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Auswahl der wissenschaftlichen Literatur zum Thema „Dynamic covalent bond“
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Zeitschriftenartikel zum Thema "Dynamic covalent bond"
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Zheng, Shuyuan, und Guofeng Liu. „Polymeric Emissive Materials Based on Dynamic Covalent Bonds“. Molecules 27, Nr. 19 (06.10.2022): 6635. http://dx.doi.org/10.3390/molecules27196635.
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Dynamic covalent polymers, composed of dynamic covalent bonds (DCBs), have received increasing attention in the last decade due to their adaptive and reversible nature compared with common covalent linked polymers. Incorporating the DCBs into the polymeric material endows it with advanced performance including self-healing, shape memory property, and so forth. However, the emissive ability of such dynamic covalent polymeric materials has been rarely reviewed. Herein, this review has summarized DCBs-based emissive polymeric materials which are classified according to the different types of DCBs, including imine bond, acylhydrazone bond, boronic ester bond, dynamic C-C bond, as well as the reversible bonds based on Diels–Alder reaction and transesterification. The mechanism of chemical reactions and various stimuli-responsive behaviors of DCBs are introduced, followed by typical emissive polymers resulting from these DCBs. By taking advantage of the reversible nature of DCBs under chemical/physical stimuli, the constructed emissive polymeric materials show controllable and switchable emission. Finally, challenges and future trends in this field are briefly discussed in this review.
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Lascano, Santiago, Kang-Da Zhang, Robin Wehlauch, Karl Gademann, Naomi Sakai und Stefan Matile. „The third orthogonal dynamic covalent bond“. Chemical Science 7, Nr. 7 (2016): 4720–24. http://dx.doi.org/10.1039/c6sc01133k.
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Bracchi, Michael E., und David A. Fulton. „Orthogonal breaking and forming of dynamic covalent imine and disulfide bonds in aqueous solution“. Chemical Communications 51, Nr. 55 (2015): 11052–55. http://dx.doi.org/10.1039/c5cc02716k.
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4
Heinen, Laura, und Andreas Walther. „Programmable dynamic steady states in ATP-driven nonequilibrium DNA systems“. Science Advances 5, Nr. 7 (Juli 2019): eaaw0590. http://dx.doi.org/10.1126/sciadv.aaw0590.
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Inspired by the dynamics of the dissipative self-assembly of microtubules, chemically fueled synthetic systems with transient lifetimes are emerging for nonequilibrium materials design. However, realizing programmable or even adaptive structural dynamics has proven challenging because it requires synchronization of energy uptake and dissipation events within true steady states, which remains difficult to orthogonally control in supramolecular systems. Here, we demonstrate full synchronization of both events by ATP-fueled activation and dynamization of covalent DNA bonds via an enzymatic reaction network of concurrent ligation and cleavage. Critically, the average bond ratio and the frequency of bond exchange are imprinted into the energy dissipation kinetics of the network and tunable through its constituents. We introduce temporally and structurally programmable dynamics by polymerization of transient, dynamic covalent DNA polymers with adaptive steady-state properties in dependence of ATP fuel and enzyme concentrations. This approach enables generic access to nonequilibrium soft matter systems with adaptive and programmable dynamics.
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Zhao, Jingwen, Louis Debertrand, Tetsuharu Narita und Costantino Creton. „Fracture of dual crosslink gels with permanent and transient crosslinks: Effect of the relaxation time of the transient crosslinks“. Journal of Rheology 66, Nr. 6 (01.11.2022): 1255–66. http://dx.doi.org/10.1122/8.0000460.
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We investigate the fracture properties of poly(acrylamide- co-1-vinylimidazole) dual crosslink hydrogels [P(AAm- co-VIm)-M2+ gels] containing a small fraction of covalent bonds and a majority of dynamic bonds based on metal coordination bonds (Ni2+ or Zn2+). Unlike a previous study on a different dual crosslink hydrogel system having slower dynamic bonds based on poly(vinylalcohol) and borate ions (PVA-Borax gels), the presence of these faster dynamic coordination bonds has two main effects: They significantly toughen the P(AAm- co-VIm)-M2+ gels even at high stretch rates, where the dynamic bonds should in principle behave as covalent bonds at the crack tip, and they toughen the gels at very low stretch rates, where the dynamic bonds are invisible during the loading stage. We propose two additional molecular mechanisms to rationalize this behavior of P(AAm- co-VIm)-M2+ gels: we hypothesize that fast exchanging dynamic bonds remain slow compared to the characteristic time of bond scission and are, therefore, able to share the load upon covalent bond scission even at low loading rates. We also argue of the existence of longer-lived clusters of dynamic bonds that introduce a stretch rate-dependent strain hardening in uniaxial tension and stabilize and increase the size of the dissipative zone at the crack tip, thereby introducing a strain-dependent dissipative mechanism.
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Liu, Shengda, Shengchao Deng, Tengfei Yan, Xin Zhang, Ruizhen Tian, Jiayun Xu, Hongcheng Sun, Shuangjiang Yu und Junqiu Liu. „Biocompatible Diselenide-Containing Protein Hydrogels with Effective Visible-Light-Initiated Self-Healing Properties“. Polymers 13, Nr. 24 (13.12.2021): 4360. http://dx.doi.org/10.3390/polym13244360.
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Smart hydrogels are typical functional soft materials, but their functional and mechanical properties are compromised upon micro- or macro-mechanical damage. In contrast, hydrogels with self-healing properties overcome this limitation. Herein, a dual dynamic bind, cross-linked, self-healing protein hydrogel is prepared, based on Schiff base bonds and diselenide bonds. The Schiff base bond is a typical dynamic covalent bond and the diselenide bond is an emerging dynamic covalent bond with a visible light response, which gives the resulting hydrogel a dual response in visible light and a desirable self-healing ability. The diselenide-containing protein hydrogels were biocompatible due to the fact that their main component was protein. In addition, the hydrogels loaded with glucose oxidase (GOx) could be transformed into sols in glucose solution due to the sensitive response of the diselenide bonds to the generated hydrogen peroxide (H2O2) by enzymatic catalysis. This work demonstrated a diselenide-containing protein hydrogel that could efficiently self-heal up to nearly 100% without compromising their mechanical properties under visible light at room temperature.
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Dunn, Megan F., Tao Wei, Ronald N. Zuckermann und Timothy F. Scott. „Aqueous dynamic covalent assembly of molecular ladders and grids bearing boronate ester rungs“. Polymer Chemistry 10, Nr. 18 (2019): 2337–43. http://dx.doi.org/10.1039/c8py01705k.
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Mimicking the self-assembly of nucleic acid sequences into double-stranded molecular ladders that incorporate hydrogen bond-based rungs, dynamic covalent interactions enable the fabrication of molecular ladder and grid structures with covalent bond-based rungs.
