Supramolecular polymers, formed via noncovalent self-assembly of elementary monomers, are extremely interesting for their dynamic bioinspired properties. In order to understand their behavior, it is ...necessary to access their dynamics while maintaining high resolution in the treatment of the monomer structure and monomer–monomer interactions, which is typically a difficult task, especially in aqueous solution. Focusing on 1,3,5-benzenetricarboxamide (BTA) water-soluble supramolecular polymers, we have developed a transferable coarse-grained model that allows studying BTA supramolecular polymerization in water, while preserving remarkable consistency with the atomistic models in the description of the key interactions between the monomers (hydrophobic, H-bonding, etc.), self-assembly cooperativity, and amplification of order into the growing fibers. This permitted us to monitor the amplification of the key interactions between the monomers (including H-bonding) in the BTA fibers during the dynamic polymerization process. Our molecular dynamics simulations provide a picture of a stepwise cooperative polymerization mechanism, where initial fast hydrophobic aggregation of the BTA monomers in water is followed by the slower reorganization of these disordered aggregates into ordered directional oligomers. Supramolecular polymer growth then proceeds on a slower time scale. We challenged our models via comparison with the experimental evidence, capturing the effect of temperature variations and subtle changes in the monomer structure on the polymerization and on the properties of the fibers seen in the real systems. This work provides a multiscale spatiotemporal characterization of BTA self-assembly in water and a useful platform to study a variety of BTA-based supramolecular polymers toward structure–property relationships.
To rationally design supramolecular polymers capable of self-healing or reconfiguring their structure in a dynamically controlled way, it is imperative to gain access into the intrinsic dynamics of ...the supramolecular polymer (dynamic exchange of monomers) while maintaining a high-resolution description of the monomer structure. But this is prohibitively difficult at experimental level. Here we show atomistic, coarse-grained modelling combined with advanced simulation approaches to characterize the molecular mechanisms and relative kinetics of monomer exchange in structural variants of a synthetic supramolecular polymer in different conditions. We can capture differences in supramolecular dynamics consistent with the experimental observations, revealing that monomer exchange in and out the fibres originates from the defects present in their supramolecular structure. At the same time, the submolecular resolution of this approach offers a molecular-level insight into the dynamics of these bioinspired materials, and a flexible tool to obtain structure-dynamics relationships for a variety of polymeric assemblies.Accessing the dynamics of soft self-assembled materials at high resolution is very difficult. Here the authors show atomistic and coarse-grained modelling combined with enhanced sampling to characterize the molecular mechanisms and kinetics of monomer exchange in synthetic supramolecular polymers.
Photoswitchable molecules are employed for many applications, from the development of active materials to the design of stimuli-responsive molecular systems and light-powered molecular machines. To ...fully exploit their potential, we must learn ways to control the mechanism and kinetics of their photoinduced isomerization. One possible strategy involves confinement of photoresponsive switches such as azobenzenes or spiropyrans within crowded molecular environments, which may allow control over their light-induced conversion. However, the molecular factors that influence and control the switching process under realistic conditions and within dynamic molecular regimes often remain difficult to ascertain. As a case study, here we have employed molecular models to probe the isomerization of azobenzene guests within a Pd(II)-based coordination cage host in water. Atomistic molecular dynamics and metadynamics simulations allow us to characterize the flexibility of the cage in the solvent, the (rare) guest encapsulation and release events, and the relative probability/kinetics of light-induced isomerization of azobenzene analogues in these host–guest systems. In this way, we can reconstruct the mechanism of azobenzene switching inside the cage cavity and explore key molecular factors that may control this event. We obtain a molecular-level insight on the effects of crowding and host–guest interactions on azobenzene isomerization. The detailed picture elucidated by this study may enable the rational design of photoswitchable systems whose reactivity can be controlled via host–guest interactions.
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•The utilization of vegetable oil for polyurethane synthesis has been researched and documented in the past decade.•Derivatives of vegetable oil are also known to be an excellent ...feedstock for polyurethane coatings.•Challenges continue to remain in terms of properties, performance and reaction conditions of polyurethane.•The review focuses on various synthesis routes that transform triglycerides and derivatives into polyurethane precursors.•Different types of polyurethane coatings have also been studied in this review.
The scientific community has been pooling all its resources, for the past decade, towards the development of “sustainable development” to usher into an eternally green and sustainable tomorrow. As part of this endeavor, the conventional petroleum-based polyurethane (PU) coatings have been replaced by their green counterparts, i.e., bio-based polyurethane coatings. These green alternatives provide a suitable replacement for the coating industry due to their easy availability, biodegradability, low cost, and lesser environmental impact. The production of such green PU coatings is further facilitated by the utilization of bio-based materials, including vegetable oils and their derivatives such as methyl ester, fatty acid, and other bio-renewable sources. This review discusses the different chemical modifications used to convert these bio-based precursors into desired polyols and isocyanates. Furthermore, the formulation of different PU coatings and their subsequent potential applications are also elaborated on in this review. The coatings sector has already been introduced to the notion of eco-friendly technologies such as UV-curable, less or zero solvent, waterborne, hyperbranched, and high solids coatings, complemented by the incorporation of renewable feedstock in monomer synthesis. The review examines the future hurdles that hinder the utilization of these materials in a wide range of applications and presents technologies that facilitate potential solutions and mention key players in the coating sectors that are at the forefront of bringing these revolutionary changes.
