The richness of optical and electronic properties of graphene attracts enormous interest. Graphene has high mobility and optical transparency, in addition to flexibility, robustness and environmental ...stability. So far, the main focus has been on fundamental physics and electronic devices. However, we believe its true potential lies in photonics and optoelectronics, where the combination of its unique optical and electronic properties can be fully exploited, even in the absence of a bandgap, and the linear dispersion of the Dirac electrons enables ultrawideband tunability. The rise of graphene in photonics and optoelectronics is shown by several recent results, ranging from solar cells and light-emitting devices to touch screens, photodetectors and ultrafast lasers. Here we review the state-of-the-art in this emerging field.
Understanding the fluid-structure interaction is crucial for an optimal design and manufacturing of soft mesoscale materials. Multi-core emulsions are a class of soft fluids assembled from cluster ...configurations of deformable oil-water double droplets (cores), often employed as building-blocks for the realisation of devices of interest in bio-technology, such as drug-delivery, tissue engineering and regenerative medicine. Here, we study the physics of multi-core emulsions flowing in microfluidic channels and report numerical evidence of a surprisingly rich variety of driven non-equilibrium states (NES), whose formation is caused by a dipolar fluid vortex triggered by the sheared structure of the flow carrier within the microchannel. The observed dynamic regimes range from long-lived NES at low core-area fraction, characterised by a planetary-like motion of the internal drops, to short-lived ones at high core-area fraction, in which a pre-chaotic motion results from multi-body collisions of inner drops, as combined with self-consistent hydrodynamic interactions. The onset of pre-chaotic behavior is marked by transitions of the cores from one vortex to another, a process that we interpret as manifestations of the system to maximize its entropy by filling voids, as they arise dynamically within the capsule.
By using direct numerical simulations (DNS) at unprecedented resolution, we study turbulence under rotation in the presence of simultaneous direct and inverse cascades. The accumulation of energy at ...large scale leads to the formation of vertical coherent regions with high vorticity oriented along the rotation axis. By seeding the flow with millions of inertial particles, we quantify—for the first time—the effects of those coherent vertical structures on the preferential concentration of light and heavy particles. Furthermore, we quantitatively show that extreme fluctuations, leading to deviations from a normal-distributed statistics, result from the entangled interaction of the vertical structures with the turbulent background. Finally, we present the first-ever measurement of the relative importance between Stokes drag, Coriolis force, and centripetal force along the trajectories of inertial particles. We discover that vortical coherent structures lead to unexpected diffusion properties for heavy and light particles in the directions parallel and perpendicular to the rotation axis.
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Efficient and scalable production of two-dimensional (2D) materials is required to overcome technological hurdles towards the creation of a 2D-material-based industry. Here, we present a novel ...approach developed for the exfoliation of layered crystals, i.e. , graphite, hexagonal-boron nitride and transition metal dichalcogenides. The process is based on high-pressure wet-jet-milling (WJM), resulting in a 2 L h −1 production of 10 g L −1 of single- and few-layer 2D crystal flakes in dispersion making the scaling-up more affordable. The WJM process enables the production of defect-free and high quality 2D-crystal dispersions on a large scale, opening the way for their full exploitation in different commercial applications, e.g. , as anode active material in lithium ion batteries, as reinforcement in polymer–graphene composites, and as conductive inks, as we demonstrate in this report.
Density gradient ultracentrifugation (DGU) has emerged as a promising tool to prepare chirality enriched nanotube samples. Here, we assess the performance of different surfactants for DGU. Bile salts ...(e.g., sodium cholate (SC), sodium deoxycholate (SDC), and sodium taurodeoxycholate (TDC)) are more effective in individualizing Single Wall Carbon Nanotubes (SWNTs) compared to linear chain surfactants (e.g., sodium dodecylbenzene sulfonate (SDBS) and sodium dodecylsulfate (SDS)) and better suited for DGU. Using SC, a narrower diameter distribution (0.69−0.81 nm) is achieved through a single DGU step on CoMoCAT tubes, when compared to SDC and TDC (0.69−0.89 nm). No selectivity is obtained using SDBS, due to its ineffectiveness in debundling. We assign the reduced selectivity of dihydroxy bile salts (SDC and TDC) in comparison with trihydroxy SC to the formation of secondary micelles. This is determined by the number and position of hydroxyl (−OH) groups on the α-side of the steroid backbone. We also enrich CoMoCAT SWNTs in the 0.84−0.92 nm range using the Pluronic F98 triblock copolymer. Mixtures of bile salts (SC) and linear chain surfactants (SDS) are used to enrich metallic and semiconducting laser-ablation grown SWNTs. We demonstrate enrichment of a single chirality, (6,5), combining diameter and metallic versus semiconducting separation on CoMoCAT samples.
