Thermal analysis of PMMA/gel silica glass composites

Thermal analysis of poly-methylmethacrylate (PMMA) impregnated porous gel silica glasses confirms that the PMMA chains form hydrogen bonds with the pore surface silanol groups. The adopted conditions for the insitu polymerisation result in about 4% of residual monomers trapped in the polymer, most of them in the amorphous structure. The polymer and monomer mixture takes up the whole of the free pore volume. Most of the residual monomer polymerises during the DSC scans above the glass transition temperature providing an excellent probe for the weak glass transition. Polymerisation in the gel silica glass medium affects the glass transition temperature, the length of polymer chains, and the degree of polymerisation.     

Preparation and properties of wheat gluten/silica composites

Wheat gluten (WG)/silica (SiO₂) hybrids were prepared through in-situ synthesis of SiO₂ in WG dispersion of aqueous ammonia. The hybrids with different SiO₂ contents were mixed with glycerol plasticizer to form cohesive dough and the dough was compressively molded to form cross-linked sheets. Morphology, moisture absorption, protein solubility in water, tensile mechanical properties and dynamic rheological behavior of the WG/SiO₂ composites were investigated in relation to SiO₂ contents. Supported by the National Natural Science Foundation of China (Grant No. 50773068) and Natural Science Foundation of Zhejiang Province (Grant No. Y407011)     

Optical characterisation of sol-gel optical composites

Sol-gel optical composites doped with optically active materials prepared by the post-doping method have been characterised in relation to their optical and structural properties. The dopants of interest have been found to be homogeneously distributed throughout the gel matrix. The in-situ impregnation of an index-matching polymer such as PMMA within the porous structure improves both the optical and mechanical properties of the composites significantly. The as-prepared materials have a non-porous feature and show a low optical loss.     

Preparation and properties investigation of PMMA/silica composites derived from silicic acid

Hybrid materials based on silicic acid and polymethyl methacrylate (PMMA) were prepared by in situ bulk polymerization of a silicic acid sol and MMA mixture. Silicic acid sol was obtained by tetrahydrofuran (THF) extraction of silicic acid from water. Silicic acid was prepared by hydrolysis and condensation of sodium silicate in the presence of 3.6 M HCl. As a comparative study, PMMA composites filled by silica particles, which were derived from calcining the silicic acid gel, were prepared by a comparable in situ polymerization. Each set of PMMA/silica composites was subjected to thermal and mechanical studies. Residual THF in PMMA/silicic acid composites impacted the properties of the polymer composites. With increase in silica content, the PMMA composites filled with silica particles showed improved thermal and mechanical properties, whereas a decrease in thermal stability and mechanical strength was found for PMMA composites filled with silicic acid dissolved in THF. With a better compatibility with polymer matrix, silicic acid sol shows better reinforcement than silica particles in PMMA films prepared via blending of the corresponding THF solutions. Copyright © 2008 John Wiley & Sons, Ltd.     

Spectroscopic studies of post-doped silica gel monoliths

This paper describes the interfacial molecular interactions of cobalt, neodymium, Rhodamine 6G and polymethyl methacrylate with silica gel-glass monoliths for samples prepared by the post doping method.Formerly at Chemistry Department, Brunel University, Uxbridge, Middlesex UB8 3PH, UK.Formerly Carole C. Perry.     

Experimental investigation on mechanical properties of unidirectional and woven fabric glass/epoxy composites under off-axis tensile loading

Mechanical properties of unidirectional (UD) and woven fabric glass/epoxy composites under off-axis tensile loading were experimentally investigated. A number of off-axis tests considering different fibre orientations were performed to study the character and failure mechanisms of the composite laminates. The experimental results indicated that both off-axis elastic moduli and strength degrade with increasing off-axis angle in all cases, and the woven fabric composites present nonlinear stress-strain behaviour under off-axial tension loading. The Tsai-Wu criteria used for failure analysis of the UD and woven fabric composites were compared and discussed, especially considering different values of interaction coefficient F₁₂. The prediction results demonstrated that the Tsai-Wu criterion can be used successfully to analyse failure properties of the woven fabric composites under multiaxial stress conditions, where the criterion with the modified coefficient F₁₂ obtained from the 45° off-axial tension tests is better and has higher accuracy. Finally, the specific failure modes were compared in the UD and woven fabric composites. The selected fracture surfaces were also observed by scanning electron microscopy (SEM), and the corresponding failure mechanisms of the woven fabric composites under off-axis tensile loading were identified.     

