The chemical and dielectric properties of epoxy/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites for embedded capacitor application

The characteristics of epoxy/(Ba_0.8Sr_0.2)(Ti_0.9Zr_0.1)O₃ (BSTZ) composites are investigated for the further application in embedded capacitor device. The effects of BSTZ ceramic powder filler ratio on the chemical, physical and dielectric properties of epoxy/BSTZ composites are studied. Differential scanning calorimeter (DSC) thermal analysis is conducted to determine the optimum values of hardener agent, curing temperature, reaction heat, and glass transition temperature (T_g). The hardener reaction process starts at about 115 °C and completes at about 200 °C, for that it is appropriate to process of epoxy/BSTZ composites in the range of temperature. The highest glass transition temperature (T_g) of 155 °C is obtained at one equivalent weight ratio (hardener/epoxy). Only the BSTZ phase can be detected in the XRD patterns of epoxy/BSTZ composites. The more BSTZ ceramic powder is mixed with epoxy, the higher crystalline intensity of tetragonal BSTZ phase are revealed in the XRD patterns. The dielectric constant measured at 1 MHz increases from 5.8 to 23.6 as the content of BSTZ ceramic powder in the epoxy/BSTZ composites increases from 10 to 70 wt%. The loss tangents of the epoxy/BSTZ composites slightly increase with the increase of measurement frequency.     

Effect of the aspect ratio of silicate platelets on the mechanical and barrier properties of hydrogenated acrylonitrile butadiene rubber (HNBR)/layered silicate nanocomposites

The role of the aspect ratio of the layered silicate platelets on the mechanical and oxygen permeation properties of hydrogenated nitrile rubber (HNBR)/organophilic layered silicate nanocomposites was investigated. Montmorillonite (MMT) and fluorohectorite (FHT) bearing the same type of intercalant (i.e., octadecylamine; ODA), however, showing different aspect ratio was involved in this study. The dispersion of the layered silicates was assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Increasing aspect ratio (MMT < FHT) resulted in higher stiffness under uniaxial tensile loading. The dispersion state (“secondary structure”) of the organophilic layered silicates reduced dramatically the oxygen permeability of the rubber matrix based on the labyrinth principle. The lowest oxygen permeability was measured for the HNBR/FHT-ODA films in which the layered silicates had the highest aspect ratio. By varying the FHT-ODA volume fraction in the latter compound the mechanical and permeation properties were measured and modelled. It was found that the modified Guth’s and Nielsen’s equations predicted accurately the mechanical and permeation responses, respectively.     

Functional copolymer/organo‐MMT nanoarchitectures. XIX. Nanofabrication and characterization of poly(MA‐alt‐1‐octadecene)‐g‐PLA layered silicate nanocomposites with nanoporous core–shell morphology

Novel bioengineering functional copolymer‐g‐biopolymer‐based layered silicate nanocomposites were fabricated by catalytic interlamellar bulk graft copolymerization of L‐lactic acid (LA) monomer onto alternating copolymer of maleic anhydride (MA) with 1‐octadecene as a reactive matrix polymer in the presence of preintercalated LA…organo‐MMT clay (reactive ODA‐MMT and non‐reactive DMDA‐MMT) complexes as nanofillers and tin(oct)₂ as a catalyst under vacuum at 80°C. To characterize the functional copolymer layered silicate nanocomposites and understand the mechanism of in situ processing, interfacial interactions and nanostructure formation in these nanosystems, we have utilized a combination of variuous methods such as FT‐IR spectroscopy, X‐ray diffraction (XRD), dynamic mechanical (DMA), thermal (DSC and TGA‐DTG), SEM and TEM morphology. It was found that in situ graft copolymerization occurred through the following steps: (i) esterification of anhydride units of copolymer with LA; (ii) intercalation of LA between silicate galleries; (iii) intercalation of matrix copolymer into silicate layers through in situ amidization of anhydride units with octadecyl amine intercalant; and (iv) interlamellar graft copolymerization via in situ intercalating/exfoliating processing. The main properties and observed micro‐ and nanoporous surface and internal core–shell morphology of the nanocomposites significantly depend on the origin of MMT clays and type of in situ processing (ion exchanging, amidization reaction, strong H‐bonding and self‐organized hydrophobic/hydrophilic interfacial interactions). This developed approach can be applied to a wide range of anhydride‐containing copolymers such as random, alternating and graft copolymers of MA to synthesize new generation of polymer‐g‐biopolymer silicate layered nanocomposites and nanofibers for nanoengineering and nanomedicine applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Nanoscale highly filled epoxy nanocomposite