Hot-carriers, that is, charge carriers with an effective temperature higher than that of the lattice, may contribute to the high power conversion efficiency (PCE) shown by perovskite-based solar ...cells (PSCs), which are now competitive with silicon solar cells. Hot-carriers lose their excess energy in very short times, typically in a few picoseconds after excitation. For this reason, the carrier dynamics occurring on this time scale are extremely important in determining the participation of hot-carriers in the photovoltaic process. However, the stability of PSCs over time still remains an issue that calls for a solution. In this work, we demonstrate that the insertion of graphene flakes into the mesoscopic TiO2 scaffold leads to stable values of carrier temperature. In PSCs aged over 1 week, we indeed observe that in the graphene-free perovskite cells the carrier temperature decreases by about 500 K from 1800 to 1300 K, while the graphene-containing cell shows a reduction of less than 200 K after the same aging time delay. The stability of the carrier temperature reflects the stability of the perovskite nanocrystals embedded in the mesoporous graphene-TiO2 layer. Our results, based on femtosecond transient absorption measurements, show that the insertion of graphene can be beneficial for the design of stable PSCs with the aim of exploiting the hot-carrier contribution to the PCE of the PSCs.
Regioregular poly(3-hexylthiophene-2,5-diyl) (rr-P3HT), the workhorse of organic photovoltaics, has been recently exploited in bulk heterojunction (BHJ) configuration with phenyl-C61-butyric acid ...methyl ester (PCBM) for solution-processed hydrogen-evolving photocathodes, reaching cathodic photocurrents at 0 V vs RHE (J 0 V vs RHE) of up to 8 mA cm–2. The photoelectrochemical performance of these photocathodes strongly depends on the presence of the electron- (ESL) and hole- (HSL) selective layers. While TiO2 and its substoichiometric phases are consolidated ESL materials, the currently used HSLs (e.g., MoO3, CuI, PEDOTT:PSS, WO3) suffer electrochemical degradation under hydrogen evolution reaction (HER) working conditions. In this work, we use solution-processed graphene derivatives as HSL to boost the efficiency and durability of rr-P3HT:PCBM-based photocathodes, demonstrating record-high performance. In fact, our devices show cathodic J 0 V vs RHE of 6.01 mA cm–2, onset potential (V o) of 0.6 V vs RHE, ratiometric power-saved efficiency (φsaved) of 1.11%, and operational activity of 20 h in 0.5 M H2SO4 solution. Moreover, the designed photocathodes are effectively working in different pH environments ranging from acidic to basic. This is pivotal for their exploitation in tandem configurations, where photoanodes operate only in restricted electrochemical conditions. Furthermore, we demonstrate the scalability of our all-solution-processed approach by fabricating a large-area (∼9 cm2) photocathode on flexible substrate, achieving a remarkable cathodic J 0 V vs RHE of 2.8 mA cm–2, V o of 0.45 V vs RHE, and φsaved of 0.31%. This is the first demonstration of highly efficient rr-P3HT:PCBM flexible photocathodes based on low-cost and solution-processed manufacturing techniques.
The study of the underlying physics of soft flowing materials depends heavily on numerical simulations, due to the complex structure of the governing equations reflecting the competition of ...concurrent mechanisms acting at widely disparate scales in space and time. A full-scale computational modelling remains a formidable challenge since it amounts to simultaneously handling six or more spatial decades in space and twice as many in time. Coarse-grained methods often provide a viable strategy to significantly mitigate this issue, through the implementation of mesoscale supramolecular forces designed to capture the essential physics at a fraction of the computational cost of a full-detail description. Here, we review some recent advances in the design of a lattice Boltzmann mesoscale approach for soft flowing materials, inclusive of near-contact interactions (NCIs) between dynamic interfaces, as they occur in high packing-fraction soft flowing crystals. The method proves capable of capturing several aspects of the rheology of soft flowing crystals, namely, (i) a 3/2 power-law dependence of the dispersed phase flow rate on the applied pressure gradient, (ii) the structural transition between an ex-two and ex-one (bamboo) configurations with the associated drop of the flow rate, (iii) the onset of interfacial waves once NCI is sufficiently intense.
This article is part of the theme issue ‘Fluid dynamics, soft matter and complex systems: recent results and new methods’.
Microscale modelling of dielectrophoresis assembly processes Tiribocchi, A.; Montessori, A.; Lauricella, M. ...
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
10/2021, Volume:
379, Issue:
2208
Journal Article
Peer reviewed
Open access
This work presents a microscale approach for simulating the dielectrophoresis assembly of polarizable particles under an external electric field. The model is shown to capture interesting dynamical ...and topological features, such as the formation of chains of particles and their incipient aggregation into hierarchical structures. A quantitative characterization in terms of the number and size of these structures is also discussed. This computational model could represent a viable numerical tool to study the mechanical properties of particle-based hierarchical materials and suggest new strategies for enhancing their design and manufacture.
This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.
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