A new method for preparing completely exfoliated epoxy/clay nanocomposites: nano-disassembling method

Completely exfoliated epoxy/clay nanocomposites with comprehensive high performance were successfully prepared using Nano-disassembling method. In this method, nano-SiO₂ was added into the montmorillonite and epoxy mixture system as disassembler to interact with montmorillonite (MMT). By means of the strong interaction between nanoscale particles, the MMT layers were completely disassembled into elemental nanometric mono-platelets. These mono-platelets took interlacing arrangement with the disassembler particles in the resultant nanocomposites. Mechanical testing and thermal analysis results indicated that the epoxy/MMT nanocomposites prepared by the Nano-disassembling method displayed dramatic improvements in multiple properties over conventional epoxy/organo-MMT nanocomposites. At the optimal MMT content of 5 phr, tensile modulus and tensile strength increased by 64.2 and 52.3%, respectively. Flexural modulus enhanced by 7.1%, flexural strength by 14.6% and notch impact strength by 37.7%. Glass transition temperature and thermal decomposition temperature moved to higher temperatures by 10.1 and 5.7 °C, respectively.     

Thermal Studies of Metal Poly(4-methyl styrene-co-styrene) with BPO. Part XVII

Abstract

Metal poly(4-methyl styrene-co-styrene) copolymers were obtained by radical polymerization with benzoyl peroxide. The monomers were cocondensed simultaneously with the metals: Pd, Cu, Ag, Au, Zn, Ga, In, Ge, Sn, Sb, and Bi. The metals were evaporated to produce atoms and with the monomer they can generate a matrix at 77 K. After the warm up process, metal comonomer colloids can be obtained. The colloids were polymerized with benzoyl peroxide at 70°C for 0.5 h at 70°C. Four different initiator concentrations (0.1, 0.5, 1.0 and 2.5 mol%) were used. The yields are around 25% and the viscosimetric molecular weight ranges from 10⁴-10⁵ g/mol. The higher Mv are Ag, Ga and Sn-poly(4-methyl styrene-co-styrene). The thermal stabilities of these metal polymers have been studied by thermogravimetry (TG) between 25 and 550°C under nitrogen flow. The decomposition temperature was obtained from the maximum of the first derivative from TG curve. The kinetic parameters of the thermal decomposition were determined by the Arrhenius equation. All these copolymers degrade in a single step around 300°C. The kinetic data thus obtained show the thermostabilities decrease in the order: Ga-(4-MeS-S) > Sb-(4-MeS-S) > Ge-(4-MeS-S) > In-(4-MeS-S) > Zn-(4-MeS-S) > Ag-(4-MeS-S) > Pd-(4-MeS-S) > Cu-(4-MeS-S) > Sn-(4-MeS-S) > Au-(4-MeS-S) > Bi-(4-MeS-S). The thermal stability is depending upon the amount and metal incorporated in the polymer matrix. The decomposition reaction order is zero and we are in the presence of a single decomposition reaction. The pre-exponential factor, the activation energy, the reaction order and the decomposition temperature for all the copolymers have been determined.     

Formation of carbon nanotubes through ethylene decomposition over supported Pt catalysts and silica-coated Pt catalysts

Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5-50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2-5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8-10 nm) despite the uniform coverage of Pt metal particles with silica layers.     

Synthesis of nanocrystalline Mn-Zn ferrite powders through thermolysis of mixed oxalates