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Karatrantos, Argyrios V., Olivier Couture, Channya Hesse und Daniel F. Schmidt. „Molecular Simulation of Covalent Adaptable Networks and Vitrimers: A Review“. Polymers 16, Nr. 10 (11.05.2024): 1373. http://dx.doi.org/10.3390/polym16101373.
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Covalent adaptable networks and vitrimers are novel polymers with dynamic reversible bond exchange reactions for crosslinks, enabling them to modulate their properties between those of thermoplastics and thermosets. They have been gathering interest as materials for their recycling and self-healing properties. In this review, we discuss different molecular simulation efforts that have been used over the last decade to investigate and understand the nanoscale and molecular behaviors of covalent adaptable networks and vitrimers. In particular, molecular dynamics, Monte Carlo, and a hybrid of molecular dynamics and Monte Carlo approaches have been used to model the dynamic bond exchange reaction, which is the main mechanism of interest since it controls both the mechanical and rheological behaviors. The molecular simulation techniques presented yield sufficient results to investigate the structure and dynamics as well as the mechanical and rheological responses of such dynamic networks. The benefits of each method have been highlighted. The use of other tools such as theoretical models and machine learning has been included. We noticed, amongst the most prominent results, that stress relaxes as the bond exchange reaction happens, and that at temperatures higher than the glass transition temperature, the self-healing properties are better since more bond BERs are observed. The lifetime of dynamic covalent crosslinks follows, at moderate to high temperatures, an Arrhenius-like temperature dependence. We note the modeling of certain properties like the melt viscosity with glass transition temperature and the topology freezing transition temperature according to a behavior ruled by either the Williams–Landel–Ferry equation or the Arrhenius equation. Discrepancies between the behavior in dissociative and associative covalent adaptable networks are discussed. We conclude by stating which material parameters and atomistic factors, at the nanoscale, have not yet been taken into account and are lacking in the current literature.
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Theodosis-Nobelos, Panagiotis, Despina Charalambous, Charalampos Triantis und Maria Rikkou-Kalourkoti. „Drug Conjugates Using Different Dynamic Covalent Bonds and their Application in Cancer Therapy“. Current Drug Delivery 17, Nr. 7 (15.09.2020): 542–57. http://dx.doi.org/10.2174/1567201817999200508092141.
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Polymer-drug conjugates are polymers with drug molecules chemically attached to polymer side chains through either a weak (degradable bond) or a dynamic covalent bond. These systems are known as pro-drugs in the inactive form when passing into the blood circulation system. When the prodrug reaches the target organ, tissue or cell, the drug is activated by cleavage of the bond between the drug and polymer, under certain conditions existing in the target organ. The advantages of polymer-drug conjugates compared to other controlled-release carriers and conventional pharmaceutical formulations are the increased drug loading capacity, prolonged <i>in vivo</i> circulation time, enhanced intercellular uptake, better-controlled release, improved therapeutic efficacy, and enhanced permeability and retention effect. The aim of the present review is the investigation of polymer-drug conjugates bearing anti-cancer drugs. The polymer, through its side chains, is linked to the anti-cancer drugs <i>via</i> dynamic covalent bonds, such as hydrazone/imine bonds, disulfide bonds, and boronate esters. These dynamic covalent bonds are cleaved in conditions existing only in cancer cells and not in healthy ones. Thus, ensuring the selective release of drug to the targeted tissue, reducing in this way, the frequent side effects of chemotherapy, leading to a more targeted application, despite the nature of the applied polymer, possessing the ability to aim tumors selectively <i>via</i> incorporation of a relative ligand.
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Hu, Yong, Jin Li, Yu Zhou, Jie Shi, Guopeng Li, Hang Song, Yang Yang, Jia Shi und Wenjing Hong. „Single Dynamic Covalent Bond Tailored Responsive Molecular Junctions“. Angewandte Chemie 133, Nr. 38 (11.08.2021): 21040–46. http://dx.doi.org/10.1002/ange.202106666.
Der volle Inhalt der QuelleDissertationen zum Thema "Dynamic covalent bond"
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Garavini, Valentina. „Native chemical ligation for the design of dynamic covalent peptides“. Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAF053/document.
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Utiliser la liaison peptidique dans des systèmes dynamiques covalents est très difficile en raison de sa stabilité intrinsèque. Dans ce travail, une nouvelle méthodologie pour échanger fragments peptidiques dans des conditions biocompatibles est décrite. Légères modifications du groupe amine d'un résidu de cystéine en peptides modèle permettent l'activation spécifique de cette jonction peptidique pour des réactions d'échange covalent. Grâce à un mécanisme de ligation chimique native réversible, fragments peptidiques sont échangés en solution aqueuse à pH physiologique et en présence de dithiothréitol (DTT), avec des demi-temps d'équilibration de 2 à 10 heures. Différentes possibles applications biologiques de cette nouvelle réaction réversible à peptides et glycopeptides sont aussi proposéesThe possibility to use the peptide bond in dynamic covalent systems is very challenging because of its intrinsic stability. In this work, a novel methodology to exchange peptide fragments in bio-compatible conditions is described. The introduction of small modifications to the N-terminus of a cysteine residue in model peptides allows for the specific activation of that peptide bond for exchange reactions. Through a reverse Native Chemical Ligation (NCL) mechanism, peptide fragments were scrambled in aqueous solution at physiological pH and in the presence of dithiothreitol (DTT), with half-times of equilibration in the 2-10 h range. Additionally, possible biological applications of this new reversible reaction to both peptides and glycopeptides are proposed
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Zanirati, Stefano. „Synthesis and nanostructuring modulations of self-assembled dynamic covalent amphiphiles“. Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAF039.
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Contrôler les forces supramoléculaires et chirales a toujours été un défi pour la communauté scientifique. Dynablocks sont amphiphile basés sur des liaisons covalentes réversibles (imine) qui, dans l’eau, s’auto–assemblent en mésophases. Avec un nouveaux aldéhydes chargés et avec divers types d'amines (pKa et chaînes de PEG variables) dynablocks chargées ont été utilisés pour ajuster les surfaces micellaires (inversion noyau/coquille). Nous avons également étudié les propriétésd'auto-réplication (autopoiesis) et leur intérêt pour les premiers réplicateurs de la Terre prébiotique. Dynablocks non chargés ont plutôt été utilisés pour l'étude des structures à haute concentration et pour l’amplification chirale. Dans ce dernier,peptides amphiphiles dynablocks agissaient comme gelators avec une matrice formée d’un réseau 3D entrelacé. Une torsion supramoléculaire a été observée et une amplification chirale au niveau de la morphologie des structures a pu être détectée par AFM et TEMTaking the control over supramolecular and chiral forces has always been a challenge for the scientific community. Dynablocks are amphiphiles based on reversible imine covalent bond that, in water, self-assemble in mesophases. With a new charged aldehyde, charged dynablocks were used to tune the surface of the assemblies directing the charged heads inward or outward, changing the PEG units and the pKa of the amines. Moreover, we continued the study on focusing the interest on self-replicating properties (autopoiesis), topic that provides insights for the first replicators that could have appeared in the prebiotic Earth. Non-charged dynablocks were instead employed for the study of structures in high concentration and for chiral amplification. In this latter, peptide amphiphilic dynablocks acted as gelators with a typical 3D intertwined network matrix. A supramolecular twist was observed and a chiral amplification in the structures morphologies was detected in AFM and TEM pictures
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Lutz, Eric. „Dynamic covalent surfactants for the controlled release of bioactive volatiles“. Thesis, Strasbourg, 2014. http://www.theses.fr/2014STRAF041/document.