A new technique has been developed to prepare a highly filled epoxy-montmorillonite (MMT) nanocomposite using an organically modified MMT. Composites with clay content up to 70 wt.% exhibit unusual transparency, which is related to the spatial distribution of the mineral nanodomains. Dispersion of the layered silicate within the crosslinked epoxy matrix was verified using X-ray diffraction pattern, revealing layer spacings of 30 and 70 Å. Examination of these materials by scanning electron microscopy and transmission electron microscopy showed that intercalates have wholly layered morphology at all scales, oriented parallel to the surface of the specimen and have good wetting to the silicate surface by the epoxy matrix. Silicate lamellae intercalated with epoxy resin assembled into a cluster of about 50-120 nm thickness. These clusters assembled into superclusters with an average thickness of 300 nm. Studies by the Vickers hardness test of an epoxy-MMT nanocomposite containing 60 wt.% MMT indicated that the diamond pyramid hardness was 10-29 kg/mm².     

Tb/Na tobermorite: Thermal behaviour and high temperature products

By heating a sample of Tb/Na tobermorite we obtained a phase which was identified through its X-ray diffraction (XRD) pattern, as terbium silicate apatite. Subsequently this compound has been directly prepared by solid state reaction and we carried out a structural refinement from XRD data in space group P6₃/m obtaining cell parameters a=9.39199(4) Å and c=6.84041(5) Å. Terbium silicate apatite heated in melted NaF led to Tb₄O₇ crystals.     

Layered confinement of protein in synthetic fluorinated mica via stepwise polyamine exchange

We have developed a process to incorporate the model protein, bovine serum albumin (BSA), into the layered spacing of swelled mica. By a stepwise intercalation, the sodium form of synthetic fluorinated mica (Mica) was first exchanged with the poly(oxyalkylene)-diamine salts (POA-amine) through an ionic exchange reaction and then the BSA embedment. The first step of the Mica space expansion from the pristine 12 A to 18-93 A was affected by hydrophobic POP-amines (POP2000 of 2000 g/mol and POP4000 of 4000 g/mol M(w)) and the hydrophilic POE2000 that intercalated Na+-Mica to afford different basal spacing (39, 93, and 18 A, respectively). The POA modification was necessary for the BSA intercalation and resulted in an uncompressed form of protein conformation in the layered confinement (XRD d spacing = 60-71 A). For comparison, direct intercalation rendered only low d spacing (30 A), in which BSA was embedded in a compressed conformation. The BSA-mica complexes were characterized by X-ray, TGA, and solution analyses. The stepwise process provides a new method for embedding large protein molecules into the clay layered structure generating protein/layered silicate complexes.     

Electrical and positron annihilation study on epoxy and epoxy acrylate composites

Epoxy acrylate resin was prepared by endcapping the acrylic acid to epoxy resin backbone in the presence of triphenyl phosphene as catalyst. The structure was elucidated by IR and NMR spectroscopy. Epoxy and epoxy acrylate composites were prepared by mixing different concentrations of mica, magnesium hydroxide and calcium silicate with each epoxy/hardener and epoxy acrylate/styrene mixtures, respectively. The permittivity ε′, dielectric loss ε′′ and loss tangent tan δ were measured for these composites in the frequency range (10²-10⁶ Hz) and at 30 °C. The data obtained were analyzed into two absorption regions related to Maxwell-Wagner effect and to some local molecular motions rather than the main chain motion. The higher values of ε′ and the lower values of tan δ given for the composites containing the epoxy acrylate resin indicate some improvement in the dielectric properties when compared with those containing the epoxy resin. The effect of filler type and filler content on the positron annihilation lifetime and its intensity as well as S-parameter for epoxy and epoxy acrylate composites were also studied. The high values of S-parameter noticed by with increasing filler content indicates some increase in free electrons which lead to an increase in electrical conductivity. The highest value of hardness was obtained in the case of calcium silicate followed by mica and magnesium hydroxide.     

Epoxy nanocomposites co-reinforced by two dimensionally different nanoscale particles

Comprehensive high-performance epoxy nanocomposites were prepared by simultaneous incorporating montmorillonite (MMT) and nanoSiO₂ into epoxy. Mechanical tests and thermal analyses showed that the epoxy/MMT/nanoSiO₂ nanocomposites obtained considerable improvement over basic epoxy in tensile modulus, tensile strength, flexural modulus, flexural strength, notch impact strength, glass transition temperature, and thermal decomposition temperature. X-ray diffraction measurements and transmission electronic microscopy observations revealed that the layered structure of MMT was completely exfoliated into two-dimensional nanoscale mono-platelets. These 2D mono-platelets formed intermingled structure with the zero-dimensional nanoSiO₂ spheres in the nanocomposites. This study suggests that employing the synergistic reinforcement effect of two dimensionally different nanoscale particles is one pathway to success in developing comprehensive high-performance polymer nanocomposites.     

