70 results on '"Wengui Weng"'
Search Results
2. Tough self-reporting elastomer with NIR induced shape memory effect
- Author
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Liulin Yang, Pufan Ouyang, Yuan Chen, Shishuai Xiang, Yonghong Ruan, Wengui Weng, Xumin He, and Haiping Xia
- Subjects
Dynamic covalent ,Tough ,Mechanochromism ,Carbolong ,Shape memory ,Science (General) ,Q1-390 - Abstract
Multi-responsive polymers have attracted great attention in materials science. Herein, we report a tough self-reporting polyurethane elastomer with near infrared light induced shape memory. A radically exchangeable covalent 2,2′-bis(2-phenylindan-l,3-dione) bond is used as a dynamic covalent crosslink together with permanent crosslink and an organometallic complex carbolong 556 as a photothermal agent in the polyurethane network. The dynamic covalent 2,2′-bis (2-phenylindan-l,3-dione) bond, which is reversibly responsive to both thermal and mechanical stimuli, endows the elastomer with high toughness, mechanochromism, thermochromism, photothermochromism and shape memory behavior which can be triggered by direct heating or near infrared light irradiation mediated by the carbolong 556. Mechanochromism and thermochromism/photothermochromism are practically useful to self-reporting of mechanical failure and thermal condition, respectively. The near infrared light responsiveness facilitates a precisely spatial and temporal control of the shape memory behavior. This strategy opens up new opportunities to smart polymers.
- Published
- 2021
- Full Text
- View/download PDF
3. Multi-modal mechanophores based on cinnamate dimers
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Huan Zhang, Xun Li, Yangju Lin, Fei Gao, Zhen Tang, Peifeng Su, Wenke Zhang, Yuanze Xu, Wengui Weng, and Roman Boulatov
- Subjects
Science - Abstract
Mechanochemistry offers exciting opportunities for molecular engineering of stress-responsive properties of polymers. Here the authors show that macrocyclic cinnamate dimers in a polymer chain can undergo dissociation on the sub-second timescale under 1–2 nN stretching to yield a chromophore that then can be optically healed.
- Published
- 2017
- Full Text
- View/download PDF
4. Author Correction: Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties
- Author
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Ru-Qiang Lu, Xiao-Yun Yan, Lei Zhu, Lin-Lin Yang, Hang Qu, Xin-Chang Wang, Ming Luo, Yu Wang, Rui Chen, Xiao-Ye Wang, Yu Lan, Jian Pei, Wengui Weng, Haiping Xia, and Xiao-Yu Cao
- Subjects
Science - Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
- Published
- 2020
- Full Text
- View/download PDF
5. Structure Identification for Force-Induced Reaction Using Single-Molecule Conductance Measurement
- Author
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Jueting Zheng, Wenli Gao, Taige Lu, Lijue Chen, Luchun Lin, Ruiyun Huang, Yongxiang Tang, Gang Dong, Junyang Liu, Yifei Pan, Wengui Weng, and Wenjing Hong
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General Chemistry - Published
- 2022
6. Dynamic covalent polymer networks with mechanical and mechanoresponsive properties reinforced by strong hydrogen bonding
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Wenli Gao, Rui Tang, Minghao Bai, Hengzhe Yu, Yonghong Ruan, Jinli Zheng, Yinjun Chen, and Wengui Weng
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Polymers and Plastics ,Organic Chemistry ,Bioengineering ,Biochemistry - Abstract
Mechanoresponsive dynamic covalent networks were designed and synthesized by embedding radical mechanophores into the polymer backbone as crosslinkers. The mechanical properties and mechanoresponsiveness of the polymers were reinforced by hydrogen bonds.
- Published
- 2022
7. Optically reconfigurable shape memory metallo-polymer mediated by a carbolong complex and radically exchangeable covalent bond
- Author
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Liulin Yang, Haibo Zhao, Yulin Xie, Pufan Ouyang, Yonghong Ruan, Jiangxi Chen, Wengui Weng, Xumin He, and Haiping Xia
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Polymers and Plastics ,Organic Chemistry ,Bioengineering ,Biochemistry - Abstract
A novel polymer network with NIR induced shape memory behaviour and plasticity.
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- 2022
8. Mechanical Activation of Mechanophore Enhanced by Strong Hydrogen Bonding Interactions
- Author
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Huan Zhang, Yuanze Xu, Xiuli Fang, Yangju Lin, Wengui Weng, and Yinjun Chen
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Spiropyran ,Materials science ,Polymers and Plastics ,Hydrogen bond ,Organic Chemistry ,Supramolecular chemistry ,law.invention ,Catalysis ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,law ,Polymer chemistry ,Materials Chemistry ,Crystallization ,Prepolymer - Abstract
A mechanically active spiropyran (SP) mechanophore is incorporated into the backbone of prepolymer which is further end-capped with ureidopyrimidinone (UPy) or urethane. Strong mechanochromic reaction of SP arises in the bulk films of UPy containing materials whereas much weaker activation occurs in urethane containing counterparts, coincident with their stress–strain responses. The difference in the magnitudes of supramolecular interactions leads to different degrees of chain orientation and strain induced crystallization (SIC) in the bulk and consequently distinct capabilities to transfer the load to the mechanophores. This study may aid the design of novel mechanoresponsive materials whose mechanoresponsiveness can be tailored by tuning supramolecular interactions.
- Published
- 2022
9. Single-molecule observation of mechanical isomerization of spirothiopyran and subsequent Click addition
- Author
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Wengui Weng, Ruixiang Yao, Wenke Zhang, Xun Li, and Nan Xiao
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chemistry.chemical_classification ,Materials science ,Atomic force microscopy ,Intermolecular force ,Force spectroscopy ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Photochemistry ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Mechanochemistry ,Molecule ,General Materials Science ,Electrical and Electronic Engineering ,0210 nano-technology ,Isomerization ,Maleimide - Abstract
Spirothiopyran (STP) is particularly attractive when used as a mechanophore to endow polymers with both damage-signaling and self-reinforcing capacity. It is, however, not clear the actual force required to induce the cycloreversion of STP into ring-opened thiomerocyanine (TMC), which reacts spontaneously with activated C-C bonds. Here, we used atomic force microscopy (AFM)-based single molecule force spectroscopy (SMFS) to study the mechanochemistry of STP mechanophore. It is found that the ring-opening of STP at room temperature requires forces of ∼ 200–400 pN, depending on the pulling speed. In addition, the reversibility of STP to TMC isomerization is demonstrated. Finally, mechanochemically induced intermolecular Click addition is achieved in single molecule level by pulling STP in the presence of maleimide.
- Published
- 2020
10. A Polymer with Mechanochemically Active Hidden Length
- Author
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Xiaodong Cao, Yuanze Xu, Cai-Li Sun, Xun Li, Wengui Weng, Yancong Tian, Wenke Zhang, Roman Boulatov, and Huan Zhang
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chemistry.chemical_classification ,Cyclobutene ,Dimer ,Fracture mechanics ,General Chemistry ,Polymer ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Dissociation (chemistry) ,Article ,0104 chemical sciences ,Polyester ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Chemical physics ,Mechanochemistry ,Isomerization - Abstract
Incorporating hidden length into polymer chains can improve their mechanical properties, because release of the hidden length under mechanical loads enables localized strain relief without chain fracture. To date, the design of hidden length has focused primarily on the choice of the sacrificial bonds holding the hidden length together. Here we demonstrate the advantages of adding mechanochemical reactivity to hidden length itself, using a new mechanophore that integrates (Z)-2,3-diphenylcyclobutene-1,4-dicarboxylate, with hitherto unknown mechanochemistry, into macrocyclic cinnamate dimers. Stretching a polymer of this mechanophore more than doubles the chain contour length without fracture. DFT calculations indicate that the sequential dissociation of the dimer, followed by cyclobutene isomerization at higher forces yields a chain fracture energy 11 times that of a simple polyester of the same initial contour length and preserves high energy-dissipating capacity up to ∼3 nN. In sonicated solutions cyclobutene isomerizes to two distinct products by competing reaction paths, validating the computed mechanochemical mechanism and suggesting an experimental approach to quantifying the distribution of single-chain forces under diverse loading scenarios.
