Effect of MMT,SiO2, CaCO3, and PTFE nanoparticles on the morphology and crystallization of poly(vinylidene fluoride)

The crystallization and melting behaviors of poly (vinylidene fluoride) (PVDF) with small amount of nanoparticles (1 wt %), such as montmorillonite (MMT), SiO₂, CaCO₃, or polytetrafluoroethylene (PTFE), directly prepared by melt‐mixing method were investigated by scanning electron microscopy (SEM), polarizing optical microscopy, Fourier transform infrared spectroscopy, wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC). The nanoparticle structure and the interactions between PVDF molecule and nanoparticle surface predominated the crystallization behavior and morphology of the PVDF. Small amount addition of these four types of nanoparticles would not affect the original crystalline phase obtained in the neat PVDF sample (α phase), but accelerated the crystallization rate because of the nucleation effect. In these four blend systems, MMT or PTFE nanoparticles could be well applied for PVDF nanocomposite preparation because of stronger interactions between particle surface and PVDF molecules. The nucleation enhancement and the growth rate of the spherulites were decreased in the order SiO₂ > CaCO₃ > PTFE > MMT. The melting and recrystallization of PVDF was found in MMT addition sample, because of the special ways of ordering of the PVDF chains. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Preparation of hollow silica microspheres with controlled shell thickness in supercritical fluids

This article presents a novel route to prepare hollow silica microspheres with well-defined wall thickness by using cross-linked polystyrene (PS) microspheres as templates with the assistance of supercritical carbon dioxide (SC-CO₂). In this approach, the cross-linked PS templates can be firstly prepared via emulsifier-free polymerization method by using ethylene glycol dimethacrylate or divinylbenzene as cross-linkers. Then, the silica shell from the sol–gel process of tetraethyl orthosilicate (TEOS) which was penetrated into the PS template with the assistance of SC-CO₂ was obtained. Finally, the hollow silica spheres were generated after calcinations at 600 °C for 4 h. The shell thickness of the hollow silica spheres could be finely tuned not only by adjusting the TEOS/PS ratio, which is the most frequently used method, but also by changing the pressure and aging time of the SC-CO₂ treatment. Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscope were used to characterize these hollow silica spheres.     

Construction of 3D hierarchical SnO2 microspheres from porous nanosheets towards NO decomposition

Three-dimensional (3D) hierarchical architectures are currently attracting worldwide interest owing to their fascinating morphology-dependent properties and potential applications. Herein we constructed SnO₂ microspheres with 3D hierarchical flower-like architectures self-assembled with porous SnS₂ nanosheets by a facile hydrothermal method with subsequent calcination. The chemical and physical properties as well as photocatalytic application of SnO₂ microspheres were investigated. The size and morphology were examined with scanning electron microscopy and transmission electron microscopy. The phase and crystalline structure were determined with powder X-ray diffraction. The UV–Vis absorption property was determined with UV–Vis diffuse reflectance. The photocatalytic activities were evaluated with nitrogen monoxide (NO) decomposition under UV–Vis light irradiation. The effects of calcination temperature on morphology and NO decomposition were also studied.     

Preparation and characterization of a polyimide nanofoam through grafting of labile poly(propylene glycol) oligomer

Preparation of a polyimide nanofoam (PI‐F) for microelectronic applications was carried out using a polyimide precursor synthesized from poly[(amic acid)‐co‐(amic ester)] and grafted with a labile poly(propylene glycol) (PPG) oligomer. Polyimide precursor was synthesized by partial esterification of poly(amic acid) (PAA) derived from pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline (ODA). The precursor was then grafted with bromide‐terminated poly(propylene glycol) in the presence of K₂CO₃ in hexamethylphosphoramide and N‐methylpyrrolidone, imidized at 200°C in nitrogen and the product was subsequently decomposed in air at 300°C to eliminate the labile PPG oligomer to produce PMDA/ODA polyimide nanofoam. Nuclear magnetic resonance spectroscopy (¹H‐NMR) and Fourier transform infrared spectroscopy (FT‐IR) techniques were used to characterize the formation of polyimide precursor and extent of grafting of PPG with polyimide. The results of thermogravimetric analysis (TGA) showed three step decomposition of nanofoam with the removal of PPG at 350°C and decomposition of polyimide at around 600°C. The polyimide nanofoams were also characterized by small angle X‐ray scattering (SAXS), field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). The morphology showed nanophase‐separated structures with uniformly distributed and non‐interconnected pores of 20–40 nm in size. Dynamic mechanical analysis (DMA) indicated higher storage modulus for the foamed structure compared to the pure PI with reduction in loss tangent for the former system. Copyright © 2004 John Wiley & Sons, Ltd.     