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Ce projet consiste à fabriquer et à étudier des micelles à la fois biocompatibles et capables de relarguer des molécules volatiles bioactives à partir d’une solution aqueuse sous l’influence de stimuli extérieurs tel que le pH, la température ou la concentration. Pour atteindre ce but, nous avons étudiés un nouveau type d’objets micellaires qui sont formés par l’auto-assemblage d’amphiphiles covalents dynamiques (DCAs), des surfactants peu onéreux formés de l’association moléculaire réversible d’un bloc hydrophile et d’un bloc hydrophobe. Ces systèmes peuvent relarger une large gamme de fragrances à partir d’une solution, que cela soit à partir du coeur hydrophobe de la micelle ou alors à partir de l’amphiphile (profragrance). Ils ont aussi été capables de stabiliser en solution des aldéhydes sensibles à l’hydrolyseThis project relies on the simple design and the study of biocompatible responsive micelles, capable of releasing a hydrophobic bioactive volatile from an aqueous solution and that, depending on the modulation of external factors such as pH, temperature, and concentration. To reach this goal, we have taken advantages of a new kind of micellar objects that are formed by the efficient self-assembly of biodegradable Dynamic Covalent Amphiphiles (DCAs), low cost surfactants that are made by the reversible molecular association of one hydrophilic and one hydrophobic block. These systems can release a broad variety of fragrances from solution, both from the hydrophobic micellar core or directly from the amphiphile (profragrance). It also proved able to stabilise some sensitive aldehydes in solution
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Beaugendre, Maxime. „Etude et développement de latex vitrimères obtenus par PISA“. Electronic Thesis or Diss., Université Paris sciences et lettres, 2023. http://www.theses.fr/2023UPSLS003.
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La chimie covalente dynamique est un outil efficace pour développer des matériaux polymères qui répondent aux enjeux écologiques actuels (recyclabilité, réparabilité). Nous avons implémenté la liaison imine dans des films de latex synthétisés selon les concepts PISA (Polymerization-Induced Self-Assembly). Les particules de latex sont constituées d’une écorce hydrophile de PMAA et d’un cœur hydrophobe de MMA, BA et d’un monomère porteur d’une fonction pendante benzaldéhyde (B). La réticulation imine des latex est réalisée à l’étape de séchage par ajout d’une diamine. L’étude de ces films montrent que leurs propriétés mécaniques et vitrimères sont limitées par (i) une réticulation permanente qui apparait au cours de la polymérisation en raison de réactions de transfert du monomère BA activées par le monomère B et (ii) la percolation des écorces de PMAA, polaires et rigides, qui restreignent la coalescence des particules. Pour pallier ces difficultés, le monomère BA a été remplacé par le monomère EHMA. Les films obtenus ont des propriétés mécaniques comparables au système initial et sont solubles. Dans une autre étude, le macro-agent RAFT ionique PMAA a été remplacé par un agent non ionique, le PNAM. Les propriétés thermo-mécaniques et la remise en forme à chaud de ces films sont nettement améliorées, démontrant ainsi que la nature ionique de l’écorce est un frein à l’obtention de revêtements performants et durables. Enfin, nous avons montré l’efficacité de liens uréthane vinylogue pour leur apporter aux films une résistance au fluage (double réticulation), notamment aux hautes températures quand les réactions d’échange des imines sont rapidesDynamic covalent chemistry is an efficient tool to develop polymeric materials that respond to current ecological issues (recyclability, repairability). We have implemented imine bonds in latex films synthesized according to PISA concepts (Polymerization-Induced Self-Assembly). The latex particles consist of a hydrophilic shell of PMAA and a hydrophobic core of MMA, BA and a monomer bearing a benzaldehyde pendant function (B). The imine cross-linking of the latexes is achieved at the drying stage by adding a diamine. The characterization of these films shows that their mechanical and vitrimeric properties are limited by (i) a permanent cross-linking which appears during the polymerization due to transfer reactions of the BA monomer activated by the B monomer and (ii) the percolation of the polar and rigid PMAA shells, which restrict particules coalescence. To overcome these issues, the BA monomer was replaced by the EHMA monomer. The new films have mechanical properties comparable to the initial system and are soluble. In another study, the ionic RAFT macro-agent PMAA was replaced by a non-ionic agent, PNAM. The thermo-mechanical properties and the reprocessing of these films are significantly improved, thus demonstrating that the ionic nature of the shell is a hindrance to obtain efficient and durable coatings. Finally, we have shown the efficiency of vinylogous urethane bonds to provide creep resistance to the films (double cross-linking), especially at high temperatures when the imine exchange reactions are fast
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Lewandowska, Urszula. „Spontaneous small molecule migration via reversible Michael reactions“. Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/10635.
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Small molecule walkers developed to date take advantage of the reversibility of dynamic covalent bond formation to transport molecular fragments along molecular tracks using both diffusion processes and ratchet mechanisms. However, external intervention (the addition of chemical reagents and/or irradiation with light) is required to mediate each step taken by the walker unit in systems reported so far. In this Thesis, the first synthetic small molecule able to walk back-and-forth upon an oligoethylenimine track without external intervention via intramolecular Michael and retro- Michael reactions is described. The 1D random walk is highly processive and exchange takes place between adjacent amine groups in a stepwise fashion. The walker is used to perform a simple task: quenching of the fluorescence of an anthracene group situated at one end of the track as a result of the walking progress. In the presence of excess of base, the molecule preferentially ‘walks’ towards the favoured final foothold of tracks of increasing length and it is possible to monitor the population of all or a few positional isomers over time. In each case the molar fraction of walkers reaching the final foothold is determined quantitatively by 1H NMR. Control over the rate of exchange is achieved by varying the amount of base added. The dynamic migration of a small molecule upon the track is a diffusion process limited to one dimension and as such can in principle be described using the one dimensional random walk. Chapter I identifies a set of fundamental walker characteristics and includes an overview of the DNA-based and small molecule transporting systems published to date. Chapter II describes the inspiration for this work and model studies which lay the groundwork for the research presented in this thesis. The initial track architecture and optimisation of reaction conditions are demonstrated using a simple model compound which then led to the development and a detailed investigation of a first synthetic small molecule able to walk upon an oligoethylenimine track without external intervention. Chapter III presents a modified synthetic route towards the desired walker-track architectures and a comprehensive investigation of the dynamic properties of a series of tracks of increasing length upon which the walker migrates in a unidirectional fashion. The Outlook contains closing remarks about the scope and significance of the presented work as well as ideas for the design of novel small-molecule walkers, some of which are well under way in the laboratory. Chapter II (with the exception of model studies included at the beginning of the chapter) is presented in the form of article that has recently been published. No attempt has been made to re-write this work out of context other than merging content of the article with the supplementary information published together with the article. Chapter II is reproduced in the Appendix in its published format.
