Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

A strain sensor has been fabricated from a polymer nanocomposite with multiwalled carbon nanotube (MWNT) fillers. The piezoresistivity
of this nanocomposite strain sensor has been investigated based on an improved three-dimensional (3D) statistical resistor network
model incorporating the tunneling effect between the neighboring carbon nanotubes (CNTs), and a fiber reorientation model. The
numerical results agree very well with the experimental measurements. As compared with traditional strain gauges, much higher sensitivity
can be obtained in the nanocomposite sensors when the volume fraction of CNT is close to the percolation threshold. For a small
CNT volume fraction, weak nonlinear piezoresistivity is observed both experimentally and from numerical simulation. The tunneling
effect is considered to be the principal mechanism of the sensor under small strains.

Tunneling effect in a polymer/carbon nanotube nanocompositestrain sensor

Conductive hydrogels have become one of the most promising materials for skin-like sensors because of their excellent biocompatibility and mechanical flexibility. However, the limited stretchability, low toughness, and fatigue resistance lead to a narrow sensing region and insufficient durability of the hydrogel-based sensors. In this work, an extremely stretchable, highly tough, and anti-fatigue conductive nanocomposite hydrogel is prepared by integrating hydrophobic carbon nanotubes (CNTs) into hydrophobically associated polyacrylamide (HAPAAm) hydrogel. In this conductive hydrogel, amphiphilic sodium dodecyl sulfate was used to ensure uniform dispersion of CNTs in the hydrogel network, and hydrophobic interactions between the hydrogel matrix and the CNT surface formed, greatly improving the mechanical properties of the hydrogel. The obtained CNTs/HAPAAm hydrogel showed excellent stretchability (ca. 3000%), toughness (3.42 MJ m-3), and great anti-fatigue property. Moreover, it exhibits both high tensile strain sensitivity in the wide strain ranges (gauge factor = 4.32, up to 1000%) and high linear sensitivity (0.127 kPa-1) in a large-pressure region within 0-50 kPa. The CNTs/HAPAAm hydrogel-based sensors can sensitively and stably detect full-range human activities (e.g., elbow rotation, finger bending, swallowing motion, and pronouncing) and handwriting, demonstrating the CNTs/HAPAAm hydrogel's potential as the wearable strain and pressure sensors for flexible devices.

Carbon Nanotubes/Hydrophobically Associated Hydrogels as Ultrastretchable, Highly Sensitive, Stable Strain, and Pressure Sensors.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/inf2.12177

Strain engineering of two‐dimensional materials: Methods, properties, and applications

Liquid phase exfoliation is a commonly used method to produce 2D nanosheets from a range of layered crystals. However, such nanosheets display broad size and thickness distributions and correlation...

Equipartition of Energy Defines the Size-Thickness Relationship in Liquid-Exfoliated Nanosheets.

Nanocomposite strain sensors, particularly those consisting of polymer-graphene composites, are increasingly common and are of great interest in the area of wearable sensors. In such sensors, application of strain yields an increase in resistance due to the effect of deformation on interparticle junctions. Typically, widening of interparticle separation is thought to increase the junction resistance by reducing the probability of tunnelling between conducting particles. However, an alternative approach would be to use piezoresistive fillers, where an applied strain modifies the intrinsic filler resistance and so the overall composite resistance. Such an approach would broaden sensing capabilities, as using negative piezoresistive fillers could yield strain-induced resistance reductions rather than the usual resistance increases. Here, we introduce nanocomposites based on polyethylene oxide (PEO) filled with MoS2 nanosheets. Doping of the MoS2 by the PEO yields nanocomposites which are conductive enough to act as sensors, while efficient stress transfer leads to nanosheet deformation in response to an external strain. The intrinsic negative piezoresistance of the MoS2 leads to a reduction of the composite resistance on the application of small tensile strains. However, at higher strain the resistance grows due to increases in junction resistance. MoS2-PEO composite gauge factors are approximately -25 but fall to -12 for WS2-PEO composites and roughly -2 for PEO filled with MoSe2 or WSe2. We develop a simple model, which describes all these observations. Finally, we show that these composites can be used as dynamic strain sensors.

