Using the molecular dynamics method, dynamics of hydrogen bond (HB) networks emerging on the surface of a graphene sheet during its functionalization with hydroxyl groups OH are simulated. It is ...demonstrated that two OH groups form an energetically more advantageous structure when they are covalently attached on one side of the sheet to carbon atoms forming opposite vertices of one hexagon of valence bonds of the sheet. Attaching of OH groups to carbon atoms located at the opposite vertices of hexagons of valence bonds leads to the emergence of hydroxygraphene C4(OH). In such sheet lying on a flat substrate, attached oxygen atoms on its outer surface form a hexagonal lattice, and hydroxyl groups due to their turns can in various ways form chains of hydrogen bonds. The modification of the sheet from two sides results in forming of hydroxygraphene C2(OH) with HB networks on both sides of the graphene sheet. Simulation of the dynamics of these sheets shows that their heat capacity at low temperatures T < T0 increases monotonously when the temperature rises, reaches its maximum at T = T0 and then decreases monotonically. The initial growth is caused by the accumulation of orientational defects in the lattice of hydrogen bonds whereas the decrease at T > T0 is explained by the “melting” of the lattice. For one chain of OH groups connected to the outer side of a nanoribbon the melting temperature is T0 = 500K, while for a graphene sheet C4(OH) modified on one side T0 = 260K, and for a graphene sheet C2(OH) modified on both sides T0 = 485K.
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•Two OH groups form hydrogen bond when they are attached to graphene carbon atoms forming opposite vertices of the hexagon.•In the chain of hydrogen bonds (HB) OH⋯OH⋯OH⋯ on graphene surface can exist four types of orientational defects.•In the 2D hexagonal lattice of HB bonds on surface of hydroxygraphene (HG) can exist two types of orientational defects.•Heat capacity of HG increases monotonically with increase of temperature, it reaches its maximum value at T0.•Increases of heat capacity is caused by the accumulation of orientational defects in the HB lattice.
Cross-linked networks feature exceptional chemical and mechanical resilience but consequently lack recyclability. Vitrimers have emerged as a class of materials that feature the robustness of ...thermosets and the recyclability of thermoplastics without compromising network integrity. Most examples of vitrimers have involved new polymers with exchangeable bonds within their backbones. In pursuit of a more universal, commercially viable route, we propose a method utilizing commercially available and inexpensive reagents to prepare vitrimers from vinyl monomer-derived prepolymers that contain cross-linkable β-ketoester functional groups. Controlled radical copolymerization of methyl methracrylate and (2-acetoacetoxy)ethyl methacrylate afforded linear prepolymers that were converted into vitrimers in a single step by treatment with a trifunctional amine. These materials displayed the characteristic features and reprocessability of vitrimers over as many as six (re)processing cycles. Critically, the networks prepared through this process largely retain the chemical and thermal properties of their linear counterparts, suggesting this method holds significant utility as a user-friendly and commercially relevant approach to the rational design of vitrimers with diverse properties.
It is shown by the molecular dynamics method using the two-dimensional chain model that the motion of graphene nanoparticles (nanoribbons and nanotubes) on a flat thermalized multilayer h-BN ...substrate is described as the motion of particles in a viscous medium with a constant friction coefficient. The effective friction that occurs during movement has a wave nature, the reason of braking is the interaction of the nanoparticle with thermal bending vibrations of the substrate sheets. The friction coefficient increases monotonically with temperature and decreases upon an increase in the nanoparticle size. The friction emerging for nanoribbons can be divided into two types: internal friction and edge friction (the friction of the inner surface of a nanoribbon and the friction of its edges with the substrate surface). Edge friction plays the major role for lengths
L
< 35 nm, while internal friction is more important for
L
> 35 nm. Under the action of a constant longitudinal force, the nanoparticle dynamics is always characterized by the regime of motion at a constant velocity, the value of which is directly proportional to the force and inversely proportional to the friction coefficient. The simulation of the motion of a nanoribbon in the presence of a normal load (pressure) shows that an increase in the load reduces the internal friction due to a decrease in the amplitude of thermal bending vibrations of the substrate layers under the nanoribbon and enhances the edge friction due to pressing of nanoribbon edges into the substrate. For this reason, the effect of reduction of friction upon an increase of the normal load can be observed only for quite long nanoribbons (
L
> 250 nm), when the internal friction plays the major role.
Pulmonary fibrosis is a chronic progressive lung disease that steadily leads to lung architecture disruption and respiratory failure. The development of pulmonary fibrosis is mostly the result of ...previous acute lung inflammation, caused by a wide variety of etiological factors, not resolved over time and causing the deposition of fibrotic tissue in the lungs. Despite a long history of study and good coverage of the problem in the scientific literature, the effective therapeutic approaches for pulmonary fibrosis treatment are currently lacking. Thus, the study of the molecular mechanisms underlying the transition from acute lung inflammation to pulmonary fibrosis, and the search for new molecular markers and promising therapeutic targets to prevent pulmonary fibrosis development, remain highly relevant tasks. This review focuses on the etiology, pathogenesis, morphological characteristics and outcomes of acute lung inflammation as a precursor of pulmonary fibrosis; the pathomorphological changes in the lungs during fibrosis development; the known molecular mechanisms and key players of the signaling pathways mediating acute lung inflammation and pulmonary fibrosis, as well as the characteristics of the most common in vivo models of these processes. Moreover, the prognostic markers of acute lung injury severity and pulmonary fibrosis development as well as approved and potential therapeutic approaches suppressing the transition from acute lung inflammation to fibrosis are discussed.