Properties of water-soluble carboxymethyl chitosan film modified by hydrophobic poly(propylene glycol)

A series of water-soluble carboxymethyl chitosan (CMCS)/poly(propylene glycol) (PPG) blend films with various CMCS/PPG mole ratios were prepared by the solution casting method. Morphology of the CMCS/PPG blend films was investigated by scanning electron microscopy (SEM). Thermal, mechanical, and chemical properties of the CMCS/PPG blend films were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), tensile tests, and contact angle tests. It was found that the introduction of PPG can markedly affect the morphology and the properties of CMCS films.     

Morphology and Thermal Characteristics of Polyethylene Nanocomposites Made Using Montmorillonite‐Supported Cp2ZrCl2 and Ni‐Diimine Precatalysts

Bis(cyclopentadienyl)‐zirconium dichloride (Cp₂ZrCl₂) and (1,4‐bis(2,6‐diisopropylphenyl)‐acenaphthenediimine) dichloronickel (Ni‐diimine) were supported on montmorillonite (MMT) pretreated with triisobutylaluminum and 10‐undecence‐1‐ol to produce in situ polyethylene–clay nanocomposites in a gas‐phase reactor. The development of the nanocomposite morphology was investigated with transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis. During polymerization, the MMT layers were partially exfoliated by the growing polymer chains, starting from the openings of the clay galleries, but intercalation and exfoliation occurred only to a certain extent. The thermal properties of the nanocomposites we also analyzed by differential scanning calorimetry (DSC).

     

聚乙烯醇/氟基蒙脱土纳米复合材料的合成及性能研究

采用水热方法,在493 K条件下反应72小时,合成了氟基蒙脱土(F-MMT),在这种F-MMT中,硅酸盐结构中的一些OH-被F-取代。采用溶液插层方法,制备了聚乙烯醇/F-MMT纳米复合材料(PVA/F-MMT)。采用X 射线衍射、扫描电镜和透射电镜对F-MMT 和 PVA/F-MMT纳米复合材料进行了表征;结果表明,片状结构的F-MMT均匀分散于PVA中,形成了层离结构的纳米复合材料。热重分析、力学性能和紫外可见光谱的测试结果表明,在没有牺牲光学性能情况下,PVA/F-MMT纳米复合材料的热稳定性和力学性能都得到了提高。力学和热学性能的提高归功于F-MMT均匀而好的分散于聚合物基体中,以及PVA中的 OH- 和F-MMT 中F-之间强的氢键作用。     

N2流量对GaN的形貌及光学和电学性能的影响

采用化学气相沉积法(CVD)在Si(100)衬底上以Ni为催化剂,金属Ga和NH3为原料合成了GaN微纳米结构,并研究了N2流量对产物GaN的形貌及光学和电学性能的影响。利用场发射扫描电子显微镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、Xray能谱仪(EDS)、光致发光谱(PL)和霍尔效应测试仪(HMS-3000)等测试手段对样品的形貌、结构、成分、光学和电学性能进行了分析。结果表明,随着N2流量的增加,产物GaN的形貌发生了由微米棒到蠕虫状线再到光滑纳米线的转变;生成的GaN均为六方纤锌矿结构;样品均表现出383 nm的近带边紫外发射峰和470 nm左右的蓝光发射峰;所有样品均为p型;并对产物GaN的形貌转变机理进行了分析。     

Electron microscopic characterization of SrTiO3 films obtained by anodic spark deposition

Crystalline strontium titanate layers were deposited on titanium anodes from Sr(OH)₂ aqueous electrolyte solutions by a plasmachemical-electrochemical process of anodic spark deposition. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to study the properties of the polycrystalline material. Strontium titanate was deposited on the titanium anode surface as a ceramic layer from an aqueous electrolyte. The typical pore structure morphology of the anodic spark deposit (ASD) was characterized by SEM as well as fractures which provide an intimate contact between layer and substrate. XRD-study showed that the layers are composed of a mixture of SrTiO₃ and TiO₂.     

不同形貌Bi4Ti3O12粒子的可控合成及光催化性能

研究了用一步水热法制备的不同形貌的钛酸铋(Bi₄Ti₃O₁₂, BIT)粒子的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. XRD结果表明, 所制备的BIT 样品为层状钙钛矿结构. FESEM结果表明, 通过控制水热过程的反应参数可以得到不同形貌的纳米粒子. 紫外-可见漫反射光谱(UV-Vis DRS)表明BIT 样品的带隙能约为2.88-2.93 eV. 利用可见光(λ>420 nm)照射下的甲基橙(MO)降解实验评价了BIT 样品的光催化性能. 结果表明, BIT 的光催化活性比掺氮TiO₂ (N-TiO₂)高得多. 研究了形貌对BIT 光催化性能的影响. 所制备的BIT纳米带光催化效率最高, 经可见光照射360 min, 甲基橙溶液的降解率可达到95.0%.     

