Porphyrin LB film as a catalyst for alkene epoxidation

A synthetic iron ortho-substituted tetradecylpyridyl porphyrin was used to prepare Langmuir-Blodgett films. Better spreading at the gas-liquid interface was obtained for mixed films using palmitic acid in a 1:4 proportion. The minimum area per molecule from π-A curves for the pure porphyrin monolayers is correlated to the value obtained for the flat orientation of the porphyrinic center on the water surface, as determined by the CPK model. The fatty acid causes a decrease in the porphyrin minimum area per molecule. Single monolayer LB deposition gives a monomeric film without the presence of aggregates as attested by UV-visible spectra. The film was used in the heterogeneous catalysis of cyclohexene oxidation furnishing a yield two times higher than that obtained for the homogeneous system, using the same porphyrin amount and reagent ratio. The reaction was highly selective: only cyclohexene oxide was recorded as the product, confirming that the system is a good model for cytochrome P450.     

梯形聚苯基倍半硅氧烷/聚甲基丙烯酸甲酯溶液浇注共混物的相容性

用溶液浇注法制备了具有不同质量配比的高分子量、低分子量梯形聚苯基倍半硅氧烷（ＰＰＳＱ）与聚甲基丙烯酸甲酯（ＰＭＭＡ）的共混物。用扭辫分析技术研究了不同分子量ＰＰＳＱ与ＰＭＭＡ间的相容性及热历史对其相容性的影响。ＰＰＳＱ、ＰＭＭＡ在其溶液浇注膜中是部分相容的。红外光谱分析表明，低分子量的ＰＰＳＱ（Ｙ）与ＰＭＭＡ间有较强的相互作用，故其与ＰＭＭＡ的相容性比高分子量ＰＰＳＱ的好。热历史对该类溶液浇注共混体系的相容性影响较大，加热使ＰＰＳＱ（Ｙ）／ＰＭＭＡ共混物分相，但加热可增加高分子量ＰＰＳＱ与ＰＭＭＡ间的相容性。     

Properties of polycarbonate (PC)/multi-wall carbon nanotube (MWCNT) nanocomposites prepared by melt blending

This investigation deals with an easy method to develop electrical conductivity in polycarbonate (PC)/multi-wall carbon nanotube (MWCNT) nanocomposites with low loading of MWCNT. This was achieved by melt-blending of in-situ bulk polymerized low molecular weight poly(methyl methacrylate) (PMMA)/MWCNT nanocomposites and PC in various compositions at 280 degrees C in internal mixer. Differential scanning calorimetry (DSC) study showed single Tg in (85/15 w/w) PC/PMMA blend, indicating miscibility of PC and PMMA in the blend. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies of the melt-blended PC/PMMA/MWCNT nanocomposites revealed homogeneous dispersion and distribution of MWCNTs in PC matrix. Finally, through optimizing the blending composition of PC and PMMA/MWCNT nanocomposites, electrical conductivity of 3.74 x 10(-7) S x cm(-1) was achieved in the (85/15 w/w) PC/PMMA/MWCNT nanocomposites with the MWCNTs loading as low as approximately 0.37 wt%. Storage modulus of PC was found to increase significantly in presence of small amount (0.37 wt%) of MWCNTs in the nanocomposites.     

α-PSMA共聚物与PMMA共混物的相容性

用浊点测定、傅里叶变换红外光谱、微差扫描热分析和透射电子显微镜等方法研究了苯乙烯-顺丁烯二酸酐交替共聚物(α-PSMA)与聚甲基丙烯酸甲酯(PMMA)的相容性。结果表明:α-PSMA共聚物与PMMA共混物在共混比7/93～30/70范围内相容性得到改善,其原因是由于α-PSMA与PMMA之间存在特殊的相互作用。     

PVC/PVDF/PMMA共混膜的研制

采用剪切黏度法对聚氯乙烯(PVC)/聚偏氟乙烯(PVDF)/聚甲基丙烯酸甲酯(PMMA)体系的相容性进行研究,结果表明,该体系为部分相容体系,在此基础上采用稀溶液黏度法对各共混配比的相容性进行预测.对相容性较好的PVC/PVDF/PMMA共混体系由相转化法制备共混膜,并用扫描电镜对共混膜的形态结构进行了观察.对共混膜的...     

