Novel vinyl-modified sepiolite-based polymer nanocomposites: synthesis and characterization

An environmental-friendly synthesis of polymer clay nanocomposites (PCNs) was carried out by incorporation of nanoclay into polymer matrix for their potential application as sorbent of metals present in aqueous media. Polyacrylonitrile was chemically grafted onto 77% vinyl triethoxysilane-modified sepiolite. The polymerization was carried out with benzoyl peroxide (BPO, C₁₄H₁₀O₄) initiator in three different weight ratios of 1.0, 2.0, and 3.0%. The maximum polymer grafting of about 83% was obtained in nanocomposite initiated by 2.0% ratio of BPO. The surface modification of nanocomposites was carried out using hydroxyl amine hydrochloride (NH₂OH·HCl). The prepared nanocomposites were characterized by Fourier transform infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis, and Brunauer–Emmett–Teller technique. The copper removal tendency of nanocomposites was studied by atomic absorption spectroscopy. The maximum adsorption of copper was 86%, which could be achieved by nanocomposites synthesized with 2% initiator. The results have revealed the practical potential of the prepared PCN as efficient adsorbents.     

Synthesis and characterization of PMMA/SiO2 nanocomposites by in situ suspension polymerization

Poly(methyl methacrylate) (PMMA)/SiO₂ nanocomposites were prepared by in situ suspension polymerization. Two types of modified methods were used to modify nano‐SiO₂: one was modification by γ‐methacyloxypropyl trimethoxy silane (KH570) and lauryl alcohol (12COH) while the other was grafting PMMA onto the surface of KH570 treated SiO₂. Transmission electron microscopy (TEM) and Fourier transformed infrared (FTIR) were used to characterize the structures of the nanocomposites. The influence of synthetic conditions, for instance, surface modification, initial SiO₂ contents and reaction temperature, on the microsphere's size and molecular weight of the extracted PMMA were studied by gel permeation chromatograph (GPC) and optical microscopy (OM) in details. Thermal property of the nanocomposites was investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results indicate that the presence and content of SiO₂ have a vital effect on the shape and size of the nanocomposite microspheres, as well as molecular weight of the extracted PMMA. Grafting polymer to the surface of SiO₂ is an effective way for the purpose of effective in situ suspension polymerization. Compared to pure PMMA, the thermal properties of the nanocomposites were improved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis,characterization, and thermal stability of PMMA/SiO2/TiO2 tertiary nanocomposites via non‐hydrolytic sol–gel method

In this study, we use PMMA, tetraethoxysilane and titanium ethoxide to prepare tertiary nanocomposites via non‐hydrolytic sol–gel method. Boron trifluoride monoethylamine was used as catalyst. Silica and titanium dioxide are incorporated into nanocomposites to improve the thermal stability. Thermogravimetric analysis was used for rapid evaluation of the thermal stability of different materials. The integral procedural decomposition temperature has been correlated the volatile parts of polymeric materials and used for estimating the inherent thermal stability of polymeric materials. The thermal stability of hybrids increased with the contents of inorganic components. The inorganic components can improve the thermal stability of PMMA copolymer. Two methods have been used to study the degradation of hybrid during thermal analysis. These investigated methods are Kissenger', Ozawa's methods to classify the thermal stability of nanocomposites. The activation energies of hybrids were higher than that of the copolymer. From the results, silica and titania will enhance the thermal stability of PMMA. We use the solubility test to check the network structure of nanocomposites. The results show the residues of composites after extraction increase with the increasing of inorganic contents. We can conclude that the composites possess network structure. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of Ce/SiOC nanocomposites through the polymer derived ceramic method and evaluation of their catalytic activity

Cerium oxide and silicon oxycarbide (Ce/SiOC) porous nanocomposites have been synthesized through the polymer derived ceramic route. In the synthesis of the preceramic precursors, the addition of urea facilitates the deposition of Cerium atoms on the surface of SiO₂ nanoparticles since it prevents the SiO₂ from agglomeration. Both Ce and urea affects the structural and textural parameters of the obtained ceramics. Less crosslinked structures are formed when the urea concentration increases and it also provokes a reduction of the carbon crystallite size. Cerium, on the other hand, induces an increase of the carbon size as well as the number of SiOC units. Pore anisotropy and smoothness of the surface are also dependent on the composition of the material. As expected, the better thermocatalytic behavior against CO₂ decomposition is found at the largest Ce amounts but also, smooth surfaces and low pore anisotropies favor the accessibility of the gases to the thermocatalytic centers.     

