Showing papers by "Ming Qiu Zhang published in 2014"
TL;DR: In this paper, a cross-linked polysulfide containing the phosphine exhibited repeated autonomous self-healing resulting in restoration of tensile strength as a result of the dynamic exchange of disulfide bonds.
Abstract: Tri-n-butylphosphine (TBP) has been shown to effectively catalyze an air-insensitive disulfide metathesis reaction under alkaline conditions at room temperature. A cross-linked polysulfide containing the phosphine exhibited repeated autonomous self-healing resulting in restoration of tensile strength as a result of the dynamic exchange of disulfide bonds. Interestingly, the cross-linked polysulfide can also be reshaped and reprocessed at room temperature via the TBP-mediated reshuffling of the macromolecular networks. The mechanical properties and self-healing ability of polymeric specimens made from chopped samples remain surprisingly constant. In sharp contrast, control specimens without the phosphine catalyst or S–S bonds are neither self-healable nor reprocessable.
424 citations
TL;DR: In this paper, the effects of stretching conditions on the transformation from α to β phase of polyvinylidene fluoride (PVDF) were studied in situ under an optical tensile stress microscopy tester, and the samples after being stretched were investigated using a 3D digital microscope and an infrared microscope.
Abstract: Poly(vinylidene fluoride) (PVDF) has excellent pyro- and piezoelectric properties which are related to the β-crystal of PVDF. Most of the β-crystal of PVDF can be transformed from the α-crystal by mechanical stretching. The effects of stretching conditions on the transformation from α to β phase of PVDF were studied in this paper. In addition, changes of crystalline structure of PVDF during the stretching process were observed in situ under an optical tensile stress microscopy tester, and the samples after being stretched were investigated using a 3D digital microscope and an infrared microscope. The results show that stretching temperature (Ts) and drawing ratio (λ) are critical to the transformation from α-crystal to β-crystal of PVDF. The Ts around 100 °C and λ above 3 is recommended. The in situ observation indicates that the deformation of crystalline structure began from the middle of α-spherulite and extended to another spherulite, and caused the large-scale transformation. Scanning results of infrared microspectroscopic and 3D digital microscopy revealed that α phase of PVDF would change into β phase with the deformation of the spherulite, and the distribution of the different crystalline phase in PVDF after being stretched was also given. It is believed that this work is instructive and meaningful to studies on phase transformation and production of the piezoelectric film of PVDF.
239 citations
TL;DR: In this article, a one-step approach for synthesis of carbon dots (CDs) under mild conditions is reported, where CDs are self-assembled in solution and exhibit excitation wavelength independent photoluminescence (PL) performance.
156 citations
TL;DR: In this paper, an alkoxyamine-based diol was synthesized and reacted with tri-functional homopolymer of hexamethylene diisocyanate (tri-HDI) and polyethylene glycol (PEG).
142 citations
TL;DR: In this paper, high-water-content boron-cross-linked graphene oxide/polyvinyl alcohol (B-GO/PVA) hydrogels were obtained by a freeze/thaw method and immersion in boric acid solution.
Abstract: In this study, high-water-content boron-cross-linked graphene oxide/polyvinyl alcohol (B-GO/PVA) hydrogels were prepared by a freeze/thaw method and immersion in boric acid solution for boron cross-linking. High-water-content B-GO/PVA hydrogels with a water/polymer mass ratio ranging from 19 : 1 to 49 : 1 (water content 95–98) could be obtained. It is found that a small addition of GO can lead to significant reinforcement of the tensile strength of B-GO/PVA hydrogels with an increase in elongation. Compared to B-PVA hydrogel, a 144% increase of fracture tensile strength is achieved when the content of GO is 0.1 wt% (∼0.609 MPa, water content ∼ 95%). Meanwhile, compression and shear strength (0.1 MPa and 0.201 MPa, water content ∼ 95%) of such hydrogels are increased by 26% and 35%, respectively. A method of acquiring high-water-content PVA hydrogels and the reinforcing mechanism of B-GO/PVA hydrogels are suggested. It is believed that such new high-water-content hydrogels are promising materials in the application of biomedical engineering and polymer electrolytes.
