首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 11 毫秒
1.
Utilizing an ingenious control over the enhanced segmental mobility of polymer chains, we proposed a novel low‐temperature processing strategy for polymeric materials, where the materials were processed substantially below their normal glass transition temperature. This state of art was achieved by the combination of the confinement effects and the stress‐induced effects on polymer nanoparticles. This method proved to be universal for various polymer systems, that is, polystyrene, polyvinyl chloride, polycarbonate, and polyphenylene oxide. Compared with the traditional high‐temperature processing, the low‐temperature processing efficiently avoids thermal degradation, and the processed polymer maintains moderate mechanical properties. In addition, this approach provides a straightforward method for the preparation of heat‐labile bioactive polymer composites without biological surface modification. The prepared lysozyme/polystyrene composite exhibits excellent bactericidal activity and striking sustained release characteristics. This facile, universal and energy‐saving low‐temperature processing strategy is expected to open avenues toward expanding manufacturing methodology and the applications of polymeric materials, especially for bioactive composites, where conventional high‐temperature processing is not applicable. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2514–2520  相似文献   

2.
Polytetrafluoroethylene (PTFE) latices with spherical and rod‐like particles in the submicrometer size range, were employed as seeds in the emulsifier‐free methylmethacrylate (MMA) emulsion polymerization to obtain PTFE‐polymethylmethacrylate (PMMA) core‐shell nanoparticles. Stable latices were generally obtained. No residual PTFE was found at the end of the reaction. By appropriately choosing the ratio between MMA and PTFE in the reaction mixture, particles with predetermined size and monodisperse or narrow size distribution were prepared. The high structural regularity of the core‐shell samples allows the preparation of film with a periodic distribution of the cores thus ultimately leading to a well structured 2D colloidal crystal. A very peculiar crystallization behavior was observed because of the PTFE compartmentalization in the composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2928–2937, 2009  相似文献   

3.
The tribological properties of Silicon‐containing diamond‐like‐carbon (Si‐DLC) films, deposited by magnetron sputtering Si target in methane/argon atmosphere, were studied in comparison with diamond‐like‐carbon (DLC) films. The DLC films disappeared because of the oxidation in the air at 500 °C, whereas the Si‐DLC films still remained, implying that the addition of Si improved significantly the thermal stability of DLC films. Retarded hydrogen release from DLC film at high temperature and silicon oxide on the surface might have contributed to lower friction coefficient of the Si‐DLC films both after annealing treatment and in situ high‐temperature environment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

4.
《先进技术聚合物》2018,29(8):2273-2280
Multiresponsive amphiphilic poly(N,N‐dimethylaminoethyl methacrylate)‐b‐poly(N‐isopropylacrylamide) (PDMAEMA‐b‐PNIPAM) was successfully synthesized by reversible addition‐fragmentation chain transfer polymerization. Poly(N,N‐dimethylaminoethyl methacrylate)‐b‐poly(N‐isopropylacrylamide) has thermal and pH stimuli responsiveness. Their lower critical solution temperature and hydrodynamic radius can be adjusted by varying the copolymer composition, block length, solution pH, and temperature. In addition, a convenient method has been established to prepare cross‐linked silica‐coated nanoparticles with PDMAEMA‐b‐PNIPAM micelles as a template, resulting in good organic/inorganic hybrid nanoparticles defined as 175 to 220 nm. The structure and morphology were characterized by proton nuclear magnetic resonance (1HNMR), Fourier‐transform infrared spectroscopy (FT‐IR), transmission electron microscopy (TEM), and transmission electron microscopy‐energy dispersive X‐ray spectroscopy (TEM‐EDS).  相似文献   

5.
Aqueous‐Phase Reforming (APR) is a promising hydrogen production method, where biomass is catalytically reformed under high pressure and high temperature reaction conditions. To eventually study APR, in this paper, we report a high‐pressure and high‐temperature microfluidic platform that can withstand temperatures up to 200°C and pressures up to 30 bar. As a first step, we studied the phase transition of four typical APR biomass model solutions, consisting of 10 wt% of ethylene glycol, glycerol, xylose or xylitol in MilliQ water. After calibration of the set‐up using pure MilliQ water, a small increase in boiling point was observed for the ethylene glycol, xylitol and xylose solutions compared to pure water. Phase transition occurred through either explosive or nucleate boiling mechanisms, which was monitored in real‐time in our microfluidic device. In case of nucleate boiling, the nucleation site could be controlled by exploiting the pressure drop along the microfluidic channel. Depending on the void fraction, various multiphase flow patterns were observed simultaneously. Altogether, this study will not only help to distinguish between bubbles resulting from a phase transition and/or APR product formation, but is also important from a heat and mass transport perspective.  相似文献   