Layered silicate/epoxy nanocomposites: synthesis,characterization and properties

Novel epoxy‐clay nanocomposites have been prepared by epoxy and organoclays. Polyoxypropylene triamine (Jeffamine T‐403), primary polyethertriamine (Jeffamine T‐5000) and three types of polyoxypropylene diamine (Jeffamine D‐230, D‐400, D‐2000) with different molecular weight were used to treat Na‐montmorillonite (MMT) to form organoclays. The preparation involves the ion exchange of Na⁺ in MMT with the organic ammonium group in Jeffamine compounds. X‐ray diffraction (XRD) confirms the intercalation of these organic moieties to form Jeffamine‐MMT intercalates. Jeffamine D‐230 was used as a swelling agent for the organoclay and curing agent. It was established that the d₀₀₁ spacing of MMT in epoxy‐clay nanocomposites depends on the silicate modification. Although XRD data did not show any apparent order of the clay layers in the T5000‐MMT/epoxy nanocomposite, transmission electron microscopy (TEM) revealed the presence of multiplets with an average size of 5 nm and the average spacing between multiplets falls in the range of 100 Å. The multiplets clustered into mineral rich domains with an average size of 140 nm. Scanning electron microscopy (SEM) reveals the absence of mineral aggregate. Nanocomposites exhibit significant increase in thermal stability in comparison to the original epoxy. The effect of the organoclay on the hardness and toughness properties of crosslinked polymer matrix was studied. The hardness of all the resulting materials was enhanced with the inclusion of organoclay. A three‐fold increase in the energy required for breaking the test specimen was found for T5000‐MMT/epoxy containing 7 wt% of organoclay as compared to that of pure epoxy. Copyright © 2004 John Wiley & Sons, Ltd.     

On the effect of montmorillonite in the curing reaction of epoxy nanocomposites

The procedure for the fabrication of epoxy-based polymer layered silicate nanocomposites is important in respect of the nanostructure that is developed. To further our understanding of this, the influence of an organically modified clay (montmorillonite, MMT) on the curing kinetics of an epoxy resin has been studied by differential scanning calorimetry. Clay loadings of 10 and 20 mass% are used, and isothermal as well as dynamic cures have been investigated. For both cure schedules the effect of the MMT is to advance the reaction. Kinetic analysis yields values for the activation energy, but shows that the reaction cannot be described simply by the usual autocatalytic equation. The glass transition of the cured nanocomposites is lower than that for the cured neat resin, a result that is attributed to homopolymerisation taking place in addition to the epoxy–amine reaction.     

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites

Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B^® and Nanofil 784^®, and a sodium MMT (Cloisite Na^®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis-gas-mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B^® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784^® compatibilizer has been conversely found.As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B^®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784^®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes -OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.     

Isoconversional kinetic analysis of stoichiometric and off-stoichiometric epoxy-amine cures

The curing reaction of stoichiometric and off-stoichiometric diglycidyl ether of bisphenol A (DGEBA) and 1,3-phenylene diamine (m-PDA) mixtures was studied by differential scanning calorimetry, thermogravimetric analysis and rheological measurements. In order to highlight the side reactions such as etherification and homopolymerization, the neat DGEBA and DGEBA/DMBA (N,N-dimethylbenzylamine) mixture were examined. The classical model-fitting and the advanced isoconversional methods were used to determine the activation energy of the different reactions. The advanced isoconversional method leads to a good agreement between isothermal, nonisothermal and rheological results. The effective activation energies of primary amine epoxy reaction, etherification and homopolymerization were estimated to about 55-60, 104 and 170 kJ mol⁻¹, respectively.     

