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Pentatomidae is the third largest family of true bugs, comprising over 40 tribes. Few tribes have been studied in a phylogenetic context, and none of them have been examined using molecular data. Moreover, little is known about the evolution of key morphological characters widely used in taxonomic and phylogenetic studies at multiple levels. Here, we conduct a phylogenetic study of the tribe Chlorocorini (Pentatominae) combining 69 morphological characters and five DNA loci. We use the inferred phylogeny to reconstruct the evolution of key morphological characters such as the spined humeral angles of the pronotum, a dorsal projection on the apices of the femora and characters of male genitalia. We provide solid evidence that the tribe as currently recognized is not monophyletic based both on DNA and morphological data. The generaArveliusSpinola andEludocorisThomas were consistently placed outside of the Chlorocorini, while the remaining genera were found to form a monophyletic group. We also show that nearly all morphological diagnostic characters for the tribe are homoplastic. The only exception is the development of the hypandrium, which, contrary to expectations for genital traits, showed the slowest evolutionary rates. In contrast, the most rapidly evolving trait is the length of the ostiolar ruga, which may be attributed to selection favoring anti-predatory behavior and other functions of its associated scent glands. Lastly, we also provide a preliminary glimpse of the main phylogenetic relationships within the Pentatomidae, which indicates that most of the included subfamilies and tribes are not monophyletic. Our results suggest that the current subfamily-level classification of Pentatomidae is not adequate to reflect its evolutionary history, and we urge for a more complete phylogeny of the family.

New forms of carbon-based materials have received great attention, and the developed materials have found many applications in nanotechnology. Interesting novel carbon structures include the carbon peapods, which are comprised of fullerenes encapsulated within carbon nanotubes. Peapod-like nanostructures have been successfully synthesized, and have been used in optical modulation devices, transistors, solar cells, and in other devices. However, the mechanical properties of these structures are not completely elucidated. In this work, we investigated, using fully atomistic molecular dynamics simulations, the deformation of carbon peapods under high-strain rate conditions, which are achieved by shooting the peapods at ultrasonic velocities against a rigid substrate. Our results show that carbon peapods experience large deformation at impact, and undergo multiple fracture pathways, depending primarily on the relative orientation between the peapod and the substrate, and the impact velocity. Observed outcomes include fullerene ejection, carbon nanotube fracture, fullerene, and nanotube coalescence, as well as the formation of amorphous carbon structures.

Triply Periodic Minimal Surfaces (TPMS) possess locally minimized surface area under the constraint of periodic boundary conditions. Different families of surfaces were obtained with different topologies satisfying such conditions. Examples of such families include Primitive (P), Gyroid (G) and Diamond (D) surfaces. From a purely mathematical subject, TPMS have been recently found in materials science as optimal geometries for structural applications. Proposed by Mackay and Terrones in 1991, schwarzites are 3D crystalline porous carbon nanocrystals exhibiting a TPMS-like surface topology. Although their complex topology poses serious limitations on their synthesis with conventional nanoscale fabrication methods, such as Chemical Vapour Deposition (CVD), schwarzites can be fabricated by Additive Manufacturing (AM) techniques, such as 3D Printing. In this work, we used an optimized atomic model of a schwarzite structure from the D family (D8bal) to generate a surface mesh that was subsequently used for 3D-printing through Fused Deposition Modelling (FDM). This D schwarzite was 3D-printed with thermoplastic PolyLactic Acid (PLA) polymer filaments. Mechanical properties under uniaxial compression were investigated for both the atomic model and the 3D-printed one. Fully atomistic Molecular Dynamics (MD) simulations were also carried out to investigate the uniaxial compression behavior of the D8bal atomic model. Mechanical testings were performed on the 3D-printed schwarzite where the deformation mechanisms were found to be similar to those observed in MD simulations. These results are suggestive of a scale-independent mechanical behavior that is dominated by structural topology.

Genitalia are multitasking structures whose development is mediated by numerous regulatory pathways. This multifactorial nature provides an avenue for multiple sources of selection. As a result, genitalia tend to evolve as modular systems comprising semi-independent subsets of structures, yet the processes that give rise to those patterns are still poorly understood. Here, we ask what are the relative roles of development and function in shaping modular patterns of genitalia within populations and across species of stink-bugs. We found that male genitalia are less integrated, more modular, and primarily shaped by functional demands. In contrast, females show higher integration, lower modularity, and a predominant role of developmental processes. Further, interactions among parts of each sex are more determinant to modularity than those between the sexes, and patterns of modularity are equivalent between and within species. Our results strongly indicate that genitalia have been subjected to sex-specific selection, although male and female genitalia are homologous and functionally associated. Moreover, modular patterns are seemingly constant in the evolutionary history of stink-bugs, suggesting a scenario of multivariate stabilizing selection within each sex. Our study demonstrates that interactions among genital parts of the same sex may be more fundamental to genital evolution than previously thought.

The organic matrix of a bone mainly composed of a collagen matrix serves as a crucial component for remarkable toughness and strength in bones. The porous collagen matrix can also serve as an efficient template for various applications such as nanoparticle synthesis, catalysis or catalysis supports, electrochemical separator, filtration membrane, and tissue engineering. However, fabricating collagen matrix from bones without degrading its morphological structure still remains a challenge. Here, we present evidence of how ceramic crystals from a bone can be removed to fabricate a complete ‘transparent bone’ structure with improved porosity and elasticity. We show that demineralization or selective etching using dilute acid (citric) can remove ceramic mineral nanoparticles without degrading the collagen matrix. The transparent bone collagen matrix is investigated as the separator in electrochemical supercapacitor with aqueous electrolyte where it shows better performance compared with conventional separators.