Self-quenching of a photo-excited ruthenium complex in component-controllable mixed Langmuir-Blodgett films

The miscibility and phase behavior of the mixed monolayer of Ru(dpphen)₃²⁺ (dpphen=4,7-diphenyl-1,10-phenanthroline) (abbreviated as Ru(II)), octadecyltrichlorosilane (OTS) and stearic acid (SA) at air/water interface had been investigated in detail. Two-dimensional density of Ru(II) could be easily adjusted by changing the mixing ratio of Ru(II)/SA/OTS. The mixed monolayer of Ru(II)/SA/OTS with different molar proportions had been deposited and characterized by low angle X-ray diffraction, UV-visible absorption spectra and photo-induced emission spectra. The possible structure of its resulting LB film was proposed based on the results of the π-A isotherms and low angle X-ray diffraction. Photo-induced electron transfer and self quenching of Ru(II) in mixed LB films had been investigated in detail.     

Platelet reactions to modified surfaces under dynamic conditions

The influence of surfaces on the reactions of platelets in whole blood under laminar flow was investigated in a cone and plate viscometer. Citrated whole blood was exposed to steel, PMMA and PMMA modified with PEO at low (500 s–1) and high (4000 s–1) wall shear rates at room temperature for a period of 100 s. Treated blood samples were fixed with paraformaldehyde, stained with a monoclonal antibody for CD41 (platelet GPIIb/IIIa) conjugated with phycoerythrin and analyzed by flow cytometry. The reactions of platelets (microparticle generation and formation of platelet–platelet, platelet–red blood cell and red blood cell–microparticle aggregates) to these environments were quantified. Additionally, the size of platelet–platelet aggregates was assessed. The percentage platelet aggregation and numbers of microparticles generated were independent of surface type at any shear rate. The composition of the aggregates formed was influenced by the surface: at low and high shear rates PMMA caused the generation of platelet–platelet aggregates of the greatest size. The numbers of red blood cell–platelet and red blood cell–microparticle aggregates also varied depending on the surface. Fewer red blood cell–platelet aggregates were formed at higher shear rates, whereas the reverse was true for red blood cell–microparticle aggregates. It is concluded that these variations may help to explain the differential effects of surfaces to the induction of distant thrombotic events: microparticles may be protected from loss from the blood stream by their association with red blood cells at high shear rates. © 1998 Kluwer Academic Publishers     

Facile synthesis of silver immobilized-poly(methyl methacrylate)/polyethyleneimine core–shell particle composites

A facile route to synthesize silver-embedded-poly(methyl methacrylate)/polyethyleneimine (PMMA/PEI-Ag) core–shell particle composites was illustrated in this present work. PMMA/PEI core–shell particle templates were first prepared by a surfactant-free emulsion polymerization. PEI on the templates' surface was further used to complex and reduce Ag⁺ ions (from silver nitrate solution) to silver nanoparticles (AgNPs) at ambient temperature, resulting in the PMMA/PEI-Ag particle composites. The formation of AgNPs was affected by the pHs of the reaction medium. The pH of reaction medium at 6.5 was optimal for the formation of PMMA/PEI-Ag with good colloidal stability, which was confirmed by size and size distribution, FTIR spectroscopy, UV–vis spectroscopy and X-ray diffraction. Moreover, the amount of AgNO₃ solution (4.17–12.50 g) was found to affect the formation of AgNPs. Transmission electron microscopy (TEM) indicated that the AgNPs were incorporated in the PMMA/PEI core–shell matrix, and had 6–10 nm in diameter. AgNPs immobilized on PMMA/PEI core–shell particles were also investigated by energy dispersive X-ray spectroscopy analysis mode extended from scanning electron microscopy (SEM/EDS). Furthermore, the presence of AgNPs was found to influence the thermal degradation behavior of PMMA/PEI particle composites as observed through thermogravimetric analysis (TGA).     

Poly(methyl methacrylate) monolayers at the air–water interface

Several poly(methyl methacrylate) (PMMA) molecules with various chain numbers has been synthesised using Emulsifier-free emulsion polymerisation method. Langmuir–Blodgett thin film technique is an excellent method to investigate the surface behaviours of organic monolayers at the air–water interface. In this study, PMMA molecules have been studied at the air–water interface using Langmuir–Blodgett thin film method. Area per molecule for several PMMA molecules is found to be between 0.29 ± 0.01 and 0.98 ± 0.01 nm². The surface pressure–area graphs were taken in two stages i.e. during the first compression of the monolayer and also during the second compression of the same monolayer before the collapsed stage of the monolayer. It is also found that first surface pressure–area graph for the first compressing of the monolayer at the water surface is different than the surface pressure–area graph obtained after a decompression of the monolayer. Isotherm graphs show that long alkyl chain groups of these molecules may cause aggregation behaviours on water surface and a model for the behaviour of PMMA molecules on the air–water interface due to surface interactions has been proposed.     