- Published
- 2020
11. Dynamic Polymer Network System Mediated by Radically Exchangeable Covalent Bond and Carbolong Complex
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Wei Zheng, Yuan Chen, Haiping Xia, Wengui Weng, Liulin Yang, Yonghong Ruan, Pufan Ouyang, Huan Zhang, and Xumin He
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chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Polymer network ,Organic Chemistry ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Polyurethane elastomer ,0104 chemical sciences ,Inorganic Chemistry ,chemistry ,Chemical engineering ,Covalent bond ,Materials Chemistry ,0210 nano-technology - Abstract
It is appealing to develop dynamic polymer systems with multifunctionl properties. Herein, we report a polyurethane elastomer with a dynamic covalent polymer network containing a radically exchangeable 2-arylindane-l,3-dione dimer as thermally sensitive and reversible cross-links. In addition, the carbolong complex, an excellent photothermal agent, is incorporated into the dynamic network backbone. With the irradiation of NIR light, the carbolong complex rapidly generates thermal energy, which subsequently triggers the cleavage of the dynamic covalent bond to generate radicals and activate the polyurethane network. In proof-of-concept experiments, we demonstrate that the utility of a combination of radically exchangeable covalent bond and carbolong moiety brings multiple functional characteristics to the polymer network with a capability of spatiotemporal control, including thermochromism, photochromism, rewritability, malleability, and self-healing. This study holds potentials for exploring more tunable dynamics and improved material properties.
- Published
- 2020
12. Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties
- Author
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Lei Zhu, Wengui Weng, Hang Qu, Xiao-Yu Cao, Rui Chen, Xinchang Wang, Haiping Xia, Jian Pei, Xiao-Ye Wang, Ru-Qiang Lu, Yu Lan, Lin-Lin Yang, Ming Luo, Yu Wang, and Xiao-Yun Yan
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Materials science ,Photochemistry ,Dimer ,Science ,Stacking ,Organic chemistry ,General Physics and Astronomy ,010402 general chemistry ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,chemistry.chemical_compound ,Single bond ,lcsh:Science ,Author Correction ,Multidisciplinary ,010405 organic chemistry ,General Chemistry ,Chromophore ,0104 chemical sciences ,Homolysis ,Crystallography ,chemistry ,Asymmetric carbon ,Intramolecular force ,Optical materials ,lcsh:Q ,Chirality (chemistry) - Abstract
Covalently linked π-stacked dimers represent the most significant platform for elucidating the relationship between molecular alignments and their properties. Here, we present the one-pot synthesis of two intramolecularly π-stacked dimers and disclose how intramolecular stacking modes dictate photoswitching properties. The dimer, which features cofacially stacked chromophores and geometrically favours intramolecular photochemical [2 + 2] cycloadditions, displays a nearly irreversible photoswitching behaviour. By contrast, the dimer, bearing crosswise stacked chromophores, is geometrically unfavourable for the cycloaddition and exhibits a highly reversible photoswitching process, in which the homolysis and reformation of carbon−carbon single bonds are involved. Moreover, the chiral carbon centres of both dimers endow these photoswitches with chirality and the separated enantiomers exhibit tuneable chiroptical properties by photoswitching. This work reveals that intramolecular stacking modes significantly influence the photochemical properties of π-stacked dimers and offers a design strategy toward chiral photoswitchable materials., Covalently bridged π-stacked dimers are excellent molecular platforms for understanding the relationship between stacking orientation and properties. Here, the authors synthesize a pair of π-stacked dimers that are aligned either cofacially or crosswise, allowing them to compare how the intramolecular stacking mode affects each dimer’s photoswitching properties.
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- 2019
13. Carbon dot crosslinking towards mechanochemically and photochemically induced fluorescence resonance energy transfer
- Author
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Wenli Gao, Shishuai Xiang, Minghao Bai, Yonghong Ruan, Jinli Zheng, Xuezheng Cao, Yuanze Xu, Yinjun Chen, and Wengui Weng
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Polymers and Plastics ,Organic Chemistry ,Materials Chemistry - Published
- 2022
14. A cyclic cinnamate dimer mechanophore for multimodal stress responsive and mechanically adaptable polymeric materials
- Author
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Yuanze Xu, Dezhi Zeng, Mengxiao Li, Yonghong Ruan, Huan Zhang, Wengui Weng, Zhen Tang, Fei Gao, Peifeng Su, and Yi-Fei Pan
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chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Dimer ,Organic Chemistry ,Bioengineering ,Polymer ,Biochemistry ,Toughening ,Fluorescence ,Cycloaddition ,Stress (mechanics) ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Molecule - Abstract
Smart molecules that undergo orthogonal chemical transformations in response to force and other stimuli are highly attractive in materials science. Such moieties, when incorporated into polymer chains, allow fine tuning of material responses including mechanical properties to mechanical loads. Here we show that the unique mechanochemical and photochemical properties of the methanone tethered cinnamate dimer (MTCD) make it a promising candidate to achieve multimodal stress-responsive and mechanically adaptable polymeric materials. Stretching a polymer of the MTCD results in a force induced retro [2 + 2] cycloaddition and produces methanone-biscinnamate (MBC) moieties. This mechanochemical reaction simultaneously increases the fluorescence and releases a stored length of >6 A per MTCD, suggesting its potential in damage indication and material toughening. Moreover, on-demand strengthening/healing of the pristine and/or the mechanically degraded polymers can be achieved by the photochemical reaction of the MTCD and/or [2 + 2] cycloaddition of the mechanically generated MBC and this feature is orthogonal to the mechanochemical reaction of the MTCD.
- Published
- 2019
15. 'Carbolong' polymers with near infrared triggered, spatially resolved and rapid self-healing properties
- Author
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Jiangxi Chen, Yuhui Hua, Huan Zhang, Haibo Zhao, Kaiyue Zhuo, Wengui Weng, Haiping Xia, and Xumin He
- Subjects
chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Organic Chemistry ,Photothermal effect ,Near-infrared spectroscopy ,Bioengineering ,Nanotechnology ,02 engineering and technology ,Polymer ,Photothermal therapy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Dissociation (chemistry) ,0104 chemical sciences ,chemistry ,Covalent bond ,Self-healing ,Crystallite ,0210 nano-technology - Abstract
Metallopolymers combine the functionality of metal centres with the processabilities of polymers, leading to rapidly expanding interest in the design and development of novel functional materials and devices. Carbolong complexes are a brand-new family of Mobius metalla-aromatics among which specific structures exhibit excellent photothermal properties under near infrared (NIR) light. Here, NIR photothermally healable carbolong polyurethanes (CLPUs) carrying covalently embedded 12C-carbolong motifs in the backbone are reported for the first time. CLPUs with a very low content of 12C-carbolong (down to 0.10 wt%) exhibit fast ( 5 cycles) healing whose efficiency can be tuned by the content of the carbolong complex and NIR power. The healing mechanism is ascribed to the accelerated dissociation of physical interactions, melting of polymer crystallites and chain diffusion induced by the NIR photothermal effect of carbolong embedded in the CLPUs. The fruitful chemistry and the unique photothermal properties of carbolong complexes make them versatile for the design of light-controlled and light-powered self-healing materials.
