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1.
三嵌段共聚物EO20PO70EO20相分离行为的耗散粒子动力学模拟   总被引:1,自引:0,他引:1  
采用耗散粒子动力学(DPD)方法研究了嵌段共聚物EO20PO70EO20(P123)在水、乙醇/水溶液及二氧化硅溶胶体系中的相分离行为. 不同质量分数的P123在水溶液中共形成4种相分离状态: 球状胶束(10%); 椭球胶束(20%)、棒状胶束(30%)和三维立方胶束(50%). 在模板剂质量分数为10%的乙醇/水溶液中, 模板剂胶束稳定性随着乙醇含量的增加而变差. 在二氧化硅溶胶体系中, 模板剂质量分数低于5%时无胶束形成; 模板剂质量分数增至10%时, P123发生相分离形成三维球状胶束; 随着模板剂质量分数的进一步增加, 模板剂分子夹含着水分子形成三维椭球状结构(20%)、三维立方结构(40%)和层状结构(60%). 模拟结果与实验结果一致, 说明DPD模拟可以从计算角度推测模板剂对介孔材料结构的影响.  相似文献   

2.
以十六烷基三甲基溴化铵(CTAB)为模板剂, Ce(NO3)3和Mn(NO3)2为前驱体, 通过沉淀法制备了一系列晶粒小于5 nm的高比表面积MnOx-CeO2催化剂, 并考察了催化剂的CO氧化反应性能. 采用XRD、Raman光谱、TPR和N2气吸附脱附等手段对催化剂的比表面积、晶粒大小和物相组成进行了表征. 当Mn摩尔分数≤34%时, 催化剂的比表面积在160~170 m2/g之间; 当锰含量进一步提高后, 催化剂的比表面积呈下降趋势. 当Mn摩尔分数≤34%时, XRD只检测到CeO2物相, 而Raman光谱则检测到α-Mn2O3的存在. 催化剂上表现出较好的CO氧化活性, 这主要归因于高比表面积. 随着锰含量的增加, 催化剂的轻化频率(TOF)下降, 表明高分散、小晶粒的氧化锰物种是催化剂的活性物种. H2-TPR结果表明, 催化剂的CO氧化活性还与催化剂中高价锰物种有关. 焙烧温度升高使催化剂的晶粒增大、比表面积减小, 同时催化剂中锰的平均价态降低, 导致CO氧化活性下降.  相似文献   

3.
Porous sulfated zirconia foams were manufactured by a simple methodology based on the sol–gel process combined with a liquid foam template that used a surfactant mixture. A block copolymer (Pluronic F-127) and an anionic surfactant [sodium dodecylsulfate (SDS)] were mixed in different proportions in order to optimize the porous and surface properties of the ceramic material. By adjusting the SDS/Pluronic ratio, it was possible to obtain sulfated zirconia with a combination of macropores and mesopores that provided high porosity (≈90 %) and surface area (≈80 m2 g?1). The sulfate groups linked to the zirconia surface stabilized the tetragonal phase, to the detriment of the thermodynamically stable monoclinic phase. The sulfate groups and the tetragonal phase decreased as a function of the amount of SDS in the liquid foam template. The combined porous and structural characteristics, together with surface acidity, provided enhanced catalytic activity when the sulfated zirconia foams were employed in the isopropanol dehydration reaction. A further benefit was the selectivity towards propene and negligible formation of acetone.  相似文献   

