Preparation and properties of novel fluorosilicone thermoplastic vulcanizate with cross‐linking–controlled core‐shell structure

A new fluorosilicone thermoplastic vulcanizate (TPV) composed of poly(vinylidene fluoride) (PVDF), silicone rubber (SR), and fluororubber (FKM) was successfully prepared through dynamic vulcanization. The morphological structure of the TPVs had core‐shell elastomer particles dispersed in a continuous PVDF matrix. Furthermore, the cross‐linking of core‐shell structure was controlled by adopting different curing agent. The effect of cross‐linking–controlled core‐shell structure on the morphology, crystallization behavior, stress relaxation test, solvent‐resistant properties of the obtained TPVs were investigated. It was found that the shell cross‐link had a significant influence on the crystallinity of the PVDF phase. The core‐shell bicross‐linked TPV was found to provide the lowest rate of relaxation. An obvious stress softening phenomenon was observed in the uniaxial loading‐unloading cycles in tension. The bicross‐linked TPV had good solvent resistant properties. The tensile strength of the bicross‐linked TPV was still 12 MPa even after immersed in butyl acetate for 48 hours.     

Preparation and characterization of polytetrafluoroethylene‐polyacrylate core–shell nanoparticles

Polytetrafluoroethylene (PTFE)‐polyacrylate core–shell nanoparticles were produced by using PTFE micropowder and acrylate via seeded emulsion polymerization in the presence of fluorosurfactant. The properties of emulsion under various polymerization conditions were investigated and optimized. The chemical composition of the PTFE‐polyacrylate nanoparticles was characterized by Fourier‐transform infrared spectrometry (FTIR). The particle size and core–shell structure of the resulting PTFE‐polyacrylate nanoparticles were confirmed by transmission electron microscopy (TEM). Wettability of the PTFE‐polyacrylate core–shell particles was higher than the pristine PTFE. The formation of this kind of PTFE‐polyacrylate core–shell nanoparticles could improve the compatibility of PTFE with other materials because PTFE is covered by polyacrylate shell, which make them promising in various fields. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis, characterization and optical properties of silver and gold nanowires embedded in mesoporous MCM-41

Uniform nanowires of silver and gold inside the channels of MCM-41 were prepared by controlled reduction of their respective metal salts with sodium borohydride (NaBH₄). Presence of nanowires of silver and gold in MCM-41 were confirmed by high angle X-ray diffraction (XRD) data (peaks between 2ϑ = 30 − 60°) and transmission electron microscopy (TEM) confirmed the diameter of the nanowires. Diameter of nanowires is found to be ∼ 2.8 nm which is coincident with channel diameter of MCM-41. Optical properties of these heterostructured materials Ag-MCM-41 and Au-MCM-41 reveals the presence of surface plasmon absorption peaks of silver and gold respectively, and the shift in the absorption bands are associated to agglomeration of clusters inside the channels. Room temperature photoluminescence spectra exhibits interesting optical properties as observed for direct band gap semiconductors. Non-linear optical properties (NLO) corresponding to second harmonic generation (SHG) values were also recorded for self supported films of these heterostructured materials. Enhanced optical non-linearity was found to be arising from a corresponding increase of local field near the surface plasmon resonance. Further enhancement in SHG was found with poling due to an induction of orientation order.     

Preparation of magnetic Fe3O4/P (GMA‐DVB)‐PEI/Pd highly efficient catalyst with core‐shell structure

In this paper, a simple route for palladium (Pd) nanoparticles attached to the surface of hollow magnetic Fe₃O₄/P (GMA‐DVB)‐polyethyleneimine (PEI) microspheres was established. Due to the large amount of imidogen groups and tertiary amine groups presenting in the PEI, Pd²⁺ ions could be anchored to the support by complexation with a polyfunctional organic ligand. Thereafter, a magnetic Pd catalyst having a high loading amount and good dispersibility was obtained by reducing Pd²⁺ ions. Afterwards, the prepared catalyst was characterized by TEM, SEM, FTIR, XRD, TGA, VSM, and UV–vis in detail. Ultimately, their catalytic activity was evaluated using the reduction of 4‐nitrophenol (4‐NP). Research showed that the Fe₃O₄/P (GMA‐DVB)‐PEI/Pd catalyst possessed high catalytic performances for the reduction of 4‐NP with a conversion rate of 98.43% within 540 s. Furthermore, the catalyst could be easily recovered and reused at least for nine successive cycles.     