We report a detailed study through fully atomistic molecular dynamics simulations and DFT calculations on the mechanical properties of protomene. Protomene is a new carbon allotrope composed of a mixture of sp2 and sp3 hybridized states. Our results indicate that protomene presents an anisotropic behavior about tensile deformations. At room temperature, protomene presents an ultimate strength of ∼100 GPa and Young’s modulus of ∼600 GPa, lower than the same for other carbon allotropes. Despite that, protomente presents the highest ultimate strain along the z-direction (∼24.7%). Our results also show that stretching the protomene along the z-direction or heating it can induce a semiconductor-metallic phase transition, due to a high amount of sp3 bonds that are converted to sp2 ones.

We have investigated through fully atomistic reactive molecular dynamics and density functional theory simulations, the mechanical properties and fracture dynamics of single-ringed novamene (1R-novamene), a new 3D carbon allotrope structure recently proposed. Our results showed that 1R-novamene is an anisotropic structure with relation to tensile deformation. Although 1R-novamente shares some mechanical features with other carbon allotropes, it also exhibits distinct ones, such as, extensive structural reconstructions. 1R-novamene presents ultimate strength (∼100 GPa) values lower than other carbon allotropes, but it has the highest ultimate strain along the z-direction (∼22.5%). Although the Young's modulus (∼600 GPa) and ultimate strength values are smaller than for other carbon allotropes, they still outperform other materials, such as for example silicon, steel or titanium alloys. With relation to the fracture dynamics, 1R-novamene is again anisotropic with the fracture/crack propagation originating from deformed heptagons and pentagons for x and y directions and broken sp 3 bonds connecting structural planes. Another interesting feature is the formation of multiple and long carbon linear chains in the final fracture stages.

We propose a new 2D semiconductor material (TTA-2D) based on the molecular structure of Thiophene-Tetrathia-Annulene (TTA). The TTA-2D structural, electronic, and optical properties were investigated using \textit{ab initio} methods. Our results show that TTA-2D is a small indirect bandgap semiconductor ($0.6$ eV). A semiconductor-metal transition can be induced by applying a uniaxial strain. Our results also show that TTA-2D is thermally stable up to $T=1000$ K. TTA-2D absorbs in a large spectral range, from infrared to ultraviolet regions. Values of refractive index and reflectivity show that TTA-2D reflects only $10\%$ of the incident light in the visible region. These results suggest that TTA-2D is a promising material for solar cell applications., 28 pages, 9 figures

Since graphene was synthesized the interest for building new 2D and 3D structures based on the carbon allotropes has been growing every day. One of these 3D structures is know as carbon schwarzites. Schwarzites consist of carbon nanostructures possessing the shape of Triply-Periodic Minimal Surfaces (TPMS), which is characterized by a negative Gaussian curvature introduced by the presence of carbon rings with more than six atoms. Some examples of schwarzite families include: primitive (P), gyroid (G) and diamond (D). Previous studies considering different element species of schwarzites have investigated the mechanical, electrical and thermal properties. In this work, we investigated the stability of germanium (Ge) schwarzites using density functional theory with GGA exchange-correlation functional. We chose one structure of each family (P8bal), (G688) and (D688). It was observed that regions usually flat in carbon schwarzites acquires buckled configurations as previously observed on silicene and germanene monolayers. The investigated structures presented a semiconducting bandgap ranging from $0.13$ to $0.27$ eV. We also performed calculations of optical properties within the linear regime, where it was shown that Ge schwarzites structures absorb light from infrared to ultra-violet frequencies. Therefore, our results open new perspectives of materials that can be used in optelectronics devices application., 23 pages, 6 figures

Graphynes and graphdiynes are generic names for families of two-dimensional carbon allotropes, where acetylenic groups connect benzenoid-like hexagonal rings, with the coexistence of sp and sp2 hybridized carbon atoms. The main differences between graphynes and graphdiynes are the number of acetylenic groups (one and two for graphynes and graphdiynes, respectively). Similarly to graphene nanoscrolls, graphyne and graphdiynes nanoscrolls are nanosized membranes rolled into papyrus-like structures. In this work we studied through molecular dynamics simulations, using reactive potentials, the structural and thermal (up to 1000 K) stability of α,β,γ-graphyne and α,β,γ-graphdiyne scrolls. Our results demonstrate that stable nanoscrolls can be created for all the structures studied here, although they are less stable than corresponding graphene scrolls. This can be elucidated as a result of the higher graphyne/graphdiyne structural porosity in relation to graphene, and as a consequence, the π–π stacking interac...