N2流量对GaN的形貌及光学和电学性能的影响

采用化学气相沉积法(CVD)在Si(100)衬底上以Ni为催化剂, 金属Ga和NH₃为原料合成了GaN微纳米结构, 并研究了N₂流量对产物GaN的形貌及光学和电学性能的影响。利用场发射扫描电子显微镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、X-ray能谱仪(EDS)、光致发光谱(PL)和霍尔效应测试仪(HMS-3000)等测试手段对样品的形貌、结构、成分、光学和电学性能进行了分析。结果表明, 随着N₂流量的增加, 产物GaN的形貌发生了由微米棒到蠕虫状线再到光滑纳米线的转变;生成的GaN均为六方纤锌矿结构;样品均表现出383 nm的近带边紫外发射峰和470 nm左右的蓝光发射峰;所有样品均为n型;并对产物GaN的形貌转变机理进行了分析。     

High strength cellulose composite films reinforced with clay for applications as antibacterial materials

High strength cellulose composite films with antibacterial activities were prepared by dispersing montmorillonites (MMT) into cellulose solution in LiOH/urea aqueous solvent followed by regeneration in ethanol coagulation bath, and then by soaking in 5 wt% hexadecylpyridine bromide ethanol solutions to induce the antibacterial action. The cellulose/MMT composite films were characterized by field emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, FTIR, UV-spectra, wide angle X-ray diffraction and mechanical test. The results revealed that MMT was dispersed well in the cellulose matrix to form layer structure with a thickness of approximately 3 nm. The mechanical properties of the cellulose/MMT composite films were significantly improved to achieve 132 MP for tensile strength as a result of the MMT delamination. The hexadecylpyridine bromide was fixed well in the cellulose/MMT matrix through cation exchange, leading to the excellent antibacterial activities against Staphylococcus aureus and Escherichia coli, which is important in their practical applications.     

UV curable epoxy acrylate-clay nanocomposites

UV curable epoxy acrylates were reinforced with two different organically modified montmorillonites (MMTs) and an unmodified MMT. Conversion and rate of polymerization was monitored by real time infrared spectroscopy (RTIR) and photo-DSC. Microstructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and optical clarity. Optical clarity of the films containing clay was quite good as only a slight decrease was observed. Physical properties of the reinforced films were examined by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), hardness and tensile testing. Enhancements in glass transition temperature (T_g), thermal stability and mechanical properties were observed. The films reinforced with the unmodified MMT exhibit the most significant enhancements in properties.     

Electrospinning and characterization of poly(vinyl alcohol)/chitosan oligosaccharide/clay nanocomposite nanofibers in aqueous solutions

Submicron fibers of the composite of poly(vinyl alcohol) (PVA), chitosan oligosaccharide [COS, (1→4)2-amino-2-deoxy-β-d-glucose], and montmorillonite clay (MMT) were prepared using electrospinning method with aqueous solutions. Scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), thermal gravimetric analyzer, and tensile strength testing machine (Zwick) were utilized to characterize the PVA/COS/MMT nanofiber mats morphology and properties. The PVA/COS ratio and MMT concentration play important roles in nanofiber mat properties. XRD and TEM data demonstrated that exfoliated MMT layers were well-distributed within nanofiber. It was also found that the mechanical property and thermal stability were increased with COS and MMT contents.     

Synthesis of Bi-doped TiO2 Nanotubes and Enhanced Photocatalytic Activity for Hydrogen Evolution from Glycerol Solution

Bi‐doped TiO₂ nanotubes with variable Bi/Ti ratios were synthesized by hydrothermal treatment in 10 mol·L^?1 NaOH (aq.) through using Bi‐doped TiO₂ particles derived from conventional sol‐gel method as starting materials. The effects of Bi content on the morphology, textural properties, photo absorption and photocatalytic activity of TiO₂ nanotubes were investigated. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) observations of the obtained samples revealed the formation of titanate nanotube structure doped with Bi, which exists as a higher oxidation state than Bi³⁺. Bi‐doping TiO₂ nanotubes exhibited an extension of light absorption into the visible region and improved photocatalytic activities for hydrogen production from a glycerol/water mixed solution as compared with pure TiO₂ nanotubes. There was an optimal Bi‐doped content for the photocatalytic hydrogen production, and high content of Bi would retard the phase transition of titanate to anatase and result in morphology change from nanotube to nanobelt, which in turn decreases the photocatlytic activity for hydrogen evolution.     