- Published
- 2019
16. Mechanochromism and optical remodeling of multi-network elastomers containing anthracene dimers
- Author
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Yonghong Ruan, Wengui Weng, Yinjun Chen, Yuanze Xu, Yi-Fei Pan, Costantino Creton, Dezhi Zeng, Roman Boulatov, Huan Zhang, Xiamen University, Sciences et Ingénierie de la Matière Molle (UMR 7615) (SIMM), Ecole Superieure de Physique et de Chimie Industrielles de la Ville de Paris (ESPCI Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), and University of Liverpool
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Anthracene ,Mechanical load ,Materials science ,010405 organic chemistry ,Dimer ,General Chemistry ,010402 general chemistry ,Elastomer ,01 natural sciences ,Fluorescence ,0104 chemical sciences ,chemistry.chemical_compound ,[CHIM.POLY]Chemical Sciences/Polymers ,chemistry ,Chemical engineering ,Covalent bond ,Moiety - Abstract
International audience; Multi-network elastomers are both stiff and tough by virtue of containing a pre-stretched stiff network that can rupture and dissipate energy under load. However, the rupture of this sacrificial network in all described covalent multi-network elastomers is irreversible. Herein, we describe the first example of multi-network elastomers with a reformable sacrificial network containing mechanochemically sensitive anthracene-dimer cross-links. These cross-links also make our elastomers mechanochromic, with coloration that is both persistent and reversible, because the fluorogenic moiety (anthracene dimer) is regenerated upon irradiation of the material. In proof-of-concept experiments we demonstrate the utility of incorporating anthracene dimers in the backbone of the sacrificial network for monitoring mechanochemical remodeling of multi-network elastomers under cycling mechanical load. Stretching or compressing these elastomers makes them fluorescent and irradiating them eliminates the fluorescence by regenerating anthracene dimers. Reformable mechanochromic cross-links, exemplified by anthracene dimers, hold potential for enabling detailed studies of the molecular origin of the unique mechanical properties of multi-network elastomers.
- Published
- 2019
17. Correction to 'A Healable Supramolecular Polymer Blend Based on Aromatic π–π Stacking and Hydrogen Bonding Interactions'
- Author
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Ian W. Hamley, Stuart J. Rowan, Michael E. Mackay, Wengui Weng, Howard M. Colquhoun, Jonathan E. Seppala, Stefano Burattini, Wayne Hayes, Barnaby W. Greenland, and Daniel Hermida Merino
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Supramolecular polymers ,chemistry.chemical_classification ,Crystallography ,Colloid and Surface Chemistry ,Chemistry ,Hydrogen bond ,Stacking ,General Chemistry ,Biochemistry ,Catalysis - Published
- 2021
18. A Mechanochemical Reaction Cascade for Controlling Load-Strengthening of a Mechanochromic Polymer
- Author
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Shishuai Xiang, Huan Zhang, Wengui Weng, Yancong Tian, Piaoxue Xu, Chenxu Wang, Roman Boulatov, and Yi-Fei Pan
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010402 general chemistry ,Photochemistry ,01 natural sciences ,Catalysis ,Dissociation (chemistry) ,Adduct ,mechanophores ,chemistry.chemical_compound ,Mechanochemistry ,spirothiopyran ,Merocyanine ,crosslinking ,Maleimide ,chemistry.chemical_classification ,010405 organic chemistry ,Chemistry ,Communication ,Intermolecular force ,General Chemistry ,Polymer ,General Medicine ,Mechanochromism | Hot Paper ,maleimide ,Communications ,0104 chemical sciences ,Isomerization ,mechanochromism - Abstract
We demonstrate an intermolecular reaction cascade to control the force which triggers crosslinking of a mechanochromic polymer of spirothiopyran (STP). Mechanochromism arises from rapid reversible force‐sensitive isomerization of STP to a merocyanine, which reacts rapidly with activated C=C bonds. The concentration of such bonds, and hence the crosslinking rate, is controlled by force‐dependent dissociation of a Diels–Alder adduct of anthracene and maleimide. Because the adduct requires ca. 1 nN higher force to dissociate at the same rate as that of STP isomerization, the cascade limits crosslinking to overstressed regions of the material, which are at the highest rate of material damage. Using comb polymers decreased the minimum concentration of mechanophores required to crosslinking by about 100‐fold compared to previous examples of load‐strengthening materials. The approach described has potential for controlling a broad range of reaction sequences triggered by mechanical load., A mechanochemical reaction cascade for controlling load‐strengthening of a mechanochromic polymer is realized by using two comb polymers, each containing either spirothiopyran or a Diels–Alder adduct in the proximity of the branch points. The threshold force to trigger crosslinking is increased by ca. 1 nN and the minimum concentration of mechanophores required for crosslinking is decreased by 100‐fold compared to previous examples.
- Published
- 2020
19. Author Correction: Unveiling how intramolecular stacking modes of covalently linked dimers dictate photoswitching properties
- Author
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Lin-Lin Yang, Xiao-Yun Yan, Hang Qu, Xinchang Wang, Wengui Weng, Yu Lan, Rui Chen, Xiao-Yu Cao, Ming Luo, Lei Zhu, Yu Wang, Haiping Xia, Jian Pei, Xiao-Ye Wang, and Ru-Qiang Lu
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Crystallography ,Multidisciplinary ,Covalent bond ,Chemistry ,Science ,Intramolecular force ,Stacking ,General Physics and Astronomy ,lcsh:Q ,General Chemistry ,lcsh:Science ,General Biochemistry, Genetics and Molecular Biology - Abstract
An amendment to this paper has been published and can be accessed via a link at the top of the paper.
- Published
- 2020
20. Impacts of Stereoisomerism on Molecular Packing and Charge Transport of Imide-Fused Corannulene Derivatives
- Author
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Mithu Saha, Hang Qu, Shuang Wu, Rui Chen, Xiao-Yu Cao, Ru-Qiang Lu, Wengui Weng, Yu-Chen Wang, Xiao-Ye Wang, Yi Zhao, Lin-Lin Yang, and Yuxiu Liu
- Subjects
010405 organic chemistry ,Chemistry ,Silica gel ,Stereoisomerism ,General Chemistry ,010402 general chemistry ,Condensed Matter Physics ,01 natural sciences ,Cocrystal ,0104 chemical sciences ,Crystal ,chemistry.chemical_compound ,Crystallography ,Corannulene ,Group (periodic table) ,General Materials Science ,Enantiomer ,Imide - Abstract
Two chiral tertiary carbon centers bearing one mesityl group at each center are introduced into the molecular backbone of imide-fused corannulene derivatives to produce four stereoisomers (i.e., (S, S), (R, R), (R, S), or (S, R) configurations on two chiral carbons) in one pot, which are separated into two portions through column chromatography over silica gel. Portion 1, containing a pair of enantiomers ((S, S) and (R, R)), adopts layered packing in the crystal. Portion 2, consisting of a pair of mesomers ((R, S) and (S, R)), exhibits columnar packing in their cocrystal. Theoretical calculations are performed on these two packing motifs, revealing that Portion 1 displays hole-dominated transport, whereas Portion 2 shows electron-dominated transport.