Recent advances and demands in biomedical applications drive a large amount of research to synthesize easily scalable low-density, high-strength, and wear-resistant biomaterials. The chemical inertness with low density combined with high strength makes h-BN one of the promising materials for such application. In this work, three-dimensional hexagonal boron nitride (h-BN) interconnected with boron trioxide (B2O3) was prepared by easily scalable and energy efficient spark plasma sintering (SPS) process. The composite structure shows significant densification (1.6–1.9 g/cm3) and high surface area (0.97–14.5 m2/g) at an extremely low SPS temperature of 250 °C. A high compressive strength of 291 MPa with a reasonably good wear resistance was obtained for the composite structure. The formation of strong covalent bonds between h-BN and B2O3 was formulated and established by molecular dynamics simulation. The composite showed significant effect on cell viability/proliferation. It shows a high mineralized nodule formation over the control, which suggests its use as a possible osteogenic agent in bone formation., by Chandkiram Gautam , Dibyendu Chakravarty, Amarendra Gautam, Chandra Sekhar Tiwary, Cristiano Francisco Woellner, Vijay Kumar Mishra, Naseer Ahmad, Sehmus Ozden, Sujin Jose, Santoshkumar Biradar, Robert Vajtai , Ritu Trivedi, Douglas S. Galvao and Pulickel M. Ajayan

With the advent of graphene, the most studied of all two-dimensional materials, many inorganic analogues have been synthesized and are being exploited for novel applications. Several approaches have been used to obtain large-grain, high-quality materials. Naturally occurring ores, for example, are the best precursors for obtaining highly ordered and large-grain atomic layers by exfoliation. Here, we demonstrate a new two-dimensional material ‘hematene’ obtained from natural iron ore hematite (α-Fe2O3), which is isolated by means of liquid exfoliation. The two-dimensional morphology of hematene is confirmed by transmission electron microscopy. Magnetic measurements together with density functional theory calculations confirm the ferromagnetic order in hematene while its parent form exhibits antiferromagnetic order. When loaded on titania nanotube arrays, hematene exhibits enhanced visible light photocatalytic activity. Our study indicates that photogenerated electrons can be transferred from hematene to titania despite a band alignment unfavourable for charge transfer.

Hexagonal boron nitride (h-BN), graphene oxide (GO) and hybrid (GO/h-BN) nanosheets were employed as fillers in order to enhance the physical properties of the polymer matrix. Composites based in epoxy and these two-dimensional (2D) nanofillers were produced with different wt% and their microstructure, mechanical and thermal properties were investigated. Increases up to 140% in tensile strength, 177% in ultimate strain and 32% in elastic modulus were observed for the hybrid GO/h-BN composite with 0.5 wt% content. The hybrid nanofiller also contributed to the increase up to 142% on thermal conductivity with respect to the pure epoxy for GO/h-BN composite with 2.0 wt% content. Molecular dynamic simulation was used to predict the behavior of possible stacking arrangements between h-BN and GO nanosheets tensioned by normal and shear forces. The results showed that the hybrid GO/h-BN combination can prevent the re-stacking process of exfoliated layers, demonstrating the synergism between these nanostructures with the final effect of better dispersion in the composite material. The excellent thermal and mechanical performance of these hybrid composites engineered by the combination of different types of the 2D inorganic nanoparticles make them multifunctional candidates for advanced materials applications.

Made available in DSpace on 2018-12-11T17:36:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2018-07-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) The production of large-area interfaces and the use of scalable methods to build up designed nanostructures generating advanced functional properties are of high interest for many materials science applications. Nevertheless, large-area coverage remains a major problem even for pristine graphene, and here we present a hybrid, composite graphene-like material soluble in water that can be exploited in many areas such as energy storage, electrodes fabrication, selective membranes and biosensing. Graphene oxide (GO) was produced by the traditional Hummers’ method being further reduced in the presence of poly(styrene sulfonate) sodium salt (PSS), thus creating stable reduced graphene oxide (rGO) nanoplatelets wrapped by PSS (GPSS). Molecular dynamics simulations were carried out to further clarify the interactions between PSS molecules and rGO nanoplatelets, with calculations supported by Fourier transform infrared spectroscopy analysis. The intermolecular forces between rGO nanoplatelets and PSS lead to the formation of a hybrid material (GPSS) stabilized by van der Waals forces, allowing the fabrication of high-quality layer-by-layer (LbL) films with poly(allylamine hydrochloride) (PAH). Raman and electrical characterizations corroborated the successful modifications in the electronic structures from GO to GPSS after the chemical treatment, resulting in (PAH/GPSS) LbL films four orders of magnitude more conductive than (PAH/GO). POSMAT – Programa de Pós-Graduação em Ciência e Tecnologia de Materiais UNESP – Univ Estadual Paulista Universidade Federal de São Carlos – DFQM Faculdade de Engenharia de Sorocaba – FACENS Applied Physics Department State University of Campinas UNESP – Univ Estadual Paulista Centro Universitário Central Paulista – UNICEP Instituto de Física de São Carlos – USP POSMAT – Programa de Pós-Graduação em Ciência e Tecnologia de Materiais UNESP – Univ Estadual Paulista UNESP – Univ Estadual Paulista FAPESP: 2010/13033-6 FAPESP: 2012/01484-9 FAPESP: 2015/14703-9 FAPESP: 2016/00023-9 FAPESP: 2016/12340-9

Experimental evidences have shown that graphene oxide (GO) can be impermeable to liquids, vapors and gases, while it allows a fast permeation of water molecules. The understanding of filtration mechanisms came mostly from studies dedicated to water desalination, while very few works have been dedicated to distilling alcohols. In this work, we have investigated the molecular level mechanism underlying the alcohol/water separation inside GO membranes. A series of molecular dynamics and Grand-Canonical Monte Carlo simulations were carried out to probe the ethanol/water and methanol/water separation through GO membranes composed of multiple layered graphene-based sheets with different interlayer distance values and number of oxygen-containing functional groups. Our results show that the size exclusion and membrane affinities are not sufficient to explain the selectivity. Besides that, the favorable water molecular arrangement inside GO 2D-channels forming a robust H-bond network and the fast water diffusion are crucial for an effective separation mechanism. In other words, the separation phenomenon is not only governed by affinities with the membrane (enthalpic mechanisms) but mainly by the geometry and size factors (entropic mechanisms). We verified that the 2D geometry channel with optimal interlayer distance are key factors for designing more efficient alcohol-water separation membranes. Our findings are consistent with the available experimental data and contribute to clarify important aspects of the separation behavior of confined alcohol/water in GO membranes.