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Engelhart, Aaron Edward. „Nucleic acid assembly, polymerization, and ligand binding“. Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45979.
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In the past 30 years, the discovery of capabilities of nucleic acids far beyond their well-known information-bearing capacity has profoundly influenced our understanding of these polymers. The discovery by the Cech and Altman labs that nucleic acids could perform catalytic functions, coupled with the Gold and Szostak groups’ demonstration of the de novo evolution of nucleic acids that bind arbitrary ligands, has resulted in a proliferation of newfound roles for these molecules. Nucleic acids have found utility in both engineered systems, such as aptamer therapeutics, as well as in newly appreciated roles in extant organisms, such as riboswitches. As a result of these discoveries, many have pondered the potential importance of the dual (catalytic and informational) roles of nucleic acids in early evolution. A high-yielding synthetic route for the nonenzymatic polymerization of nucleic acids, based on the aqueous self-assembly of their components, would provide a powerful tool in nucleic acid chemistry, with potential utility in prebiotic and contemporary nucleic acid systems alike – however, such a route remains elusive. In this thesis, I describe several steps towards such a synthetic route. In these systems, a nucleic-acid binding ligand drives the assembly of short DNA and RNA duplexes, promoting the production of long nucleic acid polymers, while suppressing the production of short, cyclic species. Additionally, the use of a reversible covalent linkage allows for the production of long polymers, as well as the incorporation of previously cyclized products into these polymers. I also report several explorations of novel base pairings, nucleic acid-ligand interactions, and nucleic acid-ion interactions that have informed our studies of self-assembling nucleic acid systems.
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Hammer, Larissa. „Design and Characterization of Double Dynamic Networks Based on Boronic Ester and Imine Dynamic Covalent Bonds“. Electronic Thesis or Diss., Université Paris sciences et lettres, 2021. http://www.theses.fr/2021UPSLS077.
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Les réseaux dynamiques doubles (RDD) sont des matériaux polymères qui combinent deux agents de réticulation distincts (ou plus) dans un seul système. En couplant différentes stratégies de réticulation, des matériaux sur mesure peuvent être conçus. Cette thèse explore la mise en œuvre du concept de vitrimère dans les RDD. Des élastomères vitrimères constitués de deux réseaux dynamiques interpénétrés reposant respectivement sur la métathèse des esters boroniques et sur l’échange imine-aldéhyde ont été conçus dans ce but. Les deux réactions procèdent selon un mécanisme dégénéré et sont orthogonales l’une à l’autre. Par l’utilisation de deux réticulations dynamiques différentes, deux dynamiques distinctes sont établies dans le réseau. Pour obtenir et évaluer le RDD final, les sous-réseaux respectifs ont été synthétisés au préalable et caractérisés en tant que réseaux simples. Les caractéristiques des réseaux simples ont été adaptés individuellement pour répondre à leurs besoins spécifiques en termes de comportement dynamique, de mise en œuvre et de stabilité dimensionnelle. Ces propriétés ont été ajustées en modifiant la masse molaire des précurseurs thermoplastiques, leur taux de fonctionnalité, leur densité de réticulation ou le temps de vie des liens dynamiques. Les deux réseaux ont été réunis avec succès en un RDD. Une étude comparative a permis de comprendre comment les sous-réseaux individuels contribuent aux propriétés du RDD, et si des effets synergiques sont obtenus. Dans les faits, la structure interpénétrée du vitrimère RDD permet d’augmenter à la fois la résistance au fluage et l’allongement à la rupture, ce qui est particulièrement difficile à réaliser, mais hautement souhaitable pour la plupart des élastomères. Au-delà, les matériaux obtenus ont montré un très fort potentiel pour le recyclage mécanique et chimiqueDual dynamic networks (DDNs) are polymeric materials that combine two (or more) distinct crosslinkers in one system. By coupling different crosslinking strategies, precisely tailored materials can be designed. This thesis explores the implementation of the vitrimer concept into DDNs. Elastomeric vitrimers consisting of two interpenetrated dynamic networks that rely on boronic ester metathesis and on imine-aldehyde exchange, respectively, were designed to this aim. Both reactions proceed via a degenerate mechanism and are orthogonal to each other. By the engagement of two types of dynamic covalent crosslinks, two distinct dynamics are established in each subnetwork. To obtain and evaluate the final DDN, the respective subnetworks were synthesized beforehand, and characterized as single networks. The characteristics of the single networks were tailored individually to fulfill their specific needs in terms of dynamic behavior, processability and dimensional stability. These properties were adjusted by changing the molar mass of the thermoplastic precursors, their degree of functionality, their crosslinking density, or the lifetime of the dynamic bonds. The two networks were successfully united into a DDN. In a comparative study, insights were obtained how the individual subnetworks contribute to the DDN’s properties, and whether synergetic effects arise. In fact, the interpenetrated nature of the vitrimer DDN allows increasing at the time creep resistance and elongation at break, which is really challenging to achieve, yet highly desirable for most elastomers. Over and beyond, the obtained materials show great potential for mechanical and chemical recycling
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Roettger, Max. „Associative exchange reactions of boron or nitrogen containing bonds and design of vitrimers“. Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066608/document.