Nanocrystalline Mn-Zn ferrite powders were synthesized by thermal decomposition of an oxalate precursor. Two polymorphs of a mixed Mn-Zn-Fe oxalate dihydrate were obtained by precipitation of metal ions with oxalic acid: monoclinic α-(Mn, Zn, Fe)₃(C₂O₄)₃·6H₂O is obtained after precipitation and ageing at 90 °C, whereas the orthorhombic β-type is formed after precipitation at room temperature. The morphology of the oxalate crystals can be controlled by the precipitation conditions. The α-polymorph of the mixed oxalate consists of prismatic and agglomerated particles. The β-oxalate forms non-agglomerated crystallites of submicron size. Thermal decomposition of the oxalate at 350 °C in air results in an amorphous product. Nanosize Mn-Zn ferrite powders are formed at 500 °C and a mixture of haematite and spinel is observed at 750 °C. The thermal decomposition of the mixed oxalate is monitored by thermal analysis, XRD and IR-spectroscopy. The morphology of the oxalate particles is preserved during thermal decomposition; the oxide particle aggregates display similar size and shape as the oxalates. The primary particles are much smaller; their size increases from 3 nm to 50 nm after decomposition of the oxalates at 350 and 500 °C, respectively. The powder synthesized by decomposition at 500 °C was sintered at 1150 °C to dense and fine-grained Mn-Zn ferrites.     

Microporous Materials Derived from the Thermal Decomposition of the Titania/PDMS Hybrid Particles

A microporous material containing titania nano-particles was obtained by thermal decomposition of the titania/silicone hybrid spherical particles. The titania/silicone hybrid spherical particles were converted to porous silica with the BET surface area of about 360 m²/g by heat treatment at 400^∘C in air, while the spherical morphology of the particles was retained. The thermal decomposition of the organic groups of the hybrid particles was accompanied with the generation of the micropores and the transformation of the silicone to silica. The thermal decomposition of the organic groups and the micro-structural change of the hybrid particles were investigated by XRD, N₂ adsorption/desorption isotherm, CHN elemental analysis, FT-IR, and solid-state ²⁹Si magic angle spinning (MAS) NMR.     

Transition from Impact‐induced Thermal Runaway to Prompt Mechanochemical Explosion in Nanoscaled Ni/Al Reactive Systems

The effect of microstructure on ignition sensitivity and reaction behavior is investigated for nanoscaled Ni/Al gasless reactive systems. Nanometric homogeneity of the reactive media was achieved through (a) conventional mixing of nanometric powders; (b) short‐term high‐energy ball milling (HEBM) of micrometer‐sized powders. Sensitivity to thermal inputs is investigated by differential thermal analysis and mechanical sensitivity is studied by high‐rate shear impacts. The composite Ni/Al particles prepared by HEBM were extremely thermally sensitive, with reaction initiating at 220 °C, compared to 559 °C for nanometric powder samples and 640 °C for un‐milled, micrometer‐sized Ni+Al powder mixture. In contrast, nanometric powder mixtures were more susceptible to ignition through mechanical means, exhibiting a high‐speed reaction mode that is not observed in HEBM samples. The high‐speed mode preferentially appears in high‐shear regions and is interpreted as a mechanically‐induced thermal explosion. Its progression is tied to the passage of a stress wave in the heterogeneous media that heats and mixes the materials, rather than being propagated due to chemical energy release. The microstructures unique to each material are considered responsible for their individually ignition sensitivities. Specifically, the finely interspersed porosity in nanometric powder mixtures allows direct heating of the reactive interface between Ni and Al particles during compression through pore collapse and plastic deformation, which leads to exceptionally high mechanical sensitivity. The HEBM materials have high specific reactant interface area in the bulk of each composite particle that enhances thermal sensitivity, but the relatively low specific interface area between particles is unfavorable to mechanical ignition.     