Graphene-based membranes have been investigated as promising candidates for water filtration and gas separation applications. Experimental evidences have shown that graphene oxide can be impermeable to liquids, vapors and gases, while allowing a fast permeation of water molecules. This phenomenon has been attributed to the formation of a network of nano capillaries that allow nearly frictionless water flow while blocking other molecules by steric hindrance effects. It is supposed that water molecules are transported through the percolated two-dimensional channels formed between graphene-based sheets. Although these channels allow fast water permeation in such materials, the flow rates are strongly dependent on how the membranes are fabricated. Also, some fundamental issues regarding the nanoscale mechanisms of water permeation are still not fully understood and their interpretation remains controversial. In this work, we have investigated the dynamics of water permeation through pristine graphene and graphene oxide model membranes that have strong impact on water/alcohol separation. We have carried out fully atomistic classical molecular dynamics simulations of systems composed of multiple layered graphene-based sheets into contact with a pure water reservoir under controlled thermodynamics conditions (e. g., by varying temperature and pressure values). We have systematically analysed how the transport dynamics of the confined nanofluids depend on the interlayer distances and the role of the oxide functional groups. Our results show the water flux is much more effective for graphene than for graphene oxide membranes. These results can be attributed to the H-bonds formation between oxide functional groups and water, which traps the water molecules and precludes ultrafast water transport through the nanochannels.

Well crystallized and interconnected SnO2 nanoparticles (

Transition metal dichalcogenides are 2D structures with remarkable electronic, chemical, optical and mechanical properties. Monolayer and crystal properties of these structures have been extensively investigated, but a detailed understanding of the properties of their few-layer structures are still missing. In this work we investigated the mechanical differences between monolayer and multilayer WSe2 and MoSe2, through fully atomistic molecular dynamics simulations (MD). It was observed that single layer WSe2/MoSe2 deposited on silicon substrates have larger friction coefficients than 2, 3 and 4 layered structures. For all considered cases it is always easier to peel off and/or to fracture MoSe2 structures. These results suggest that the interactions between first layer and substrate are stronger than interlayer interactions themselves. Similar findings have been reported for other nanomaterials and it has been speculated whether this is a universal-like behavior for 2D layered materials. We have also analyzed fracture patterns. Our results show that fracture is chirality dependent with crack propagation preferentially perpendicular to W(Mo)-Se bonds and faster for zig-zag-like defects.

Low-density, highly porous graphene/graphene oxide (GO) based-foams have shown high performance in energy absorption applications, even under high compressive deformations. In general, foams are very effective as energy dissipative materials and have been widely used in many areas such as automotive, aerospace and biomedical industries. In the case of graphene-based foams, the good mechanical properties are mainly attributed to the intrinsic graphene and/or GO electronic and mechanical properties. Despite the attractive physical properties of graphene/GO based-foams, their structural and thermal stabilities are still a problem for some applications. For instance, they are easily degraded when placed in flowing solutions, either by the collapsing of their layers or just by structural disintegration into small pieces. Recently, a new and scalable synthetic approach to produce low-density 3D macroscopic GO structure interconnected with polydimethylsiloxane (PDMS) polymeric chains (pGO) was proposed. A controlled amount of PDMS is infused into the freeze-dried foam resulting into a very rigid structure with improved mechanical properties, such as tensile plasticity and toughness. The PDMS wets the graphene oxide sheets and acts like a glue bonding PDMS and GO sheets. In order to obtain further insights on mechanisms behind the enhanced mechanical pGO response we carried out fully atomistic molecular dynamics (MD) simulations. Based on MD results, we build up a structural model that can explain the experimentally observed mechanical behavior.

Two-dimensional (2D) nanomaterials as molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), and their hybrid (MoS2/h-BN) were employed as fillers to improve the physical properties of epoxy composites. Nanocomposites were produced in different concentrations and studied in their microstructure, mechanical and thermal properties. The hybrid 2D mixture imparted efficient reinforcement to the epoxy leading to increases of up to 95% in tensile strength, 60% in ultimate strain, and 58% in Young’s modulus. Moreover, an enhancement of 203% in thermal conductivity was achieved for the hybrid composite as compared to the pure polymer. The incorporation of MoS2/h-BN mixture nanofillers in epoxy resulted in nanocomposites with multifunctional characteristics for applications that require high mechanical and thermal performance.