105 citations
TL;DR: A new family of boron crosslinked graphene oxide/polyvinyl alcohol (GO-B-PVA) nanocomposite gels is prepared by freeze-thaw/boron cross-linking method, and then the gel electrolytes saturated with KOH solution are assembled into electric double layer capacitors.
72 citations
TL;DR: In this article, a new alkoxyamine based diol was synthesized and incorporated into an epoxy monomer, which was then compounded with traditional bisphenol A diglycidyl ether and cured by diethylenetriamine.
Abstract: To provide epoxy with intrinsic self-healing ability, a new alkoxyamine based diol was synthesized and incorporated into an epoxy monomer, which was then compounded with traditional bisphenol A diglycidyl ether and cured by diethylenetriamine. Taking advantage of dynamic equilibrium of thermally reversible reaction of C–ON bond in alkoxyamine, cracked portions of the functionalized epoxy material can be repeatedly reconnected at certain temperature, as characterized by restoration of impact strength and visual inspection as well. Unlike the two-step self-healing approach based on reversible Diels–Alder reaction, the present one only needed one step. Owing to the steric hindrance of tertiary butyl group in the diol, onset of scission of C–ON bonds and radical recombination (i.e., healing reaction) occurred at lower temperature. Additionally, reversibility of the alkoxyamine derivatives was improved with incorporation of Si–O bonds into the epoxy chains. The present work carefully studied thermal reversibility, thermal stability, dynamic mechanical behavior and healing performance of the epoxy in relation to molecular structure. The outcomes might help to optimize the material and guide future design of novel epoxy monomers.
68 citations
TL;DR: Epoxy material with the embedded healant capsules can thus be healed within a few seconds, as demonstrated by impact and fatigue tests.
Abstract: Self-healing materials should take effect immediately following crack generation in principle, but the speed of autonomic recovery of mechanical properties through either extrinsic or intrinsic healing strategy reported so far is not that fast. Mostly, a couple of hours are taken for reaching steady state or maximum healing. To accelerate the healing process, the authors of this work make use of antimony pentafluoride as instant hardener of epoxy and successfully encapsulate the highly active antimony pentafluoride–ethanol complex in terms of hollow silica spheres. Accordingly, self-healing agent based on microencapsulated antimony pentafluoride–ethanol complex and epoxy monomer is developed. Epoxy material with the embedded healant capsules can thus be healed within a few seconds, as demonstrated by impact and fatigue tests. It is believed that the outcome presented here might help to move the self-healing technique closer to practical application, especially when the engineering significance of epoxy ma...
56 citations
TL;DR: In this paper, a tri-functional homopolymer of hexamethylene diisocyanate (tri-HDI) and polyethylene glycol (PEG) is synthesized, in which photo-reversible coumarin moieties act as pendant groups.
Abstract: Polyurethanes consisting of tri-functional homopolymer of hexamethylene diisocyanate (tri-HDI) and polyethylene glycol (PEG) are synthesized, in which photo-reversible coumarin moieties act as pendant groups Accordingly, the polyurethanes can be repeatedly self-healed under UV lights at room temperature by taking advantages of the photodimerization and photocleavage habits of coumarin Molecular weight of the soft segment, PEG, is found to be closely related to the healing performance of the polyurethanes Lower molecular weight PEG that corresponds to higher initial coumarin concentration in the polymer is critical for obtaining higher healing efficiency in the case of the first healing action Nevertheless, it does not guarantee high reversibility of the photo-remendability during the repeated healing events In contrast, the polyurethane with moderate molecular weight PEG has achieved balanced performance Reaction kinetics is less important for the healing effect
50 citations
TL;DR: Self-healing of polymers and polymer composites initially represented a process capable of autonomic restoration of mechanical strength upon cracking of the materials, but it is moving into the area of restoration of functionality as discussed by the authors.