Pickering emulsions stabilized with PANI-NP. Study of the thermoresponsive behavior under heating and radiofrequency irradiation

Micrometric Pickering emulsions in 1-octanol or cyclohexane were stabilized with water-dispersible electroactive polyaniline nanoparticles (PANI-NP). The emulsions were characterized by optical and electronic microscopy as well as spectroscopic techniques. It was demonstrated that nanoparticles maintain their functional properties (e.g., pH sensitivity and electromagnetic absorption) in the emulsion. Furthermore, as a proof of concept, smart Pickering emulsions employing PANI-NP stabilized with a thermosensitive polymer (PNIPAM) were obtained. The thermal behavior of the obtained structures was evaluated by turbidimetric techniques and an IR camera. The thermoresponsive emulsions have shown an important increment of the local temperature (>12°C) under radiofrequency (RF) irradiation. Phase transition of PNIPAM induced by heating or RF absorption provokes the breaking of the emulsions. In this context, the proposed systems herein could induce endothermal reactions carried out in organic solvents. Besides, Pickering emulsions formed by using electroactive PANI-NP could be applied in several medical or industrial applications.     

Determination of Melting Parameters of Cyclodextrins Using Fast Scanning Calorimetry

The first evidence of native cyclodextrins fusion was registered using fast scanning calorimetry (FSC) with heating rates up to 40,000 K s⁻¹. The endothermal effects, detected at low heating rates, correspond to the decomposition processes. Upon the increase of the heating rate the onset of these effects shifts to higher temperatures, reaching a limiting value at high heating rates. The limiting temperatures were identified as the melting points of α-, β- and γ-cyclodextrins, as the decomposition processes are suppressed at high heating rates. For γ-cyclodextrin the fusion enthalpy was measured. The activation energies of thermal decomposition of cyclodextrins were determined by dependence of the observed thermal effects on heating rates from 4 K min⁻¹ in conventional differential scanning calorimetry to 40,000 K s⁻¹ in FSC. The lower thermal stability and activation energy of decomposition of β-cyclodextrin than for the other two cyclodextrins were found, which may be explained by preliminary phase transition and chemical reaction without mass loss. The obtained values of fusion parameters of cyclodextrins are needed in theoretical models widely used for prediction of solubility and solution rates and in preparation of cyclodextrin inclusion compounds involving heating.     

Morphological evolution of boron carbide particles: Sol-gel synthesis of nano/micro B4C fibers

Herein we present a novel non-catalytic sol-gel route to synthesize nano/micro boron carbide fibers. By in-situ decoration of the precursor surface with boric acid crystals during the thermal decomposition stage, the growth kinetics of boron carbide particles was manipulated. Therefore, the formation of anisotropic crystals instead of polyhedral-equiaxed ones was successfully enabled. The results indicated that highly crystalline boron carbide (B₄C) particles with a low amount (<1 ± 5 wt%) of free carbon were obtained. The SEM and HR-FESEM micrographs revealed that B₄C particles with fully polyhedral-equiaxed morphology were obtained from the precursors, which were thermally decomposed with 2 h holding time at 675 °C. As a result of increased thermal decomposition duration of precursor, B₄C particles with various morphologies, such as rhomboid-plate, nanobelt, and fiber were formed beside the polyhedral-equiaxed particles. The yield of boron carbide fiber formation was increased, and polyhedral-equiaxed particles were decreased in the final products by tailoring the structure of the preceramic precursor. The products containing at least 50% of boron carbide fiber were achieved using 12 h of thermally decomposed precursors. The formation and growth mechanisms of boron carbide particles were speculated and comprehensively discussed.     

Cellulose peroxides derived from carbonylated cellulose and hydrogen peroxide

Cellulose peroxides derived from hydrogen peroxide and cellulose derivative into which a ketone group is introduced by reaction with methyl vinyl ketone were investigated. The amount of peroxide formed on the cellulose substrate increased linearly with increasing carbonyl content of the sample, and sulfuric acid activated the formation of peroxide. The cellulose peroxide was gradually decomposed at 60°C in aqueous medium, and the decomposition was accelerated by addition of ferrous salt or irradiation with light of λ > 300nm. Grafting was initiated by adding methyl methacrylate to the thermal decomposition system under nitrogen. The formation, stability, thermal decomposition, and structure of the cellulose peroxide were discussed in comparison with one derived from aldehyde cellulose and hydrogen peroxide.     