Preparation and evaluation of poly glycerol sebacate/poly hydroxy butyrate core‐shell electrospun nanofibers with sequentially release of ciprofloxacin and simvastatin in wound dressings

Biodegradable wound dressing of poly glycerol sebacate/poly hydroxy butyrate was fabricated via the coaxial electrospinning process. Simvastatin and ciprofloxacin were loaded in the core and shell of the fibers, respectively. Scanning electron microscopy and transmission electron microscopy images showed a uniform core/shell structure. Introducing drugs into the polymers would cause the dressing samples to become more hydrophilic and degradation to occur faster. Drugs release would face no interventions, in which, approximately 60% of ciprofloxacin was released during the first 24 hours. Simvastatin exhibited a slower and controlled release behavior, with its release peak recorded after 2 days. The drug‐containing samples showed a proper bactericidal activity against both Gram‐positive and Gram‐negative bacteria. It may be concluded that the drug‐laden wound dressing fabricated in this study is capable of releasing the 2 drugs sequentially and that it is the ideal conditions for controlling infections and reducing wound healing duration.     

Preparation and characterization of multi‐walled carbon nanotubes decorated with silver nanoparticles through ultraviolet irradiation reduction

A facile, green and efficient approach was applied to synthesize multi‐walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (MWNT‐Ag) for further potential application. Oxidized MWNTs were decorated with silver nanoparticles (Ag NPs) via a method combining ultraviolet irradiation‐induced reduction and conventional silver mirror reaction without any reducing agent. The obtained product was characterized using various methods. X‐ray diffraction proved that the Ag NPs were synthesized successfully. Moreover, Ag NPs with a diameter of 80 nm, attached onto MWNTs, could be clearly observed in field emission scanning electron microscopy images, which also confirmed Ag NPs. Energy‐dispersive spectroscopy and transmission electron microscopy also indicated the presence of Ag NPs. Furthermore, thermogravimetric analysis was used to measure the content of Ag NPs in MWNT‐Ag, the result indicating that the weight content of Ag NPs was up to 31.88%. UV–visible absorption spectroscopy was adopted to evaluate the dispersion property of MWNT‐Ag. The result illustrated that MWNT‐Ag had a good dispersibility and stability in water. Characterization was also carried out through Fourier transform infrared spectroscopy, Raman spectroscopy and dynamic light scattering analysis.     

One‐pot synthesis of composite microspheres with core‐shell structure

One‐pot synthesis of thermoresponsive magnetic composite microspheres with a poly(N‐isopropylacrylamide) (PNIPAM) shell and a Fe₃O₄ core is demonstrated. Temperature sensitivity of PNIPAM was adopted to design the novel synthesis pathway. The as‐prepared composite microspheres have an obvious core‐shell structure with a mean size of approximately 250 nm. The Fe₃O₄ core is approximately 5 nm and the thickness of the PNIPAM shell is approximately 10 nm. The content of Fe₃O₄ in the composite microspheres can be controlled by this method. The composite microspheres experience a swelling and shrinking process in water by adjusting the temperature below and above the lower critical solution temperature (LCST) around 32 °C. These microspheres also show fine response to an external magnetic field. This work presents a platform to synthesize organic/inorganic composite microspheres in a facile and efficient approach. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2702–2708     

A New Class of “All‐Metal” Aromatic Hydrido‐Bridged Binary Coinage Metal Heterocycles. A DFT Study

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.     

Development of core‐shell structure aided by SiC‐coated MWNT in ABS/LCP blend

Agglomeration is an issue of major concern for unmodified multi‐walled carbon nanotubes (MWNTs)‐aided polymeric composites. To overcome the above‐mentioned problem, multi‐walled carbon nanotubes (MWNTs) are modified by polycarbosilane (PCS)‐derived Silicone carbide (SiC). Acrylonitrile Butadiene Styrene (ABS)/Liquid Crystalline polymer (LCP)/MWCNT nanocomposites are prepared through melt blending in a twin screw extruder. X‐Ray Diffraction (XRD) studies authenticate the creation of ß‐SiC particles. Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) studies reveal the formation of core–shell morphology involving MWNT as the core and SiC‐coated MWNT as the shell. The degree of dispersion of MWNT is far better when it has been coated with SiC. As viewed from Thermo‐gravimetric analysis (TGA), the thermal stability is substantially increased in SiC‐aided nanocomposite in comparison to ABS/LCP/unmodified CNT blend. Glass transition temperature as well as mechanical properties are improved significantly (in the presence of SiC‐coated MWNT) as a result of homogeneous dispersion exhibited by MWNT. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and characterization of carbopol‐silver nanocomposites for efficient antimicrobial applications