Atomic force microscopy studies of lateral phase separation in mixed monolayers of dipalmitoylphosphatidylcholine and dilauroylphosphatidylcholine

Atomic force microscopy imaging of dipalmitoylphosphatidylcholine (DPPC)/dilauroylphosphatidylcholine (DLPC) monolayers deposited onto alkanethiol modified-gold surfaces by the Langmuir–Schaefer technique was used to investigate domain formation in a binary system where phase separation arises from a difference in the alkyl chain lengths of the lipids. We have established how the condensed domain structure (shape and size) in DPPC/DLPC monolayers depends on the surface pressure and lipid composition. The mixed monolayers exhibit a positive deviation from an ideal mixing behavior at surface pressures of 32 mN/m. Lateral compression to pressures greater than the liquid-expanded-to-liquid-condensed (LE-to-LC) phase transition pressure of the mixed monolayer (8–16 mN/m) induces extensive separation into condensed DPPC-rich domains and a fluid DLPC matrix. The condensed structures observed at a few milliNeutons per meter above the LE-to-LC transition pressure resemble those reported for pure DPPC monolayers in the LE/LC co-existence region. At a bilayer equivalence pressure of 32 mN/m and 20 °C, condensed domains exist between x_DPPC 0.25 and 0.80, analogous to aqueous DPPC/DLPC dispersions. Compression from 32 to 40 mN/m results in either a striking distortion of the DPPC domain shape or a break-up of the microscopic DPPC domains into a network of nanoscopic islands (at higher DPPC mol fractions), possibly reflecting a critical mixing behavior. The results of this study provide a fundamental framework for understanding and controlling the formation of lateral domain structures in mixed phospholipid monolayers.     

嵌段共聚物增容共混聚合物的相形貌及胶束迁移行为研究

主要研究了对称性的聚苯乙烯-聚甲基丙烯酸甲酯嵌段共聚物(PS-b-PMMA,简称SM)对聚甲基丙烯酸甲酯/聚甲基丙烯酸环己酯(PMMA/PCHMA)熔融共混体系的增容。采用透射电子显微镜(TEM)表征了SM和PMMA分子量对共混体系微观相形态和胶束迁移行为的影响。研究表明,SM分别在PMMA与PCHMA均聚物中形成不同结构的胶束,当SM在PMMA/PCHMA界面上形成"湿刷"时,SM在PCHMA相中形成的胶束才能迁移到PMMA相中。SM的加入改善了PMMA与PCHMA之间的相容性,但其增容效果取决于SM的分子量。随着分散相PMMA分子量从19kg/mol增加到39kg/mol,PMMA粒子的平均粒径逐渐增加。     

水热反应温度对PMMA/TiO_2复合纳米纤维膜的形貌和性能的影响

利用静电纺丝技术成功制备了聚甲基丙烯酸甲酯/钛酸四正丁酯(PMMA/TBT)复合纳米纤维膜,通过水热法处理得到了PMMA/TiO_2柔性复合纳米纤维膜。通过傅立叶红外光谱(FTIR)、热失重分析法(TGA)、X射线衍射法(XRD)等手段对PMMA/TiO_2复合纳米纤维膜进行了表征,借助扫描电子显微镜(SEM)、全自动比表面积及孔隙分析仪(BET)对该材料的形貌结构、孔隙结构进行分析,最后探讨了所制备的纳米纤维膜的光催化降解能力,综合分析了反应温度对水热法制备PMMA/TiO_2复合纳米纤维膜的形貌、结构及性能的影响。结果表明:水热反应温度为200℃时,得到的PMMA/TiO_2复合纳米纤维膜中TiO_2晶型为纯锐钛矿型,且晶体生长速率较快,比表面积较大,对污染物亚甲基蓝的脱色效率最高,可达98.93%。     

Morphology, defect evolutions and nano-mechanical anisotropy of behenic acid monolayer