- Published
- 2018
21. Multi-modal mechanophores based on cinnamate dimers
- Author
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Wenke Zhang, Yuanze Xu, Roman Boulatov, Xun Li, Wengui Weng, Fei Gao, Yangju Lin, Huan Zhang, Zhen Tang, and Peifeng Su
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Toughness ,Materials science ,Science ,Kinetics ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,Photochemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Dissociation (chemistry) ,Article ,Strain energy ,chemistry.chemical_compound ,Mechanochemistry ,lcsh:Science ,chemistry.chemical_classification ,Multidisciplinary ,General Chemistry ,Polymer ,Chromophore ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Monomer ,chemistry ,lcsh:Q ,0210 nano-technology - Abstract
Mechanochemistry offers exciting opportunities for molecular-level engineering of stress-responsive properties of polymers. Reactive sites, sometimes called mechanophores, have been reported to increase the material toughness, to make the material mechanochromic or optically healable. Here we show that macrocyclic cinnamate dimers combine these productive stress-responsive modes. The highly thermally stable dimers dissociate on the sub-second timescale when subject to a stretching force of 1–2 nN (depending on isomer). Stretching a polymer of the dimers above this force more than doubles its contour length and increases the strain energy that the chain absorbs before fragmenting by at least 600 kcal per mole of monomer. The dissociation produces a chromophore and dimers are reformed upon irradiation, thus allowing optical healing of mechanically degraded parts of the material. The mechanochemical kinetics, single-chain extensibility, toughness and potentially optical properties of the dissociation products are tunable by synthetic modifications., Mechanochemistry offers exciting opportunities for molecular engineering of stress-responsive properties of polymers. Here the authors show that macrocyclic cinnamate dimers in a polymer chain can undergo dissociation on the sub-second timescale under 1–2 nN stretching to yield a chromophore that then can be optically healed.
- Published
- 2017
22. Dual-responsive reversible photo/thermogelling polymers exhibiting high modulus change
- Author
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Qingqing Dou, Wengui Weng, Xian Jun Loh, and Sing Shy Liow
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chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Organic Chemistry ,Modulus ,Biomaterial ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Dual (category theory) ,chemistry ,Self-healing hydrogels ,Materials Chemistry ,Self-assembly ,Composite material ,0210 nano-technology ,Water soluble polymers - Published
- 2016
23. Compositional- and time-dependent dissipation, recovery and fracture toughness in hydrophobically reinforced hybrid hydrogels
- Author
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Huan Zhang, Yuanze Xu, Huiying Peng, Yanqun Li, and Wengui Weng
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Materials science ,Polymers and Plastics ,Butyl acrylate ,Organic Chemistry ,Pure shear ,Mole fraction ,chemistry.chemical_compound ,Fracture toughness ,chemistry ,Ultimate tensile strength ,Self-healing hydrogels ,Materials Chemistry ,Copolymer ,medicine ,Swelling ,medicine.symptom ,Composite material - Abstract
The compositional- and time-dependent mechanical properties, recovery, and fracture toughness of hybrid gels having chemical and transient cross-links are systematically studied. The hybrid gels are prepared via micellar copolymerization of acrylamide (AAm) with n -Butyl acrylate (nBA) and the hydrophobic associations of nBA form the transient cross-links. The hybrid gels exhibited excellent mechanical properties (ultimate strength ∼ 400 kPa), fast recovery, and high tolerance to cracks (fracture toughness up to 378.0 J m − 2 ). Swelling, tensile, and pure shear measurements all revealed that the reinforcement is more pronounced when the mole fraction of nBA is above 0.05 and/or the stretch rate is above 0.1 s −1 . The compositional dependence is related to the onset of the formation of transient network while the time-dependent mechanical responses are ascribed to the dynamics of the hydrophobic associations. We also confirmed the separability of strain and time in hydrophobically reinforced hybrid gels for the first time. Our results emphasize the role of the transient network and its responses under external loading in the design of next-generation tough gels.
- Published
- 2015
24. Cocrystallization of Imide-Fused Corannulene Derivatives and C
- Author
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Ru-Qiang, Lu, Shuang, Wu, Yue-Hua, Bao, Lin-Lin, Yang, Hang, Qu, Mithu, Saha, Xiao-Ye, Wang, You-Zhen, Zhuo, Binbin, Xu, Jian, Pei, Hui, Zhang, Wengui, Weng, and Xiao-Yu, Cao
- Abstract
A pair of interconvertible stereoisomers of imide-fused corannulene derivatives was mixed with C
- Published
- 2018
25. Tailoring Mechanochemical Reactivity of Covalent Bonds in Polymers by Non-covalent Interactions
- Author
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Wengui Weng, Yinjun Chen, Huan Zhang, Yangju Lin, and Linxing Zhang
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chemistry.chemical_classification ,Polymer science ,Hydrogen bond ,Supramolecular chemistry ,Polymer ,Supramolecular polymers ,symbols.namesake ,chemistry ,Covalent bond ,Mechanochemistry ,symbols ,Non-covalent interactions ,Organic chemistry ,van der Waals force - Abstract
The last decade has witnessed a growing interest in the field of polymer mechanochemistry, where exogenous forces are utilized to trigger the chemical transformation of covalent and non-covalent bonds embedded in polymer chains. This chapter summarizes the effects of non-covalent interactions on the mechanochemical reactivity of covalent bonds, including the degradation of polymer chains, the unfolding of biomacromolecules, and the activation of mechanophores (mechanical sensitive groups). After a brief overview of contemporary polymer mechanochemistry, we will discuss in detail the effects of non-covalent interactions (i.e. hydrogen bonding, van der Waals and metal–ligand interactions) on polymer mechanochemistry, specifically the physical aspects of these interactions at different length scales, followed by discussions of stress-responsive materials. It is shown how the mechanochemical reactivity of covalent bonds is tuned by the incorporation of supramolecular motifs in both isolated polymer chains and bulk materials, and how the non-covalent interactions of oligomers – and hence the microscopic structures of polymers – are altered by mechanical force. We expect that this chapter will aid in the future development of polymer mechanochemistry, especially the design of advanced mechanophores and stress-responsive materials that utilize non-covalent interactions.
- Published
- 2017
26. Mechanochemistry: Inspiration from Biology
- Author
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Yoan C. Simon, Wengui Weng, and Tamuka Chidanguro
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Chemistry ,Mechanochemistry ,Nanotechnology ,Materials design ,Mechanotransduction - Abstract
Mechanochemistry refers to the study of the evolution of the formation and disruption of chemical bonds upon application of an external force. In this chapter, the roles of mechanical forces in different biological systems are highlighted along with mechanisms and mechanotransduction pathways showing how complex biological systems can provide inspiration for materials design. Examples of how mechano-based systems have been mimicked by other scientists are also discussed including self-healing systems.