4.
The electrically conductive polypyrrole/dodecylbenzene sulfonic acid/poly(N‐isopropylacrylamide‐co‐acrylic acid) (PPy/DBSA/poly(NIPAAm‐co‐AA)) composite microgels were synthesized by a chemical oxidation of pyrrole in the presence of DBSA as the primary dopant, and poly(NIPAAm‐co‐AA) microgels as the polymeric codopant and template, in which APS was used as the oxidant. It was proposed to prepare “intelligent” polymer microgel particles containing both thermosensitive and electrically conducting properties. The polymerization of pyrrole took place directly inside the microgel networks, leading to formation of composite microgels and the morphology was observed by transmission electron microscope. PPy particles interacted strongly with microgels, as the acid groups of microgels acted as the polymeric codopant. The composite microgels thus formed showed electrically conducting behavior dependent on humidity and temperature. At temperatures lower than lower critical solution temperature, the conductivity decreased with increasing the humidity and a small hysteresis phenomenon was observed. The hysteresis became indistinct when temperature was near volume phase transition temperature. However, after the treatment of high temperature and high humidity, the conductivity increased surprisingly due to the structure reorganization inside the composite microgels. The distinctive functionality of the PPy composite microgels was expected to be utilized in many attractive applications. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1648–1659, 2006  相似文献   

5.
Concepts leading to single enantiomers of chiral molecules are of crucial importance for many applications, including pharmacology and biotechnology. Recently, mesoporous metal phases encoded with chiral information have been developed. Fine‐tuning of the enantioaffinity of such structures by imposing an electric potential is proposed, which can influence the electrostatic interactions between the chiral metal and the target enantiomer. This allows the binding affinity between the chiral metal and the target enantiomer to be increased, and thus, the discrimination between two enantiomers to be improved. The concept is illustrated by generating chiral encoded metals in a microfluidic channel by reduction of a platinum salt in the presence of a liquid crystal and l ‐tryptophan as a chiral model template. After removal of the template molecules, the modified microchannel retains a pronounced chiral character. The chiral recognition efficiency of the microchannel can be fine‐tuned by applying a suitable potential to the metal phase. This enables the separation of both components of a racemate flowing through the channel. The approach constitutes a promising and complementary strategy in the frame of chiral discrimination technologies.  相似文献   

6.
Agarose template for the fabrication of macroporous metal oxide structures   总被引:1,自引:0,他引:1  
Agarose gels have been applied as templates for the formation of macroporous metal oxide structures. The preparation of the agarose template is extremely simple, and with variation of the agarose content, control over morphology is demonstrated: The average pore size decreases from 180 to 55 nm and the surface area increases from 238 to 271 m2 g(-1) with increasing agarose content in the gel. The gelling temperature was also found to influence the final template morphology. Conducting sol-gel chemistry within the template structure followed by removal of the template by heating to 450 degrees C gives porous inorganic oxides. The technique has been demonstrated for the oxides of titanium, zirconium, niobium, and tin. The final morphology of the metal oxide is homogeneous and results from a coating of the agarose structure. The pore diameter decreased and the specific surface area of the titanium dioxide materials increased from 28 to 66 m2 g(-1) as the agarose content in the template is increased from 0.5 to 5.0 wt%. The overall pore size and surface area are lower than the original gel due to shrinkage occurring with the sol-gel process, as well as crystallization and a loss of microporosity in the final material.  相似文献   

7.
Polyacrylonitrile/polystyrene micrometer‐sized composite particles of narrow size distribution were prepared by a single‐step swelling of uniform polystyrene template microspheres with emulsion droplets of methylene chloride containing the monomer acrylonitrile and the initiator benzoyl peroxide. Methylene chloride was then evaporated carefully, followed by polymerization of acrylonitrile at 70 °C within the shrunken template particles. Polymerization of acrylonitrile also occurred at the particles' surface due to the interaction of surface polyacrylonitrile oligoradicals with acrylonitrile dissolved in the aqueous phase. Uniform polyacrylonitrile particles of higher surface area were formed by dissolving the template polystyrene polymer of the composite particles. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, TGA‐DSC, XRD, XPS, advancing contact angle, light microscope, SEM and cross‐sectional TEM. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4847–4861, 2004  相似文献   

8.
Summary: Electro‐active shape‐memory composites were synthesized using conducting polyurethane (PU) composites and multi‐walled carbon nanotubes (MWNTs). Surface modification of the MWNTs (by acid treatment) improved the mechanical properties of the composites. The modulus and stress at 100% elongation increased with increasing surface‐modified MWNT content, while elongation at break decreased. MWNT surface modification also resulted in a decrease in the electrical conductivity of the composites, however, as the surface modified MWNT content increased the conductivity increased (an order of 10−3 S · cm−1 was obtained in samples with 5 wt.‐% modified‐MWNT content). Electro‐active shape recovery was observed for the surface‐modified MWNT composites with an energy conversion efficiency of 10.4%. Hence, PU‐MWNT composites may prove promising candidates for use as smart actuators.