Abstract: Self-healing of polymers and polymer composites initially represented a process capable of autonomic restoration of mechanical strength upon cracking of the materials, but it is moving into the area of restoration of functionality. This mini-review is focused on recent efforts to develop functional polymers with built-in stimuli-responsive ability to heal for recovery of their specific physical or chemical properties. Molecular design and synthesis, compounding and assembly of organic and inorganic species, inherent reversibility, etc., are summarized. It is hoped that much more interest will be aroused in this emerging and promising frontier topic. © 2014 Society of Chemical Industry
48 citations
TL;DR: In this paper, a self-healing crosslinked epoxy elastomer is cured with polythiol to achieve room temperature selfhealing ability in air without manual intervention (heating).
TL;DR: In this article, trifluoromethanesulfonic acid (TfOH), an ultra-strong Bronsted acid, is successfully encapsulated in silica microspheres, which cooperates with epoxy monomer, forming a group of novel self-healing agent having practical value.
TL;DR: By using epoxy silane as a modifier and stabilizer, ZnO quantum dots (QDs) were synthesized by a one-step precipitation approach and acquired showed satisfactory redispersibility and exhibited strong and stable photoluminescence in both solution and dry states.
Abstract: By using epoxy silane as a modifier and stabilizer, ZnO quantum dots (QDs) were synthesized by a one-step precipitation approach. The ZnO QDs acquired showed satisfactory redispersibility and exhibited strong and stable photoluminescence in both solution and dry states. When the ZnO QDs content was as high as 8 wt%, the ZnO QDs–epoxy nanocomposite was still highly transparent and luminescent. Accordingly, the ZnO QDs can be used as a luminescent material, and a cool white light emitting diode (WLED) lamp was made by encapsulating a UV chip with the nanocomposite, without traditional tricolor rare earth phosphors. Additionally, the high loading nanocomposite possessed high ultraviolet resistance, which would help to improve the lifetime of the WLED.
TL;DR: In this paper, two types of microcapsules were embedded in epoxy to produce self-healing epoxy composite and upon fracture of the material, the core substances in the broken capsules were released and polymerization of styrene initiated by benzoyl peroxide took place, rebinding the cracked planes.
Abstract: To impart self-healing ability to epoxy, styrene-loaded and benzoyl peroxide–loaded microcapsules were prepared by in situ polymerization in emulsion using melamine–formaldehyde resin as the wall former. Afterward, the two types of microcapsules were embedded in epoxy to produce self-healing epoxy composite. Upon fracture of the material, the core substances in the broken capsules were released and polymerization of styrene initiated by benzoyl peroxide took place, rebinding the cracked planes. The parameters for manufacturing the microcapsules and the factors that influence healing efficiency of the system were discussed in detail.
TL;DR: In this article, photo-induced chemisorption of hydrophilic radicals and water molecules on graphene is found to be responsible for the transition from original hydrophobicity to hydrophilicity.
Abstract: Graphene films which are fabricated by simple dispensing method without surface modification exhibit reversible switching between superhydrophobicity and superhydrophilicity under alternative UV illumination and dark storage. Careful study of the mechanisms is conducted in view of surface geometry, microstructure, and chemical compositions, and focused on chemical compositions. Photo-induced chemisorption of hydrophilic radicals and water molecules on graphene is found to be responsible for the transition from original hydrophobicity to hydrophilicity, even superhydrophilicity, while replacement of water molecules by oxygen during storage in the dark environment induces the hydrophobicity recovery of graphene films from hydrophilic state. Appearance and disappearance of hydroxyl radicals are closely related to the lattice structure of graphene and energy supply. This wettability conversion is fully reversible. The outcomes not only reveal micro-processes involved in wettability conversion of graphene but also help to purposely design and produce devices from carbon materials with tailor-made tunable surface wettability according to our actual need.
TL;DR: In this article, the authors used silver nanoparticles for enhancement of photoluminescence of polyfluorene copolymer (PCFOz) through localized surface plasmon resonance (LSPR) coupling effect.
