聚氨酯/聚甲基丙烯酸甲酯/有机蒙脱土纳米复合材料的制务、结构与性能

首次将插层纳米复合技术与互穿聚合物网络（IPN）技术相结合,通过同步插层聚合法制备了聚氨酯/聚甲基丙烯酸甲酯/有机蒙脱土（PU/PMMA/OMMT）纳米复合材料.XRD、SEM、TGA等研究表明,在聚氨酯/有机蒙脱土（PU/OMMT）体系中蒙脱土以40～700 nm的团聚体不均匀地分散在聚氨酯基体中,且部分蒙脱土被插层,其层间距增加了0.95nm,体系为插层型纳米复合材料.PU/PMMA/OMMT体系中蒙脱土以20～80nm的粒子分布于聚合物基体中,且蒙脱土的插层效果显著,是PU/OMMT体系的2.5倍,形成了插层型纳米复合材料.同时,蒙脱土的加入使得聚氨酯和聚甲基丙烯酸甲酯的互穿聚合物网络（PU/PMMA-IPN）体系中PU相与PMMA相间相分离更明显,塑性相畴粒子尺寸显著增加,且各相中两组分相互作用加强,分布更均匀.PU/PMMA/OMMT纳米复合材料的热稳定性高于其他材料.同时对其力学性能进行了研究,发现其力学性能明显优于聚氨酯、基于聚氨酯和PU/PMMA-IPN和PU/OMMT纳米复合材料.     

Fabrication and characterization of carbon nanotube reinforced poly(methyl methacrylate) nanocomposites

Multiwall carbon nanotube (CNT) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been successfully fabricated with melt blending. Two melt blending approaches of batch mixing and continuous extrusion have been used and the properties of the derived nanocomposites have been compared. The interaction of PMMA and CNTs, which is crucial to greatly improve the polymer properties, has been physically enhanced by adding a third party of poly(vinylidene fluoride) (PVDF) compatibilizer. It is found that the electrical threshold for both PMMA/CNT and PMMA/PVDF/CNT nanocomposites lies between 0.5 to 1 wt% of CNTs. The thermal and mechanical properties of the nanocomposites increase with CNTs and they are further increased by the addition of PVDF For 5 wt% CNT reinforced PMMA/PVDF/CNT nanocomposite, the onset of decomposition temperature is about 17 degrees C higher and elastic modulus is about 19.5% higher than those of neat PMMA. Rheological study also shows that the CNTs incorporated in the PMMA/PVDF/CNT nanocomposites act as physical cross-linkers.     

Properties of well aligned SWNT modified poly (methyl methacrylate) nanocomposites

The PMMA/SWNT composites with good uniformity, dispersion and alignment of SWNT were fabricated in a stretching process. The semidried mixture was stretched along one direction at a draw ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The TEM and SEM observation demonstrated that SWNT in the PMMA/SWNT composite tend to align in the stretching direction. The electrical conductivity and the mechanical properties of composite rise with the increase of SWNT concentration, composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The TGA revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.     

Anisotropic properties of aligned SWNT modified poly (methyl methacrylate) nanocomposites

The poly (methyl methacrylate) (PMMA)/single-walled carbon nanotube (SWNT) composites with good uniformity, dispersion and alignment of SWNT were fabricated in an improved figuration process. The semidried mixture was stretched along one direction at a drawing ratio of 50 before it was dried, and then folded along the same direction stretching repeatedly for 100 times. The transmission electron microscopic (TEM) observation demonstrated that SWNT in the PMMA/SWNT composite tends to align in the stretching direction owing to a torque exerting on it in the stretching process. The electrical and mechanical properties of PMMA/SWNT composite were studied as a function of SWNT orientation and concentration. The aligned SWNT modified PMMA/SWNT composite presented highly anisotropic properties. The experimental results showed that the electrical conductivity and mechanical properties of composite rise with the increase of SWNT concentration, and that composite films showed higher conductivity and higher mechanical draw ratios along the stretched direction than perpendicular to it. The thermogravimetric analysis (TGA) revealed that embedding the SWNTs into the PMMA matrix also improves the thermal stability of the composite.     