Micro-mesoporous TiO2/SiO2 nanocomposites: Sol-gel synthesis,characterization, and enhanced photodegradation of quinoline

Micro-mesoporous TiO₂/SiO₂ nanocomposite powders have been successfully synthesized by the sol-gel process with different TiO₂/SiO₂ molar ratios and were applied in the UV-photodegradation of quinoline (λ = 254 nm). The structural, morphological, and textural characterization of the powders showed a homogeneous distribution of TiO2 nanoparticles within a porous amorphous SiO2 matrix. Due to the micro-mesoporous character of the materials, their textural characteristics were evaluated by the N2 adsorption method, by comparing BET, DR, Langmuir, and DFT theories. Si₆₀Ti₄₀ powders (60%SiO₂/40%TiO₂) presented the highest specific surface area (SSA) obtained from BET (SSA = 363 m²g^-1), DR (SSA = 482 m²g^-1), and Langmuir (SSA = 492 m²g^-1) due to the adequate particle size of TiO₂ and its high dispersion in the porous matrix. A higher degradation of quinoline in the presence of H₂O₂ (66%) was achieved using Si₈₀Ti₂₀ powders (80%SiO₂/20%TiO₂), as compared to pure sol-gel TiO₂ powders, (51%) under the same reaction conditions (1 UVC lamp - 250W, t = 180 min). The better performance of the Si₈₀Ti₂₀ nanocomposite could be attributed to the small TiO₂ anatase crystallite size (<5.7 nm), high dispersion of these crystallites in the SiO₂ matrix, great specific surface area (DR SSA = 342 m² g^?1), and the formation of Ti–O–Si bond, which is associated with new catalytic sites in TiO₂/SiO₂ composite.     

Preparation and characterization of Co/SiO2, Co-Mg/SiO2 and Mg-Co/SiO2 catalysts and their activity in CO hydrogenation

Co/SiO₂, Mg-Co/SiO₂ and Co-Mg/SiO2 catalysts were prepared from acetate, nitrate or carbonyl precursors. The catalysts were characterized by XRD, XPS, SIMS and TGA. The steady-state activity and product distribution of the catalysts were evaluated in synthesis gas reactions at 0.5 MPa and 235-290°C using 3 : 1 : 3 molar ratio of Ar : CO : H₂. The activity in CO hydrogenation decreased in the precursor order Co₂(CO)₈>Co(NO₃)₂> Co(CH₃COO)₂, and the probability of chain growth decreased in the precursor order Co(NO₃)₂>Co₂(CO)₈>Co(CH₃COO)₂. Alcohol yields were highest with Co₂(CO)₈, and lowest with Co(NO₃)₂, Magnesium promotion influenced the catalyst activity and decreased the CO₂ formation, but the promotion effects were less profound than those of the precursor. Surface studies on partially magnesium covered cobalt foil model catalysts suggested that magnesium promotes CO dissociation and chain growth, neither of which were, however, observed in the supported catalysts.     

Synthesis and pyrolysis of non-oxide precursors for ZrC/SiC and HfC/SiC composite ceramics

Multiphase ceramics like ZrC/SiC are promising candidates as ultra-high temperature ceramics for applications in extreme environments. In this work, non-oxide precursors for ZrC/SiC and HfC/SiC composite ceramics were synthesized by a one-pot reaction of three components – metal source, silicon source, and activating reagent. Molecular structures of the precursors were identified by ¹H NMR and FTIR. Transformation process of the precursors to the ZrC/SiC ceramics was investigated via XRD and SEM. After heat-treatment at 1600 °C under argon, the obtained ZrC/SiC and HfC/SiC ceramics features a particle size of 100–200 nm and high metal content without excess carbon. The elemental composition of pyrolyzed ceramics can be tuned by varying the ratio of the reagents in the synthesis of precursors. This strategy also inspires a facile fabrication of composite ceramics with other elemental compositions.     