胆酸盐与Gemini表面活性剂复合物构建的纳米纤维和囊泡

Gemini表面活性剂(Cs H2s-α,ω-(Me2N+Cm H2m+1Br-)2,m-s-m)与胆汁酸盐(BS)利用静电作用构建超分子复合物,通过改变m-s-m和BS的结构,可以分别得到纳米纤维和囊泡状超分子聚集体.聚集体的形貌、结构和性质分别通过偏光显微镜(POM)、透射电子显微镜(TEM)、场发射扫描电子显微镜(FE-SEM)、X射线粉末衍射(XRD)及其它测试手段进行了表征.研究发现,通过改变m-s-m的烷基链长和间隔基团的长度,以及BS胆甾骨架上羟基的数目和位置,聚集体的形貌会发生明显的变化,聚集体主要依靠静电相互作用,并在疏水作用及氢键的协同作用下形成,本文的结果将有助于更好地理解离子自组装机理,并对超分子聚集体的设计提供新的思路.     

Solubility-dependent complexation of active pharmaceutical ingredients with trimethyl-β-cyclodextrin under supercritical fluid condition

The effect of the solubility of active pharmaceutical ingredients (APIs) in supercritical carbon dioxide (SC-CO₂) on their complexation behavior with trimethyl-β-cyclodextrin (TM-β-CD) has been investigated. Flurbiprofen or naproxen, the solubility of which is lower than that of ibuprofen, was mixed with TM-β-CD and the complexation phenomena on SC-CO₂ processing was evaluated using powder X-ray diffraction, differential scanning calorimetry and IR measurement. Drug complexation depended both on SC-CO₂ treatment time and on drug solubility in CO₂. The inclusion complex formation of flurbiprofen with TM-β-CD proceeded slowly compared with the case of ibuprofen. The slower complexation behavior was also observed when naproxen was used as the guest molecule. These results indicate that dissolution of drug molecules in SC-CO₂ is a rate-determining step for the inclusion complex formation with TM-β-CD and that complexation proceeds after dissolving the both components in SC-CO₂.     

S/Cd物质的量比对微波水热制备CdS微晶的形貌影响及光学性能研究

采用微波水热法,以CdCl2·H2O和Na2S2O3·5H2O为镉源和硫源,在不同的S/Cd物质的量比条件下合成了CdS微晶。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、场发射扫描电子显微镜(FE-SEM)、EDS、透射电子显微镜(TEM)等对样品的物相、形貌和元素组分进行了分析。结果表明:随着S/Cd物质的量比的增大,产物CdS的形貌发生规律性变化,由四面体结构逐渐转变为准球形结构;准球形结构具有分级结构,是由更小的纳米晶组装而成;光致发光性质研究结果表明,所得的CdS微晶具有较好的蓝光发射性能。     

Magnetic hollow poly(N-isopropylacrylamide-co-N,N′-methylenebisacrylamide-co-glycidyl acrylate) particles prepared by inverse emulsion polymerization

To prepare functionalized magnetic polymer particles that are thermally responsive, inverse emulsion copolymerization of N-isopropylacrylamide, N,N′-methylenebisacrylamide and glycidyl acrylate (GA) was investigated in paraffin oil in the presence of γ-Fe₂O₃ nanoparticles dispersed in a water/glycerol mixture. The resulting polymer particles were characterized regarding the morphology, size, polydispersity, iron content, and the temperature-dependent phase transition using optical microscopy, transmission electron microscopy, scanning electron microscopy, atomic absorption spectroscopy, and differential scanning calorimetry. Magnetic properties were examined using hysteresis loop measurements and by analyzing the magnetic susceptibility with respect to temperature. We have also investigated the influence of the concentration of γ-Fe₂O₃ and GA in monomers on properties of the particles (morphology, size, and presence of oxirane groups). The particles possessed a hollow structure as a result of phase separation between water/glycerol hydrophilic solvents in the polymerization feed and the forming polymer. Depending on the concentration of γ-Fe₂O₃ in the monomer phase, the magnetic hollow particles contained 5–24 wt% iron. In water, the particles gradually collapsed when the temperature was raised to 40 °C because the elevated temperature weakened hydration and the PNIPAAm chains gradually became more hydrophobic.     

Poly(lactic acid) nanocomposites with various organoclays. I. Thermomechanical properties,morphology, and gas permeability

The thermomechanical properties, morphology, and gas permeability of hybrids prepared with three types of organoclays were compared in detail. Hexadecylamine–montmorillonite (C₁₆–MMT), dodecyltrimethyl ammonium bromide–montmorillonite (DTA‐MMT), and Cloisite 25A were used as organoclays in the preparation of nanocomposites. From morphological studies using transmission electron microscopy, most clay layers were found to be dispersed homogeneously in the matrix polymer, although some clusters or agglomerated particles were also detected. The initial degradation temperature (at a 2% weight loss) of the poly(lactic acid) (PLA) hybrid films with C₁₆–MMT and Cloisite 25A decreased linearly with an increasing amount of organoclay. For hybrid films, the tensile properties initially increased but then decreased with the introduction of more of the inorganic phase. The O₂ permeability values for all the hybrids for clay loadings up to 10 wt % were less than half the corresponding values for pure PLA, regardless of the organoclay. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 94–103, 2003