The intercalation of poly(methyl methacrylate)/aluminophosphate nanocomposites and the properties improvement

Poly(methyl methacrylate) (PMMA)/dodecylamine templated lamellar aluminophosphate (DDA-LAP) intercalated nanocomposites are prepared by in situ bulk polymerization of MMA. The intercalated structure is characterized. With the intercalation of DDA-LAP in PMMA matrix, the glass-transition temperatures of nanocomposites (T_g) are increased. The nanocomposites obtained keep relatively high transparency in optical property and have a significant improvement in mechanical properties and thermal stability. The mechanism for the properties enhancement is investigated. The strong interfacial interaction between the aluminophosphate layers and the PMMA chains, the homogeneously distribution and the graphitized char formation during heating are three key roles for the properties improvement.     

In-situ synthesis and performance of titanium oxide/poly(methyl methacrylate) nanocomposites

Polymer nanocomposites have elicited extensive research efforts due to their potential to exhibit spectacular properties. They have immense potential and are befitting materials to serve as an ideal and futuristic alternative for varied applications. Poly(methyl methacrylate) (PMMA) and titanium oxide (TiO2) nanocomposites used in this study were fabricated by an in-situ free radical polymerization process. Three point bend tests were conducted with a modified universal microtribometer to evaluate fracture toughness. The results indicated that the stress intensity values increase as the concentration of titanium oxide increases up to 1 vol% and subsequently decrease at higher concentrations. Scanning electron microscopy (SEM) images of fracture surfaces afforded clues as to the possible deformation mechanism. Ultraviolet-visible spectroscopy (UV-vis) evaluated the degree of transparency of the nanocomposites. It was observed that samples became opaque as the concentration was increased beyond 0.01% volume fraction. X-ray diffraction characterized the TiO2 crystalline phase and Scherrer's equation was used to calculate the crystallite size. Among the concentrations considered the 3% volume fraction sample had the largest crystallite size. Finally, microhardness measurements further characterized the mechanical properties of the composites.     

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.     

Synthesis,structure and tribological performance of tungsten disulphide nanocomposites

Tungsten disulphide nanocomposites were prepared in large scale by employing the direct reaction between tungsten nanoparticles and sulphur powders. The nanocomposites include a variety of shapes such as isolated WS₂ multi-layered sheets, WS₂-coated WO₃ nanoparticles, and enclosed fullerene-like WS₂ structures. Pin-on-disc wear tests indicate that the addition of a small amount (5 wt%) of these nanoparticles to paraffin decreases significantly the wear loss of the pin. Additives of these WS₂/WO₃ nanoparticles possess much better tribological performance than micrometer-sized WS₂ powders additives do. The surface topography of wear scar of the pins after wear tests with different additives and different loads were studied by scanning electron microscopy. Small (severe) damage of the pin surface was observed for WS₂/WO₃ nanoparticles (WS₂ micropowders) additives.     

Preparation, structure and properties of uniaxially oriented polyethylene-silver nanocomposites

Uniaxially oriented composites of high-density polyethylene and silver nanoparticles were prepared using solution-casting, melt-extrusion and solid-state drawing techniques. The absorption spectrum in the visible wavelength range of the drawn nanocomposites was observed to strongly depend on the polarisation direction of the incident light. For instance, the nanocomposites appear bright yellow or red when the vibration direction of linearly polarised light is perpendicular or parallel, respectively, to the drawing axis. The optical anisotropy of the drawn nanocomposites originates from uniaxially oriented, pearl-necklace type of arrays of nanoparticles of high aspect ratios. The absorption spectrum of the nanocomposites can be shifted to higher wavelengths using appropriate annealing procedures. The annealing results in an increased size of the primary silver particles, due to Ostwald ripening, and consequently a range of polarisation-dependent colours can be generated in the drawn nanocomposites.     