细乳液聚合制备和表征聚（BA—St）／SiO2杂化微球

在纳米二氧化硅水分散介质中,使用阴离子乳化剂（SDS）,通过细乳液聚合成功制备了一系列聚（BA—St）／SiO2杂化微球。杂化微球的平均粒径在98nm～130nm。研究了纳米二氧化硅用量和单体组成等影响因素对杂化粒子粒径和形态的影响,提出了一种可能的反应机理。     

Synthesis of silver/SiO2/Eu:Lu2O3 core-shell nanoparticles and their polymer nanocomposites

We report a core-shell approach that combines silver nanoparticles as the metal core component with Eu:Lu₂O₃ as the phosphor shell component. The core-shell design contains an optically transparent SiO₂ intermediate layer that separates the metallic nanoparticle core and the phosphor shell. The thickness of the SiO₂ layer is in the nanometer range and can be tuned, so as to provide for different interactions between the core and shell. To demonstrate the versatility of the design, spherical silver nanoparticles or wavelength-tunable plasmonic silver nanoplates are used as the core component. In addition, a nanocomposite phosphor was fabricated by embedding the core-shell nanoparticles into a transparent polymeric matrix. The core-shell metal-phosphor design presented here serves as framework for the fabrication of inexpensive nanocomposite scintillator.     

Synthesis of hierarchical structured porous MoS2/SiO2 microspheres by ultrasonic spray pyrolysis

Hierarchical structure porous MoS₂/SiO₂ microspheres were prepared by ultrasonic pyrolysis technique. The nanostructured MoS₂/SiO₂ materials were characterised by scanning electron micrograph (SEM), energy dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), high‐resolution transmission electron microscope (HRTEM), as well as nitrogen isotherm. The MoS₂/SiO₂ microspheres, synthesised using polystyrene latex spheres as a template, showed two pore sizes: 5.8 and 68 nm. The micro‐, meso‐ and macropore volume was also calculated. Effect of PSL:SiO₂ ratio on the hierarchical structure was also investigated. © 2011 Canadian Society for Chemical Engineering     

High‐frequency dielectric characterization for liquid crystalline polyimide/SiO2 nanocomposites

In this study, we investigated the influence of frequency, film thickness, and SiO₂ content on the dielectric constant (K) and loss tangent (tan δ) of liquid crystalline polyimide (LCPi) and liquid crystalline polyimide/SiO₂ (LCPi/SiO₂) nanocomposites in a high frequency environment. We tested the loss tangent of the LCPi and LCPi/SiO₂ nanocomposites within the high frequency 1 MHz to 3 GHz range, and determined its value to be between 0.01 and 0.001. In addition, we found a formant for frequencies ranging from 0.5 GHz to 1 GHz. We also inferred from the dielectric loss graphs of films with different thicknesses that the formants of the loss tangent shifted toward higher frequencies with increasing thicknesses. When measuring the dielectric constant at high frequencies, we found that the dielectric constant decreased markedly with increased SiO₂ contents. Using the dielectric constant of high‐frequency circuit board materials as the standard, the dielectric constant of the LCPi/SiO₂ nanocomposites at the frequency range from 1 MHz to 3 GHz was found to be as high as 2.2–3.4, thereby confirming the viability of LCPi/SiO₂ nanocomposites as candidate materials for high‐frequency circuit board. In addition, the volume resistivity (ρ_V) of the LCPi and LCPi/SiO₂ nanocomposites also increased with increased SiO₂ contents. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of polymer/multiwall carbon nanotube/nanoparticle nanocomposites and preparation of their metal complexes

Carbon nanotube‐polymer nanocomposites were synthesized and characterized successfully. In this work, multiwall carbon nanotubes (MWCNT) were opened using HNO₃/H₂SO₄ mixture and filled by metal nanoparticles such as silver nanoparticles through wet‐chemistry method. The oxidized MWCNT were reacted subsequently with thionyl chloride, 1,6‐diaminohexane, producing MWNT‐amine functionalized. Then the MWCNT containing metal nanoparticles were used as a monomer with different weight percentages in melt polymerization with An and CNCl separately. Furthermore, the polyamide and polytriazine modified MWCNT were used for the preparation of metal ion complexes such as Fe⁺² and La⁺³. The structures and properties of nanocomposites were evaluated by TEM, DSC, TGA, and FT‐IR methods. The chelating behavior and sorption capacities of prepared nanocomposites were carried out by using some metal ions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of sPS/montmorillonite nanocomposites