Electrical conduction in composites containing copper core-copper oxide shell nanostructure in silica gel

Composites of nanometre-sized copper core-copper oxide shell with diameters in the range 6.1 to 7.3 nm dispersed in a silica gel were synthesised by a technique comprising reduction followed by oxidation of a suitably chosen precursor gel. The hot pressed gel powders mixed with nanometre-sized copper particles dispersed in silica gel showed electrical resistivities several orders of magnitude lower than that of the precursor gel. Electrical resistivities of the different specimens were measured over the temperature range 30 to 300°C. Activation energies for the coreshell nanostructured composites were found to be a fraction of that of the precursor gel. Such dramatic changes are ascribed to the presence of an interfacial amorphous phase. The resistivity variation as a function of temperature was analysed on the basis of Mott’s small polaron hopping conduction model. The effective dielectric constant of the interfacial phase as extracted from the data analysis was found to be much higher than that of the precursor glass. This has been explained as arising from the generation of very high pressure at the interface due to the oxidation step to which the copper nanoparticles are subjected. Dedicated to Professor C N R Rao on his 70th birthday     

Dielectric properties and molecular mobility of organic/inorganic polymer composites

Microstructure-dielectric properties relationship and molecular mobility of organic/inorganic polymer composites (OIPCs), consisting of polyurethane (PU) and sodium silicate (NaSi), were investigated in this work. Broadband dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization current (TSDC) techniques were employed. Our interest was focused on the study of the glass transition mechanism and conductivity relaxation. The influence of the molecular weight of PU and inorganic phase content on the dielectric properties of the composites was of particular interest. Glass transition temperature shifts to higher temperatures with the addition of NaSi. The overall molecular mobility was found to increase in the composites, compared to the pure PU matrix. The results are more intense for the composites based on the PU with low molecular weight.     

纳米羟基磷灰石/聚乙烯醇/明胶复合材料的结构和力学性能

采用机械共混法、原位化学合成法、原位水热法制备了一系列纳米羟基磷灰石/聚乙烯醇/明胶(n-HA/PVA/GEL)复合材料;利用X射线衍射仪、透射电镜及傅立叶变换红外光谱仪等分析了复合材料的结构;利用材料试验机测定了复合材料的力学性能.结果表明,利用原位水热法可使n-HA有效地在PVA高分子中均匀分散,并提高n-HA颗粒...     

Fabrication of zinc oxide nanowires/polymer composites by two‐photon polymerization

We present an approach to fabricate ZnO nanowires/polymer composite into three‐dimensional microstructures, based on two‐photon polymerization direct laser writing, a fabrication method that allows submicrometric spatial resolution. The structural integrity of the structures was inferred by scanning electron microscopy, while the presence and distribution of ZnO nanowires was investigated by energy dispersive X‐ray, Raman spectroscopy, and X‐ray diffraction. The optical properties of the produced composite microstructures were verified by imaging the characteristic ZnO emission using a fluorescence microscope. Hence, such approach can be used to develop composite microstructures containing ZnO nanowires aiming at technological applications. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 333–337     

Structural and morphological properties of silver nanoparticles–phosphate glass composites

New types of composite materials belonging to the (100 − x) [50P₂O₅ · 30CaO · 20Na₂O]xAg₂O glasses system with 0 ? x ? 0.25 are obtained. Their local structure is analyzed with the help of Raman and infrared spectroscopy and it was found that the glasses structure is built up from predominantly ionic phosphate units. UV–VIS absorption measurements performed on the samples reveal the existence of silver nanoparticles within the soda–calcium-phosphate glass matrix. The electronic absorption spectra and TEM pictures analyses indicate the presence of silver nanoparticles of almost spherical shapes and various sizes inside the glass matrix, depending on the Ag₂O content. By using the experimental UV–VIS data and a theoretical approach important structural and morphological parameters, such as the radius of the silver nanospheres and the volume fraction of the spheres are determined for one of the investigated composites (x = 0.05 mol%).     

Positron annihilation lifetime study of PTFE/silica composites

Positron annihilation lifetime spectroscopy (PALS) was used to study the microstructure of PTFE/silica composites. The positron lifetimes (τ_n) and intensities (I_n) of PTFE and the composites (30-62% silica) were measured at room temperature as a function of specimen thickness. Four lifetime components were found in PTFE and the composites. The longer lifetime components, τ₃ = 1.4 ns and τ₄ = 4.4 - 4.1 ns, were interpreted to be due to the presence of two different sized free volume cavity distributions within the PTFE/silica composites. A strong silica concentration dependence was found in the bulk intensities (I_3b and I_4b). The I_3b value increased from 13.0% in PTFE to 28.2% in the 62% composite, while the I_4b value decreased from 17.5% in PTFE to 4.5% in the 62% composite. The smaller-void size, free volume fraction (τ₃I_3b) values increased linearly between 0 and 100% silica concentration, while the larger void size, free volume fraction (τ₄I_4b) values decreased nonlinearly with silica concentration. Since silica has a long lifetime component (τ₃ = 1.6 ns), this behavior is ascribed to silica particles occupying the large free volume cavities (370 ų) in the PTFE/silica composites. © 1996 John Wiley & Sons, Inc.     