Weak van der Waals forces between inert hexagonal boron nitride (h-BN) nanosheets make it easy for them to slide over each other, resulting in an unstable structure in macroscopic dimensions. Creating interconnections between these inert nanosheets can remarkably enhance their mechanical properties. However, controlled design of such interconnections remains a fundamental problem for many applications of h-BN foams. In this work, a scalable in situ freeze-drying synthesis of low-density, lightweight 3D macroscopic structures made of h-BN nanosheets chemically connected by poly(vinyl alcohol) (PVA) molecules via chemical cross-link is demonstrated. Unlike pristine h-BN foam which disintegrates upon handling after freeze-drying, h-BN/PVA foams exhibit stable mechanical integrity in addition to high porosity and large surface area. Fully atomistic simulations are used to understand the interactions between h-BN nanosheets and PVA molecules. In addition, the h-BN/PVA foam is investigated as a possible CO2 abs...

Recently, a new class of carbon allotrope called protomene was proposed. This new structure is composed of sp2 and sp3 carbon-bonds. Topologically, protomene can be considered as an sp3 carbon structure (~80% of this bond type) doped by sp2 carbons. First-principles simulations have shown that protomene presents an electronic bandgap of ~3.4 eV. However, up to now, its mechanical properties have not been investigated. In this work, we have investigated protomene mechanical behavior under tensile strain through fully atomistic reactive molecular dynamics simulations using the ReaxFF force field, as available in the LAMMPS code. At room temperature, our results show that the protomene is very stable and the obtained ultimate strength and ultimate stress indicates an anisotropic behavior. The highest ultimate strength was obtained for the x-direction, with a value of ~110 GPa. As for the ultimate strain, the highest one was for the z-direction (~25% of strain) before protomene mechanical fracture.

Recently, a new 3D carbon allotrope named pentadiamond was proposed composed by mixed sp 2 and sp 3 -like hybridization. In this work, we have carried out a detailed investigation of the electronic, optical and thermoelectric properties of pentadiamond structure using first-principles methods. Our results show that pentadiamond has an indirect bandgap semiconductor of 2 . 50 eV with GGA-PBE and 3 . 31 eV with HSE06. Its static dielectric constant is 4.70 and the static refractive index is 2.16. Pentadiamond presents low reflectivity, making it a good structure to be used as a UV collector. Also, pentadiamond is a material that presents good thermoelectric properties.

The behavior of nanostructures under high strain-rate conditions has been object of interest in recent years. For instance, recent experimental investigations showed that at high velocity impacts carbon nanotubes can unzip resulting into graphene nanoribbons. Carbon nanoscrolls (CNS) are among the structures whose high impact behavior has not yet been investigated. CNS are graphene membranes rolled up into papyrus-like structures. Their unique open-ended topology leads to properties not found in close-ended structures, such as nanotubes. Here we report a fully atomistic reactive molecular dynamics study on the behavior of CNS colliding at high velocities against solid targets. Our results show that the velocity and scroll axis orientation are key parameters to determine the resulting formed nanostructures after impact. The relative orientation of the scroll open ends and the substrate is also very important. We observed that for appropriate velocities and orientations, the nanoscrolls can experience large structural deformations and large-scale fractures. We have also observed unscrolling (scrolls going back to planar or quasi-planar graphene membranes), unzip resulting into nanoribbons, and significant reconstructions from breaking and/or formation of new chemical bonds. Another interesting result was that if the CNS impact the substrate with their open ends, for certain velocities, fused scroll walls were observed.

Recent studies on graphene hydrogenation processes showed that hydrogenation occurs via island growing domains, however how the substrate can affect the hydrogenation dynamics and/or pattern formation has not been yet properly investigated. In this work we have addressed these issues through fully atomistic reactive molecular dynamics simulations. We investigated the structural and dynamical aspects of the hydrogenation of graphene membranes (one-side hydrogenation, the so called graphone structure) on different substrates (graphene, few-layers graphene, graphite and platinum). Our results also show that the observed hydrogenation rates are very sensitive to the substrate type. For all investigated cases, the largest fraction of hydrogenated carbon atoms was for platinum substrates. Our results also show that a significant number of randomly distributed H clusters are formed during the early stages of the hydrogenation process, regardless of the type of substrate. These results suggest that, similarly to graphane formation, large perfect graphone-like domains are unlikely to be formed. These findings are especially important since experiments have showed that cluster formation influences the electronic transport properties in hydrogenated graphene.

Nanocomposites based on graphene oxide (GO), hexagonal boron nitride (h-BN), and their hybrid GO/h-BN as nanofillers in polyurethane (PU) were prepared, and their structures and morphologies were studied. The efficient production of a few layers of nanofillers was completed using the direct liquid-phase exfoliation process. Mechanical and thermal tests were carried out to study the effect of the addition of GO, h-BN, and GO/h-BN at different wt% in the PU system. The tensile strength and Young's modulus showed an increase of up to 85% and 140%, respectively, for the composite containing 0.5 wt% of the hybrid GO/h-BN mixture. An impressive improvement of up to ~1450% in thermal conductivity was observed for the same sample when compared to neat polymer. In order to gain further insights regarding the mechanism behind the nanofiller dispersion and adhesion processes in PU, fully atomistic classical molecular dynamics simulations were carried out. Based on these simulations, it was possible to build structural models that help to explain the thermal and mechanical improvements in the hybrid GO/h-BN composites, with a focus on its stabilization energy.