The electro‐active shape‐recovery behavior of PU‐MWNT composites. The pictured transition occurs within 10 s when a constant voltage of 40 V is applied.  相似文献   


9.
Titanium is successfully incorporated in hexagonal mesoporous silica to form Ti‐MCM41 at low temperature. Silatrane and titanium glycolate synthesized from the oxide one‐pot synthesis process are used as the precursors. Using the cationic surfactant cetyltrimethylammonium bromide as a template, the resulting meso‐structure mimics the liquid‐crystal phase. The percentage of titanium loading is varied in the range 1–35%. The temperatures used in the preparation are 60 °C and 80 °C. After heat treatment, very high surface area mesoporous silica was obtained and characterized using diffuse reflectance UV (DRUV) spectroscopy, X‐ray diffraction (XRD), BET surface area, X‐ray fluorescence, energy dispersive spectroscopy and transmission electron microscopy (TEM). At 35% titanium, the titanium atom is also in the framework showing the pattern of hexagonal mesostructure, as shown by DRUV, XRD and TEM results. The surface area is extraordinarily high, up to more than 2300 m2 g?1, and the pore volume is as high as 1.3 cm3 g?1 for a titanium loading range of 1–5%. Oxidative bromination reaction using Ti‐MCM‐41 as catalyst showed impressive results, with the 60 °C catalysts having higher activity. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

10.
 以十六烷基三甲基溴化铵(CTMAB)为模板剂,合成出Zr-FSM-16中孔分子筛,并采用XRD,IR和BET等对分子筛进行了表征. 考察了Zr掺杂量和pH值等因素对分子筛结构的影响,并考察了合成出的Zr-FSM-16分子筛对苯羟基化反应的催化性能. 结果表明,Zr能有效地嵌入FSM-16的骨架之中,但Zr的嵌入对分子筛中孔结构的形成具有一定的不利影响,随着Zr嵌入量的增加,分子筛的长程有序度会下降; pH值对分子筛中孔结构的形成也具有十分显著的影响,在n(Si)/n(Zr)=40的条件下, pH<12.5时,有序度随着pH值的升高而升高,pH>12.5时则相反. 一般在n(Si)/n(Zr)>40时,催化剂均能保持较好的六方晶体结构和较大的比表面积; n(Si)/n(Zr)<20时,则较难形成中孔结构. Zr-FSM-16对于苯的羟基化反应具有良好的催化性能,催化活性和选择性均随Zr嵌入量的增加而升高,n(Si)/n(Zr)=40时,苯酚的选择性可达65%以上.  相似文献   

11.
The effect of the triblock copolymer poly[styrene‐b‐(ethylene‐co‐butylene)‐b‐styrene] (SEBS) on the formation of the space charge of immiscible low‐density polyethylene (LDPE)/polystyrene (PS) blends was investigated. Blends of 70/30 (wt %) LDPE/PS were prepared through melt blending in an internal mixer at a blend temperature of 220 °C. The amount of charge that accumulated in the 70% LDPE/30% PS blends decreased when the SEBS content increased up to 10 wt %. For compatibilized and uncompatibilized blends, no significant change in the degree of crystallinity of LDPE in the blends was observed, and so the effect of crystallization on the space charge distribution could be excluded. Morphological observations showed that the addition of SEBS resulted in a domain size reduction of the dispersed PS phase and better interfacial adhesion between the LDPE and PS phases. The location of SEBS at a domain interface enabled charges to migrate from one phase to the other via the domain interface and, therefore, resulted in a significant decrease in the amount of space charge for the LDPE/PS blends with SEBS. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2813–2820, 2004  相似文献   