- Published
- 2017
27. A simple and versatile approach to self-healing polymers and electrically conductive composites
- Author
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Haiping Xia, Huan Zhang, Tingwan Xie, Wengui Weng, Yuanze Xu, Yonghong Ruan, and Yangju Lin
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chemistry.chemical_classification ,Filler (packaging) ,Acrylate ,Materials science ,General Chemical Engineering ,Composite number ,General Chemistry ,Polymer ,chemistry.chemical_compound ,Monomer ,chemistry ,Copolymer ,Composite material ,Self-healing material ,Glass transition - Abstract
In this study, a simple and versatile approach to self-healing polymers and electrically conductive composites is reported. A series of self-healing polymers are readily synthesized by radical copolymerization of two acrylate monomers bearing a hydrogen-bonding motif. Subsequent blending with nanofillers leads to self-healing electrically conductive composites. Their glass transition temperature, the mechanical and electrical properties, and the self-healing capability can be readily tuned by the composition of the polymer as well as the filler fraction. The composite exhibits mechanical force sensing capabilities and high efficiency of both mechanical and electrical self-healing properties. Our design starts from simple chemistry and inexpensive materials, and may offer a new route towards economic self-healing electronic/electrical devices.
- Published
- 2015
28. Host–guest interaction between fluoro-substituted azobenzene derivative and cyclodextrins
- Author
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Wengui Weng, Huiying Peng, Yuanze Xu, Yonghong Ruan, Lingxing Zhang, Huan Zhang, and Fei Gao
- Subjects
chemistry.chemical_compound ,Aqueous solution ,chemistry ,Azobenzene ,General Chemical Engineering ,Polymer chemistry ,Organic chemistry ,General Chemistry ,Nuclear magnetic resonance spectroscopy ,Derivative (chemistry) ,Visible spectrum - Abstract
An azobenzene derivative (F-azo-COOH) was synthesized and could be E/Z isomerized by visible light. The host–guest interaction between F-azo-COOH and cyclodextrins (CDs) in alkaline aqueous solution was studied by NMR spectroscopy for the first time. The results revealed that F-azo-COOH did not form a stable host–guest complex with α-CD. However, both trans- and cis-F-azo-COOH could form stable 1 : 1 complexes with β-CD. Most interestingly, cis-F-azo-COOH could fit the cavity of β-CD more tightly (3.0 ± 0.3 × 103 M−1) than its trans form (2.1 ± 0.2 × 103 M−1), which was completely opposite to the conventional azobenzene/β-CD system.
- Published
- 2015
29. A corannulene-based donor–acceptor polymer for organic field-effect transistors
- Author
-
Wei Xuan, Yu-Qing Zheng, Yi-Nyu Zhou, Xiao-Yun Yan, Rui Chen, Jian Pei, Ru-Qiang Lu, Wengui Weng, Xiao-Yu Cao, and Jin-Hu Dou
- Subjects
chemistry.chemical_classification ,Electron mobility ,Materials science ,Ambipolar diffusion ,General Chemical Engineering ,General Chemistry ,Polymer ,Conjugated system ,Photochemistry ,Acceptor ,Amorphous solid ,chemistry.chemical_compound ,chemistry ,Corannulene ,Polymer chemistry ,Field-effect transistor - Abstract
For the first time, the corannulene unit was incorporated directly into the backbone of conjugated polymers. A new donor–acceptor (D–A) copolymer PICBT using imide-fused corannulene as acceptor was synthesized and its performance in organic field-effect transistors (OFETs) was tested. PICBT exhibited ambipolar transporting property with a hole mobility of 0.025 cm2 V−1 s−1 and electron mobility of 7.45 × 10−5 cm2 V−1 s−1 when the substrates were treated with octyltrimethoxysilane (OTS). If the substrates were not modified with OTS, PICBT showed lower device performances with a hole mobility of 4.62 × 10−3 cm2 V−1 s−1 and electron mobility of 1.54 × 10−4 cm2 V−1 s−1. The device performances are competitive among the amorphous materials. This work paved the way for incorporating the corannulene unit into conjugated materials.
- Published
- 2014
30. Spiropyran as a Mechanochromic Probe in Dual Cross-Linked Elastomers
- Author
-
Wengui Weng, Yinjun Chen, Huan Zhang, Yuanze Xu, Yonghong Ruan, Yangju Lin, and Xiuli Fang
- Subjects
Spiropyran ,Materials science ,Polymers and Plastics ,Organic Chemistry ,Strain hardening exponent ,Strain rate ,Elastomer ,Inorganic Chemistry ,chemistry.chemical_compound ,Photochromism ,chemistry ,Materials Chemistry ,Polytetrahydrofuran ,Organic chemistry ,Merocyanine ,Composite material ,Isomerization - Abstract
We study the mechanical activation of spiropyran (SP) in a doubly cross-linked polyurethane elastomer. Besides chemical cross-linking, the elastomer comprises polytetrahydrofuran as soft segments and hydrogen-bonding 2-ureido-4-pyrimidone (UPy) as hard segments. The material shows two color changes because of the ring-opening reaction of SP to merocyanine (MC) at strained state and the isomerization about the methane bridge of MC at relaxed state. Increasing tensile strain rate leads to stiffer and stronger elastomer as well as earlier activation of SP. The activation point of SP to MC always coincides well with strain hardening of the stress–elongation curves. We further use the two-color transitions of SP to study the fracture of the elastomer during crack propagation.
- Published
- 2014
31. Self-healing metallo-supramolecular polymers from a ligand macromolecule synthesized via copper-catalyzed azide–alkyne cycloaddition and thiol–ene double 'click' reactions
- Author
-
Yuanze Xu, Bowei Wu, Huiying Peng, Wengui Weng, Lei Li, Bo Yang, and Huan Zhang
- Subjects
chemistry.chemical_classification ,Polymers and Plastics ,Chemistry ,Ligand ,Organic Chemistry ,technology, industry, and agriculture ,Supramolecular chemistry ,Alkyne ,Bioengineering ,Biochemistry ,Cycloaddition ,Supramolecular polymers ,chemistry.chemical_compound ,Polymer chemistry ,Azide ,Ene reaction ,Macromolecule - Abstract
In this study, we develop a series of new materials that can simultaneously and reversibly self-heal without external stimuli based on metallo-supramolecular interactions. Multiple tridentate 2,6-bis(1,2,3-trizaol-4-yl)pyridine (BTP) ligand units synthesized via a copper-catalyzed azide–alkyne cycloaddition (CuAAC) “click” reaction are incorporated into the polymer backbone of a ligand macromolecule through a thiol–ene “click” reaction. 3D transient supramolecular networks are formed from the ligand macromolecule upon coordination with transition and/or lanthanide metal ions. As compared to the ligand macromolecule, the resultant supramolecular films exhibit improved mechanical properties, such as Young's modulus, strength and toughness, which can be readily tuned by the stoichiometric ratio of Zn2+ to Eu3+ to Tb3+. The supramolecular films exhibit characteristics of weakly crosslinked networks where the storage modulus G′ and loss modulus G′′ scaled with normalized frequency ωaT by the same slope of 0.5. Both the supramolecular bulk films and gels are found to exhibit fast and effective self-healing properties by virtue of the kinetically labile nature of the metal–ligand interactions.