Comparison of Biopolymer Emulsifier Performance in Formation and Stabilization of Orange Oil-in-Water Emulsions

The effectiveness of various biopolymer emulsifiers at forming and stabilizing model beverage emulsions was examined: β-lactoglobulin (BLG); gum arabic (GA); conventional modified starch (MS-old); new modified starch (MS-new). Orange oil-in-water emulsions (5% oil) were prepared using high pressure homogenization. For BLG, MS-new, MS-old and GA, the minimum droplet diameters produced were 171, 254, 222 and 497 nm, while the minimum mass ratio of emulsifier-to-oil required to produce small droplets were 0.5:5, 1:5, 3:5 and 5:5, respectively. The influence of pH (3–8), ionic strength (0–500 mM NaCl, 0–50 mM CaCl₂) and thermal treatment (30–90 °C) on the stability of the emulsions was examined. Extensive droplet aggregation occurred in BLG-stabilized emulsions around their isoelectric point (pH ≈ 5), at high salt concentrations (≥300 mM NaCl, ≥10 mM CaCl₂, pH 7) and at high temperatures (>70 °C, 200 mM NaCl, pH 7) due to changes in electrostatic and hydrophobic interactions. There was little effect of pH, ionic strength and temperature on emulsions stabilized by GA or MS due to strong steric (rather than electrostatic) stabilization. The new type of modified starch used in this study was capable of forming stable emulsions with small droplet sizes at low concentrations.     

Magnetic solid phase extraction for chromatographic separation of carbamates

Magnetic solid phase extraction particles (MSPE) were produced using magnetite nanoparticles with diameters between 9 and 13 nm as nucleating agent. The produced particles with magnetite cores were smaller, and more irregular and poly‐dispersed, than those produced in the absence of the magnetite particles. The average diameters of the particles were 377 and 521 nm, respectively, for silica particles with and without magnetic core, whereas the diameters of the different grafted particles were of the same order of magnitude than the silica particles with magnetic cores. BET results indicated surface areas ranging between 9 and 37 m² g^?1 The TGA results showed that the particles contained about 10% water and other solvents, and between 5 to 6% grafted groups. The thermal decomposition of the particles (presented under Supplementary Information ) was autocatalytic with activation energies of 367, 546, and 616 kJ mol^?1 for particles grafted with cyanopropyl (cyano), octyl, and trimethyl (TMS), respectively. The order of dispersity of the particles in water followed the sequence cyano > PMA > TMS ? octyl, whereas the pesticides removing efficiency followed the reverse order.     

Novel and efficient electrochemical way for silver nanoparticles deposition onto solid conductors: a new concept of metal-silver cathodes

The deposit of very small silver particles onto a very large palette of solid electronic conductors was achieved by means of the cathodic reduction of alkyl iodides RIs in the presence of a suspension of silver–palladium alloy particles (diameter >250 μm). The potential applied to the conductor is so that RIs are not directly reduced at its surface. The observed cathodic reaction is then the discharge of silver grains reacted in surface and covered by a transient assigned to be [RAg⁺, I⁻]. The main heterogeneous products are homo-dimers R–R while the deposition of silver aggregates of very small size (nanometric scale) occurs onto the conductor. By this way, the efficient silverization of many surfaces is possible. Stable layers of Ag particles were made onto many solid surfaces like platinum, palladium, copper, nickel, iron, gold, graphite, and glassy carbon. Preliminary evidences for the use of those new silvered electrodes are presented.     