12.
Poly‐l‐lactic acid (PLLA) is considered as a potential bone scaffold material because of good biocompatibility and bioabsorbability, whereas too slow degradation rate limits its application. In this study, montmorillonite (MMT) was introduced into PLLA scaffolds fabricated via selective laser sintering to accelerate degradation by reducing crystallinity. To be specific, MMT was a layered silicate with large surface area and aspect ratio, which provided nucleation site for the crystallization of PLLA molecular chain along their surface during the sintering process. As the surface of MMT plate was randomly oriented in the matrix, the growth direction of crystallite was also random, which interrupted the orderly crystallization, thus decreasing the overall crystallinity of PLLA. As a result, the crystallinity of PLLA scaffolds was decreased from 32.3% to 27.4% when introducing 4.5% MMT. Accordingly, weight loss was increased from 0.83% to 7.25% after immersing for 4 weeks. Besides, the tensile strength and modulus of the scaffolds increased by 44.1% and 66.9% because of the change of fracture mode from brittle fracture to ductile fracture. In addition, the scaffolds also demonstrated good hydrophilic property and cell compatibility.  相似文献   

13.
Molecularly imprinted microspheres containing binding sites for the extraction of 4‐cumylphenol have been prepared for the first time. The imprinted microspheres were synthesized by a precipitation method using 4‐cumylphenol as a template molecule, methacrylic acid as a functional monomer and divinylbenzene‐80 as a cross‐linker for polymer network formation. The formation and the morphology of molecularly imprinted microspheres were well characterized using infrared spectroscopy, thermogravimetric studies, and scanning electron microscopy. The Brunauer–Emmett–Teller analysis revealed the high surface area of the sorbent indicating formation of molecularly imprinted microspheres. The developed microspheres were employed as a sorbent for the solid‐phase extraction of 4‐cumylphenol and showed fast uptake kinetics. The sorption parameters were optimized to achieve efficient sorption of the template molecule, like pH, quantity of molecularly imprinted microspheres, time required for equilibrium set‐up, sorption kinetics, and adsorption isotherm. A standard method was developed to analyze the sorbed sample quantitatively at 279 nm using high‐performance liquid chromatography with diode array detection. It was validated by determining target analyte from synthetic samples, bottled water, spiked tap water, and soil samples. The prepared material is a selective and robust sorbent with good reusability.  相似文献   

14.
以Na2WO4·2H2O和Bi(NO3)3·5H2O为原料,通过不同表面活性剂为模板剂对所制备催化剂的形貌进行调控,将调控形貌后的催化剂固载不同种类杂多酸(HPA),再进行超临界流体干燥制得HPA/Bi2WO6光催化剂。并采用X射线衍射(XRD)、紫外-可见漫反射(UV-vis)、扫描电镜(SEM)、比表面积测定仪(BET)对所制备的催化剂进行表征,通过含氮模拟油对固载杂多酸后的催化剂的脱氮性能进行评价。结果表明,十二烷基硫酸钠(SDS)能起到更好的模板导向作用,从而获得由二维纳米片组装成的三维中空花状结构。采用超临界流体萃取干燥技术对催化剂进行提纯干燥,可有效地避免孔塌陷、团聚等现象,进一步增大了催化剂的比表面积,其脱氮效果有了进一步的提高。固载磷钨酸能有效地提高催化剂的表面酸性位点,从而显著提高了催化剂的催化活性,磷钨酸固载量为10%、剂油比为1∶100时、氙灯光照3 h脱氮率可达92.08%。  相似文献   