Biomolecular systems serve as an inspiration for the creation of multicomponent synthetic supramolecular systems that can be utilized to develop functional materials with complexity. However, ...supramolecular systems rapidly reach an equilibrium state through dynamic and reversible noncovalent bonds, resulting in a disorganized mixture of components rather than a system in which individual components function cooperatively and/or independently. Thus, efficient synthetic strategies and characterization methods for intricate multicomponent supramolecular assemblies need to be developed. Herein, we report the synthesis of porphyrin-based supramolecular polymers (SPs) in which two distinct block segments consisting of different metal porphyrins are connected: i.e., block supramolecular polymers (BSPs). BSPs with a controlled length and narrow polydispersity were achieved through seeded-growth by a solvent mixing protocol. Interestingly, the block structure permitted the SP as an inner block to coexist with a reagent that was otherwise incompatible with the SP alone. We infer that the inner SP block is compartmentalized in the block structure and endowed with the kinetic stability. Molecular simulations revealed that monomer exchange occurs from the termini of the SP, which corroborated the enhanced stability of the BSP. These results are expected to pave the way for the design of more complex multicomponent supramolecular systems.
The effect of active component addition and support modification of Ag/Al2O3 has been reviewed to examine their contribution to HC-SCR of NOx. This review has depicted the possible mechanisms of ...reduction of NO by hydrocarbon using metal/metal oxide doped Ag/Al2O3. The addition of second metal results in the maximum formation of well dispersed Agnδ+ clusters. Specifically, addition of Au improves the low-temperature activity of the catalyst. However, the role of second metal also depends on the pretreatment to the catalyst and nature of the reductants. The support modification of Ag/Al2O3 by the addition of different metal oxides has also been reviewed. Modification by MgO showed improvement in activity besides sulfur tolerance. In situ DRIFT study demonstrates that the modification by MgO leads to the inhibition of sulfate formation of Ag and Al2O3. Enhancement in activity after second metal addition and support modification attributed to the synergistic effect and improved surface properties of Ag/Al2O3 catalyst.
•Active component modification of Ag/Al2O3 significantly improves activity.•Second metal addition increases the partial oxidation of HC at low temperature.•Interaction of second metal and Ag leads to the formation of more Agnδ+ clusters.•Support modification of Ag/Al2O3 improves its surface properties and SO2 tolerance.•The mechanism of modification of Ag/Al2O3 catalyst is discussed.
•Laser peening induced a fully compressive residual stress field in the specimen.•Laser peened samples reported a fatigue life 4x longer than pristine components.•FCGR dramatically decreased within ...the laser peened areas.•Numerical modelling allowed to accurately predict FCGR and fatigue lives.•A crack-closure mechanism is essential to correctly simulate the crack behaviour.
Laser Shock Peening is a surface treatment technique used in the aerospace sector to increase fatigue life, as well as resistance to fretting fatigue and stress corrosion cracking. In this study, laser shock peening was applied to a 6-mm-thick middle-crack tension specimen made of aluminium 2524-T351. Residual stress was measured with neutron diffraction and the contour method, along the predicted crack path prior to fatigue testing. Fatigue crack growth test results showed that fatigue life improved by a factor of 4 compared to an untreated component, owing to a significant crack growth rate reduction inside the laser peened area. A linear-elastic finite-element crack growth prediction model was also developed, obtaining predicted results in excellent agreement with the experimental data.
Dominant Sets and Pairwise Clustering Pavan, M.; Pelillo, M.
IEEE transactions on pattern analysis and machine intelligence,
2007-Jan., 2007, 2007-Jan, 2007-1-00, 20070101, Letnik:
29, Številka:
1
Journal Article
Recenzirano
We develop a new graph-theoretic approach for pairwise data clustering which is motivated by the analogies between the intuitive concept of a cluster and that of a dominant set of vertices, a notion ...introduced here which generalizes that of a maximal complete subgraph to edge-weighted graphs. We establish a correspondence between dominant sets and the extrema of a quadratic form over the standard simplex, thereby allowing the use of straightforward and easily implementable continuous optimization techniques from evolutionary game theory. Numerical examples on various point-set and image segmentation problems confirm the potential of the proposed approach
Multi-component systems often display convoluted behavior, pathway complexity and coupled equilibria. In recent years, several ways to control complex systems by manipulating the subtle balances of ...interaction energies between the individual components have been explored and thereby shifting the equilibrium between different aggregate states. Here we show the enantioselective chain-capping and dilution-induced supramolecular polymerization with a Zn
-porphyrin-based supramolecular system when going from long, highly cooperative supramolecular polymers to short, disordered aggregates by adding a monotopic Mn
-porphyrin monomer. When mixing the zinc and manganese centered monomers, the Mn
-porphyrins act as chain-cappers for Zn
-porphyrin supramolecular polymers, effectively hindering growth of the copolymer and reducing the length. Upon dilution, the interaction between chain-capper and monomers weakens as the equilibria shift and long supramolecular polymers form again. This dynamic modulation of aggregate morphology and length is achieved through enantioselectivity in the aggregation pathways and concentration-sensitive equilibria. All-atom and coarse-grained molecular simulations provide further insights into the mixing of the species and their exchange dynamics. Our combined experimental and theoretical approach allows for precise control of molecular self-assembly and chiral discrimination in complex systems.
In this letter, we present in detail the system-level modeling of reconfigurable intelligent surface (RIS)-assisted cellular systems by considering a 3-dimensional channel model between base station, ...RIS, and user. We prove that the optimal placement of RIS to achieve wider coverage is exactly opposite to the base station, under the constraint of single RIS in each sector. We propose a novel beamforming design for RIS-assisted cellular systems and derive the achievable sum rate in the presence of ideal, discrete, and random phase shifters at RIS. Through extensive system-level evaluations, we then show that the proposed beamforming design achieves significant improvements as compared to the state-of-the-art algorithms.
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