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Dans l'optique de préparer des vitrimères à partir des thermoplastiques communément utilisés, tels le PMMA et le PS, des réactions d'échange dynamiques reposant les liens imine et esters boroniques ont été étudiées. Des paramètres importants comme la constante de dissociation de certaines molécules, la constante de vitesse et l'énergie d'activation ont été mesurées. Des monomères porteurs de liaisons échangeables ont été synthétisés et polymérisés. Des vitrimères, avec des liaisons C-C dans la chaine principale, ont été créés par différentes stratégies (PMMA et PS). Ces matériaux sont réticulés et insolubles avec un plateau caoutchouteux mais également façonnables et recyclables par moulage par compression ou par injection. Ces vitrimères peuvent relaxer les contraintes et couler à une température supérieure à celle de leur transition vitreuse. Des viscosités de 105-107 Pa.s ont été estimées pour les vitrimères PMMA reposant sur la chimie des esters boroniques. Des tests de traction montrent que leurs propriétés mécaniques de ces matériaux ne subissent pas de baisse significative après plusieurs cycles de recyclage par moulage par injection. Même après plusieurs cycles de moulage, les vitrimères basés sur la chimie des esters boroniques peuvent être complètement dé-réticulés, signe de leur stabilité à haute température lors du moulage. Ces vitrimères ont une résistance supérieure dans les conditions "d'environmental stress cracking" comme des réseaux polymères conventionnelsWith the aim to generate vitrimers from commonly used thermoplastics with carbon-carbon based backbones, such as PMMA and PS, dynamic covalent exchange reactions relying on Schiff’s bases and boronic esters were investigated. Two different approaches, i.e. crosslinking in solution or in extrusion, were used. These materials are processable via extrusion, compression and injection molding like their thermoplastic counterparts. The crosslinked nature of these systems was confirmed by solubility tests and DMA. Rheological measurements revealed the vitrimers ability to flow and viscosities between 105-107 Pa.s for boronic ester based PMMA vitrimers were measured. Consecutive tensile testing/reprocessing sequences proved the full recyclability of these vitrimers, and selective cleavage of the vitrimer networks followed by precise chemical analyses showed the thermal and chemical stabilities of vitrimers relying on boronic ester bonds. The stress cracking resistance of these vitrimers was significantly higher than that of parent thermoplastics, as can be expected for crosslinked systems
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Bracchi, Michael Edward. „Exploring the orthogonal dynamic covalent imine and disulfide bonds in polymer systems“. Thesis, University of Newcastle upon Tyne, 2017. http://hdl.handle.net/10443/3989.
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In the field of supramolecular systems chemistry the desire of researchers to endow functional macromolecular systems with orthogonal stimuli-responsiveness has fueled interest in the incorporation of multiple orthogonal dynamic covalent chemistries within a single chemical system. Dynamic covalent chemistry involves reversible bond forming processes which can be harnessed in the development of dynamic supramolecular systems providing a mechanism for structural reconfiguration of system components in response to external stimuli. Despite the inspiring gamut of recently brandished studies, there is a still a call on the resourcefulness of chemists to expand the capacity for the introduction of multi-faceted, orthogonal, stimuli-responsive behaviors. Herein, a critical analysis of recently reported landmark studies has been undertaken wherein the utility of orthogonal dynamic covalent bonding motifs in functional systems is highlighted. Furthering the concepts of orthogonality with respect to dynamic covalent chemistry presented therein, a small molecule ‘model system’ was developed with which the orthogonality of imine and disulfide dynamic covalent bonds was demonstrated by its operation. A key focus of this preliminary work was the orthogonal bond forming and bond breaking processes of imine and disulfide dynamic covalent bonds. Upon the establishment of conditions necessary to exploit the orthogonal utility of imine and disulfide bonds, the incorporation of aldehydes, amines and thiols within acrylamide-based copolymers as pendant functional groups was achieved. These pre-formed functional polymer building blocks were shown to undergo stimuli-responsive intermolecular cross-linking in aqueous media yielding disulfide or imine cross-linked nanoparticles or hydrogels. The scope and utility of imine and disulfide bonds in the formation of these nanostructured materials is compared and contrasted. It is reasoned that expanding understanding and availability of dynamic covalent bonding motifs will facilitate evolution of systems of greater sophistication capable of embodying increasingly information-rich processes.
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Roettger, Max. „Associative exchange reactions of boron or nitrogen containing bonds and design of vitrimers“. Electronic Thesis or Diss., Paris 6, 2016. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2016PA066608.pdf.
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Dans l'optique de préparer des vitrimères à partir des thermoplastiques communément utilisés, tels le PMMA et le PS, des réactions d'échange dynamiques reposant les liens imine et esters boroniques ont été étudiées. Des paramètres importants comme la constante de dissociation de certaines molécules, la constante de vitesse et l'énergie d'activation ont été mesurées. Des monomères porteurs de liaisons échangeables ont été synthétisés et polymérisés. Des vitrimères, avec des liaisons C-C dans la chaine principale, ont été créés par différentes stratégies (PMMA et PS). Ces matériaux sont réticulés et insolubles avec un plateau caoutchouteux mais également façonnables et recyclables par moulage par compression ou par injection. Ces vitrimères peuvent relaxer les contraintes et couler à une température supérieure à celle de leur transition vitreuse. Des viscosités de 105-107 Pa.s ont été estimées pour les vitrimères PMMA reposant sur la chimie des esters boroniques. Des tests de traction montrent que leurs propriétés mécaniques de ces matériaux ne subissent pas de baisse significative après plusieurs cycles de recyclage par moulage par injection. Même après plusieurs cycles de moulage, les vitrimères basés sur la chimie des esters boroniques peuvent être complètement dé-réticulés, signe de leur stabilité à haute température lors du moulage. Ces vitrimères ont une résistance supérieure dans les conditions "d'environmental stress cracking" comme des réseaux polymères conventionnelsWith the aim to generate vitrimers from commonly used thermoplastics with carbon-carbon based backbones, such as PMMA and PS, dynamic covalent exchange reactions relying on Schiff’s bases and boronic esters were investigated. Two different approaches, i.e. crosslinking in solution or in extrusion, were used. These materials are processable via extrusion, compression and injection molding like their thermoplastic counterparts. The crosslinked nature of these systems was confirmed by solubility tests and DMA. Rheological measurements revealed the vitrimers ability to flow and viscosities between 105-107 Pa.s for boronic ester based PMMA vitrimers were measured. Consecutive tensile testing/reprocessing sequences proved the full recyclability of these vitrimers, and selective cleavage of the vitrimer networks followed by precise chemical analyses showed the thermal and chemical stabilities of vitrimers relying on boronic ester bonds. The stress cracking resistance of these vitrimers was significantly higher than that of parent thermoplastics, as can be expected for crosslinked systems
Bücher zum Thema "Dynamic covalent bond"
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Dynamic Covalent Chemistry: Principles, Reactions, and Applications. Wiley & Sons, Limited, John, 2017.
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Zhang, Wei, und Yinghua Jin. Dynamic Covalent Chemistry: Principles, Reactions, and Applications. Wiley & Sons, Incorporated, John, 2017.
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Zhang, Wei, und Yinghua Jin. Dynamic Covalent Chemistry: Principles, Reactions, and Applications. Wiley & Sons, Limited, John, 2017.
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Zhang, Wei, und Yinghua Jin. Dynamic Covalent Chemistry: Principles, Reactions, and Applications. Wiley & Sons, Incorporated, John, 2017.