Preparation and characterization of micron and submicron-sized vermiculite powders by ultrasonic irradiation

Micron and submicron-sized vermiculite lamellar particles with nanometric thickness (< 10 nm) were prepared by ultrasonic treatments (< 12 h) of aqueous and hydrogen peroxide suspensions of thermally exfoliated vermiculite. Laser granulometry characterizations showed that the particles size distribution was dependent on the treatment time and that the use of H₂O₂ afforded smaller particles than H₂O. In both media, an exfoliation and a size reduction were observed after only 1 h of ultrasonic treatment by Scanning Electron Microscopy, X-ray diffraction, and Nitrogen Adsorption Measurements at 77 K. X-ray diffraction studies showed the absence of damage in crystals structure after sonication and also a reduction of crystallites size along the basal direction (00l). The different ultrasonic treatments also induced modifications of the surface properties of the vermiculite particles, brought out by BET surface measurements, infrared spectroscopy, pH modifications of the materials and zeta potential analyses. Sonication of the vermiculites yielded to the formation of carbonate anions from the dissolved CO₂ and hydroxide anions released from the clay layers. The long ultrasound irradiation of the vermiculite in hydrogen peroxide (> 5 h) generated the decrease of the surface charge, pointed out by pH and zeta potential modifications, allowing an aggregation of the submicron particles in the suspensions.     

Correlation between the morphology of cobalt oxalate precursors and the microstructure of metal cobalt powders and compacts

Metal cobalt powders of well-controlled size and morphology were synthesized by thermal decomposition under hydrogen of precipitated cobalt oxalates. Green compacts were prepared by uniaxial pressing of metal powders at 290 MPa. The bending green strength of the metal compacts was measured.A precipitation from ammonium oxalate and oxalic acid gives rise to the formation of β-CoC₂O₄·2H₂O particles of parallelepipedic and acicular morphology, respectively. An increase in the length to diameter ratio of the precursor particles favours an entanglement of the elementary grains during the thermal decomposition. Therefore, irregular and rough metal particles have been obtained. This specific morphology favours a mechanical interlocking of the particles during the compaction, leading to high values of green density and green strength of the metal compacts.     

Pd–Al interaction at elevated temperatures: a TEM and SAED study

Epitaxially grown Pd particles partly embedded in amorphous Al₂O₃ were subjected to annealing and reductive treatments in the temperature range 523–873 K to induce a possible Pd–Al interaction. The structural, morphological and compositional changes were monitored by transmission electron microscopy and selected area electron diffraction. Formation of Pd₄Al₃ and PdAl alloys has been observed upon annealing in 1 bar He for 1 h at T > 523 K and upon reduction in 1 bar H₂ for 1 h at T ≥ 523 K, respectively. Both alloys appear to be stable up to 873 K, although Pd₄Al₃ shows beginning decomposition at and above 873 K. The stability under oxidative conditions was found to be very similar, a transformation back into metallic Pd sets in for both compounds at around 573–623 K. In agreement with previous studies on Pd/SiO₂, the formation of an amorphous hydride phase and/or a heavily distorted Pd lattice has been detected after reduction in hydrogen at 523 K.     

Behavior of mercury release during thermal decomposition of coals

The mercury release behavior during thermal decomposition of three Chinese coals with different types was studied under nitrogen, carbon dioxide and air at temperatures of 800, 900, 1,000 and 1,100 °C. The thermal treatment experiments were carried out in a quartz tube reactor. Results showed that the release ratio of total mercury during thermal decomposition of coals increases with the increasing temperature. The order of the amount of mercury released under the three atmospheres is nitrogen<carbon dioxide<air for all three coals during thermal decomposition. This indicates that air and carbon dioxide can promote the mercury release due to their reactivity with coal. However, the order of amount of elemental mercury released under the three atmospheres is nitrogen>carbon dioxide>air for all three coals. The release behavior of the total mercury under air is independent of the coal type. Under the other two atmospheres the release behavior is distinguished by the coal type. This work was presented at the 7 ^th China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

Selection of quaternary ammonium groups for optimizing properties of water‐soluble,photosensitive phenolic resins and study of their postcuring mechanism