Langmuir-Blodgett monolayers of behenic acid (BA) were prepared by the vertical deposition method and their morphological evolutions and nano-mechanical anisotropy were studied by atomic force microscopy (AFM) and lateral force microscopy. Results show that there are platforms in the differential surface pressure-area (π-A) isotherm presenting linear relations between the chain tilting angles and surface pressures. The reorganization, appearance and disappearance of defects such as pinholes and holes can strongly affect the profile of π-A isotherm; AFM images reflect evolution rules from pinholes to holes, and from monolayer to bilayers along with compression and relaxation of structures in BA monolayer. Due to higher molecule density and larger real contact area, the tip-monolayer contacts at 15 and 25 mN/m correspond to the Derjaguin-Muller-Toporov (DMT) model showing long-ranged interaction forces. But owing to more easily-deformed conformations, contacts at 5 and 35 mN/m accord with the Johnson-Kendall-Robert and DMT transition cases exhibiting short-ranged interface interactions. A little higher friction is proved in the direction perpendicular to the deposition.     

HA改性短切碳纤维/PMMA生物复合材料力学性能的研究

采用原位合成与溶液共混的方法,制备了纳米羟基磷灰石(HA)-短切碳纤维（C_f）/聚甲基丙烯酸甲酯(PMMA)生物复合材料, 研究了HA对HA-C_f/PMMA复合材料的力学性能和微观结构的影响. 采用万能材料试验机测试了HA-C_f/PMMA复合材料的力学性能,用X射线衍射仪（XRD）、透射电镜（TEM）、场发射扫描电子显微镜（FESEM）和红外吸收光谱仪(FT-IR)分析测试手段对材料的组成结构及断面的微观形貌等进行了测试和表征. 结果表明,采用卵磷脂改性后的HA纳米片与PMMA基体的界面结合性能得到了有效改善,显著提高了复合材料的力学性能;随着HA含量的增加,HA-C_f/PMMA复合材料的弯曲强度、拉伸强度、压缩强度、弯曲模量和拉伸模量均呈先增大后减小的趋势. 当HA含量在8wt%时,复合材料的力学性能最佳.     

In vitro evaluation of a new polymethylmethacrylate cement reinforced with hydroxyapatite

The nature of the orthopedic implant surface affects the interaction between cells and subsequent bone formation. The bone/cement interface in cement-held prostheses is considered to be the main cause of fracture leading to implant revision. It is thought that the introduction of a bioactive phase, such as hydroxyapatite (HA), to cement may permit a stronger implant by encouraging direct bone apposition rather than encapsulation of the implant by fibrous tissue. Thus, a poly(methylmethacrylate) (PMMA) cement incorporating 17.5% HA by weight has been investigated. In this study, in order to analyze the interaction at the cellular level, the in vitro biological response of the HA/PMMA to a similar PMMA without HA incorporation has been studied. Primary human osteoblast-like cells (HOB) were used as they are a model of the cell type the cements might encounter in vivo. Cell proliferation and growth were assessed by measurement of total cellular DNA and tritiated thymidine ([³H]-TdR) incorporation. Alkaline phosphatase (ALP) production was measured as an indicator of HOB phenotype upon the cements. The results showed that HA/PMMA was a better substrate for HOB cells, resulting in increased proliferation and ALP activity. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed that HOB cells cultured on the HA-filled PMMA preferentially anchored to HA particles exposed at the cement surface, with a close intimacy observed between HA and HOB cells.     

Langmuir-blodgett multilayers of polymer-merocyanine-dye mixtures

Deposition studies of mixed monolayers of poly(methylmethacrylate) (PMMA) and merocyanine chromophore (M₂₂) were carried out by the Langmuir-Blodgett technique. The equilibrium surface pressure vs. specific area of the monolayers at the air-water interface was measured for several mixtures. The specific area vs. film composition at a fixed surface pressure deviated from linear behavior. The deposition of the monolayer onto a glass substrate was Z type for mixtures with high PMMA content, while Y type was preferred for mixtures with high dye content. The former structure exhibited second harmonic generation and should be of considerable interest in exploring the non-linear optical effects in Langmuir-Blodgett films. When prepared under a class 100 modular laminar flow hood and observed with reflection microscopy, the films showed no evidence of aggregate formation, suggesting that the PMMA-M₂₂ mixtures were miscible.     

