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Crosslink network and phenyl content on the optical, hardness, and thermal aging of PDMS LED encapsulant
摘要： This work aims to synthesize new series of polysiloxane copolymer through hydrosilylation reaction based on different level of crosslink densities and phenyl content. The results revealed that polysiloxanes resins with phenyl rings increased viscosity up to 3800 cps while displaying a relatively high refractive index of 1.531. The asymmetric phenyl substitution onto chain backbone led to formation of densely packed structure resulting in reduced water absorption and gas permeability of PDMS resins. High level of crosslinking contributed to a high shore A hardness and adhesion strength. It displayed transparency of 97% whose percentage reduction was 1.6% under thermal and 0.6% UV aging. No obvious discoloration was observed during accelerated thermal aging up to 210 min at 80 (cid:1)C. These results are key attributes that make the synthesized polysiloxane series as ideal candidate for high brightness LED encapsulant. ? 2019 Wiley Periodicals, Inc. ? 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47895.
关键词： copolymers,thermal properties,ring-opening polymerization,optical properties,synthesis and processing techniques
更新于2025-11-19 16:56:42
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Effect of Unsymmetrically Branched Alkyl Chains on the Electrochemical Band Gap and Thermal Stability of the PCDTBT
摘要： This work introduces a modified poly[N-9’-heptadecanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (PCDTBT) with the unsymmetrically branched N-alkyl chain, which name as poly[N-9’-(2-hexyldecyl)-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (P1). The synthesis of P1 involves dimerization, cyclization, tosylation, N-alkylation, bromination, Stille’s and Suzuki’s coupling reactions. Suitable analysis techniques have used to study the chemical, physical, electrochemical, optical, and thermal properties of P1. The analysis results show that P1 possesses higher HOMO and LUMO energy levels than the previously reported PCDTBT, which have been narrowing the electrochemical band gap down to 1.58 eV. However, the P1 experiences 5% thermal degradation at 280 °C, which is relatively less favourable than the PCDTBT. Hence, the replacement of the symmetrically branched alkyl chains of PCDTBT with unsymmetrically branched alkyl chains results in both improvement and draw-back on the characteristics of the polymer.
关键词： bond energy,Alkylation,cyclic voltammetry,electrochemistry,polymerization
更新于2025-11-19 16:56:35
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A direct one-step synthesis of ultrathin g-C3N4 nanosheets from thiourea for boosting solar photocatalytic H2 evolution
摘要： Two-dimensional (2D) graphitic carbon nitride (g-C3N4) nanosheets, as the promising photocatalyst with fascinating properties, have become a 'rising star' in the field of photocatalysis. Although g-C3N4 nanosheets exfoliated from the bulk g-C3N4 powders are extensively emerged, developing a simple synthetic approach is still full of challenge. To this end, here we report a direct polymerization strategy to fabricate the ultrathin g-C3N4 nanosheets, that is only heating treatment of thiourea in air without addition of any template. The photocatalytic activities of as-prepared samples were evaluated by photoreduction of water to hydrogen (H2) using triethanolamine as sacrificial agent and Pt as co-catalyst under visible-light irradiation (λ > 420 nm). As a result, our few-layered g-C3N4 nanosheets with an average thickness of 3.5 nm exhibit a superior visible-light photocatalytic H2 evolution rate (HER) of 1391 μmol g?1 h?1 and a remarkable apparent quantum efficiency of 6.6% at 420 nm. Eventually, the HER of as-fabricated ultrathin g-C3N4 nanosheets is not only much higher than the dicyandiamide-derived g-C3N4 or melamine-derived g-C3N4, but also greater than the thermal-oxidation etched g-C3N4 nanosheets under the same condition.
关键词： g-C3N4 nanosheets,Template-free polymerization,Solar energy conversion,2D materials,Photocatalysis,One-step synthesis
更新于2025-11-14 17:03:37
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Direct laser writing of birefringent photonic crystals for the infrared spectral range
摘要： Infrared optical photonic crystals fabricated using direct laser writing, which is based on the two-photon polymerization of suitable monomers, have received substantial interest since the emergence of this process. Two-photon polymerization could be a disruptive technology for the fabrication of all-dielectric photonic crystals in the infrared spectral range, as it allows the synthesis of large scale arrays of uniform structures with arbitrary geometries and arrangements. However, all-dielectric photonic crystals that provide birefringent optical responses in the infrared spectral range have not yet been demonstrated using direct laser writing techniques. Here, the authors explore the form birefringence observed in photonic crystals composed of arrays of subwavelength-sized slanted polymer microwires. The photonic crystals investigated here were fabricated in a single fabrication step using direct laser writing of an infrared transparent photoresist (IP-Dip). A strong contrast of the cross-polarized re?ectance of photonic crystals as a function of the in-plane orientation is observed in the mid-infrared spectral range at λ ≈ 6:5 μm. This observation is indicative of an anisotropic optical behavior. Finite element based techniques corroborate the experimentally observed responses qualitatively.