Mechanistic modeling of the reaction kinetics of phenyl glycidyl ether (PGE) + aniline using heat flow and heat capacity profiles from modulated temperature DSC

Modulated temperature DSC (MTDSC) has been performed on phenyl glycidyl ether (PGE) + aniline in order to obtain the non-reversing heat flow and heat capacity profiles simultaneously in a wide range of cure temperatures and mixture compositions. The epoxy (PGE) conversion as determined from the former signal corresponds to the one obtained from separate high performance liquid chromatography (HPLC), while the latter signal contains information on the individual reaction steps. Optimized kinetic parameters using a mechanistic approach, including both reactive and non-reactive complexes can successfully simulate MTDSC measurements for isothermal reaction temperatures ranging from 50 to 120 °C and for non-isothermal experiments with mixture compositions corresponding to concentrations of aniline in a range from 1.68 to 6.53 mol kg⁻¹. Concentration profiles for three mixture compositions as obtained from HPLC are also well predicted. The activation energies for the primary amine and secondary amine-epoxy reaction catalyzed by hydroxyl groups are 50 and 52 kJ mol⁻¹, respectively, while the initiation of the reaction corresponds to the primary amine-epoxy reaction catalyzed by primary amine groups with an activation energy of 72 kJ mol⁻¹. A negative substitution effect can be calculated at 0.18 from the ratio of secondary amine to primary amine-epoxy reaction rate constants.     

Thermal characterization of montmorillonite clays saturated with various cations

Emanation thermal analysis (ETA), thermogravimetry and high temperature XRD were used to characterize the thermal behavior during dehydration of natural Na montmorillonite (Upton Wyoming, USA) and homoionic montmorillonite (MMT) samples saturated with different cations, i.e. Li⁺, Cs⁺, NH₄⁺, Mg²⁺ and Al³⁺. ETA results characterized radon mobility and microstructure changes that accompanied the mass loss of the samples due to dehydration on heating in air. A collapse of interlayer space between the silicate sheets after water release from the MMT samples was characterized by a decrease of the radon release rate, ΔE. Decreases in c-axis basal spacing (d ₀₀₁) values determined from XRD patterns for the different montmorillonite samples follow the sequence:

Biopolymer-layered polysilicate micro/nanocomposite based on chitosan intercalated in magadiite

On the basis of their high adsorption and cation exchange capacity, swelling potential and low toxicity, layered sodium silicate magadiite (Na–magadiite) is an attractive solid for intercalation of polymers. This study envisages the intercalation of cationic biopolymer chitosan (Chit) in Na–magadiite to prepare a Chit/magadiite micro/nanocomposite. Characterisation of starting-magadiite, pure chitosan and Chit/magadiite were investigated using powder X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and thermal analysis. XRD confirmed that the chitosan had been intercalated into the interlayer space of magadiite by increasing the basal spacing, d₀₀₁ from 15.6 Å to 21.45 Å. The presence of characteristic bands of biopolymer and layered silicate in Chit/magadiite were confirmed by FTIR analysis. The thermal stability of micro/nanocomposite was evaluated by thermogravimetry analysis. The results suggested the formation of electrostatic interactions by protonated amine groups with the negatively charged magadiite surface as well as intercalation in the form of a predominant monolayer arrangement of chitosan chains in layered silicate magadiite.     

Rapid and direct speciation of methyltins in seawater by an on-line coupled high performance liquid chromatography-hydride generation-ICP/MS system

A novel on-line coupled HPLC-hydride generation (HG)-ICP/MS system was developed for rapid, direct and sensitive speciation of methyltins in seawater without any pretreatment step. Methyltin compounds were separated by reversed phase HPLC, and then on-line reacted with potassium borohydride and acetic acid to generate volatile hydride products. The volatile derivatization products were separated in the spray chamber of ICP/MS and then introduced into ICP/MS by argon gas for detection. Monomethyltin (MMT), dimethyltin (DMT) and trimethyltin (TMT) were baseline separated in less than 15 min by reversed phase HPLC. The influence of KBH₄ concentration and type of acid on the system performance was investigated and optimized. Calibration curves, based on peak heights against concentration, were linear in the range of 0.5-50 ng (Sn) mL⁻¹ of methyltins with correlation coefficients of 0.9990, 0.9990 and 0.9996 for MMT, DMT and TMT, respectively. The relative standard deviations measured at 10 ng (Sn) mL⁻¹ for these three methyltins were in the range of 0.6-1.4% (n = 5), and the calculated detection limits (S/N = 3) for MMT, DMT and TMT were 0.266, 0.095 and 0.039 ng (Sn) mL⁻¹, respectively. This method was successfully applied to the speciation of methyltins in seawater with spiked recovery in the range of 95.4-106.9%. MMT and DMT were detected in all the seawater samples with concentrations in the range of 1.0-1.5 and 0.30-0.57 ng (Sn) mL⁻¹ for MMT and DMT, respectively.     