The present work analyzed the possibility of obtaining and producing syndiotactic polystyrene (sPS)–based nanocomposites. The work first focused on possible technology to use for intercalation from solution and melt intercalation. Using a blend of sPS with atactic polystyrene (aPS) as the matrix was also considered. Thermal analysis techniques, such as differential scanning calorimetry (DSC) and thermogravimetry (TGA), were used to study the thermal properties and stability of the nanocomposites obtained and to select the most appropriate nanocharges. The effect of the introduction of nanofillers on these properties also was evaluated. X–ray diffraction was used to investigate the degree of clay exfoliation. Finally, mechanical characterization of the nanocomposites obtained was performed and compared to that of the pure material. The tests demonstrated that nanodispersion of phyllosilicate layers improved the mechanical behavior of the polymers analyzed, especially the annealed sPS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4957–4963, 2006     

Synthesis and characterization of polyurethane/organo-montmorillonite nanocomposites

Polyurethane (PU)/organo-montmorillonite nanocomposites were prepared by in situ polymerization of toluene diisocyanate and butanediol in the presence of different contents of organo-montmorillonite (9–18 mass%). Organo-montmorillonite were prepared by an ion exchange process of sodium montmorillonite with –NH₃⁺ groups in polyoxyalkylene amine hydrochloride with two different molecular masses of 403 and 5000. To change the degree of surface modification, sodium montmorillonite was reacted with polyoxyalkylene amine hydrochloride in equivalent ratios (1:1 and 1:2). Dimethyl formamide (DMF) was used as a swelling agent for the prepared organo-montmorillonite. Different nanocomposite structures, depending on the molecular mass of the polyoxyalkylene and the degree of surface modification of montmorillonite were studied. The results of X-ray analysis and transmission electron microscopy showed that the organo-montmorillonite with polyoxyalkylene of higher molecular mass (T₅₀₀₀) produced the exfoliated PU nanocomposites; (T₄₀₃), led to an intercalated structure. Nanocomposites exhibited lower water adsorption values and higher thermal stability than that of pure PU₀. In addition, the hardness of the nanocomposites was measured.     

聚氨酯/有机蒙脱土纳米复合材料的合成与表征

采用共沸法精制有机蒙脱土，估算了有机蒙脱土中吸附水质量分数约为8．3％。结构水的质量分数约为4．1％。用两步法原位聚合制备了聚氨酯／有机蒙脱土(PU／MMT)纳米复合材料，表征了纳米复合材料的形态、动态力学性能和物理机械性能。结果表明，有机蒙脱土对聚氨酯有增强和增韧双重作用。有机蒙脱土对聚合物分子的限制作用使PU／MMT纳米复合材料的玻璃化转变温度升高，储能模量和损耗模量也有明显提高。     

Synthesis and characterization of polypropylene/clay nanocomposites

Polypropylene/clay (PP/clay) nanocomposites were synthesized via intercalative polymerization. The nanostructure of the composites was investigated by wide‐angle X‐ray diffractometry (WAXD) and transmission electron microscopy (TEM). The WAXD patterns of the PP/clay nanocomposites indicated that the characteristic diffraction peak of the clay disappeared. The TEM image showed the clay was exfoliated into nanometer size and dispersed uniformly in the PP matrix. The composites exhibited much higher storage modulus compared to that of pure PP. At temperatures higher than T_g, the storage modulus of the PP/clay nanocomposites with 8.1 wt % clay content increased three times that of the pure PP. Additionally, the thermal stability of the nanocomposites significantly increased. The maximum decomposition temperature was increased by 44°C with the introduction of about 10 wt % clay. The heat‐distortion temperatures (HDTs) of the nanocomposites also increased. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3611–3617, 2001     

CdS／PAA纳米复合材料的合成及光学性质研究

以氯化镉、硫化钠、偶氮二异丁氰（AIBN）和丙烯酸（AA）等为原料,原位一步法合成CdS／PAA纳米复合材料。产物通过红外光谱（IR）、紫外-可见吸收光谱（UV—Vis）、荧光光谱（PL）、扫描电子显微镜（SEM）及X-射线衍射花样（XRD）进行表征。根据实验结果给出可能的机理：金属离子首先与聚合物的羧基络合,生成硫化物纳米微粒后,聚合物又包覆在纳米微粒的表面形成保护层。     