关键词： two-photon polymerization,direct laser writing,infrared spectral range,birefringent photonic crystals,all-dielectric photonic crystals
更新于2025-11-14 15:18:02
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UV/thermal dual curing of tung oil-based polymers induced by cationic photoinitiator
摘要： With the increasing shortage of petroleum-based resources, the exploitation and application of the polymers derived from the renewable resources has becomes increasingly important for the industrial development. In this work, in order to promote the direct application of tung oil in the coating ?eld, the tung oil-based polymers with the excellent mechanical properties by using cationic photoinitiator as the “green” initiator were prepared. The cationic polymerization mechanism and the optimal polymerization conditions of methyl eleostearate (ME) induced by triarylsulfonium salt (TAS) are characterized via the nuclear magnetic resonance spectroscopy. The e?ects of di?erent monomers on the properties of tung oil-based polymers and the post curing behaviors of the polymers are studied by dynamic mechanical test and microtensile test. The results display that the heating treatment after UV irradiation is necessary and favorable for the cationic polymerization of ME induced by TAS. And the optimal reaction condition is 500 W of irradiation energy, 5 wt% of initiator concentration, 60 min of irradiation time, 100 °C of heating temperature and 3 h of heating time. Moreover, tung oil-based polymers with good hydrophobicity can be obtained under the optimal reaction condition. In addition, adding 20 wt% divinylbenzene and 10 wt% styrene to the tung oil can e?ectively increase the mechanical properties and glass transition temperatures (Tg) of tung oil-based polymers.
关键词： Dual curing,Triarylsulfonium salts,Cationic polymerization,Tung oil-based
更新于2025-11-14 15:14:40
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Characterization of atypical polyaniline nano-structures prepared via advanced techniques
摘要： Conductive polymers had been the topic of a vast number of investigations during the last decades, so, the synthesis of conducting polymers and study of their physical properties has been of prime importance. One of these conductive polymers is polyaniline. The current work is to prepare polyaniline (PANI) nanostructured material via four different preparation techniques which were sol-gel, rapid mixing, sonochemical and supercritical carbon dioxide (SC-CO2) assisted polymerization. The morphology of the prepared PANI samples was determined using Transmission electron microscopy (TEM) and Scanning Electron Microscope (SEM). The molecular structure of prepared PANI samples was characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The electrical conductivity of the synthesized samples was assessed by using the four-probe method at room temperature. The surface area of the prepared samples was determined using Brunauer Emmett Teller (BET). The characterization results of the prepared PANI con?rm that the morphology, chemical composition, crystallinity, conductivity and surface area were altered signi?cantly as a consequence of its synthesis via atypical techniques.
关键词： Supercritical carbon dioxide assisted polymerization,Nanoparticles,Sonochemical,Polyaniline nano-structures,Nano?bers,Polyaniline characterization,Nanorods,Sol gel,Rapid mixing polymerization
更新于2025-09-23 15:23:52
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Inorganic Protection of Polymer Nanocapsules: A Strategy to Improve the Efficiency of Encapsulated Optically Active Molecules
摘要： We demonstrate that the efficiency under ambient conditions of optically active molecules encapsulated in polymer nanocapsules can be significantly improved by depositing an inorganic layer onto the polymeric shell. A triplet-triplet annihilation upconversion (TTA-UC) system consisting of a porphyrin derivative and perylene is used as a representative case. Different inorganic materials are deposited on the surface of functionalized polymer nanocapsules synthesized by free-radical polymerization in miniemulsion. First, a silicate clay with formula [Si8(Mg5.45Li0.4)O20(OH)4]Na0.7 is deposited on the surface of positively charged polystyrene nanocapsules via layer-by-layer deposition. Second, controlled in situ mineralization of hydroxyapatite and cerium(IV) oxide are carried out on the surface of negatively charged polystyrene nanocapsules. In both cases the inorganic materials on the nanocapsule surface act as a scavenger and avoid the entry of oxygen from the external environment. By avoiding the entry of oxygen, the photo-oxidation process of perylene molecules is avoided within the system, and an increase in the TTA-UC properties occurs.