15.
The facile synthesis of a porous carbon material that is doped with iron‐coordinated nitrogen active sites (FeNC‐70) is demonstrated by following an inexpensive synthetic pathway with a zeolitic imidazolate framework (ZIF‐70) as a template. To emphasize the possibility of tuning the porosity and surface area of the resulting carbon materials based on the structure of the parent ZIF, two other ZIFs, that is, ZIF‐68 and ZIF‐69, are also synthesized. The resulting active carbon material that is derived from ZIF‐70, that is, FeNC‐70, exhibits the highest BET surface area of 262 m2 g?1 compared to the active carbon materials that are derived from ZIF‐68 and ZIF‐69. The HR‐TEM images of FeNC‐70 show that the carbon particles have a bimodal structure that is composed of a spherical macroscopic pore (about 200 nm) and a mesoporous shell. X‐ray photoelectron spectroscopy (XPS) reveals the presence of Fe‐N‐C moieties, which are the primary active sites for the oxygen‐reduction reaction (ORR). Quantitative estimation by using EDAX analysis reveals a nitrogen content of 14.5 wt. %, along with trace amounts of iron (0.1 wt. %), in the active FeNC‐70 catalyst. This active porous carbon material, which is enriched with Fe‐N‐C moieties, reduces the oxygen molecule with an onset potential at 0.80 V versus NHE through a pathway that involves 3.3–3.8 e? under acidic conditions, which is much closer to the favored 4 e? pathway for the ORR. The onset potential of FeNC‐70 is significantly higher than those of its counterparts (FeNC‐68 and FeNC‐69) and of other reported systems. The FeNC‐based systems also exhibit much‐higher tolerance towards MeOH oxidation and electrochemical stability during an accelerated durability test (ADT). Electrochemical analysis and structural characterizations predict that the active sites for the ORR are most likely to be the in situ generated N? FeN2+2/C moieties, which are distributed along the carbon framework.  相似文献   

16.
A new class of porous materials, having hydrophobic scaffold embedded with aligned porous hydrophilic domains, was in situ fabricated through combination of emulsion‐templated method and unidirectional freezing technique. A water‐in‐oil high internal phase emulsion (HIPE) was prepared with the mixture of styrene and divinylbenzene as continuous phase and a poly(vinyl alcohol) (PVA) aqueous solution as dispersed phase. After polymerization of the continuous phase and subsequently unidirectional freezing, the dispersed phase, a macroporous poly(styrene/divinylbenzene) embedded with an aligned PVA domain, was obtained. The effects of the polymerization temperature, PVA concentration, and freezing rate on these porous materials were investigated. It was found that the PVA domain size and the aligned channel size were dependent on the polymerization temperature, the PVA concentration, and freezing rate. The fabrication method in this work, combining of unidirectional freezing and emulsion template, not only allows to prepare hydrophobic–hydrophilic polyHIPEs having a sea island structure but also dramatically improves the stiffness and specific surface area of the resulting polyHIPEs. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

17.
This article shows that there is great interest in using an electrochromatographic microchip made of hexyl acrylate (HA) based porous monolith cast within the channel of a cyclic olefin copolymer (COC) device. The monolith is simultaneously in situ synthesized and anchored to the inner walls of the channel in less than 10 min. By appropriate choice of light intensity used during the synthesis, the separation efficiency obtained for nonpolar solutes such as polycyclic aromatic hydrocarbons (PAH) is increased up to 250 000 plates/m. The performance of this HA‐filled COC microchip was investigated for a wide range of analytes of varying nature. The reversed‐phase separation of four aflatoxins is obtained in less than 2 min. The baseline separation of a mixture of neurotransmitters including six amino acids and two catecholamines is possible thanks to the superimposition of the differences in electrophoretic mobility on the chromatographic process. The durability of the system at pH 13 allows the separation of five biogenic amines and the quantitative determination of two of them in numerous wine samples. The feasibility of on‐line preconcentration is also demonstrated. Hydrophilic surface modification of COC channel via UV‐photografting with poly(ethylene glycol) methacrylate (PEGMA) before in situ synthesis of HA, is necessary to reduce the adsorption of very hydrophobic solutes such as PAH during enrichment. The detection limit of fluoranthene is decreased down to less than 1 ppb with a preconcentration of 4.5 h on the HA‐filled PEGMA functionalized COC microchip.  相似文献   