Synthesis and photocatalytic property of metal@SnO2 core-shell structure nanocomposites

A simple soft-chemical technique for processing of metal@SnO2 nanocomposites with core-shell morphology is reported. In the present technique metal nanoparticles are prepared by chemical reduction technique followed by deposition of tin dioxide. Thus a core-shell type structure is produced. The phase and morphology has been investigated by X-ray diffraction technique (XRD) and transmission electron microscopy (TEM). As prepared Au@SnO2 and Ag@SnO2 core-shell nanocomposites have shown distinct surface Plasmon band in the UV-visible spectrum at 540 nm and 400 nm respectively. The core-shell morphology is confirmed from the TEM images. XRD patterns have suggested the presence of noble metal and tin dioxide in the Cassiterite form. These metal@SnO2 nanocomposites have been successfully used for the photocatalytic oxidation of acetaldehyde. Our investigations suggest that presence of noble metal core in contact with tin dioxide shell enhances the photocatalytic activity of the material.     

Porous nanocomposites prepared from layered clay and PMMA [poly(methyl methacrylate)]

The aim of the present work is the preparation of PMMA based porous nanocomposites that contain clay (montmorillonite, MMT) platelets as reinforcements within the cell walls of the porous structure. To render the clay layers organophilic, MMT was surface treated by an ion exchange reaction between interlayer cations of the clay and ammonium ions of a surfactant. Clay/PMMA based porous nanocomposites were prepared by polymerization of water-in-oil emulsions with and without clay addition. The microstructure and compressive mechanical behavior of the nanocomposites were investigated. The results of mechanical tests showed that the porous systems with the addition of 1 wt.% of organoclay (OMMT) exhibited a 90% and 50% increase of collapse stress and elastic modulus values, respectively, as compared to neat porous PMMA.     

SiC/C nanocomposites with inverse opal structure

The synthesis, morphology, structural and optical characteristics of SiC/C nanocomposites with an inverse opal lattice have been investigated. The samples were prepared by thermochemical treatment of opal matrices filled with carbon compounds which was followed by silicon dioxide dissolution. The samples were studied by electron microscopy, x-ray diffraction, photoluminescence, IR and Raman scattering spectroscopy. The electron microscopy data revealed a highly porous periodic structure which was a three-dimensional replica of the voids of the initial opal lattice. The hexagonal silicon carbide was found to be non-uniformly distributed throughout the volume, its greater part located in the surface layer up to 50?μm deep. The data of x-ray diffraction, IR and Raman scattering spectroscopy enabled us to assume that the composite had hexagonal diamond fragments. The photoluminescence and optical reflection spectra of the composites have been measured.     

盐酸西替利嗪/蒙脱土纳米复合物的制备及其结构与性能

以钙基蒙脱土为原料,采用微波-力化学法制备钠基蒙脱土(MMT)。采用溶液离子交换法制备盐酸西替利嗪(CTH/MMT) 纳米复合物,研究了MMT 对CTH 的吸附规律。利用XRD、FTIR、TG等分析了CTH/MMT复合物的结构。通过体外人工模拟胃、肠液中的释放实验表征了CTH/MMT的缓释效果、缓释机制及其动力学。结果表明,CTH插层于MMT层间,层间距由1. 25 nm增至2. 13 nm。MMT对CTH 插层吸附等温线符合Freundlich吸附等温方程,其吸附动力学符合二级动力学方程。体外的缓释试验表明,CTH/MMT具有良好的缓释效果,MMT可作为盐酸西替利嗪的控释载体材料。      

Study on the structure and properties of RTV/FR-DOMt nanocomposites

The aim of our research was to study the effect of flame-retardant dendrimer modified organic montmorillonite (FR-DOMt) with different ratios on the structure and properties of room-temperature-vulcanised silicone rubber (RTV). The physical and mechanical properties of RTV nanocomposites were improved with the addition of FR-DOMt additives. The RTV nanocomposites exhibited better thermal stability. T_onset of RTV/FR-DOMt-3 was 310 °C, 100 °C higher than that of pure RTV. RTV/FR-DOMt-3 nanocomposite possessed the highest elongation at break, 500%. This was 46% higher than that of pure RTV. In addition, these RTV nanocomposites showed an increased FR behavior. By adding 3–15 phr of FR-DOMt into pure RTV matrix, a linear decrease of burning rate together with an increase of LOI values were obtained. SEM and TEM observations of RTV/FR-DOMt-3 demonstrated that the exfoliated silicate layers dispersed uniformly in this nanocomposite.     