Deep-level traps’ capture and emission time constants are known to impact the GaN HEMT models' ability to reproduce the device behavior when subject to RF modulated signals. Since deep level traps' capture time constants are usually much shorter than current pulse duration, they are usually neglected as assumed infinitesimally short. This work demonstrates, through basic semiconductor physics and experimental results, that such an assumption may not be verified, therefore justifying the effort of modeling such time constants as they may fall within the low-frequency components of modern communication signals.

The realization of quasicrystals has attracted a considerable attention due to their unusual structures and properties. The concept of quasicrystals in the atomically thin materials is even more appealing due to the in‐plane covalent bonds and weak interlayer interactions. Here, it is demonstrated that 2D quasicrystals can be created/isolated from bulk phases because of long‐range interlayer ordered aperiodic arrangements. An ultrasonication‐assisted exfoliation of polygrained icosahedral Al–Pd–Mn quasicrystals at room temperature shows the formation of a large area of mono‐ and few layers in threefold quasicrystalline plane. The formation of these layers from random grain orientation consistently indicates that the threefold plane is most stable in comparison to the twofold and fivefold planes in icosahedral clusters. The above experimental observations are further supported with help of theoretical simulations. The mono‐ and few‐layered aperiodic planes render plentiful active sites for the catalysis of hydrogen evolution reaction. The threefold 2D quasicrystalline plane exhibits a hydrogen evolution reaction overpotential of ≈100 mV (160 times less than bulk counterpart) and long‐term durability. These systems constitute the first demonstration of quasicrystalline monolayer ordering in a free‐standing thin layer without requiring the support of periodic or aperiodic substrate., by Thakur Prasad Yadav, Cristiano F. Woellner, Shyam K. Sinha, Tiva Sharifi, Amey Apte, Nilay Krishna Mukhopadhyay, Onkar Nath Srivastava, Robert Vajtai, Douglas S. Galvao, Chandra Sekhar Tiwary and Pulickel M. Ajayan

Biological materials are multifunctional performing more than one function in a perfect synergy. These materials are built from fairly simple and limited components at ambient conditions. Such judicious designs have proven elusive for synthetic materials. Here, we demonstrate a multifunctional phase change (pc) composite from simple building blocks, which exhibits high stiffness and optical transmittance control. We show an increase of more than one order of magnitude in stiffness when we embed paraffin wax spheres into an elastomer matrix, polydimethylsiloxane (PDMS) in a dynamic compression test. High stiffness is mainly influenced by presence of microcrystals within the wax. We further show fast temperature-controlled optical switching of the composite for an unlimited number of cycles without any noticeable mechanical degradation. Through experimental and finite element method, we show high energy absorption capability of pc-composite. Based on these properties, the pc-composite could be used as an effective coating on glasses for cars and windows. This simple approach to multi-functionality is exciting and could pave way for designs of other multifunctional materials at the macro-scale., by Peter Samora Owuor, Varun Chaudhary, Cristiano F. Woellner, V Sharma, R.V. Ramanujan, Anthony S. Stender, Matias Soto, Sehmus Ozden, Enrique V. Barrera, Robert Vajtai and Douglas S. Galvao

Schwarzites are crystalline, 3D porous structures with a stable negative curvature formed of sp2-hybridized carbon atoms. These structures present topologies with tunable porous size and shape and unusual mechanical properties. In this work, we have investigated the mechanical behavior under compressive strain and energy absorption of four different Schwarzites. We considered two Schwarzites families, the so-called Gyroid and Primitive and two structures from each family. We carried out reactive molecular dynamics simulations, using the ReaxFF force field as available in the LAMMPS code. Our results also show they exhibit remarkable resilience under mechanical compression. They can be reduced to half of their original size before structural failure (fracture) occurs.

We show that thermoelectric materials can function as electrocatalysts and use thermoelectric voltage generated to initiate and boost electrocatalytic reactions. The electrocatalytic activity is promoted by the use of nanostructured thermoelectric materials in a hydrogen evolution reaction (HER) by the thermoelectricity generated from induced temperature gradients. This phenomenon is demonstrated using two-dimensional layered thermoelectric materials Sb2Te3 and Bi0.5Sb1.5Te3 where a current density approaching ∼50 mA/cm2 is produced at zero potential for Bi0.5Sb1.5Te3 in the presence of a temperature gradient of 90 °C. In addition, the turnover frequency reaches to 2.7 s–1 at 100 mV under this condition which was zero in the absence of temperature gradient. This result adds a new dimension to the properties of thermoelectric materials which has not been explored before and can be applied in the field of electrocatalysis and energy generation.

Graphynes and graphdiynes are carbon 2D allotrope structures presenting both sp2 and sp hybridized atoms. These materials have been theoretically predicted but due to intrinsic difficulties in their synthesis, only recently some of these structures have been experimentally realized. Graphyne nanoscrolls are structures obtained by rolling up graphyne sheets into papyrus-like structures. In this work we have investigated, through fully atomistic reactive molecular dynamics simulations, the dynamics of nanoscroll formation for a series of graphyne ({\alpha}, \b{eta}, and {\delta} types) structures. We have also investigated their thermal stability for a temperature range of 200-1000K. Our results show that stable nanoscrolls can be formed for all structures considered here. Their stability depends on a critical value of the ratio between width and height of the graphyne sheets. Our findings also show that these structures are structurally less stable then graphene-based nanoscrolls. This can be explained by the graphyne higher structural porosity which results in a decreased pi-pi stacking interactions