Dispersion characteristics and properties of poly(methyl methacrylate)/multi-walled carbon nanotubes nanocomposites

The preparation, characterization, and properties of poly(methyl methacrylate) (PMMA)/multi-walled carbon nanotubes (MWCNTs) nanocomposites are described. Nanocomposites have been prepared by melt-blending in a batch mixer. Both unmodified and surface modified MWCNTs have been used for the nanocomposites preparation. Using both unmodified and modified MWCNTs, the effect of surface modification in nanocomposites is investigated by focusing on three major aspects: dispersion characteristics, mechanical properties, and electrical conductivity measurements. Dispersion of the MWCNTs in the PMMA matrix is examined by scanning and transmission electron microscopy that revealed a homogeneous distribution-dispersion of MWCNTs in the PMMA matrix for both unmodified and modified MWCNTs. Thermomechanical behavior is studied by dynamic mechanical analyzer and results showed a substantial improvement in the mechanical properties of PMMA in conjunction to an increase in the elastic behavior. The tensile properties of neat PMMA moderately improved after nanocomposites preparation with both modified and unmodified MWCNTs, however, electrical conductivity of neat PMMA significantly improved after nanocomposites preparation with 2 wt% unmodified MWCNTs. For example, the through plane conductivity increased from 3.6 x 10(-12) S x cm(-1) for neat PMMA to 3.6 x 10(-9) S x cm(-1) for nanocomposite. The various property measurements have been conducted and results have shown that, in overall, surface modifications have very little or no effect on final properties of neat PMMA.     

Micro-deformation mechanisms in thermoformed alumina trihydrate reinforced poly(methyl methacrylate)

Micro-deformation mechanisms involved in thermoforming of alumina trihydrate (ATH) reinforced poly(methyl methacrylate) (PMMA) was investigated in a new experimental method replicating industrial heavy-gage thermoforming procedure. Uniaxial tension tests under non-steady thermal conditions were carried out at different forming rates and forming temperatures. Stress–strain curves and load–displacement histories of thermoformed samples were studied in terms of specimen temperature at different forming conditions. Neat PMMA samples were stretched to 50% strain under identical thermoforming conditions as PMMA/ATH for comparison purposes. Stress whitening in thermoformed PMMA/ATH samples was monitored with optical microscope and degree of stress whitening was characterized by an index obtained from optical image histograms. Micro-deformation features on the surface of PMMA and PMMA/ATH samples were examined by scanning electron microscopy (SEM). Micro-deformation in neat PMMA was in the form of homogenous drawing and did not include any type of void formation. SEM images of PMMA/ATH samples showed that particle cracking is the dominant deformation mechanism at low-forming temperatures, while at high-forming temperatures, combined particle disintegration and interfacial failure are dominant mechanisms. Stress whitening was not observed in neat PMMA which was attributed to absence of micro-voids or craze-like structures. On the other hand, PMMA/ATH samples displayed different levels of stress whitening depending on density, size and type of micro-deformation features.     

Shear strength of polymers under hydrostatic pressure: Surface coatings prevent premature fracture

The effect of surface rubber coatings on the stress-strain behaviour in shear of polymethylmethacrylate (PMMA), polyethylene terephthalate (PET) and polyethylene has been examined. Uncoated PMMA fractures without yielding at high pressure, while it is ductile at lower pressures. The high pressure fracture is thought to be due to pressure fluid penetrating into surface cracks allowing them to grow in spite of the applied hydrostatic pressure. Coating in rubber prevents such penetration and PMMA remains ductile up to 7 kbar. PET and polyethylene are normally ductile at all pressures, and coating in rubber has no effect on their behaviour. Failure here is due to internal flaws.     

Rapid fabrication of large-area, corrosion-resistant superhydrophobic Mg alloy surfaces

A superhydrophobic magnesium (Mg) alloy surface was successfully fabricated via a facile electrochemical machining process, and subsequently covered with a fluoroalkylsilane (FAS) film. The surface morphologies and chemical compositions were investigated using a scanning electron microscope (SEM) equipped with an energy-dispersive spectroscopy (EDS) and a Fourier-transform infrared spectrophotometer (FTIR). The results show hierarchal rough structures and an FAS film with a low surface energy on the Mg alloy surfaces, which confers good superhydrophobicity with a water contact angle of 165.2° and a water tilting angle of approximately 2°. The processing conditions, such as the processing time and removal rate per unit area at a constant removal mass per unit area, were investigated to determine their effects on the superhydrophobicity. Interestingly, when the removal mass per unit area is constant at approximately 11.10 mg/cm(2), the superhydrophobicity does not change with the removal rate per unit area. Therefore, a superhydrophobic Mg alloy surface can be rapidly fabricated based on this property. A large-area superhydrophobic Mg alloy surface was also fabricated for the first time using a small-area moving cathode. The corrosion resistance and durability of the superhydrophobic surfaces were also examined.