This article deals with the selection of quaternary ammonium groups for synthesis of water‐soluble, photosensitive phenolic resins, containing acrylate and different quaternary ammonium salt groups (AQSPRs), via ring‐opening reactions of epoxy phenolic resin (EPR) with acrylic acid and with different tertiary amine‐protonic acid salts. Conversion of epoxy groups, solubility, photosensitive properties, and thermal decomposition of the different AQSPRs were compared. Modification of AQSPR with methanol solution of KOH to form phenolic resin containing both quaternary ammonium hydroxide groups and acrylate groups (AQHPR) was also studied. Characterization by IR spectrum, DSC, and thermal gravimetric analysis was carried out. The results showed that in the synthesis of AQSPRs containing different quaternary ammonium salt groups, the efficiency of ring‐opening reaction of epoxy phenolic resin with tertiary amine salt in terms of conversion of epoxy groups decreases in the following order: for the tertiary amine, N,N‐dimethyl benzylamine (DMBA) > triethylamine (TEA) > trimethylamine (TMA) > N,N‐dimethyl aniline (DMA) > triethanolamine (TENA) > tri(n‐butylamine) (TBA); for the protonic acid, HCl > HBr > HCOOH > HI > NaHSO₃ > Cl₃CCOOH > HClO₄ > HBF₄. All the AQSPRs except that from HClO₄ can be dissolved in water, methanol, DMF, or DMSO. The gel content formed during UV exposure decreases in the following order of acids used in forming quaternary ammonium salt groups: HCl > HCOOH > NaHSO₃ > Cl₃CCOOH; or decreases in the following order of tertiary amines or hydrohalic acids used in forming the quaternary ammonium groups: TMA. > TEA > DBMA; HCl > HBr > HI. During thermal decomposition of EPR with about half epoxy groups of EPR ring‐opened with tertiary amine salt at 160°C for 0.5 h, water‐insoluble product was formed. The insoluble content and the % decrease of epoxy groups or halide ions increase in the following order: TMA < TEA < DMBA; HCl < HBr < HI. The % decrease of epoxy groups for the insoluble residue is nearly equal to the % decrease of halide ions. A crosslinking reaction mechanism occurred in the thermal decomposition was thus proposed. During the modification of AQSPR with KOH, conversion of quaternary ammonium chloride groups can reach above 90%. The decomposition temperature of the quaternary ammonium groups was lowered from 204 to 120°C after modification of AQSPR with KOH. The photosensitive properties of the resin after modification became lower. It is better to react DMBA · HCl with EPR so as to obtain a product with higher conversion of epoxy groups, good water solubility, moderate photosensitivity, lower decomposition temperature, and better postcuring. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2914–2922, 2004     

Surface treatment of ferromagnetic nanoparticle-assembly by UV irradiation with ozone

Fe-Pt nanoparticles of 3.5 nm in average particle diameter are obtained with the simultaneous chemical reduction of platinum acetylacetonate and the thermal decomposition of iron pentacarbonyl. Because the as-synthesized particles are superparamagnetic at room temperature, they must be transformed to L1₀ ordered phase by annealing at temperatures above 773 K to apply to high-density magnetic recording media. However, the annealing at such high temperatures induces the coalescence and inter-particle sintering. In the present paper, to solve the problem caused by the annealing, we use ultraviolet-ozone treatment to modify particle surface. Even after annealing at 773 K, the crystalline size is kept at 4.4 nm. Furthermore, coercivity is higher than that without the ultraviolet-ozone treatment.     

Thermal behaviour of graft copolymers of sodium alginate

The thermal stability of sodium alginate (SA) and its graft copolymers of acrylonitrile (AN), methyl acrylate (MA), ethyl acrylate (EA) and methyl methacrylate (MMA) has been examined in air atmosphere by means of thermogravimetric analysis. The following order of decreasing stability was found from characteristic decomposition temperatures: SA-g-PAN > SA-g-PMA > SA-g-PEA > SA-g-PMMA. The overall thermal stability of the different SA graft copolymers was evaluated by comparing their activation energies of thermal degradation; it agreed with the same order of thermal stability.