18.
The miscibility of polysulfone (PSf) with various hydrophilic copolymers was explored. Among these blends, PSf gave homogeneous mixtures with poly(1‐vinylpyrrolidone‐co‐styrene) [P(VP–S)] copolymers when these copolymers contained 68–88 wt % 1‐vinylpyrrolidone (VP). Miscible PSf blends with P(VP–S) copolymers underwent phase separation on heating caused by lower critical solution temperature (LCST)‐type phase behavior. The phase behavior depended on the copolymer composition. Changes in the VP content of P(VP–S) copolymers from 65 to 68 wt % shifted the phase behavior from immiscibility to miscibility and the LCST behavior. The phase‐separation temperatures of the miscible blends first increased gradually with the VP content, then went through a broad maximum centered at about 80 wt % VP, and finally decreased just before the limiting content of VP for miscibility with PSf. The interaction energies of binary pairs involved in PSf/P(VP–S) blends were evaluated from the phase‐separation temperatures of PSf/P(VP–S) blends with lattice‐fluid theory combined with a binary interaction model. The decrease in the contact angle between water and the membrane surface with increasing VP content in P(VP–S) copolymers indicated that the hydrophobic properties of PSf could be improved via blending with hydrophilic P(VP–S) copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1401–1411, 2003  相似文献   

19.
A novel core–shell magnetic nano‐adsorbent with surface molecularly imprinted polymer coating was fabricated and then applied to dispersive micro‐solid‐phase extraction followed by determination of rhodamine 6G using high‐performance liquid chromatography. The molecularly imprinted polymer coating was prepared by copolymerization of dopamine and m‐aminophenylboronic acid (functional monomers), in the presence of rhodamine 6G (template). The selection of the suitable functional monomers was based on the interaction between different monomers and the template using the density functional theory. The ratios of the monomers to template were further optimized by an OA9 (34) orthogonal array design. The binding performances of the adsorbent were evaluated by static, kinetic, and selective adsorption experiments. The results reveal that the adsorbent possesses remarkable affinity and binding specificity for rhodamine 6G because of the enhanced Lewis acid‐base interaction between the B(Ш) embedded in the imprinted cavities and the template. The nano‐adsorbent was successfully applied to dispersive micro‐solid‐phase extraction coupled to high‐performance liquid chromatography for the trace determination of rhodamine 6G in samples with a detection limit of 2.7 nmol/L. Spiked recoveries ranged from 93.0–99.1, 89.5–92.7, and 86.9–105% in river water, matrimony vine and paprika samples, respectively, with relative standard deviations of less than 4.3%.  相似文献   

20.
In this study, the structure–property relationships for a series of statistical 2‐nonyl‐2‐oxazoline (NonOx) and 2‐phenyl‐2‐oxazoline (PhOx) copolymers were investigated for the first time. The copolymerization kinetics were studied and the reactivity ratios were calculated to be rNonOx = 7.1 ± 1.4 and rPhOx = 0.02 ± 0.1 revealing the formation of gradient copolymers. The synthesis of a systematical series of NonOx–PhOx copolymers is described, whereby the amount of NonOx was increased in steps of 10 mol %. The thermal and surface properties were investigated for this series of well‐defined copolymers. The thermal properties revealed a linear decrease in glass transition temperature for copolymers containing up to 39 wt % NonOx. Furthermore, the melting temperature of the copolymers containing 0 to 55 wt % PhOx linearly decreased most likely due to disturbance of the NonOx crystalline domains by incorporation of PhOx in the NonOx part of the copolymer. The surface energies of spincoated polymer films revealed a strong decrease in surface energy upon incorporation of NonOx in the copolymers due to strong phase separation between NonOx and PhOx allowing the NonOx chains to orient to the surface. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6433–6440, 2009  相似文献   

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