- Published
- 2014
32. Multiresponsive supramolecular gels constructed by orthogonal metal–ligand coordination and hydrogen bonding
- Author
-
Wengui Weng, Huiying Peng, Yinjun Chen, Yangju Lin, Huan Zhang, and Xiuli Fang
- Subjects
Metal ,Materials science ,Polymers and Plastics ,Ligand ,Hydrogen bond ,visual_art ,Organic Chemistry ,Materials Chemistry ,visual_art.visual_art_medium ,Supramolecular chemistry ,General Physics and Astronomy ,Nanotechnology - Abstract
National Natural Science Foundation of China [21074103]; Fundamental Research Funds for the Central Universities [2010121018]; Scientific Research Foundation for Returned Scholars
- Published
- 2013
33. Mechanoresponsive Healable Metallosupramolecular Polymers
- Author
-
Haiping Xia, Yuanze Xu, Wengui Weng, Huan Zhang, Yinjun Chen, Guangning Hong, and Yangju Lin
- Subjects
Inorganic Chemistry ,chemistry.chemical_classification ,Engineering ,Polymers and Plastics ,chemistry ,business.industry ,Organic Chemistry ,Materials Chemistry ,Natural science ,Foundation (engineering) ,Nanotechnology ,Polymer ,business - Abstract
Natural Science Foundation of China [21074103, 21174115]; Fundamental Research Funds for the Central Universities [2010121018]; Scientific Research Foundation for Returned Scholars
- Published
- 2013
34. Biomimetic Modular Polymer with Tough and Stress Sensing Properties
- Author
-
Yangju Lin, Yuanze Xu, Huan Zhang, Xiuli Fang, Wengui Weng, and Yinjun Chen
- Subjects
chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,business.industry ,Hydrogen bond ,Atomic force microscopy ,Organic Chemistry ,Nanotechnology ,Polymer ,Modular design ,Inorganic Chemistry ,Stress (mechanics) ,chemistry ,Covalent bond ,Nanofiber ,Stress sensing ,Materials Chemistry ,business - Abstract
With the aim of designing novel polymeric materials that exhibit superb mechanical performance and at the same time can sense stress, the hydrogen bonding ureidopyrimidinone (UPy) and covalent mech...
- Published
- 2013
35. Mechanoresponsive PS-PnBA-PS Triblock Copolymers via Covalently Embedding Mechanophore
- Author
-
Wengui Weng, Shengchao Jiang, Lizong Dai, Huan Zhang, Yangju Lin, Tingwan Xie, Lingxing Zhang, and Yuanze Xu
- Subjects
ComputingMilieux_GENERAL ,Inorganic Chemistry ,Materials science ,Polymers and Plastics ,Polymer science ,Basic research ,Organic Chemistry ,Materials Chemistry ,Copolymer ,Mechanical force - Abstract
National Natural Science Foundation of China [21074103, U1205113]; Fundamental Research Funds for the Central Universities [2010121018]; Special Program for Key Research of Chinese National Basic Research Program [2011CB612303]; Scientific Research Foundation for Returned Scholars
- Published
- 2013
36. A healable supramolecular polymer blend based on aromatic [pi]?[pi] stacking and hydrogen-bonding interactions
- Author
-
Burattini, Stefano, Greenland, Barnaby W., Merino, Daniel Hermida, Wengui Weng, Seppala, Jonathan, Colquhoun, Howard M., Hayes, Wayne, Mackay, Michael E., Hamley, Ian W., and Rowan, Stuart J.
- Subjects
Fourier transform infrared spectroscopy -- Usage ,Hydrogen bonding -- Analysis ,Nanotechnology -- Research ,Polymers -- Structure ,Polymers -- Chemical properties ,Chemistry - Abstract
The article explains the development of a new healable supramolecular polymer blend, which is shown to be completely based on the different aromatic [pi]?[pi] stacking and hydrogen-bonding interactions. The nanophase-separated morphology exhibited by the blend is also analyzed.
- Published
- 2010
37. Advances in the Surface Engineering of Upconversion Nanocrystals
- Author
-
Qifeng Zheng, Feixiang Luo, Lingxing Zhang, Wengui Weng, Yuanze Xu, and Chao Liu
- Subjects
Fluorescent nanoparticles ,Materials science ,Nanocrystal ,Energy transfer ,Foundation (engineering) ,General Materials Science ,Nanotechnology ,Upconverting nanoparticles ,Core shell nanoparticles ,Surface engineering ,Photon upconversion - Abstract
National Natural Science Foundation of China [21074103]; Natural Science Foundation of Fujian Province [2010J05033]; Fundamental Research Funds for the Central Universities [2010121018]
- Published
- 2012
38. Mechanochromism and Mechanical-Force-Triggered Cross-Linking from a Single Reactive Moiety Incorporated into Polymer Chains
- Author
-
Xiaodong Cao, Huan Zhang, Wengui Weng, Roman Boulatov, Yuanze Xu, Fei Gao, and Yanqun Li
- Subjects
chemistry.chemical_classification ,Addition reaction ,010405 organic chemistry ,02 engineering and technology ,General Chemistry ,Polymer ,General Medicine ,021001 nanoscience & nanotechnology ,Mechanical force ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,chemistry ,Polymer chemistry ,Moiety ,Polymer physics ,Reactivity (chemistry) ,0210 nano-technology ,Macromolecule - Abstract
Incorporation of small reactive moieties, the reactivity of which depends on externally imposed load (so-called mechanophores) into polymer chains offers access to a broad range of stress-responsive materials. Here, we report that polymers incorporating spirothiopyran (STP) manifest both green mechanochromism and load-induced addition reactions in solution and solid. Stretching a macromolecule containing colorless STP converts it into green thiomerocyanine (TMC), the mechanically activated thiolate moiety of which undergoes rapid thiol-ene click reactions with certain reactive C=C bonds to form a graft or a cross-link. The unique dual mechanochemical response of STP makes it of potentially great utility both for the design of new stress-responsive materials and for fundamental studies in polymer physics, for example, the dynamics of physical and mechanochemical remodeling of loaded materials.
- Published
- 2015
39. A Healable Supramolecular Polymer Blend Based on Aromatic π−π Stacking and Hydrogen-Bonding Interactions
- Author
-
Stuart J. Rowan, Barnaby W. Greenland, Wengui Weng, Michael E. Mackay, Daniel Hermida Merino, Howard M. Colquhoun, Wayne Hayes, Ian W. Hamley, Stefano Burattini, and Jonathan E. Seppala
- Subjects
Models, Molecular ,Toughness ,Macromolecular Substances ,Polyurethanes ,Stacking ,Young's modulus ,Imides ,Elastomer ,Biochemistry ,Catalysis ,chemistry.chemical_compound ,symbols.namesake ,Colloid and Surface Chemistry ,Diimide ,Polymer chemistry ,Polyurethane ,chemistry.chemical_classification ,Molecular Structure ,Chemistry ,Hydrogen Bonding ,Stereoisomerism ,General Chemistry ,Supramolecular polymers ,Chemical engineering ,symbols ,Polyimide - Abstract
An elastomeric, healable, supramolecular polymer blend comprising a chain-folding polyimide and a telechelic polyurethane with pyrenyl end groups is compatibilized by aromatic pi-pi stacking between the pi-electron-deficient diimide groups and the pi-electron-rich pyrenyl units. This interpolymer interaction is the key to forming a tough, healable, elastomeric material. Variable-temperature FTIR analysis of the bulk material also conclusively demonstrates the presence of hydrogen bonding, which complements the pi-pi stacking interactions. Variable-temperature SAXS analysis shows that the healable polymeric blend has a nanophase-separated morphology and that the X-ray contrast between the two types of domain increases with increasing temperature, a feature that is repeatable over several heating and cooling cycles. A fractured sample of this material reproducibly regains more than 95% of the tensile modulus, 91% of the elongation to break, and 77% of the modulus of toughness of the pristine material.
- Published
- 2010
40. Understanding the mechanism of gelation and stimuli-responsive nature of a class of metallo-supramolecular gels
- Author
-
Wengui Weng, Beck, J. Benjamin, Jamieson, Alex M., and Rowan, Stuart J.