Den vollen Inhalt der Quelle findenBuchteile zum Thema "Dynamic covalent bond"
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Wang, Guoshuai, Guancheng Jiang, Jun Yang, Yinbo He und Yue Fu. „Synthesis of a Novel pH-Responsive Emulsifier Based on Dynamic Covalent Bond and Its Application in Reversible Oil-Based Drilling Fluids“. In Lecture Notes in Civil Engineering, 313–23. Singapore: Springer Nature Singapore, 2022. http://dx.doi.org/10.1007/978-981-19-3983-9_27.
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Wang, Sheng, Songqi Ma und Jin Zhu. „Readily Recyclable Thermosets Based on Dynamic Covalent Bonds“. In Reactive and Functional Polymers Volume Four, 159–206. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-52052-6_7.
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Yang, Yang, Yen Wei und Yan Ji. „New Properties of Epoxy Vitrimers Brought by Dynamic Covalent Bonds“. In Functional and Sustainable Epoxy Vitrimers, 41–58. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-15082-1_5.
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Otsuka, Hideyuki, Yoshifumi Amamoto, Yasuhiro Matsuda, Takeshi Maeda und Atsushi Takahara. „Synthesis and Reaction of Well-defined Copolymers with Thermally Exchangeable Dynamic Covalent Bonds in the Side Chains“. In ACS Symposium Series, 319–29. Washington, DC: American Chemical Society, 2009. http://dx.doi.org/10.1021/bk-2009-1024.ch021.
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Kilic, Ruveyda, und Amitav Sanyal. „Self-Healing Hydrogels Based on Reversible Covalent Linkages: A Survey of Dynamic Chemical Bonds in Network Formation“. In Self-Healing and Self-Recovering Hydrogels, 243–94. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/12_2019_59.
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Kojima, Seiji. „Dynamic specific heat and glass transitions“. In New Advances in Calorimetry [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.1002805.
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The dynamical properties such as fragility, and non-Debye behavior of glass-forming materials have been studied by the frequency-dependent dynamic specific heat. Kubo’s formula on the fluctuation-dissipation theorem defines dynamic specific heat using the correlation function of enthalpy fluctuations. Dynamic specific heat is important for analyzing and understanding various relaxation processes. The dielectric relaxation is caused only by polar atomic motions, while the enthalpy relaxation is caused by total degrees of freedom of atomic motions. This chapter introduces two experimental methods to measure dynamic specific heat: (1) temperature-modulated differential scanning calorimetry (MDSC) and (2) photoacoustic spectroscopy. The experimental results of the dynamical properties of glass transitions in oxide glasses with covalent bond network structures and hydrogen-bonded glass-forming materials are reviewed.
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Baer, Tomas, und William L. Hase. „The Dissociation of Small and Large Clusters“. In Unimolecular Reaction Dynamics. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195074949.003.0012.
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Clusters are aggregates of loosely bonded molecules, in which each of the units retains the structure that it has as a free molecule. Because of the weak interactions among the molecules, clusters are stable only in cold environments such as are found in molecular beams. The weak intermolecular bonds provide an interesting testing ground for theories of intramolecular vibrational energy redistribution (IVR) and thus for theories of unimolecular dissociation. In addition, clusters constitute the bridge between the gas and liquid phases. Such phenomena as solvation, heat capacity, and phase transitions, which are ill defined for small clusters, become progressively more precise as the cluster size increases. Typical binding energies for neutral clusters are below 1000 cm-1. Ionic clusters, because of their ion-induced dipole forces, tend to be more strongly bonded with binding energies in excess of 5000 cm-1. Not infrequently, a neutral van der Waals dimer such as Ar2 with its binding energy of about 100 cm-1 (Tang and Toennies, 1986) changes its character upon ionization. The equilibrium bond distance is reduced from about 4 Å to 2.43 Å (Huber and Herzberg, 1979; Ma et al., 1993) and the binding energy increases to 10,000 cm-1 (Norwood et al., 1989; Furuya and Kimura, 1992). Clearly, the Ar2+ ion no longer meets our definition of a dimer. Rather, the neutral dimer is converted into a stable ion with a bond order of 1/2. A molecule that is frequently referred to as a cluster is C60. However, it is held together neither by weak bonds, nor is it composed of a collection of monomers. It is thus better classified as a large covalently bonded molecule. Table 10.1 summarizes some binding energies for various classes of dimers. When clusters comprise several loosely bound molecules, the atoms within each molecule are held together by strong bonds while the molecules themselves are attracted to neighboring molecules by weak bonds. This discrepancy in forces translates into disparities in the respective vibrational frequencies.
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Lu, Fei, und Yanan Gao. „Covalent Organic Frameworks for Ion Conduction“. In Covalent Organic Frameworks [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.108291.
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Covalent organic frameworks (COFs) are an emerging class of crystalline porous materials constructed by the precise reticulation of organic building blocks through dynamic covalent bonds. Due to their facile preparation, easy modulation and functionalization, COFs have been considered as a powerful platform for engineering molecular devices in various fields, such as catalysis, energy storage and conversion, sensing, and bioengineering. Particularly, the highly ordered pores in the backbones with controlled pore size, topology, and interface property provide ideal pathways for the long-term ion conduction. Herein, we summarized the latest progress of COFs as solid ion conductors in energy devices, especially lithium-based batteries and fuel cells. The design strategies and performance in terms of transporting lithium ions, protons, and hydroxide anions are systematically illustrated. Finally, the current challenges and future research directions on COFs in energy devices are proposed, laying the groundwork for greater achievements for this emerging material.
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Jan Veldman, Robert, Eve-Isabelle Pécheur, Sven C. D. van IJzendoorn, Jan Willem Kok und Dick Hoekstra. „Cell lipids: from isolation to functional dynamics“. In Essential Cell Biology, 317–48. Oxford University PressOxford, 1992. http://dx.doi.org/10.1093/oso/9780199638314.003.0010.
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Abstract The boundary of every cell as well as that of intracellular compartments, including intracellular transport vesicles, is provided by a membrane, the major components of which are proteins and lipids. Membrane lipids are amphipathic molecules that consist of a polar head group and usually two non-polar hydro carbon chains. The hydrocarbon chains are covalently attached to a lipid back bone structure such as glycerol (in the case of phospholipids and glycoglycero-lipids) or sphingosine (in the case of(glyco)sphingolipids) via ester, ether, amide, or C-C bonds. In biological membranes, a variety of lipid classes can be distinguished, the major lipids belonging to the class of the phospholipids. Although a minor class, the more complex (glyco)sphingolipids are biologically highly relevant (1).