Carbopol‐silver nanocomposites, CP‐Ag‐NCs, were prepared by a chemical reducing method by using formaldehyde as a reducing agent (nanocomposite F), and formaldehyde in the presence of an alkaline medium resulting from the addition of Na₂CO₃ (nanocomposite FC), or NaOH (nanocomposite FO) to enhance the rate of reduction of the silver ions. The UV‐visible spectra showed the appearance of bands centered around 275, 286, and 274 nm for the nanocomposites F, FC, and FO, respectively, attributed to small silver nanoparticles (Ag‐NPs) with an average size less than 10 nm. Other bands centered around 405 and 470 nm for the nanocomposites F and FC, respectively, were attributed to large Ag‐NPs with an average size greater than 50 nm. The absence of large Ag‐NPs in the nanocomposites FO makes them as the materials of choice for the preparation of selective ultrasmall Ag‐NPs with an average size less than 3 nm. Furthermore, photoluminescence was observed upon blue excitation of the ultrasmall colloidal Ag‐NPs. Scanning electron microscopy images showed a good dispersion of the metallic Ag‐NPs in the polymer matrix. Moreover, X‐ray diffraction patterns showed peaks corresponding to the face‐centered‐cubic of the Ag‐NPs. The nature of the interaction between carbopol and Ag‐NPs was further studied by attenuated total reflectance‐Fourier transform infrared spectroscopy, and the mechanism of reduction of the silver ions was proposed. The antimicrobial activities of the CP‐Ag‐NCs were examined against Escherichia coli and Candida albicans microorganisms. The results demonstrate that the CP‐Ag‐NCs can provide new applications of these nanocomposites as efficient sensors and antimicrobial materials.     

Preparation and thermal properties of a novel core‐shell structure flame‐retardant copolymer

In order to improve the flame retardancy of polystyrene (PS), a phosphorus and nitrogen comonomer, named AC₂NP₂, was synthesized and then incorporated into various amounts of PS by seeded emulsion polymerization. The modified methacrylate (AC₂NP₂) was used as the core phase, the styrene as the shell phase, then flame‐retardant effect copolymers with core‐shell structure were prepared successfully. The particle size was ranged from 40 to 60 nm, and the structure and properties of the copolymers were characterized in detail. Notably, despite a few amounts of the AC₂NP₂ units in the copolymers, all the copolymers exhibited significantly enhanced thermal stability and reduced flammability as compared with pure PS. Furthermore, from differential scanning calorimetry test, it was observed that the glass transition temperature was tinily influenced with the incorporation of commoner. The incorporation of P‐N comonomer into PS backbone did not lead to negative effect on the glass transition behavior of PS.     

Preparation of porous g‐C3N4/Ag/Cu2O: a new composite with enhanced visible‐light photocatalytic activity

From previous reports, graphitic carbon nitride (g‐C₃N₄) can be used as a photocatalyst, although the low efficiency of solar energy utilization, small specific surface area and high recombination rate of photogenerated electron–hole pairs limit its practical application. For the purpose of increasing photocatalytic activity, especially under irradiation of visible light, we successfully synthesized a new composite, namely porous g‐C₃N₄/Ag/Cu₂O, through chemical adsorption of Ag‐doped Cu₂O on porous g‐C₃N₄, which has not been investigated carefully worldwide. The composition, morphology and optical properties of the composite were investigated through methods including X‐ray diffraction, energy‐dispersive X‐ray, Fourier transform infrared, UV–visible and photoluminescence spectroscopies and transmission electron microscopy. Using rhodamine B as organic pollutant to be degraded under the irradiation of visible light, different mass ratios of Ag/Cu₂O doped on porous g‐C₃N₄ led to enhanced photocatalytic performance of the composite compared to pure porous g‐C₃N₄. When the mass ratio of Ag/Cu₂O is 15%, porous g‐C₃N₄/Ag/Cu₂O exhibits a degradation rate 2.015 times higher than that of pure porous g‐C₃N₄. The reasons for this phenomenon may be attributed to the increased utilization efficiency of visible light, high‐speed separation of photogenerated electron–hole pairs, accelerated interfacial transfer process of electrons and increased surface area of the composite. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis,characterization and catalytic performance of core‐shell structure magnetic Fe3O4/P(GMA‐EGDMA)‐NH2/HPG‐COOH‐Pd catalyst

A strategy has been developed for the synthesis, characterization and catalysis of magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd core‐shell structure supported catalyst. The P(GMA‐EGDMA) polymer layer was coated on the surface of hollow magnetic Fe₃O₄ microspheres through the effect of KH570. The core‐shell magnetic Fe₃O₄/P(GMA‐EGDMA) modified by ‐NH₂ could be grafted with HPG. Then, the hyperbranched glycidyl (HPG) with terminal ‐OH were modified by ‐COOH and adsorbed Pd nanoparticles. The hyperbranched polymer layer not only protected the Fe₃O₄ magnetic core from acid–base substrate corrosion, but also provided a number of functional groups as binding sites for Pd nanoparticles. The prepared catalyst was characterized by UV–vis, TEM, SEM, FTIR, TGA, ICP‐OES, BET, XRD, DLS and VSM. The catalytic tests showed that the magnetic Fe₃O₄/P(GMA‐EGDMA)‐NH₂/HPG‐COOH‐Pd catalyst had excellent catalytic performance and retained 86% catalytic efficiency after 8 consecutive cycles.     