6.
Novel microcapsules (MCs) with organic/inorganic hybrid shell were successfully fabricated using epoxy resin as core material and nano boron nitride (BN) and mesoporous silica (SBA‐15) as inorganic shell materials in aqueous solution containing a water‐compatible epoxy resin curing agent. The morphologies, thermal properties and Young's moduli of MCs were investigated. The results indicated that epoxy resins were encapsulated by BN/SBA‐15/epoxy polymer hybrid layer, the resulting MCs were spherical in shape and the introduction of inorganic particles made MCs had rough surface morphology. The mean modulus value of MCs was from 2.8 to 3.1 GPa. The initial decomposition temperature (Tdi) of MCs at 5 wt% weight loss was from 309 to 312°C. MCs showed excellent thermal stability below 260°C. The structures and properties of MCs could be tailored by controlling the weight ratio of inorganic particle. When the weight ratio of BN to SBA‐15 was 0.15:0.10, MCs had the highest Tdi and modulus. The resulting MCs were applied to high performance 4,4′‐bismaleimidodiphenylmethane/O,O′‐diallylbisphenol A (BMI/DBA) system to design high performance BMI/DBA/MC systems. Appropriate content of MCs could improve the fracture toughness and maintain the glass transition temperature (Tg) of BMI/DBA system. The core materials released from fractured MCs could bond the fracture surfaces of the BMI/DBA matrix through the polymerization of epoxy resins. When the healing temperature schedule of 100°C/2h+150°C/1h was applied, 15 wt% MCs recovered 98% of the virgin fracture toughness of BMI/DBA. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

7.
During tempering of solute supersaturated ferrous martensite, the face‐centered cubic MC‐type carbides (M is alloy elements) such as VC and NbC phases usually co‐precipitate on crystal defects such as dislocation and take on plate‐like morphology. Over‐tempering makes the plate‐like shape change to spherical shape because of Ostwald coarsening. The coarsening process strongly correlates to the diffusion behaviors of the carbon and carbide‐forming elements, and consequently inhomogeneous compositional and structural distribution in the carbides is formed. Three‐dimensional atom probe and high‐resolution transmission electron microscopy have been proved useful methods to characterize the composition, morphology and nanostructure of the carbides that precipitate in a quench‐tempered micro‐alloyed steel. Depending on the actual affinity with C and the diffusion behavior, Si and Al are rejected from the alloy carbide, whereas Mn, V and Nb are inhomogeneously enriched in it. The morphology and structure change with the compositional redistribution. During the coarsening process of the pre‐existing plate‐like carbide, transition carbide that is semi‐coherent with ferritic matrix is formed because of the disparity in diffusion ratio of different solutes. A core–shell complex nanostructure is consequently formed in the coarsening carbide, and the core and shell are identified as V8C7 enriched in Mn, Mo and Mo2C, respectively. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

8.
Parishins are high‐polarity and major bioactive constituents in Gastrodia elata Blume. In this study, the effect of several inorganic salts on the partition of parishins in two‐phase solvent systems was investigated. Adding ammonium sulfate, which has a higher solubility in water, was found to significantly promote the partition of parishins in the upper organic polar solvents. Based on the results, a two‐phase solvent system composed of butyl alcohol/acetonitrile/near‐saturated ammonium sulfate solution/water (1.5:0.5:1.2:1, v/v/v/v) was used for the purification of parishins by high‐speed counter‐current chromatography. Fractions obtained from high‐speed counter‐current chromatography were subjected to semi‐preparative high‐performance liquid chromatography to remove salt and impurities. As a result, parishin E (6.0 mg), parishin B (7.8 mg), parishin C (3.2 mg), gastrodin (15.3 mg), and parishin A (7.3 mg) were isolated from water extract of Gastrodia elata Blume (400 mg). These results demonstrated that adding inorganic salt that has high solubility in water to the two‐phase solvent system in high‐speed counter‐current chromatography was a suitable approach for the purification of high‐polarity compounds.  相似文献   