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O’Brien, Ronan, und John E. Ladbury. „Isothermal titration calorimetry of biomolecules“. In Protein-Ligand Interactions: hydrodynamics and calorimetry, 263–86. Oxford University PressOxford, 2000. http://dx.doi.org/10.1093/oso/9780199637492.003.0010.
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Abstract One of the primary goals of contemporary molecular biology is to gain an understanding of the molecular basis of specificity and recognition phenomena, between proteins and ligands. Proteins can specifically recognize, and reversibly bind to small molecular weight target molecules, other macromolecules (e.g. proteins, nucleic acids) and to macromolecular assemblies. Characterization of these interactions necessarily involves investigation of the inter-relationship between function, structure (including dynamics), kinetics, and energetics (i.e. thermodynamics) of a system under defined physico-chemical conditions. In this chapter we focus on the determination of the latter of these quantities. The measurement of thermodynamic parameters is important because all reversible biomolecular interactions involve a redistribution of non-covalent bonds. The most experimentally accessible of the thermodynamic quantities occurring on a protein going from the free (unbound) to the bound state is the heat (enthalpy) uptake or release.
Konferenzberichte zum Thema "Dynamic covalent bond"
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Cui, Fangda, I. Joga Rao und Swapnil Moon. „Modeling and Simulation of Structurally Dynamic Crystallizable Shape Memory Polymers With Light-Induced Bond Exchange Reaction“. In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-50247.
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Shape Memory polymers (SMPs) is a novel class of smart polymeric materials that have been attracted tremendous scientific interest within the last decades. SMPs have the ability to “remember” their original shape even after undergoing significant deformation into a temporary shape. For most first generation of SMPs, the shape memory effect was accomplished by a thermally induced process, triggered in many different ways, such as heating/cooling, electromagnetic field and infrared light. The transient shape in thermally induced SMPs is due to a glassy phase or a semi-crystalline phase. The thermally induced SMPs which temporary shape is fixed through crystallization is called crystallizable shape memory polymers (CSMPs). For traditional CSMPs, their original shape is predefined and is not able to be reprogrammed. This limits the applications of the CSMPs. Recently, a new class of CSMPs has been developed. These materials can perform a typical thermally induced shape memory cycle, but their original shape can be reprogrammed through exposing to UV light. The shape reprogramming effect is governed by light induced covalent bonds exchange reaction, while the shape memory effect-as typical CSMPs-is due to solid-phase crystallization. In this work, we focus on modeling the mechanical behavior of this new class of structurally dynamic CSMPs. The framework used in developing the model is built upon the theory of multiple natural configurations[1]. The model has been applied to solve a specific boundary condition problem, namely uni-axial tension. Furthermore, we implement our model through Abaqus (commercial finite element package) subroutine UMAT to simulate 3D behavior of this attractive material.
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Kaur, Anureet, Meet Fefar, Travis Hohenberger, Keizo Akutagawa und James Busfield. „Recyclable Elastomers with Dynamic Covalent Bonds: How to Characterize a Reversible Cross-linked Networks“. In Technical Meeting of the Rubber Division, ACS. Akron, OH, USA: Rubber Division - American Chemical Society (ACS), 2023. http://dx.doi.org/10.52202/073692-0037.
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Park, Jungkyu, und Paul Pena. „Strain Effect on Thermal Transport in Carbon Nanotube-Graphene Junctions“. In ASME 2018 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/imece2018-87764.
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We employ molecular dynamics simulations to explore the effect of tensile strain on the thermal conductivity of carbon nanotube (CNT)-graphene junction structures. Two different types of CNT-graphene junctions are simulated; a perfect seamless junction between CNT and graphene with complete sp2 covalent bonds, and a CNT-graphene junction with mixed sp2/sp3 covalent bonds are studied. The most interesting phenomenon observed in the present research study is that the thermal conductivity of CNT-graphene junction structures increases with an increase in mechanical strain. For the case of CNT-graphene junction structure with pillar height of 50 nm and inter-pillar distance of 15 nm, the thermal conductivity is improved by 22.4% when 0.1 tensile strain is imposed. It is observed that the thermal conductivity improvement is enhanced when a larger graphene floor is placed between junctions since larger graphene floor allows larger deformation (larger tensile strain) in the junction. In addition, the thermal conductivity of CNT-graphene junction structures with pure sp2 bonds is observed to be higher than the thermal conductivity of CNT-graphene junction structures with mixed sp2/sp3 bonds regardless of the amount of tensile strain. The obtained results will contribute to the development of flexible electronics by providing a theoretical background on the thermal transport of three dimensional carbon nanostructures under deformation.
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BISHT, ANKITA, MUNETAKA KUBOTA und JOHN W. GILLESPIE, JR. „INVESTIGATING THE STRUCTURE OF CVD DEPOSITED AMINO SILANE ON SILICA SUBSTRATE VIA HIGH RESOLUTION CHARACTERIZATION METHODS“. In Proceedings for the American Society for Composites-Thirty Eighth Technical Conference. Destech Publications, Inc., 2023. http://dx.doi.org/10.12783/asc38/36690.
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The interphase between glass fiber and an epoxy matrix is a nanometer scale region that governs the load transfer between these constituents in composites. Traditionally, sizing packages are multifunctional and are applied to a fiber surface to protect fibers during handling and weaving while improving wettability and adhesion through covalent bonds between the fiber surface and the matrix. The most conventional sizing application approach is to use epoxy emulsion of silanes and surfactants; however, it leads to non-uniform coating (i.e., coverage and thickness) and a structure that is not well understood. An adhesion promoter like organofunctionalized silanes is often a part of these sizing packages, and they can help achieve desirable interphase properties. Molecular dynamics (MD) simulation studies have shown that these glass-silane-epoxy interphase strength and energy absorption is highly dependent on bond density, interphase-coating thickness, and strain rate (monolayer and full saturation of bond density resulted in highest interphase strength). To create such thin coatings, a chemical vapor deposition (CVD) approach may be well suited since it can achieve both a uniform silane coating and control of the thickness range as low as a monolayer. A CVD method developed previously to deposit the silane coating on glass fiber surfaces, has shown improvements to the interphase strengths, though the deposited coating morphology was not well understood nor optimized. Quantifying/characterizing the uniformity and thickness of coating on a fiber surface is an experimental challenge due to its cylindrical shape. Hence, a Si substrate with an oxide layer was used as a surrogate. The current study focuses on understanding the relationship between CVD process exposure time (5 min, 30 min and 60 min) and structure of the amino silane coating on Si substrate to develop an approach for depositing a uniform and thin coatings.
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Khadem, Masoud H., und Aaron P. Wemhoff. „Molecular Dynamics Predictions of Thermal Conductivity in Graphene for Phase Change Energy Storage Applications“. In ASME 2011 5th International Conference on Energy Sustainability. ASMEDC, 2011. http://dx.doi.org/10.1115/es2011-54158.