Synthesis and characterization of poly(methyl methacrylate)/casein nanoparticles with a well‐defined core‐shell structure

Well‐defined, core‐shell poly(methyl methacrylate) (PMMA)/casein nanoparticles, ranging from 80 to 130 nm in diameter, were prepared via a direct graft copolymerization of methyl methacrylate (MMA) from casein. The polymerization was induced by a small amount of alkyl hydroperoxide (ROOH) in water at 80 °C. Free radicals on the amino groups of casein and alkoxy radicals were generated concurrently, which initiated the graft copolymerization and homopolymerization of MMA, respectively. The presence of casein micelles promoted the emulsion polymerization of the monomer and provided particle stability. The conversion and grafting efficiency of the monomer strongly depended on the type of radical initiator, ROOH concentration, casein to MMA ratio, and reaction temperature. The graft copolymers and homopolymer of PMMA were isolated and characterized with Fourier transform infrared spectroscopy and differential scanning calorimetry. The molecular weight determination of both the grafted and homopolymer of PMMA suggested that the graft copolymerization and homopolymerization of MMA proceeded at a similar rate. The transmission electron microscopic image of the nanoparticles clearly showed a well‐defined core‐shell morphology, where PMMA cores were coated with casein shells. The casein shells were further confirmed with a zeta‐potential measurement. Finally, this synthetic method allowed us to prepare PMMA/casein nanoparticles with a solid content of up to 31%. Thus, our new process is commercially viable. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3346–3353, 2003     

Preparation and characterization of Ag(Au) bimetallic core–shell nanoparticles with new seed growth method

Ag(Au) bimetallic core–shell nanoparticles were prepared by a new seed growth method. Ascorbic acid was used to reduce the complex of HAuCl₄ and hexadecyltrimethylammoniumbromide (CTAB). This resulted in the forming of colorless Au(I) (AuCl₂⁻). It was used as the growth solution to prepare these bimetallic core–shell nanoparticles. These nanoparticles were characterized by UV–vis spectroscopy, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The results showed these nanoparticles exhibited core–shell shape and there was large amount of Ag in the shell. These nanoparticles could be produced in a few minutes without violent stirring and the method was easy and convenient compared with others. The effect of amount of AuCl₂⁻ on the shape of nanoparticles was also studied. Many small gold nanoparticles were formed on the surface of bimetallic core–shell nanoparticles in the presence of excess AuCl₂⁻. The mechanisms were also proposed to explain the process of colloidal preparation.     

Preparation of gel‐silica/ammonium polyphosphate core‐shell flame retardant and properties of polyurethane composites

A novel intumescent gel‐silica/ammonium polyphosphate core‐shell flame retardant (MCAPP), which contains silicon, phosphorus, and nitrogen, has been prepared by in situ polymerization. The structure of MCAPP was characterized by Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS). The properties of MCAPP were investigated by water solubility, hydrophilicity, and morphological determination. The flame retardancy and thermal stability of polyurethane (PU) composite with MCAPP were evaluated by limiting oxygen index (LOI), UL‐94 test, cone calorimetry, and thermogravimetric analysis (TGA). The results showed that MCAPP could decrease the heat release rate (HRR) and increase the thermal stability of PU materials greatly. Finally, water‐resistant properties of PU/FR composites were also studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation and characterization of high‐molecular‐weight atactic poly(vinyl alcohol)/sodium alginate/silver nanocomposite by electrospinning