9.
Nanosized PTFE/polystyrene core‐shell particles were prepared by seed emulsion polymerization technique starting from PTFE seeds of 20 nm. At the end of the reaction, no residual PTFE nor secondary nucleation was observed and by appropriately choosing the ratio between the monomer and the PTFE seed it was possible to obtain particles, with predetermined size in the range 60–100 nm, featuring an extremely narrow size distribution. These particles were successfully employed as building blocks for the preparation of large scale nanosized monolayers through the floating technique. Reactive ion etching was further applied to modulate the size characteristics of the resulting 2D ordered nanostructure. Although for relatively short RIE times a peculiar continuous morphology was observed in which the particles are interconnected through thin arms, on further increasing the RIE time a well‐organized 2D arrangement of particles with size of about 30 nm was obtained. Considering the shell as an expendable ordering and spacing tool, the use of core‐shell nanospheres allows a wide variety of controlled morphologies to be designed and prepared thus opening new perspectives for nanostructure fabrication processes through nanosphere lithography (NSL). Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
Cu nanoparticles surface‐capped by alkanethiols were synthesized using ligand exchange method in a two‐phase system. The effects of synthetic conditions, including the pH value of CuSO4 solution, the ratio of cetyltrimethyl ammonium bromide to CuSO4, and reaction temperature, on the size and shape of as‐synthesized Cu nanoparticles were investigated. As‐synthesized Cu nanoparticles surface‐capped by alkanethiols with different chain lengths (CxS‐Cu) were characterized by means of X‐ray diffraction, transmission electron microscopy, Fourier transform infrared spectrometry, and ultraviolet–visible light spectrometry. The tribological behavior of CxS‐Cu as an additive in liquid paraffin was evaluated with a four‐ball machine. Results indicate that cetyltrimethyl ammonium bromide plays an important role in controlling the dispersion of Cu nanoparticles before adding modifier octanethiol into the reaction solution. CxS‐Cu nanoparticles as additive in liquid paraffin possess excellent antiwear and friction‐reduction performance because of the deposition of nano‐Cu with low melting point on worn steel surface leading to the formation of a self‐repairing protective layer thereon. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
Noble metal iridium is of great interest for high‐temperature applications and extreme environments. A high (110)‐oriented iridium coating was prepared by a double glow plasma process on the surface of niobium substrate. The morphology and composition of the coating were determined by scanning electron microscopy, energy‐dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy, respectively. The phase of the coating was identified by X‐ray diffraction analysis. The misorientation angle distributions of grains on the surface and cross section of the coating were characterized by electron backscatter diffraction system. The uniform and pure iridium coating consisted of the submicrometer‐sized columnar grains with high‐angle boundary. The mean misorientation angles on the surface and cross section of the coating were 38.6° and 45.6°, respectively. After high‐temperature treatment, the coating was composed of equiaxed grains with distinct grain boundaries. Micropores appeared on the fracture surface of the coating. The micropore formation mechanism in Ir coating after high‐temperature treatment was investigated. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

12.
Studies on the relationship between resistivity and dynamic rheological properties of carbon black‐filled high‐density polyethylene (CB/HDPE) composites were carried out. Change of resistivity ρ is associated with the dynamic modulus before the positive temperature coefficient/negative temperature coefficient (PTC/NTC) transition temperature. When the temperature approaches the melting point of HDPE, ρ increases rapidly with a decreasing modulus, corresponding to PTC transition. The resistivity‐dynamic viscoelasticity relationship in the PTC region can be divided into two parts in which the changes of ρ with storage modulus G′ and loss modulus G″ can be described by the scaling laws given by the critical storage modulus and loss modulus Gc and Gc; adjustable parameters ρ′1c, ρ′2c, ρ″1c and ρ″2c; and nonlinear exponents n and m, respectively. The accordance between the experimental data and the scaling functions of the dimensionless quantities (G′/Gc ? 1) and (G″/Gc ? 1) in the PTC transition region suggests that the ρ jump may be the result of a modulus‐induced percolation. Gc and Gc increase, but the four scaling resistivitis, ρ′1c, ρ′2c, ρ″1c, and ρ″2c, decrease with increasing CB concentration, implying that the microstructure change of the composites is the determinant factor for the PTC behavior and the resistivity‐dynamic modulus relationship. However, ρ′2c and ρ″2c exhibit no scaling dependence. It is suggested that a threshold concentration exists for the modulus of the composites on the basis of examining the plot of both Gc and Gc against CB concentration. The scaling laws G′ ~ Φx and G″ ~ Φy hold for the concentration dependence of the critical modulus when Φ > Φc and the estimated values of x and y are 1.10 ± 0.10 and 0.89 ± 0.29, respectively. The resistivity‐dynamic modulus can shift to form a master curve. The horizontal factors aG and aG and the vertical factors a′ and a″ are relevant to the concentration dependence of the dynamic modulus or PTC behavior. It is believed that the former would be involved in changing the mechanical microstructure formed by the complicated interaction of CB particle and polymer segments, and the latter would be involved in the overall changes of conducting a network during the PTC transition region. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 983–992, 2003  相似文献   