Preparation, microstructure, and properties of novel low-κ brominated epoxy/mesoporous silica composites

Brominated epoxy resin (BER) composites containing various amounts of SBA-15 and SBA-16 types mesoporous silicas were prepared through the thermal curing with 3-methyl-tetrahydrophthalic anhydride, and their morphologies, dielectric constants (κ), thermal properties and mechanical properties were studied. The investigation suggested that the dielectric constant could be reduced from 4.09 of the pure thermosetting BER to 3.74 and 3.7 by incorporating 3 wt.% SBA-15 and SBA-16, respectively. The reduction of the dielectric constant is attributed to the incorporation of the air voids (κ = 1) stored within the mesoporous silica materials, the air volume existing in the gaps on the interfaces between the mesoporous silica and the BER matrix, and the free volume created by introducing large-sized domains. The BER/mesoporous silica composites also present stable dielectric constants across the wide frequency range. An improvement of thermal stability of the BER is achieved by incorporation of the mesoporous silica materials. The enhanced interfacial interaction between the surface-modified mesoporous silica and the BER matrix has also led to an improvement of the toughness.     

Morphology and interphase formation in epoxy/PMMA/glass fiber composites: effect of the molecular weight of the PMMA

In this work ternary composites based on an epoxy thermoset modified with a thermoplastic polymer and reinforced with glass fibers were prepared. The aim of this study is to analyze the influence of the molecular weight of the thermoplastic polymer on the final morphologies. To obtain tailor made interphases four poly(methylmethacrylate), PMMA, which differ in their molecular weight (34,000, 65,000, 76,000 and 360,000 g/mol) were chosen to modify the epoxy resin. The amount of PMMA in the composites was fixed to 5 wt.%. Neat polymer matrices (epoxy-PMMA without fibers) were also prepared for comparison. To study all systems dynamic mechanical analysis (DMA), atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used. Although all the systems showed the typical phase separation in the epoxy/PMMA blend, DMA experiments revealed a new phase with more restricted mobility when the glass fibers are present. The amount of this phase increases as molecular weight of PMMA does. The morphologies as well as the fracture surface in the immediate surroundings of the fibers were found to be different from those observed further away from the surface of the fiber, suggesting therefore that, in this case, different fracture mechanism operates. These observations allow us to conclude that an interphase with specific properties is formed. This interphase is based on a polymer or a polymer blend (epoxy-PMMA) enriched in the component with lower mobility.     

Studies on electro‐optical properties of polymer matrix/LC/ITO nanoparticles composites

In this paper, polymer‐dispersed liquid crystal (PDLC) films consisting of liquid crystal (LC)/monomers/indium tin oxide (ITO) nanoparticles with good near‐infrared absorption property had been fabricated, and the influence of the ITO nanoparticles modified with 3‐methacryloxypropyltrimethoxysilane (KH570) on the PDLC films was systematically studied. First, different liquid crystal content was studied to obtain PDLC films with good electro‐optical properties. And then, various weight ratio of ITO nanoparticles was added to samples. While the content of ITO nanoparticles was increased, the saturation voltage increased and the CR decreased. Though the electro‐optical properties of PDLC samples reduced with the addition ITO nanoparticles, the near‐infrared absorption property of films was enhanced.     

Microstructure and properties of organosoluble polyimide/silica hybrid films

Organosoluble polyimide/silica hybrid materials were prepared via the sol-gel process and their pervaporation properties were studied. The organosoluble polyimide (PI) was based on 4,4′-oxydiphthlic dianhydride (ODPA) and 4,4′-diamino-3,3′-dimethyldiphenylmethane (DMMDA). The surface chemical structure of polyimide/silica films was analyzed by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) and the results show that the completely hydrolysis of alkoxy groups of precursors and formation of the three-dimensional Si-O-Si network in the hybrid films. The morphology and the silica domain thus obtained were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The silica particle size in the hybrid is in the range of 40-100 nm for the hybrid films when the amount of silica is less than 20 wt%. The strength and the modulus of the hybrid films are improved and the mechanical properties were found to be strongly dependent on the density of the crosslink. The glass transition temperature (T_g) of the hybrid films was determined by dynamic mechanical analysis (DMA) and the value increased 15-20 °C as the silica content increased. Furthermore, the pervaporation performances of the prepared hybrid films were also investigated for the ethanol/water mixtures at different temperature.     

