition, it would be useful to determine whether the mechanisms reported for shear exfoliation of graphene also apply to other 2D materials. In this work we show that previous models describing high-shear exfoliation of graphene apply to MoS₂ and WS₂. However, we find the minimum shear rate required to exfoliate MoS₂ and WS₂ to be ∼3  ×  10⁴ s⁻¹, somewhat higher than the value for graphene. We also demonstrate the scalability of shear exfoliation of WS₂. By measuring and then optimising the scaling parameters, shear exfoliation of WS₂ is shown to be capable of reaching concentrations of 1.82 g l⁻¹ in 6 h and demonstrating a maximum production rate of 0.95 g h⁻¹. (paper)

[en] We have developed an in situ method to estimate the lateral size of exfoliated nanosheets dispersed in a liquid. Using standard liquid exfoliation and size-selection techniques, we prepared a range of dispersions of graphene, MoS₂ and WS₂ nanosheets with different mean lateral sizes. The mean nanosheet length was measured using transmission electron microscopy (TEM) to vary from ∼40 nm to ∼1 μm. These dispersions were characterized using a standard dynamic light scattering (DLS) instrument. We found a well-defined correlation between the peak of the particle size distribution as outputted by the DLS instrument and the nanosheet length as measured by TEM. This correlation is consistent with the DLS instrument outputting the radius of a sphere with volume equal to the mean nanosheet volume. This correlation allows the mean nanosheet length to be extracted from DLS data. (paper)

[en] This research objective of this EELDRD study was to learn to electrodeposit Pt Au alloys with independently controlled composition and grain size. What was accomplished was the capability to electrodeposit PtAu alloys with controlled composition and a nanocrysolline grain size. Nanocrystalline metals as a class and, specifically, the Pt_0.9Au_0.1 alloy developed in 2015-17 via sputtering at Sandia National Labs have clear advantages in strength, wear resistance, and fatigue tolerance over commercially-available structural alloys. With this capability befitting coating of complex components and implementable at existing vendors, we can upgrade the electrical contact component reliability of selected Labs systems.

[en] To realise real-time, wearable personal health monitors, sensitive, low stiffness, inexpensive smart materials must be identified. Previously, room-temperature, low-viscosity nanocomposites based on graphene-doped Silly Putty (G-putty) were demonstrated. Displaying unprecedented electromechanical sensitivity and physical properties, G-putty is an ideal material to fill this niche. However, the relationship between processing conditions or indeed material properties and sensitivity is not known. Herein, we study the relationship between a number of processing parameters and the electromechanical properties of G-putty. We identify the processing conditions required to produce G-putty with gauge factors  >100. In addition, we found a well-defined relationship between composite viscosity and sensitivity which shows maximised gauge factors for viscosities ∼4  ×  10⁵ Pa · s. (paper)

[en] A novel amine solvent, 3-aminopropyltriethoxysilane, has been used to disperse single-walled carbon nanotubes. Well-dispersed nanotubes in the form of small bundles coexist in the liquid phase with large nanotube aggregates. A mild centrifugation step can be used to remove the aggregates. By measurement of the absorbance before and after centrifugation as a function of concentration, the fraction of the dispersed nanotube phase can be estimated. As measured by atomic force microscopy, the mean bundle diameter tends to decrease with decreasing concentration and levels off below a concentration of ∼0.012 mg ml^-1. Individual nanotubes are always observed, whose population increases with decreasing concentration before saturating at a concentration of ∼0.012 mg ml^-1. The absolute number of individual nanotubes per volume of dispersion initially increases with decreasing concentration, and then reaches a peak at a concentration of ∼0.024 mg ml^-1. Further experimental results showed that nanotubes can also be effectively dispersed in a series of aminoalkoxylsilane derivatives. In the light of these findings, possible solvent-nanotube interaction mechanisms are discussed.

[en] We have developed methods to disperse and partially size separate NbSe₃ nanowires in aqueous surfactant solutions. These dispersions can easily be formed into thin films. Optical and electrical studies show these films to display sheet resistances and transmittances ranging from (460Ω/□, 22%) to (12kΩ/□, 79%) depending on thickness. For thicker films, we measured the transparent conducting figure of merit to be σ_DC,B/σ_Op = 0.32, similar to graphene networks. Thickness measurements gave individual values of σ_Op = 17 800 S m^-1 and σ_DC,B = 5700 S m^-1. Films thinner than ∼ 70 nm displayed reduced DC conductivity due to percolative effects.