- Subjects
Gelation -- Research ,X-rays -- Diffraction ,X-rays -- Observations ,Chemistry - Abstract
A series of experimental studies is described to explore the properties of stimuli-responsive metallo-supramolecular gels, as well as the nature of the gelation mechanism. Morphological and X-ray diffraction observations suggest gelation occurs via the flocculation of semicrystalline colloidal particles, which results in the gels exhibiting pronounced yielding and thixotropic behavior.
- Published
- 2006
41. Control of Gel Morphology and Properties of a Class of Metallo-Supramolecular Polymers by Good/Poor Solvent Environments
- Author
-
Alex M. Jamieson, Stuart J. Rowan, Zheng Li, and Wengui Weng
- Subjects
chemistry.chemical_classification ,Ethylene ,Polymers and Plastics ,Chemistry ,Small-angle X-ray scattering ,Organic Chemistry ,Inorganic Chemistry ,Solvent ,Supramolecular polymers ,Crystallinity ,chemistry.chemical_compound ,Polymer chemistry ,Materials Chemistry ,Moiety ,Particle size ,Ethylene glycol - Abstract
Through the utilization of a mixed solvent system, consisting of a good solvent (DMSO) with either a nonsolvent (water) or a poor solvent (ethylene glycol), the morphology and properties of a class of stimuli-responsive metallo-supramolecular gels can be systematically tailored. These gels are formed via self-assembly of a ditopic ligand, consisting of a 2,6-bis(1′-methylbenzimidazolyl)-4-oxypyridine moiety attached to either end of a penta(ethylene glycol) core, in the presence of a transition metal ion (ZnII). In each solvent system, a composition window is located in which gels, varying in turbidity from highly opaque (water- or ethylene glycol-rich) to highly transparent (DMSO-rich), are formed. Morphological observations suggest gelation occurs by a common mechanism throughout the composition range, i.e., via the flocculation of semicrystalline colloidal particles. Increase of DMSO content leads to a reduction in the particle size, accompanied by an increase in sol concentration. WAXD and SAXS analys...
- Published
- 2008
42. Structural origin of the thixotropic behavior of a class of metallosupramolecular gels
- Author
-
Alex M. Jamieson, Stuart J. Rowan, and Wengui Weng
- Subjects
Lanthanide ,chemistry.chemical_classification ,Thixotropy ,Chemistry ,Organic Chemistry ,General Medicine ,Polymer ,Biochemistry ,law.invention ,Shear (sheet metal) ,Supramolecular polymers ,chemistry.chemical_compound ,symbols.namesake ,Transition metal ,Chemical engineering ,Rheology ,law ,Drug Discovery ,symbols ,Organic chemistry ,Crystallization ,van der Waals force ,Ethylene glycol - Abstract
Complexation, between a ditopic ligand, consisting of a 2,6-bis-(1′-methylbenzimidazolyl)-4-oxypyridine moiety (O-Mebip) attached to either end of a penta(ethylene glycol) core, with transition metal and lanthanide ions, results in the formation of metallosupramolecular polymers, soluble in acetonitrile at high temperatures. Cooling the hot sol to room temperature causes phase separation and crystallization, and produces mechanically-strong gels, which exhibit a highly thixotropic behavior. Optical microscopy indicates that the gel morphology consists of spherulitic particles, which are easily broken by mechanical shear. Reproducible gel properties are produced when the gel is formed by cooling in a sonication bath, which produces a finely-divided globular morphology, and increases the modulus of the gels. Wide angle X-ray diffraction study shows that the crystalline structures of the gels are strongly dependent on the thermal history of gel formation and the nature of the metal ion. The gel properties are a result of the interactions between the colloidal particles produced by the phase separation and crystallization process. These interactions, which may reflect electrostatic forces and possibly metal–ligand binding, in addition to the usual van der Waals interactions, give rise to the formation of a network structure. The disruption of this network by mechanical shear, and its facile reformation when shear is removed, are the origin of the pronounced thixotropic behavior of the gels.
- Published
- 2007
43. Mechanochemistry of Topological Complex Polymer Systems
- Author
-
Huan, Zhang, Yangju, Lin, Yuanze, Xu, and Wengui, Weng
- Abstract
Although existing since the concept of macromolecules, polymer mechanochemistry is a burgeoning field which attracts great scientific interest in its ability to bias conventional reaction pathways and its potential to fabricate mechanoresponsive materials. We review here the effect of topology on the mechanical degradation of polymer chains and the activation of mechanophores in polymer backbones. The chapter focuses on both experimental and theoretical work carried out in the past 70 years. After a general introduction (Sect. 1), where the concept, the history, and the application of polymer mechanochemistry are briefly described, flow fields to study polymer mechanochemistry are discussed (Sect. 2), results of mechanochemistry study are presented for linear polymers (Sect. 3), cyclic polymers (Sect. 4), graft polymers (Sect. 5), star-shaped polymers (Sect. 6), hyperbranched polymers and dendrimers (Sect. 7), and systems with dynamic topology (Sect. 8). Here we focus on (1) experimental results involving the topological effect on the coil-to-stretch transition and the fracture of the polymer chains, (2) the underlying mechanisms and the key factor that determines the mechanical stability of the macromolecules, (3) theoretical models that relate to the experimental observations, and (4) rational design of mechanophores in complex topology to achieve multiple activations according to the existing results observed in chain degradation.
- Published
- 2015
44. Piezoresistive Materials from Directed Shear-Induced Assembly of Graphite Nanosheets in Polyethylene
- Author
-
Xiangfeng Chen, Jinrong Lu, Wengui Weng, Cuiling Wu, Dajun Wu, and Guohua Chen
- Subjects
Nanocomposite ,Materials science ,Composite number ,Percolation threshold ,Polyethylene ,Condensed Matter Physics ,Piezoresistive effect ,Electronic, Optical and Magnetic Materials ,Biomaterials ,chemistry.chemical_compound ,chemistry ,Electrical resistivity and conductivity ,Electrochemistry ,Graphite ,Composite material ,Electrical conductor - Abstract
A three-dimensional conductive nanocomposite with an ordered conductive network and low percolation threshold has been successfully prepared by blending graphite nanosheets (GNs) with polyethylene on a two-roll mill. The conductive nanosheets orient intensively in the composite, leading to highly anisotropic properties. The nanocomposite with the fraction of conductive nanosheets closest to the percolation threshold possesses a sharp positive pressure coefficient of resistivity, in which the abrupt transition can be attributed to compressive-stress-induced deformation of the conductive network. Such piezoresistive effects depend strongly on filler morphology, filler spatial arrangement, and filler concentration.
- Published
- 2005
45. Transport properties of electrically conducting nylon 6/foliated graphite nanocomposites
- Author
-
Dajun Wu, Wengui Weng, and Guohua Chen
- Subjects
Nanocomposite ,Materials science ,Polymers and Plastics ,Organic Chemistry ,Conductivity ,Thermal conduction ,Microstructure ,chemistry.chemical_compound ,Nylon 6 ,chemistry ,Percolation ,Materials Chemistry ,Graphite ,Composite material ,Critical exponent - Abstract
In this work, we analyze the conductivity data of the nylon 6/FG nanocomposites using the normalized percolation equations and the general effective equation. From the interpretations of the derived results, we demonstrate that the microstructure of the nanocomposites can be readily deduced. Taking several factors into account, it turns out that the tunneling mechanism should be responsible for the observed non-universality of the critical exponents. Experimental evidences show that the existence of the tunneling conduction should be attributed to the particular structure of the prepared materials.