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Additives of highly-conducting nanoparticles such as graphene to a phase change material (PCM) improves PCM heat diffusion, which in turn produces better energy storage than pure PCM. Equilibrium Molecular Dynamics (EMD) simulations with Green-Kubo relations are used to predict the thermal conductivity of graphene sheets of various sizes and using different ensemble formulations. The Tersoff potential function has been implemented to model the covalent bonds between carbon atoms. The MD simulations predict an increase in thermal conductivity with graphene sheet size, and the predictions for the canonical (NVT) ensemble are consistently larger than those using the microcanonical (NVE) ensemble. The autocorrelation functions for the NVT simulations converge to zero for large sampling periods, which is not the case for NVE simulations.
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Torkelson, John M., Kailong Jin, Mohammed Bin Rusayyis, Lingqiao Li, Xi Chen und Sumeng Hu. „Transforming Rubber and Rubber Composite Thermosets into Themoplastics: Dynamic Covalent Bonds Enable Sustainable Recycling of Traditionally Non-Recyclable Polymer Materials“. In 200th Fall Technical Meeting of the Rubber Division, American Chemical Society 2021. Akron, Ohio, USA: Rubber Division, American Chemical Society, 2021. http://dx.doi.org/10.52202/064426-0042.
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Kikugawa, Gota, Taku Ohara, Tohru Kawaguchi, Ikuya Kinefuchi und Yoichiro Matsumoto. „Heat Transfer Characteristics Over the Interface of Alkanethiolate SAM and Alkane Liquid“. In ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ht2013-17607.
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In the present study, we performed molecular dynamics (MD) simulations of the self-assembled monolayer (SAM) interface system in order to investigate heat transfer characteristics over the SAM/alkane solvent interface. 1-dodecanethiol (C12H25S-) SAM chemisorbed on a gold substrate contacting with n-dodecane (C12H26) solvent was examined to compare the microscopic heat transfer mechanisms inside both the SAM and solvent phases. The direct nonequilibrium MD (NEMD) simulation, in which a constant heat flux across the SAM interface was imposed, was performed. The heat flux through the system was decomposed into the microscopic “building blocks”, i.e., the contribution of energy transfer associated with molecular motion and that of energy exchange by intermolecular (nonbonded) and intramolecular (covalent bond) interactions. Interestingly, inside the SAM layer, almost all of the energy is transferred by the intramolecular interaction along the alkyl chain. On the other hand, in the alkane liquid phase, the intramolecular and intermolecular interactions have comparable contributions to the total heat flux in spite of the same molecular structure and alkyl chain length as the SAM molecules. This difference in the heat transfer mechanism implies the relation between the ordering structure of alkyl chains and thermal conductivity in organic materials.
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Patel, Ajay M., und Anand Y. Joshi. „Vibration Analysis of Defective Double Walled Carbon Nanotube Based Nano Resonators“. In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-36454.
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The dynamic analysis of zigzag and armchair double walled carbon nanotubes (DWCNTs) with different boundary condition has been performed using atomistic finite element method. The double walled carbon nanotube is modeled considering it as a space frame structure similar to a three dimensional beam. The elastic properties of beam element are calculated by considering mechanical characteristics of covalent bonds between the carbon atoms in the hexagonal lattice. Spring elements are used to describe the interlayer interactions between the inner and outer tubes caused due to the van der Waals forces. The mass of each beam element is assumed as point mass at nodes coinciding with carbon atoms at inner and outer wall of DWCNT. It has been reported that multiple atomic vacancies are formed during the manufacturing process in DWCNT which tend to migrate leading to a change in the mechanical characteristics. Simulations have been carried out to visualize the behaviour of such defective DWCNTs subjected to different boundary conditions. The results clearly state that the dynamic characteristics are greatly influence by defects like vacancies in it. Comparison with the other experimental and theoretical studies exhibits good association which suggests that defective DWCNTs can further be explored for mass sensing. This investigation is helpful in applications involving ultra-high frequency nano resonators which contain one or other type of manufacturing defects in it.
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Dexheimer, S. L., D. M. Mittleman, R. W. Schoenlein, W. Vareka, X. D. Xiang, A. Zettl und C. V. Shank. „Ultrafast Dynamics of Solid C60“. In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/up.1992.fc24.
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We present the results of studies of the femtosecond dynamics of C60. This material forms a molecular crystal in the solid state, with relatively weak interactions between the covalently bound quasi-spherical C60 molecules. Thin film samples are prepared by thermal sublimation of purifed C60 powder. The samples are excited with optical pulses of ~12 fs duration in both the red and blue-green regions of the spectrum. Optical pulses centered at 620 nm are generated with a femtosecond laser system consisting of a colliding-pulse modelocked (CPM) dye laser with a copper vapor laser pumped dye amplifier that produces 50 fs pulses at an 8 kHz repetition rate. These pulses are chirped in an optical fiber and compressed using a sequence of diffraction gratings and prisms.1 To increase the energy of the compressed pulses, an additional copper vapor pumped dye amplifier is introduced prior to compression of the chirped pulse. Optical pulses at blue-green wavelengths (450 - 550 nm) are generated by using amplified CPM pulses to generate a femtosecond continuum in an ethylene glycol jet. The blue-green portion of the continuum is then re-amplified in an excimer laser pumped dye amplifier operating at a 400 Hz repetition rate, and is directly compressed using diffraction gratings and prisms.2 Time-resolved measurements of the differential transmittance are made using a pump-probe technique, and wavelength resolution is achieved by filtering the probe beam after transmission through the sample.
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Tan, Peng, Yanhui Feng, Liu Cui und Xinxin Zhang. „Heat Conduction Simulation in Double-Walled Carbon Nanotubes With Intertube Additional Atoms“. In ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/icnmm2014-22191.
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Heat conduction of double-walled carbon nanotubes (DWCNTs) with intertube additional carbon atoms was investigated using molecular dynamics (MD) simulation method. The interaction between carbon atoms was modeled using the Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) Potential. The related phonon density of states (DOS) was analyzed to help explain the heat conduction mechanism. It is indicated that intertube additional atoms of DWCNT will weaken the heat conduction along the axis. The addition of intertube atoms, which are covalently bonded to the inner and outer tubes, leads to localized structural deformation, which acting as a phonon barrier for ballistic heat transport. In addition, the intertube atoms become the new centers of phonon scattering and reduce VDOS. The deformation is the primary reason for the reduction of thermal conductivity. With the increasing number of additional atoms, the thermal conductivity of DWCNTs with atoms added at the same cross section drops sharply than that added along the tube axis, because the former addition causes more serious local deformation. Under the situation of addition at the cross section, if the number of intertube atoms is beyond a critical value, the distribution of these atoms seems to have little influences on the heat conduction in the tube.