Processing and characterization of particles reinforced SiOC composites via pyrolysis of polysiloxane with SiC or/and Al fillers

Polysiloxane loaded with SiC as inert filler, and Al as active filler, was pyrolyzed in nitrogen to fabricate SiOC composites, and the processing and properties of the filled SiOC composites were investigated. Adding SiC fillers could reduce the linear shrinkage of filler-free cured polysiloxane in order to obtain monolithic SiC/SiOC composites. The flexural strength of SiC/SiOC composites reached 201.3 MPa at a SiC filler content of 27.6 vol.%. However, SiC/SiOC composites exhibited poor oxidation resistance, thermal shock resistance and high temperature resistance. Al fillers could react with hydrocarbon generated during polysiloxane pyrolysis at 600 °C and N₂ at 800 °C to form Al₄C₃ and AlN, respectively. The volume expansions resulting from these two reactions were in favor of the reduction in linear shrinkage and the improvement in flexural strength of SiC/SiOC composites. The flexural strength of Al-containing SiC/SiOC composites was 1.36 times that of SiC/SiOC composites without Al at an Al filler content of 20 vol.%. The addition of Al fillers remarkably improved the high temperature resistance and oxidation resistance of SiC/SiOC composites, but not thermal shock resistance.     

溶胶-凝胶法制备SiO2/有机硅复合涂料

以正硅酸乙酯(tetraethoxysilane,TEOS)、甲基三乙氧基硅烷、二甲基二乙氧基硅烷和甲基丙烯酰氧基丙基三甲氧基硅烷为原料,采用溶胶–凝胶法在聚碳酸酯(polycarbonate,PC)表面上制备透明硬质的SiO2/有机硅复合涂膜。用红外光谱、紫外光谱,热重、X射线衍射、表面扫描电镜、原子力显微镜和接触角测量仪等方法对产物进行了表征。结果表明:复合膜中形成了Si—O—Si网络结构;采用浸涂工艺,经120℃热固化制备的涂膜厚度为0.84μm,表面平整,致密均质,对PC基材具有一定的增透作用(透光率提高了将近5%);复合膜对水的接触角随固化时间的延长而增大,在120℃固化3 h后接触角为93°;随着TEOS含量增加,复合膜的耐热性得到提高;当SiO2/有机硅复合树脂的n(R)/n(Si)(一个硅原子上平均连结的有机基团数目)值选择0.78,划格法测定的复合膜的铅笔硬度为2 H,附着力为0级。     

Synthesis and characterization of amorphous octakis-functionalized polyhedral oligomeric silsesquioxanes for polymer nanocomposites

We have synthesized the polyhedral oligomeric silsesquioxane (POSS) derivatives OS-POSS and OA-POSS through the hydrosilylation of styrene and 4-acetoxystyrene, respectively, with octakis(dimethylsiloxy)silsesquioxane (Q₈M₈^H). We then prepared OP-POSS through acetoxyl hydrazinolysis of OA-POSS with hydrazine monohydrate. The chemical structures of these POSS derivatives were characterized using FTIR and ¹H NMR spectroscopy and MALDI-TOF mass spectrometry. Unlike Q₈M₈^H, which is crystalline, these three hydrosilylated POSS derivatives are liquids at 25 °C. Through DSC and XRD analyses, we found that they exhibit polymer-like glass transitions and amorphous halos. These octakis-functionalized POSS derivatives can be regarded as amorphous glasses possessing low glass transition temperatures, the values of which depend on the intermolecular interactions of their outer organic groups. To investigate the dispersion of these POSS derivatives in polymer nanocomposites, we blended OS-POSS, OA-POSS, and OP-POSS with polystyrene, poly(4-acetoxystyrene), and poly(4-vinylpyridine), respectively, and investigated the effects of the resulting intermolecular aromatic hydrophobic, dipole-dipole, and hydrogen-bonding interactions, respectively. Dipole-dipole interactions provided the best dispersion of OA-POSS in poly(4-acetoxystyrene), in which the POSS-polymer intermolecular interactions were of similar strength to the POSS-POSS interactions.