/pdf/negative-gauge-factor-piezoresistive-composites-based-on-27938co0gi.pdf

Negative Gauge Factor Piezoresistive Composites Based on Polymers Filled with MoS2 Nanosheets

Extinction spectra of nanomaterial suspensions can be dominated by light scattering, hampering quantitative spectral analysis. No simple models exist for the wavelength-dependence of the scattering coefficients in suspensions of arbitrary-sized, high-aspect-ratio nanoparticles. Here, suspensions of BN, talc, GaS, Ni(OH)2, Mg(OH)2 and Cu(OH)2 nanosheets are used to explore non-resonant scattering in wide-bandgap 2D nanomaterials. Using an integrating sphere, scattering coefficient (σ) spectra were measured for a number of size-selected fractions for each nanosheet type. Generally, σ scales as a power-law with wavelength in the non-resonant regime: σ(λ)∝[λ/〈L〉]−m, where 〈L〉 is the mean nanosheet length. For all materials, the scattering exponent, m, forms a master-curve, transitioning from m = 4 to m = 2, as the characteristic nanosheet area increases, indicating a transition from Rayleigh to van der Hulst scattering. In addition, once material density and refractive index are factored out, the proportionality constant relating σ to [λ/〈L〉]−m, also forms a master-curve when plotted versus 〈L〉. Quantitative analysis of the extinction spectra of dispersions of 2D materials is complicated by light scattering. Here, the authors investigate non-resonant scattering in suspensions of wide-bandgap nanosheets, and develop a general model which allows the scattering spectra to be used as metrics for particle size in nanosheet dispersions.

/pdf/non-resonant-light-scattering-in-dispersions-of-2d-yyiydgrj0w.pdf

Non-resonant light scattering in dispersions of 2D nanosheets.

Solution-processed networks of 2D nanosheets are promising for a range of applications in the field of printed electronics. However, the electrical performance of these networks — represented, for example, by the mobility — is almost always inferior to that of the individual nanosheets. In this Review, we highlight the central role that the inter-sheet junctions play in determining the electrical characteristics of such networks. After briefly reviewing ink formulation and printing methods, we use a selection of electronic applications as examples to demonstrate the dependence of network conductivity on network morphology. We show the network morphology to be heavily influenced by the deposition method, the post-treatment regime and the nanosheet properties. In turn, the morphology of the network fundamentally determines the properties of the inter-sheet junctions, which, ultimately, control the electrical performance of the network. We use reported electrical data to show that three main conduction regimes exist: the network conductivity can be limited by the junctions, by a combination of junction and material properties or, very rarely, by the material properties. Using a meta-analysis of published data, we propose simple models relating network conductivity and mobility to the junction resistance. Solution-processed networks of 2D materials are promising for applications in printed electronics. This Review examines how these networks are often electrically limited by the junctions between nanosheets, a phenomenon rarely reported and poorly understood, and surveys the macroscopic electrical properties of printed 2D networks, with a focus on inter-sheet junctions.

The electrical conductivity of solution-processed nanosheet networks

/pdf/liquid-exfoliated-snp-3-nanosheets-for-very-high-areal-1l2ahcevlo.pdf

Cian Gabbett

Papers

Negative Gauge Factor Piezoresistive Composites Based on Polymers Filled with MoS2 Nanosheets

Non-resonant light scattering in dispersions of 2D nanosheets.

The electrical conductivity of solution-processed nanosheet networks

Liquid Exfoliated SnP 3 Nanosheets for Very High Areal Capacity Lithium-Ion Batteries

Liquid phase exfoliation of GeS nanosheets in ambient conditions for lithium ion battery applications