Bulk nanomaterials made of carbon nanotubes (CNTs) possess unique physical and mechanical properties that are used in a number of applications, for example, for creating mass or force sensors, ...protection against shock and vibration. One of the specific implementations of such materials is a CNT bundle in which aligned CNTs are held together due to van der Waals interactions. Linear and nonlinear dynamic excitations in such materials are still poorly understood. Here we study plane waves and spatially localized nonlinear dynamic modes in a CNT bundle under plane strain conditions, when the CNT cross sections completely determine the deformed state of the bundle. In particular, we analyze vibration spectrum of single CNT, dispersion curves of phonons propagating along the close packed direction of CNT bundle, compressive solitons and discrete breathers in the form of single CNT oscillating at large amplitude in the CNT bundle. It is shown that compressive solitons can propagate long distances in the bundles of CNTs having radius no more than about 0.8 nm. Discrete breathers can exist in bundles of CNTs of any radius. The results obtained revealed new channels of energy localization and transport in CNT bundles, which is important for their use in various technologies.
•Linear and nonlinear dynamics of carbon nanotube (CNT) bundles was investigated.•Bundles with CNTs of radius R<0.8 nm support propagation of compressive solitons.•Energy dissipation rate of a soliton increases as the diameter of the CNT increases.•Discrete breathers can be created by radial or angular vibrational modes of CNT.•Discrete breathers can exist in bundles of CNTs of any radius.
Hydrophobicity inherently affects a solutes behavior in water, yet how polymer chain hydrophobicity impacts aggregate morphology during solution self-assembly and reorganization is largely ...overlooked. As polymer and nanoparticle syntheses are easily achieved, the resultant nanoparticle architectures are usually attributed to chain topology and overall degree of polymerization, bypassing how the chains may interact with water during/after self-assembly to elicit morphology changes. Herein, we demonstrate how block copolymer hydrophobicity allows control over aggregate morphology in water and leads to remarkable control over the length of polymeric nanoparticle worms. Polymerization-induced self-assembly facilitated nanoparticle synthesis through simultaneous polymerization, self-assembly, and chain reorganization during a block copolymer chain extension from a hydrophilic poly( N , N -dimethylacrylamide) macro-chain-transfer agent with diacetone acrylamide and N , N -dimethylacrylamide. Slight variations in the monomer feed ratio dictated the block copolymer chain composition and were proposed to alter aggregate thermodynamics. Micelles, worms, and vesicles were synthesized, and the highest level of control over worm elongation attained during a polymerization is reported, simply due to the polymer chain hydrophobicity.
The COMPASS force field has been successfully applied in a large number of materials simulations, including the analysis of structural, electrical, thermal, and mechanical properties of carbon ...nanoparticles. This force field has been parameterized using quantum mechanical data and is based on hundreds of molecules as a training set, but such analysis for graphene sheets was not carried out. The objective of the present study is the verification of how good the COMPASS force field parameters can accurately describe the frequency spectrum of atomic vibrations of graphene, graphane and fluorographene sheets. We showed that the COMPASS force field allows us to describe with good accuracy the frequency spectrum of atomic vibrations of graphane and fluorographene sheets, whose honeycomb hexagonal lattice is formed by sp3 hybridization. On the other hand, the force field does not describe very well the frequency spectrum of graphene sheet, whose planar hexagonal lattice is formed by sp2 banding. In that case the frequency spectrum of out-of-plane vibrations differs greatly from the experimental data — bending stiffness of a graphene sheet is strongly over estimated. We present the correction of parameters of out-of-plane and torsional potentials of the force field, which allows achieving the coincidence of vibration frequency with experimental data. After such corrections, the COMPASS force field can be used to describe the dynamics of flat graphene sheets and carbon nanotubes.
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•The COMPASS force field reproduces well the vibration spectra of graphane and fluorographene sheets.•The force field does not describe very well the frequency spectrum of graphene sheet.•The correction of parameters of the COMPASS force field for graphene sheets was made.
Cod stocks dynamics and annual catches in the northwestern Bering Sea from 1965 to 2022 are determined based on materials collected in the research surveys and commercial expeditions, as well as on ...the data of fishery statistics and literature data. Various biological parameters concerning fisheries have been calculated: instantaneous fishing mortality rate, instantaneous natural mortality rate, von Bertalanffy equation parameters, etc. The decline in stocks is presumably linked to the expanding Laurentian cold spot, as well as to bottom trawl fishing on spawning grounds. It was concluded that since 2002, the fishing pressure on the cod stock was moderate, and fishing mortality did not exceed its target level. However, if the trend of rapid decline in cod stocks continues in the next 3–4 years and the fishing pressure is relatively high, the instantaneous fishing mortality rate may increase. It may exceed the target reference point, and even the limit reference point.
Generation of electric voltage in a conductor by applying a temperature gradient is a fundamental phenomenon called the Seebeck effect. This effect and its inverse is widely exploited in diverse ...applications ranging from thermoelectric power generators to temperature sensing. Recently, a possibility of thermoelectricity arising from the interplay of the non-local Cooper pair splitting and the elastic co-tunneling in the hybrid normal metal-superconductor-normal metal structures was predicted. Here, we report the observation of the non-local Seebeck effect in a graphene-based Cooper pair splitting device comprising two quantum dots connected to an aluminum superconductor and present a theoretical description of this phenomenon. The observed non-local Seebeck effect offers an efficient tool for producing entangled electrons.
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