The behavior of nanostructures under high strain-rate conditions has been object of theoretical and experimental investigations in recent years. For instance, it has been shown that carbon and boron nitride nanotubes can be unzipped into nanoribbons at high velocity impacts. However, the response of many nanostructures to high strain-rate conditions is still not completely understood. In this work we have investigated through fully atomistic reactive (ReaxFF) molecular dynamics (MD) simulations the mechanical behavior of carbon (CNS) and boron nitride nanoscrolls (BNS) colliding against solid targets at high velocities,. CNS (BNS) nanoscrolls are graphene (boron nitride) membranes rolled up into papyrus-like structures. Their open-ended topology leads to unique properties not found in close-ended analogues, such as nanotubes. Our results show that the collision products are mainly determined by impact velocities and by two impact angles, which define the position of the scroll (i) axis and (ii) open edge relative to the target. Our MD results showed that for appropriate velocities and orientations large-scale deformations and nanoscroll fracture can occur. We also observed unscrolling (scrolls going back to quasi-planar membranes), scroll unzipping into nanoribbons, and significant reconstruction due to breaking and/or formation of new chemical bonds. For particular edge orientations and velocities, conversion from open to close-ended topology is also possible, due to the fusion of nanoscroll walls.

We analyzed the impact of the complex channel network of donor and acceptor domains in nanostructured solar cells on the mobility of the charge carriers moving by thermally activated hopping. Particular attention was given to the so called intermixed phase, or interface roughness, that has recently been shown to promote an increase in the cell efficiency. The domains were obtained from a Monte Carlo simulation of a two-species lattice gas. We generated domain morphologies with controllable channel size and interface roughness. The field and density dependence of the carrier hopping mobility in different morphologies was obtained by solving a master equation. Our results show that the mobility decreases with roughness and increases with typical channel sizes. The deleterious effect of the roughness on the mobility is quite dramatic at low carrier densities and high fields. The complex channel network is shown to be directly responsible for two potentially harmful effects to the cell performance: a remarkable decrease of the mobility with increasing field and the accumulation of charge at the domains interface, which leads to recombination losses.

Induction of vitellogenin (VTG) in male and immature fish is a standardized endpoint in endocrine-disruption testing. To establish a nondestructive swab sampling method, VTG induction in the epidermis of Cypriniformes and Perciformes species was investigated. Both VTG and estrogen receptor genes are expressed in epidermal cells. Immunoaffinity and mass fingerprint analyses show induction of identical VTG peptides in liver and epidermis. Induction of VTG by estradiol (E2) and bisphenol A (BPA) in the epidermis was quantified with homolog enzyme-linked immunosorbent assays. Initial values in juveniles and males were below 1 ng VTG/mL extraction buffer. Exposure to E2 led to values between 200 ng/mL and 4600 ng/mL in cyprinids and between 10 ng/mL and 81 ng/mL in perciforms. Exposure to BPA increased VTG amounts to 250 ng/mL in fathead minnows, 1360 ng/mL in goldfish, 100 ng/mL in zebrafish, and 12 ng/mL in bluegills. Serum VTG contents demonstrated a similar dose-response pattern in the epidermis and the blood. These results show that VTG induction may be reliably assessed in the skin mucus of fishes, demonstrating the suitability of this biological sample for investigating estrogenic activity in compliance with Organisation for Economic Co-operation and Development standard protocols. This broadens the perspectives in toxicological screening and environmental monitoring, reducing the number of tested animals and minimizing harmful effects for animals, allowing for follow-up of individual induction profiles. Environ Toxicol Chem 2016;35:2916-2930. © 2016 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Schwartzites are 3D porous solids with periodic minimal surfaces having negative Gaussian curvatures and can possess unusual mechanical and electronic properties. The mechanical behavior of primitive and gyroid schwartzite structures across different length scales is investigated after these geometries are 3D printed at centimeter length scales based on molecular models. Molecular dynamics and finite elements simulations are used to gain further understanding on responses of these complex solids under compressive loads and kinetic impact experiments. The results show that these structures hold great promise as high load bearing and impact-resistant materials due to a unique layered deformation mechanism that emerges in these architectures during loading. Easily scalable techniques such as 3D printing can be used for exploring mechanical behavior of various predicted complex geometrical shapes to build innovative engineered materials with tunable properties.

The overall electrocatalytic activity toward hydrogen evolution reaction for layered transition metal dichalcogenides is governed by their intrinsic activity, the corresponding density of active sites, and the electron transfer resistance. Here, nanoengineering strategies to scale down both the lateral size and thickness of layered 1T-TiS2 powder to quantum dots (QDs) by bath sonication and probing sonication incision are employed. Uniform lateral size of 3–6 nm in the resulting QDs enhances the density of edge sites while the atomic layer thickness (1–2 nm) facilitates the electron transfer from the substrate to the edge sites. The obtained TiS2 QDs exhibit superior hydrogen evolution reaction activity over TiS2 nanosheets and MoS2 QDs prepared by the same method. The turnover frequency of TiS2 QDs with a small loading of 0.7 ng cm−2 in an optimal deposition on electrode reached ≈2.0 s−1 at an overpotential of −0.2 V versus RHE, several orders of magnitude higher than TiS2 nanosheets (0.01 s−1) and MoS2 QDs (0.07 s−1).