13.
The molecular structures, biosynthetic pathways and physiological functions of membrane lipids produced by organisms in the domain Archaea are poorly characterized as compared with that of counterparts in Bacteria and Eukaryota. Here we report on the use of high‐resolution shotgun lipidomics to characterize, for the first time, the lipid complement of the archaeon Sulfolobus islandicus. To support the identification of lipids in S. islandicus, we first compiled a database of ether lipid species previously ascribed to Archaea. Next, we analyzed the lipid complement of S. islandicus by high‐resolution Fourier transform mass spectrometry using an ion trap‐orbitrap mass spectrometer. This analysis identified five clusters of molecular ions that matched ether lipids in the database with sub‐ppm mass accuracy. To structurally characterize and validate the identities of the potential lipid species, we performed structural analysis using multistage activation on the ion trap‐orbitrap instrument as well as tandem mass analysis using a quadrupole time‐of‐flight machine. Our analysis identified four ether lipid species previously reported in Archaea, and one ether lipid species that had not been described before. This uncharacterized lipid species features two head group structures composed of a trisaccharide residue carrying an uncommon sulfono group (?SO3) and an inositol phosphate group. Both head groups are linked to a glycerol dialkyl glycerol tetraether core structure having isoprenoid chains with a total of 80 carbon atoms and 4 cyclopentane moieties. The shotgun lipidomics approach deployed here defines a novel workflow for exploratory lipid profiling of Archaea. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

14.
A new family of thermoplastic nanocomposites based on isotactic polypropylene (iPP) and inorganic fullerene‐like tungsten disulfide (IF‐WS2) has been successfully prepared. A very efficient dispersion of IF‐WS2 material was obtained by mixing in the melted polymer without using modifiers or surfactants. The addition of IF‐WS2 nanoparticles induces a remarkable enhancement of the thermal stability of iPP, as well as an increase in the crystallization rate of the matrix when compared with pure iPP. The nucleating efficiency of IF‐WS2 solid lubricant nanoparticles on the α‐phase of iPP reaches very high values (60–70%), the highest values observed hitherto for polypropylene nanocomposites. The incorporation of IF‐WS2 has also been observed to increase the size and stability of the crystals formed. The melting behavior of the nanocomposites indicates the formation of more perfect crystals as determined by differential scanning calorimetry and time‐resolved synchrotron X‐ray scattering experiments. The new nanocomposites show an increase in the storage modulus with respect to pure iPP measured by dynamic mechanical analysis. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2309–2321, 2007  相似文献   

15.
The electric self‐heating behavior of graphite‐powder‐filled high‐density polyethylene is studied. Two equations are proposed to describe the electric‐field dependence of the self‐heating temperature and resistance dependence of the critical field. Based on Ohmic and non‐Ohmic approximations and the heat‐dissipation model, the self‐heating equations are also derived theoretically. The equations show that self‐heating is determined by the initial resistance and true positive temperature coefficient (PTC) effect under fields. Design and application principles for polymer PTC heaters are suggested on the basis of the experimental results and proposed equations. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1756–1763, 2000  相似文献   

16.
Both the separation behavior and the structure of a polymer monolith column depends on both the reaction solution composition and the polymerization conditions. In photoinitiated low‐temperature polymerization, polymerization temperature, irradiation intensity, and polymerization time were key factors to control the monolith characteristics. In this study, the effect of polymerization time on the chromatographic, material, and chemical characteristics of poly(butyl methacrylate‐co‐ethylene dimethacrylate) monoliths was studied using pyrolysis‐gas chromatography, Raman spectroscopy, inverse size exclusion chromatography, scanning electron microscopy, and chromatographic methods. Both butyl methacrylate and ethylene dimethacrylate monomers were incorporated into the monolith as the polymerization time increased, and it resulted in increases in both the flow resistance (decrease in both permeability and total/through pore porosities) and retention factors. The longer polymerization time led to lower relative amounts of free methacrylate functional groups in the monolith, i.e. cross‐linking was enhanced. The increase of the polymerization time from 8 to 12 min significantly reduced the separation efficiency for the retained analyte, whereas an increase in the fraction of the mesoporosity was observed.  相似文献   