Thermally assisted semiconductor-like to insulator transition in gold-poly(methyl methacrylate) nanocomposites

Gold-polymethylmethacrylate (PMMA) nanocomposites were fabricated by mixing gold nanoparticles capped with oleylamine in polymethylmethacrylate. The samples were analysed using UV-vis absorption spectroscopy, transmission electron microscopy, small angle x-ray scattering, Fourier transform infrared spectrometry (FTIR) and x-ray photoelectron spectroscopy (XPS). Electrical resistivity of nanocomposite samples was measured by a four-probe technique in the 70-300?K range. The nanocomposites showed a transition with an onset at ～160-165?K. They exhibited a semiconductor-like conductivity at higher temperatures and nearly temperature independent conductivity at lower temperatures. The interfacial interaction of Au nanoparticles and PMMA polymer is investigated using FTIR and XPS. A ligand-exchange process occurs when capped gold nanoparticles are incorporated in PMMA polymer.     

Thermal and mechanical characterization of poly(methyl methacrylate) nanocomposites filled with TiO2 nanorods

Thick films of nanocomposites made of poly(methyl methacrylate) matrix and colloidal anatase TiO₂ nanorods fillers were prepared by solvent mixing and solution drop casting. Different concentrations of nanorods were tested in order to examine the influence of the nanoscale fillers on the composites material properties and structure. The thermal properties of the samples were investigated through thermogravimetric analysis, which showed an increase in thermal stability of the nanocomposites on increasing nanorods concentration, for the range of concentrations used. The viscoelastic properties were investigated through dynamic mechanical analysis, which showed an increase in both the storage and loss modulus on increasing nanorods concentration. The in-depth distribution of the TiO₂ nanorods in the matrix was evaluated through cross-sectional transmission electron microscopy, which pointed out a uniform dispersion of mesoscale nanorods agglomerates with increasing diameter of 100–200 nm range on increasing nanorods concentration.     

Electrical and rheological properties of double percolated poly(methyl methacrylate)/multiwalled carbon nanotube nanocomposites

Electrical and rheological properties of nanocomposites based on poly(methyl methacrylate) (PMMA) and multiwalled carbon nanotube (MWCNT) were studied from view points of double percolation by adding crosslinked methyl methacrylate-butadiene-styrene (MBS) copolymer particles to lower percolation threshold concentration of MWCNTs. It was found that the critical concentrations of MWCNTs for the percolation in the nanocomposites decrease and then increase with increasing the MBS contents of the nanocomposites. It is postulated that the addition of MBS at low concentrations results in double percolation of MWCNT and the significant decrease of critical concentration for the percolations. However, adding MBS particles in large amounts results in limited space for the distribution of MWCNTs and less efficient dispersion of the MWCNTs and the increase of the critical concentrations of MWCNTs for the percolations. Rheological properties and change of T(g)s reflect large interfacial areas in the well dispersed nanocomposite and were also interpreted to support the speculations for the effects of MBS contents and MWCNT concentrations of PMMA/MWCNT nanocomposites.     

Surface functionalization and structure characterizations of nanodiamond and its epoxy based nanocomposites

The aim of this study is the potential use of nanodiamond to make the lightweight and strong nanocomposites. Here, effects of size and surface modification of detonation nanodiamond (DND) on mechanical performance of epoxy based nanocomposites is presented. Our characterizations reveal that the process of functionalization not only removes the non-diamond content and impurities by significantly reducing DND's size but also introduces oxygen containing functional groups on its surface. The average size of functionalized DND aggregations could be decreased from 300 to 100 nm in contrast to pristine DND, which greatly benefits its homogeneous dispersion in epoxy matrix. In addition, strong chemical bonding among functionalized DND and epoxy resin due to functional groups leads to the formation of efficient interface. These interfaces overlap at high concentrations making a network which in turn significantly enhances the tensile properties. The enhancement in Young's modulus can reach up to 2.5 times higher than that of neat epoxy whereas the enhancement in tensile strength is about 1.5 times in functionalized DND/epoxy nanocomposites.