Carbon-based nanomaterials have garnered a lot of attention in the research of yesteryear. Here this study reports a composite based on fluorinated graphene oxide—a multifunctional subsidiary of graphene; and iron oxide nanoparticles as a contrast agent for magnetic resonance imaging (MRI). Extensive structural and functional characterization is carried out to understand composite behavior toward biotoxicity and its performance as a contrast agent. The electron withdrawing fluorine group decreases the charge transfer to iron oxide increasing the magnetic saturation of the composite thus enhancing the contrast. The interaction of paramagnetic and superparamagnetic systems yields a superior contrast agent for MRI and fluorescent imaging.

2D transition metals di-selenides are attracting a lot of attention due to their interesting optical, chemical and electronics properties. Here, the deformation characteristics of monolayer, multi- layer WSe2 and its heterostructure with MoSe2 were investigated using a new technique that combines nanoscratch and Raman spectroscopy. The 2D monolayer WSe2 showed anisotropy in deformation. Effect of number of WSe2 layers on friction characteristics were explored in detail. Experimental observations were further supported by MD simulations. Raman spectra recorded from the scratched regions showed strain induced degeneracy splitting. Further nano-scale scratch tests were extended to MoSe2–WSe2 lateral heterostructures. Effect of deformation on lateral hetero junctions were further analysed using PL and Raman spectroscopy. This new technique is completely general and can be applied to study other 2D materials.

Here, the scalable synthesis of low-density 3D macroscopic structure of graphene oxide (GO) interconnected with polydimethylsiloxane (PDMS) is reported. A controlled amount of PDMS is infused into the freeze-dried foam to result into a very rigid structure with improved mechanical properties, such as tensile plasticity and toughness. The PDMS wets the graphene oxide sheets and acts like glue between the 2D sheets. Molecular dynamics simulations are used to further elucidate the mechanisms of the interactions of graphene oxide layers with PDMS. The ability of using the interconnecting graphene oxide foam as an effective oil–water separator and stable insulating behavior to elevated temperatures are further demonstrated. The structural rigidity of the sample is also tested using laser impact and compared with GO foam.

Yield and disease incidence were evaluated in potato (Solanum tuberosum, cv. Atlantic) after six years of cultivation in succession with corn (Zea mays, cv. ‘AG 6080’) under conventional tillage (CT, depth of tillage: 20 cm) or in succession with three grass species [Guinea grass (Panicum maximum, cv. Tanzânia), Palisade grass (Brachiaria brizantha, cv. Marandu) and corn] under deep tillage (DT, depth of tillage: 70 cm). Total tuber yield was higher in DT in average 36% the value obtained in CT (17.76 t/ha), with no effect of the grass species. Common scab (Streptomyces scabies) incidence was influenced by treatments, the highest (16.9%) and the lowest (9.5%) values being obtained in succession with corn and Guinea grass, respectively, both under DT. The lowest incidence of tuber greening at field (2.58%) was also recorded in Guinea DT, significantly lower than obtained in Corn CT (6.33%), possibly due to a more efficient ridging operation. Grass species showed different values of aboveground dry biomass production. Guinea grass (26.56 t/ha) was the most and Corn under CT and DT (5.72 and 5.56 t/ha, respectively, without ears) were the least productive ones. Soil density, macroporosity and resistance to penetration indices were significantly better with DT, the grass species affecting them in a minor degree. The deep tillage system is, therefore, recommended for potato cultivation regardless the grass species used for crop succession. RESUMO A produtividade e a incidência de doenças foram avaliadas na cultura da batata (Solanum tuberosum, cv. Atlantic) após seis anos de cultivo em sucessão com milho (Zea mays, cv. ‘AG 6080’) sob manejo de solo convencional (CT, profundidade da operação de preparo: 20 cm) ou em sucessão de culturas com três espécies de poácea [capim Tanzânia (Panicum maximum, cv. Tanzânia), capim Marandu (Brachiaria brizantha, cv. Marandu) e milho], sob manejo profundo de solo (DT, profundidade da operação de preparo: 70 cm). A produtividade total em tubérculos para os tratamentos em DT foi, em média, 36% maior em relação ao CT (17,76 t/ha), não havendo efeito da poácea cultivada em sucessão. A incidência de sarna comum (Streptomyces scabies) foi influenciada pelos tratamentos, sendo a mais alta (16,9%) e a mais baixa (9.5%) registradas quando milho e capim Tanzânia, respectivamente, foram utilizados como cultura em sucessão, ambos sob DT. A incidência mais baixa de esverdeamento de tubérculos em campo (2,58%) foi também obtida para sucessão com capim Tanzânia sob DT, significativamente inferior ao valor obtido em milho CT (6,33%), possivelmente devido à maior eficácia da operação de amontoa. As diferentes poáceas apresentaram valores diferentes de produção de biomassa seca de parte aérea. O capim Tanzânia (26,56 t/ha) foi a poácea mais produtiva e o milho sob CT e DT (5,72 e 5,56 t/ha, respectivamente, sem considerar as espigas) foi a menos produtiva. Densidade e macroporosidade, assim como o índice de resistência à penetração do solo foram significativamente mais favoráveis nos tratamentos com DT e a espécie de poácea cultivada em sucessão os afetou em menor grau. O manejo profundo do solo é, portanto, recomendado para o cultivo da batata independentemente da espécie de poácea utilizada como cultura em sucessão.

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