A holistic evaluation of the influence of shear rates and matrix viscosity on the properties of polypropylene/multi-walled carbon nanotubes composites

In this work, a comparative study on the electrical, morphological, and thermal properties of polypropylene/multiwalled carbon nanotubes (PP/CNT) composites which were prepared by three different processing methods, such as compression molding (CM, shear rate: ~0 s⁻¹), conventional injection molding (CIM, shear rate: ~10² s⁻¹), and microinjection molding (μIM, shear rate: ~10⁵ s⁻¹), was reported. The difference in shear rates among these processing methods and matrix viscosity would significantly affect the state of filler distribution, thereby determining the properties of subsequent moldings. Electrical conductivity results showed that the percolation threshold of PP/CNT moldings followed a trend of μIM > CIM > CM. A higher degree of CNT orientation and a better filler distribution were achieved under the influence of higher shearing conditions, as corroborated by scanning electron microscope observations and Raman spectral analysis. Moreover, increasing filler concentrations played a positive role in improving the thermal stability of PP/CNT composites and the formation of CNT network was believed to be a contributing factor.     

聚氨酯/分子筛复合材料的制备及性能

以聚对苯二甲酸乙二醇酯（PEA）、甲苯二异氰酸酯（TDI-80）、扩链剂（MOCA）、分子筛为原料,采用预聚体法制备了聚氨酯／分子筛复合材料．考察了分子筛的种类及加入量对聚氨酯／分子筛复合材料的耐溶剂性能、力学性能及热分解温度的影响．结果表明：在相同加入量的前提下,采用4A和13X分子筛制备的复合材料,前者的耐溶剂性能及力学性能要优于后者,当加入量为5％时,性能达到最佳．两者的加入均能提高复合材料的热分解温度,但影响相差不大．     

Thermal stability and glass transition behavior of PANI/MWNT composites

Polyaniline/multi-walled carbon nanotube (PANI/MWNT) composites were prepared by in situ polymerization. Transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were used to characterize the PANI/MWNT composites. Thermal stability and glass transition temperature (T _g) were measured by thermogravimetry (TG) and temperature modulated differential scanning calorimetry (TMDSC), respectively. The TG and derivative thermogravimetry (DTG) curves indicated that with augment of MWNTs content, the thermal stability of PANI/MWNT composites increased continuously. While, T _g increased and then decreased with the MWNTs content increasing from 0 to 20 mass%.     

Low velocity impact and pseudo-ductile behaviour of carbon/glass/epoxy and carbon/glass/PMMA hybrid composite laminates for aircraft application at service temperature

Carbon/glass hybrid composite (CGHC) laminates are some of the most promising composites for lightweight applications. Sometimes these laminates are used in warm environment, such as aircraft frame structures, and this may affect their performance. In order to investigate this issue, the present research aims to study the effect of temperatures on the impact behavior and pseudo-ductile behaviour of CGHC in presence of different types of thermosets “epoxy” and thermoplastic “acrylic poly-methyl methacrylate-PMMA”. The experiments were started with making of CGHC laminates from different stacking sequences of unidirectional carbon and woven glass fibre layers, using a vacuum-assisted resin transfer method followed by curing treatment. In addition to CGHC laminates, four other neat batches (Carbon/epoxy, Carbon/PMMA, Glass/epoxy, Glass/PMMA) were prepared for comparison. The low velocity impact behaviour of the fabricated panels was evaluated at high temperatures (60 °C and 80 °C) according to ISO 6603-2 standard, using drop tower, while pseudo-ductile behaviour and ductility index (DI) of the specimens were estimated based on the measured total energy and elastic energy. Also, the low-velocity impact response was modeled mathematically based on a modified energy-balance model to predict the absorbed energies. Finally, the failure mechanisms were examined using optical microscope to determine the influence of these damage growth on DI of the composites under different temperatures. The results showed that the impact energy response of both hybrid composites i.e. epoxy and PMMA was stable even as the temperature rose, however, carbon/glass/PMMA exhibited better performance compared with carbon/glass/epoxy with an increase in impact energy response estimated at 50% (25 °C) and 53% (80 °C). Also, the pseudo-ductile phenomenon was strongly evident, which facilitates the predictablility of failure.