17.
Considering the vast variety of synthetic cannabinoids and herbal mixtures – commonly known as ‘Spice’ or ‘K2’ – on the market and the resulting increase of severe intoxications related to their consumption, there is a need in clinical and forensic toxicology for comprehensive up‐to‐date screening methods. The focus of this project aimed at developing and implementing an automated screening procedure for the detection of synthetic cannabinoids in serum using a liquid chromatography‐ion trap‐MS (LC‐MSn) system and a spectra library‐based approach, currently including 46 synthetic cannabinoids and 8 isotope labelled analogues. In the process of method development, a high‐temperature ESI source (IonBoosterTM, Bruker Daltonik) and its effects on the ionization efficiency of the investigated synthetic cannabinoids were evaluated and compared to a conventional ESI source. Despite their structural diversity, all investigated synthetic cannabinoids benefitted from high‐temperature ionization by showing remarkably higher MS intensities compared to conventional ESI. The employed search algorithm matches retention time, MS and MS2/MS3 spectra. With the utilization of the ionBooster source, limits for the automated detection comparable to cut‐off values of routine MRM methods were achieved for the majority of analytes. Even compounds not identified when using a conventional ESI source were detected using the ionBooster‐source. LODs in serum range from 0.1 ng/ml to 0.5 ng/ml. The use of parent compounds as analytical targets offers the possibility of instantly adding new emerging compounds to the library and immediately applying the updated method to serum samples, allowing the rapid adaptation of the screening method to ongoing forensic or clinical requirements. The presented approach can also be applied to other specimens, such as oral fluid or hair, and herbal mixtures and was successfully applied to authentic serum samples. Quantitative MRM results of samples with analyte concentrations above the determined LOD were confirmed as positive findings by the presented method. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

18.
Electroless deposition was successfully applied in developing crystalline particles of zinc oxide onto polyester textile materials; this deposition is here presented in comparison with other materials made from poly(lactic acid), polyamide or hemp. Structural and spectroscopic characterization of the raw and deposited samples has been performed. The structure of zinc oxide particles was that of wurtzite type as indicated by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Crystallites were 20–500 nm in diameter and up to 1 µm in length. The grown particles cover the fibers not only on the fabric surface but in the textile depth. Contact angle measurement by the sessile drop method was used to study the wettability behavior of the investigated composite systems. The hierarchical roughness structure generates superhydrophobic properties onto polyester fabrics, for which water contact angles exceed 150°. The other functionalized samples also become more hydrophobic after deposition. Cassie‐Baxter model was found suitable to describe the behavior, though the fraction of surface occupied by the water–solid interface is high enough. The electroless deposition technique applied previously for cotton fabrics was once more proven to be highly reproducible, easy scalable, and cheap, allowing a wide range of applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1427–1437  相似文献   

19.
Zinc oxide nanoparticles have recently been used as effective adsorbent materials for sample pretreatment in analytical chemistry because of their excellent properties, such as high specific surface area, high effective porosity, non‐toxicity, and ease of fabrication. In this study, the zinc oxide nanoparticles functionalized by an ionic liquid, 1‐carboxyethyl‐3‐methylimidazolium chloride, were fabricated and used as the adsorbent for the solid phase extraction of five triazine herbicides in corn for the first time. High‐performance liquid chromatography was employed for the determination of these triazine herbicides. Several experimental parameters affecting the extraction efficiency were investigated, including the volume of extraction solvent, the extraction time, the type of extraction solvent and elution solvent, the amount of absorbent, and the volume of elution solvent. By using the proposed method, low limits of detection and quantification for all the five triazine herbicides were obtained between 0.71–1.08 and 2.67–3.64 ng/g, respectively. Recoveries of the proposed method range from 89.05 to 100.33% with intra‐ and inter‐day relative standard deviations lower than 8.45%. The calibration curves are linear in the concentration range of 0.005–1.00 μg/g with the correlation coefficient higher than 0.9954.  相似文献   

20.
Functional polymer/AgNPs nanocomposites have been prepared. Silver nanoparticles (NPs) were synthesized to which polyacrylamide, PAAm, was covalently bound. PAAm was synthesized via a RAFT reaction and carried thiol and carboxylic acid end groups. Thiol was used to bind the polymer to the metal surface and carboxyl for further reactions. The AgNPs were used in a post‐crosslinking reaction with a separately synthesized poly(butyl acrylate‐co‐methyl methacrylate)/polyglycidyl methacrylate core/shell latex bearing epoxy functional groups. Dynamic mechanical analysis showed that the functional AgNPs effectively crosslinked the latex polymer, and that the final product had excellent mechanical strength. Antibacterial tests revealed that the nanocomposite films had strong antibacterial activity against all types of the bacteria and the immobilization of silver NPs by crosslinking retarded the release of silver in comparison to the uncrosslinked ones. With the presented method, it is possible to obtain ductile antibacterial nanocomposites to be used as waterborne functional coatings. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1435–1447  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号