TL;DR: The unique thermoresponsive properties and high enhancement ratio of the material should find application in solution fluorescence enhancers and a variety of biomedical applications, such as cellular uptake, sensing and imaging.
Abstract: A water-processable blue fluorescent silver nanoparticle@graphene–polymer composite (Ag@G–pNIPAM) consisting of graphene coated with a thermally responsive poly-(N-isopropylacrylamide) (pNIPAM) shell is prepared. The pNIPAM shell swells or collapses as a function of temperature, serving as a means to trap silver nanoparticles in solution and get them sufficiently close to the graphene core to provide fluorescence enhancement based on the local surface plasmon resonance (LSPR) effect. The unique thermoresponsive properties and high enhancement ratio of the material should find application in solution fluorescence enhancers and a variety of biomedical applications, such as cellular uptake, sensing and imaging.
TL;DR: In this paper, hollow silica microcapsules were firstly synthesized via sol-gel technique, which were then steeped in ethanol solution of SbF 5 -ethanol complex under vacuum, allowing infiltration of the latter into the capsules.
TL;DR: In this article, the phase transition process in aqueous solutions of poly (vinyl methyl ether) (PVME)/poly (2-ethyl-2-oxazoline) (PEtOx) mixtures was investigated by elastic light scattering (ELS) spectroscopy.
Abstract: Phase transition process in aqueous solutions of poly (vinyl methyl ether) (PVME)/poly (2-ethyl-2-oxazoline) (PEtOx) mixtures was investigated by elastic light scattering (ELS) spectroscopy. The two temperatures of phase transition in solutions during heating were identified, corresponding to different lower critical solution temperatures of PVME and PEtOx. The ELS spectra revealed the aggregation of molecular chains in the course of phase transition. It was found that PVME chains collapsed and aggregated during heating. Afterward, the PEtOx chains began to aggregate. In contrast, during cooling, the PEtOx aggregates were initially swelled and followed by partial dissociation. This was probably because that the PVME aggregates formed in solution might sterically hinder the further swelling and dissociation of the PEtOx aggregates. Subsequently, the aggregates of PVME chains and the independent PEtOx aggregates swelled and dissociated, while the conformation of molecular chains finally returned to its original state. In view of the phase transition behavior of PVME/PEtOx solutions, the mixtures of two thermosensitive polymers might be used to develop new polymeric materials possibly applied in fields such as drug delivery, biosensor, and bioseparation. Moreover, a model was proposed to describe the phase transition process.
TL;DR: In this article, a dual initiator system consisting of cyclohexanone peroxide and di-tert-butyl peroxide (DTBP) catalyzed by cobalt octoate (CoOct) was introduced, which provided the gel with good permeability and sufficient thermal stability for saturation in the supercritical carbon dioxide and polymerizability for freezing the depressurization induced cells during post cure at higher temperatures.
Patent•
08 Oct 2014
TL;DR: In this paper, a metal ordered array nano structure based on plasmon-model metal reinforced fluorescence is presented, which can be used in the field of solar cells, organic light emitting diodes and the like.
Abstract: The invention discloses a preparation method of a metal ordered array nano structure based on plasmon-model metal reinforced fluorescence. The preparation method mainly comprises the following steps: dispensing monodisperse polystyrene microspheres to obtain a polystyrene film; and depositing a metal layer on the polystyrene film. Microsphere templates with different sizes can be selected to obtain the metal nano structures with different sizes. The test result indicates that the nano metal arrays with different sizes have different spectral characteristics, the electric field coupling of the metal structures forms uniform hotspot distribution, and therefore, the nano metal structure has wide application prospects in fluorescence molecule light-emitting reinforcement in the field of surface fluorescence reinforcement and can be widely used in the fields of solar cells, organic light-emitting diodes and the like. The method is simple; and the prepared metal array nano structure has the advantages of uniform structure, high fluorescence molecule light-emitting reinforcement factor and high reinforcement uniformity, is easy for repetitive preparation, and has popularization and application values.