A new 1D hybrid fluoroaluminate templated by an original tetramine

An original polyamine, 2,3 di-2-aminomethyl 1,4 diaminobut-2-ene (ten), characterized by single-crystal XRD analysis, has been synthesised and leads to a new hybrid fluoroaluminate [H₄ten] · (AlF₅)₂ by microwave heating assisted hydrothermal synthesis. The structure of [H₄ten] · (AlF₅)₂ is ab initio determined from powder data.     

Preparation of porous PMMA/Na–montmorillonite cation-exchange membranes for cationic dye adsorption

Porous PMMA/Na⁺–montmorillonite (MMT) cation-exchange membranes were successfully prepared by entrapment method in this study. One approach (simple mixing) was to mix commercial PMMA polymer with Na⁺–MMT clays in solvent for membrane preparation (Membrane A). The other approach (emulsion polymerization) was to synthesize the PMMA/Na⁺–MMT polymer composite via emulsion polymerization first, followed by membrane casting (Membrane B for Kunipia F clays and Membrane C for PK-802 clays). Membrane morphology and properties were characterized. The thermogravimetric analysis (TGA) verified the near complete incorporation of feed Na⁺–MMT clays in the PMMA/Na⁺–MMT composite membranes, while X-ray diffractograms (WXRD) exhibited the slightly enlarged interlayer spacing of Na⁺–MMT. The range of cation-exchange capacity (CEC) was 9–32 μequiv./47 mm disc. For batch cationic dye adsorption, the best performance was achieved by Membrane B with feed Na⁺–MMT/MMA (M/P) ratio (w/w) = 0.5 and Membrane C with feed M/P = 0.6, where about 95% Methyl violet adsorption was attained in 2 h. The optimal desorption solution was 1 M KSCN in 80% methanol and its related dye desorption efficiency was 92%. In the flow process using one piece of 47 mm disc of Membrane B (M/P = 0.5), dye solution was recirculated for 6 h and ≥85% dye could be removed. Higher than 94% of dye was desorbed at 1 or 4 mL/min, and the membrane regenerability was proved by successfully performing three consecutive cycles.     

Thermochemistry of intercalation of n-alkylmonoamines into lamellar hydrated barium phenylarsonate

Hydrated layered crystalline barium phenylarsonate, Ba(HO₃AsC₆H₅)₂·2H₂O was used as host for intercalation of n-alkylmonoamine molecules CH₃(CH₂)_n-NH₂ (n = 1-4) in aqueous solution. The amount intercalated (n_f) was followed batchwise at 298 ± 1 K and the variation of the original interlayer distance (d) for hydrated barium phenylarsonate (1245 ppm) was followed by X-ray powder diffraction. Linear correlations were obtained for both d and n_f as a function of the number of carbon atoms in the aliphatic chain (n_c): d = (2225 ± 32) + (111 ± 11)n_c and n_f = (2.28 ± 0.15) − (11.50 ± 0.03)n_c. The exothermic enthalpies of intercalation increased with n_c, which was derived from the monomolecular amine layer arrangements with the longitudinal axis inclined by 60° to the inorganic sheets. The intercalation was followed by titration with amine at the solid/liquid interface and gave the enthalpy/number of carbons correlation: ΔH = −(7.25 ± 0.40) − (1.67 ± 0.10)n_c. The negative Gibbs free energies and positive entropic values reflect the favorable host/guest intercalation processes for this system.     

Effect of P/Si polymeric silsesquioxane and the monomer compound on thermal properties of epoxy nanocomposite

The unique polymeric silsesquioxane/4,4′-diglycidyether bisphenol A (DGEBA) epoxy nanocomposites have been prepared by sol-gel method. The structure of nanocomposites was characterized by attenuated total reflectance (ATR) and solid state ²⁹Si NMR. The characteristic intensity of trisubstituted (T) structure was higher than that of tetrasubstituted (Q) structure from solid state ²⁹Si NMR spectra of 3-isocyanatopropyltriethoxysilane (IPTS) modified epoxy. The activation energies of curing reaction of epoxy system and IPTS modified epoxy system are 28-66 kJ/mol and 57-75 kJ/mol, respectively, by Ozawa’s and Kissinger’s methods. The triethyoxysilane side chain of IPTS modified epoxy might interfere the curing reaction of epoxy/amine and increase the activation energy of curing. The thermal degradation of nanocomposites was investigated by Thermogravimetric analysis (TGA). The char yield of nanocomposites was proportional to the 2-(diphenylphosphino)ethyltriethoxysilane (DPPETES) moiety content at high temperature. A higher char content could inhibit thermal decomposition dramatically and enhance the thermal stability. Moreover, the nanocomposites possess high optical transparency.