关键词： upconversion,nanocapsule,crystallization,layer-by-layer,miniemulsion polymerization
更新于2025-09-23 15:23:52
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Multi-arm polymers prepared by atom transfer radical polymerization (ATRP) and their electrospun films as oxygen sensors and pressure sensitive paints
摘要： New oxygen and pressure sensitive paints (PSPs) with four-arm polymeric structures were prepared by using a kind of controlled living polymerizations - atom transfer radical polymerization (ATRP). The polymers composing of poly(isobutyl methacrylate)-co-poly(trifluoroethyl methacrylate)s (PolyIBMA-co-PolyTFEM)s act as the matrices for the platinum porphyrin-based phosphorescence probes, which were copolymerized in the matrices. The polymers were characterized by using 1H-NMR, 19F-NMR, and GPC to demonstrate their successful preparation. The influence of polymer structures on sensing activity including the sensitivity and response time to oxygen and/or pressure was investigated. Results showed that copolymers with suitable compositions (herein P3) can have highest sensitivity. Polymer structure's influence on response time to oxygen was also investigated. For increasing the polymer's surface area for further improving sensing sensitivity, electrospinning method was used for preparing films with micro-spherical or fibrous structures. The morphologies of electrospinning coated films were observed by SEM. Results showed that electrospinning coated films can respond much better to oxygen and pressure than their corresponding sprayed plates. This is the first time to apply the controlled living polymerization approach to prepare PSPs with multi-arm structures, which will broaden the PSP functional materials' design strategy.
关键词： oxygen sensing,pressure sensitive paints,electrospinning,multi-arm polymers,atom transfer radical polymerization
更新于2025-09-23 15:23:52
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An eco-friendly method to enhance optical and electrical properties of conducting polymers by means of carboxymethyl cellulose
摘要： In this work, an eco-friendly method is proposed for the electro-synthesis of conductive polymers with superior optical and electrical properties by means of CMC in aqueous media. For this purpose, an aqueous dispersion of a water-insoluble monomer namely 4-amino-N-[2,5-di(thiophen-2-yl)-1H-pyrrol-1-yl]benzamide (TPB) has been prepared by attaching it to CMC via hydrogen bonds and the conductive composite film (PTPB–CMC) has been obtained by electropolymerization. The TPB monomer has been chosen to interact with the CMC via hydrogen bonds which ensures to obtain dispersion with the CMC and also increase the compatibility of its polymer in the composite structure. As a result of the electrochemical, spectroelectrochemical investigation and surface morphology analyses of the obtained conductive polymer, it has been found that anionic CMC makes improvements in the electrical, optical and mechanical properties of the polymer by making the plasticizing effect and acting as a dopant. Furthermore, in the presence of nanocarbon materials on electrode surface, it has been determined that the polymerization potential reduced and more stable and long-lasting polymeric films which are crucial for technological applications have been obtained.
关键词： Electrochemical polymerization,Composite materials,Conducting polymers,Carboxymethyl cellulose
更新于2025-09-23 15:23:52
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Free Exciton Absorptions and Quasi-reversible Redox Actions in Polypyrrole–Polyaniline–Zinc Oxide Nanocomposites as Electron Transporting Layer for Organic Light Emitting Diode and Electrode Material for Supercapacitors
摘要： The ternary nanocomposite comprised of PPY–PANI (polypyrrole–polyaniline) copolymer and zinc oxide (ZnO), synthesized by implying chemical oxidative polymerization of pyrrole monomer in presence of ammonium persulfate as oxidant with varying ZnO concentrations. The shifting of bands and their corresponding change in nano-strain of as-prepared PPY–PANI–ZnO nanocomposite of varying concentration was confirmed by the Fourier transform inferred spectroscopy (FTIR). The surface morphological images of PPY–PANI–ZnO nanocomposites revealed the nano-flake like structure attributed to the embodiment of ZnO and increase in agglomeration was detected with the increasing concentration of ZnO. The optimized reduction in band gap up to ~ 1.02 eV and red-shift of absorption edge of ZnO in visible region side was detected for 10% PPY–PANI–ZnO nanocomposite. The relatively slow decay component and higher non radiative electron–hole recombination rate showed the better electron transport properties with chromaticity in ideal blue region for 10% PPY–PANI–ZnO nanocomposite. The higher current density ~ 7.95 A/cm2, high dielectric constant ~ 1960 at 373 K, high reduction potential ~ + 0.687 V with high specific capacitance (~ 436.14 F/g) at 10 mV s?1 and better thermal firmness was observed for 10% PPY–PANI–ZnO nanocomposite. The relatively high discharge time ~ 2600 s and high power density with meagre loss in energy density at high current density was also observed for 10% PPY–PANI–ZnO nanocomposite. These robust properties confirmed that the proposed 10% PPY–PANI–ZnO nanocomposite could be employed as electron transporting material for OLEDs as well as for high performance and efficient supercapacitors.
关键词： PPY–PANI–ZnO nanocomposites,Electrochemical performance,Chemical oxidative polymerization,PL,Electron transport layer
更新于2025-09-23 15:23:52