High‐molecular‐weight poly(vinyl alcohol) (PVA)/sodium alginate (SA)/ silver nanocomposite was successfully prepared via electrospinning technique. Water‐based colloidal silver in a PVA/SA blend solution was directly mixing without any chemical and structural modifications into PVA/SA matrix to form an organic‐metallic nanocomposite. The effect of the addition of silver colloidal solution on the PVA/SA/silver nanocomposite was investigated through a series of experiments varying molecular weight of PVA and electrospinning processing parameters such as concentration of PVA solution, PVA/SA blend ratio, applied voltage, and tip‐to‐collector distance. In the case of PVA with number‐average degree of polymerization of 1700, by increasing the amount of SA in spinning solution, the morphology was changed from fine uniform fiber to beaded fiber or bead‐on‐string fiber structure. Increase of the amount of silver colloidal solution resulted in higher charge density on the surface of ejected jet during spinning, thus more electric charges carried by the electrospinning jet. As the charge density increased, the diameter of the nanocomposites became smaller. Transmission electron microscopy images showed that the dense silver nanoparticles were well separately dispersed in PVA/SA matrix. Energy‐disperse X‐ray analysis indicated that carbon, oxygen, natrium, and silver were the principle element of PVA/SA/silver nanocomposite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1916–1926, 2009     

One‐Step Preparation of Antimicrobial Polyrhodanine Nanotubes with Silver Nanoparticles

A simple synthetic method has been developed for the fabrication of antimicrobial polyrhodanine nanotubes with silver nanoparticles. Rhodanine monomer first forms one‐dimensional complexes with silver ions due to coordinative interactions and consecutively reduces the silver ions during chemical‐oxidation polymerization. The polymerization procedure is analyzed by transmission electron microscopy and scanning electron microscopy in situ. The synthesized silver nanoparticles/polyrhodanine nanotubes are applied as an antimicrobial agent against Gram‐negative bacteria, E. coli and Gram‐positive bacteria, S. aureus. The antimicrobial tests demonstrate that the silver/polyrhodanine nanotubes have superior antimicrobial properties to silver nanoparticles and rhodanine monomer.

     

Preparation of core‐shell structured particle and its application in toughening PA6/PBT blends

Combining the excellent mechanical strengths of polyamide 6 (PA6) with the low water absorption of poly(butylene terephthalate) (PBT) was supposed to be a feasible way to prepare a high comprehensive performance material. However, the poor compatibility between PA6 and PBT resulted in low‐notched impact strength of PA6/PBT blends. Poly(n‐butyl acrylate)/poly(methyl methacrylate‐co‐methacrylic acid) (PBMMA), a core‐shell structured modifier with controlled particle sizes, was prepared by seed emulsion polymerization and confirmed by Transmission electron microscope (TEM). The PBMMA particles as toughening modifier and compatilizer were employed to toughen PA6/PBT blends. The notched impact strength of the PA6/PBT blends was significantly increased and the water absorption was reduced with the addition of PBMMA particles. With 23.0 wt% modifier loading, the notched impact strength of the blends was 25.66 kJ/m², which was 4.04 times higher than that of pure PA6/PBT. Meanwhile, the water absorption of the blends was only 1.3%, dropping 53.6% compared with pure PA6 and reducing by 26.6% than PA6/PBT. Scanning electron microscope results showed that the PBMMA particles were dispersed in the PA6/PBT blends homogeneously, and the toughening mechanism was the cavitation of rubber particles and shear yielding of the matrix. Thermo‐gravimetric analysis analysis demonstrated that the compatibility between PA6 and PBT was improved with the addition of core‐shell PBMMA particles. The core‐shell particles could be used as an effective modifier to achieve the high toughness and low water absorption for PA6/PBT blends. Copyright © 2016 John Wiley & Sons, Ltd.     

Visible light photochemical synthesis of ultrasmall palladium/copper bimetallic particles at room temperature and its catalytic application in degradation of p-NP

Pt-based metals are very effective catalysts widely adopted in many fields. But the high cost prevents its further industrial application. One of the effective ways to solve the problem is to replace platinum with relatively cheap palladium and its alloy with copper. However, producing Pd/Cu bimetallic catalysts efficiently and economically with controllable particle size and uniform distribution is still challenging, especially when trying to reduce the consumption of precious metals. In this paper, ultrasmall palladium/copper (Pd/Cu) bimetallic catalysts with even dispersion were prepared on multi-walled carbon nanotubes (MWCNTs) by adding polyethylene glycol 400 (PEG 400) as a reducing agent and stabilizer under visible light irradiation at room temperature. The catalytic performance was studied in the catalysis of p-nitrophenol (p-NP) reduction. Of all the bimetallic catalysts produced in different conditions, the best one was obtained under the reaction condition of pH = 7 and violet light irradiation (wavelength 380–435 nm). The average particle size of 0.85 nm, and the apparent rate constant in the catalysis is 1.47 min^?1. This research probes the role of visible light as a key kinetic controlling method in the formation of ultrasmall particles (UPs). It proves the effectiveness of using visible light irradiation as an effective and more “green chemistry” approach to get precious metal UPs as catalysts beyond the traditional ultraviolet or laser photochemistry methods.