- Published
- 2005
46. Fabrication and characterization of nylon 6/foliated graphite electrically conducting nanocomposite
- Author
-
Xiangfeng Chen, Jinrong Lu, Dajun Wu, Pingping Wang, Wengui Weng, and Guohua Chen
- Subjects
Nanocomposite ,Materials science ,Polymers and Plastics ,Scanning electron microscope ,Percolation threshold ,Condensed Matter Physics ,chemistry.chemical_compound ,Nylon 6 ,chemistry ,Percolation theory ,Percolation ,Polymer chemistry ,Materials Chemistry ,Graphite ,Physical and Theoretical Chemistry ,Composite material ,In situ polymerization - Abstract
In this study, the nylon 6/foliated graphite (FG) electrically conducting nanocomposites with a low percolation threshold of less than 0.75 vol % have been prepared via an in situ polymerization approach in the presence of FG nanosheet filler. Based on laser counting, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction characterization techniques, the structures and morphologies of the nanoscale filling particles and the resulting nanocomposites were examined. Using percolation theory, the conductivity behavior of the nanocomposite samples were modeled and analyzed. Through the use of mean-field and excluded volume approaches, it was demonstrated that the experimentally observed percolation threshold values could be approximately estimated, and a correlation between the percolation threshold and the aspect ratio of FG particles could be quasi-quantitatively established. Also, preliminary studies on the effects of FG nanosheets on the thermal properties of the host nylon 6 were performed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2844–2856, 2004
- Published
- 2004
47. HDPE/expanded graphite electrically conducting composite
- Author
-
Wengui Weng, Dajun Wu, Wen-Li Yan, and Guohua Chen
- Subjects
Materials science ,Composite number ,Ultimate tensile strength ,Ceramics and Composites ,General Physics and Astronomy ,Percolation threshold ,Izod impact strength test ,Graphite ,High-density polyethylene ,Composite material ,Conductivity ,Microstructure ,Surfaces, Coatings and Films - Abstract
In this study, HDPE/expanded graphite electrically conducting composites were prepared in the presence of expanded graphite (EG) via a melt-blending process. The microstructure, electrical, mechanical and thermal properties of the resulting HDPE/EG composites were investigated. The experimental results revealed that EG could be dispersed in the form of nanosheets in the HDPE matrix. The composite exhibited a low percolation threshold ( c ) of about 10.0 wt%, due to the high aspect ratio (width-to-thickness) of graphite nanosheets. With increase of EG content, the conductivity increases, while the tensile strength, elongation at break and impact strength decrease. When EG content reaches 30.0 wt%, the conductivity is about 3.5 × 10-2 S/cm, the tensile strength, elongation at break and impact strength remain at 23.1 MPa, 76% and 5.7 KJ/m2, respectively.
- Published
- 2004
48. Preparation and characterization of graphite nanosheets from ultrasonic powdering technique
- Author
-
Jinrong Lu, Guohua Chen, Wengui Weng, Xiangfeng Chen, Cuiling Wu, Pingping Wang, and Dajun Wu
- Subjects
Materials science ,Intercalation (chemistry) ,chemistry.chemical_element ,General Chemistry ,chemistry ,Particle ,General Materials Science ,Ultrasonic sensor ,Nanometre ,Irradiation ,Graphite ,Composite material ,Fourier transform infrared spectroscopy ,Carbon - Abstract
Natural flake graphite was exfoliated into exfoliated graphite via an acid intercalation procedure. The resulting exfoliated graphite was a worm-like particle composed of graphite sheets with thickness in the nanometer scale. Subjecting it to ultrasonic irradiation, the exfoliated graphite was effectively further foliated into isolated graphite nanosheets. SEM, TEM, SAD, laser counting, and BET measurements revealed that the graphite nanosheets prepared with 10 h irradiation were about 52 nm in thickness and 13 μm in diameter. FTIR examination showed that there were oxygen-containing groups presented on the surface of the exfoliated graphite. This result substantiated the statement reported in the literature that acid treatment could result in oxidization of carbon bonds on graphite surface.
- Published
- 2004
49. Crystallization kinetics and melting behaviors of nylon 6/foliated graphite nanocomposites
- Author
-
Guohua Chen, Dajun Wu, and Wengui Weng
- Subjects
Materials science ,Nanocomposite ,Polymers and Plastics ,Organic Chemistry ,Thermodynamics ,Activation energy ,Isothermal process ,law.invention ,Crystallization kinetics ,chemistry.chemical_compound ,Avrami equation ,Nylon 6 ,chemistry ,law ,Materials Chemistry ,Graphite ,Crystallization ,Composite material - Abstract
This article studies the crystallization kinetics and melting behaviors of nylon 6/foliated graphite electrically conducting nanocomposites. The crystallization kinetics under isothermal conditions is described by the Avrami equation. The values of the exponent found for the neat nylon 6 and the nanocomposite samples are about 3.0 and 1.2, respectively. For non-isothermal studies, the Avrami equation modified by Jeziorny, the Ozawa theory, the modified Ozawa equation and an equation combining the Avrami and Ozawa equation are employed. It is found that the Ozawa analysis fails to provide an adequate description of the non-isothermal crystallization process in both the neat nylon 6 and the nanocomposite samples. While the combination of Avrami and Ozawa equations exhibit great advantages in treating the non-isothermal crystallization kinetics. The activation energies are also determined by the Arrhenius relation and the Kissinger method for isothermal and non-isothermal crystallization, respectively. In both cases, the activation energy for the nanocomposite sample is greater than that for the neat nylon 6. In addition, subsequent DSC scans have also been performed to investigate the melting behaviors of the isothermally and non-isothermally crystallized samples. Results reveal that the isothermally crystallized samples exhibit two melting endotherms, while only the neat nylon 6 sample shows two melting endotherms after non-isothermal crystallization. The equilibrium melting temperature obtained is lower for the nanocomposite sample than for the neat nylon 6.
- Published
- 2003
50. PMMA/graphite nanosheets composite and its conducting properties
- Author
-
Wengui Weng, Cuiling Wu, Dajun Wu, and Guohua Chen
- Subjects
Materials science ,Nanocomposite ,Polymers and Plastics ,Scanning electron microscope ,Organic Chemistry ,Composite number ,General Physics and Astronomy ,Percolation threshold ,Transmission electron microscopy ,embryonic structures ,Materials Chemistry ,Graphite ,In situ polymerization ,Composite material ,Selected area diffraction - Abstract
Graphite nanosheets (NanoG) were prepared by treating the expanded graphite with sonication in aqueous alcohol solution. Nanocomposites of poly(methyl methacrylate) (PMMA) with NanoG were prepared via an in situ polymerization of MMA in the presence of NanoG with the aid of sonication. The nanocomposites were then dispersed with chloroform (CHCl3) and casted on glass slides to form conducting films. The percolation threshold of PMMA/NanoG conducting films at room temperature was as low as 0.31 vol%, much lower than that of the composites filled with conventional graphite particles. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area diffraction (SAD) and etc. were used to characterize the structure of the graphite nanosheets and the nanocomposites. Results showed that the high-aspect-ratio structure of graphite nanosheets played an important role in forming conducting network in PMMA matrix. The conducting behavior of the composite was interpreted by percolation theory.
- Published
- 2003
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