Synthesis of mesoporous silica and its modification of bismaleimide/cyanate ester resin with improved thermal and dielectric properties

A novel method is proposed to synthesize new mesoporous silica containing amine groups (MPSA), and it was further employed to modify bismaleimide‐dialllyl bisphenol (BD)/cyanate ester (CE) resin to form novel MPSA/BD/CE hybrids; in addition, the typical properties of MPSA/BD/CE were systematically investigated. Results show that these hybrids have very low dielectric constant and loss as well as good thermal properties. Compared with BD/CE resin, all hybrids have not only decreased dielectric constant and loss but also similar dependence of dielectric properties on frequency over the whole frequency from 10 to 10⁶ Hz. Specifically, with the addition of MPSA to BD/CE resin, the dielectric constant reduces from 3.5 to 3.0, and the dielectric loss is only 85% of that of BD/CE resin. Note that all hybrids show better thermal resistance (reflected by higher glass transition temperature, decreased maximum degradation rate, and higher char yield at 800°C) than BD/CE resin. All these differences in macro‐properties are attributed to the different structure between MPSA/BD/CE hybrids and BD/CE resin. Copyright © 2011 John Wiley & Sons, Ltd.     

Hybrid organic-inorganic catalytic mesoporous materials with proton sponges as building blocks

Non-ordered organic-inorganic mesoporous hybrid materials with basic sites have been synthesized following a fluoride-catalysed sol-gel process at neutral pH and low temperatures that avoids the use of structural directing agents (SDAs). Proton sponges have been used as the organic builder of the hybrids, while the inorganic part corresponds to silica tetrahedra. The proton sponges are diamines that exhibit very high basicity and, after functionalization, have been introduced as part of the walls of the mesoporous silica by one-pot synthesis. Several hybrids with different organic loadings have been synthesized and characterized by gas adsorption, thermogravimetric and elemental analysis, solid state MAS-NMR and FTIR spectroscopy. These hybrids show high activity as base catalysts and can be recycled.     

The helical structure of highly ordered smectic phases

Optical studies of smectic phases have been performed in homogeneously oriented samples of chiral 4-(2′-methylbutyl) phenyl-4′-n-octylbiphenyl-4-carboxylate (CE8). The helix structure has been found in smectic phases C, I and J, but not in the smectic G phase. Two chiral phases have been found between S_I* and S_G phases. Up to now one of them has not been observed. The pitch of the helix has been measured in all of the twisted smectic phases, including the S_J* phase. The existence of the helix in this phase suggests that the correlations between smectic layers are not very strong.     

Bismaleimide/carbon nanotube hybrids for potential aerospace application: I. Static and dynamic mechanical properties

Two kinds of hybrids based on diallyl bisphenol A modified bismaleimide (BMI‐BA) and carbon nanotubes (CNTs) or aminated carbon nanotubes (A‐CNTs) were prepared, their static and dynamic mechanical properties were investigated in detail by using impact and flexural measurements as well as dynamic mechanical analysis (DMA). Results show that these mechanical properties of hybrids greatly depended on the nature (or the functional groups on CNTs) and loading in BMI‐BA matrix of hybrids. For example, the BMI‐BA/A‐CNT hybrid with a desirable amount of A‐CNTs has a higher impact strength than the original BMI‐BA resin, while all BMI‐BA/CNT hybrids have lower impact strength than the original BMI‐BA resin. DMA test shows that all hybrids have somewhat lower storage modulus and glass transition temperature than a pure polymer, which maybe attributed to the fact that both CNTs and A‐CNTs shift the curing peak to a higher temperature range and thus decrease the crosslinking density of networks. Copyright © 2007 John Wiley & Sons, Ltd.     

Well-defined difunctional POSS macromers and related organic–inorganic polymers: Precision synthesis,structure and properties

Polyhedral oligomeric silsesquioxanes (POSS) are a class of well-defined organic–inorganic stereo molecules comprising inorganic Si O Si cores and peripheral organic moieties. Since they were first reported in 1946 by Scott et al., there have been a great number of investigations on the use of POSS macromers as the building blocks to access the organic–inorganic composites with polymers. In most of cases, monofunctional POSS macromers are employed and the linear hybrid polymers are obtained. Under this circumstance, POSS cages act as the side or end groups whereas the main chains of the polymers remain unchanged. Occasionally, octafunctional POSS macromers are involved, resulting in the generation of crosslinked (or network-like) hybrids. Recently, well-defined difunctional POSS macromers have increasingly provoked a considerable attention of investigators. From the synthetic methodology of POSS macromers to the approaches to introduce them into polymers, difunctional POSS macromers have the features quite different from mono- (or octa-) functional POSS. More importantly, the related organic–inorganic hybrids possess the different morphologies and properties. In the past years, there has been a rapid increase in the number of literatures on the studies on well-defined difunctional POSS and the related organic–inorganic hybrids. Nonetheless, the related review is lacking. In this contribution, we would summarize the recent progress in this regard, from the synthesis of POSS macromers, the approaches of introducing the POSS macromers into polymers to the correlation of morphologies with properties of the organic–inorganic hybrids. In addition, perspectives and challenges for the further advancement are envisaged and discussed.     

Polyimide-silica Hybrids: Structural and Morphological Investigations

Polyimide (PI) containing pendant hydroxyl functional groups have been employed for preparation of PI-silica hybrids through the sol-gel process. A stoichiometric amount of pyromellitic dianhydride (PMDA) was reacted with a mixture of oxydianiline (ODA) and 3,3′-diamino-4,4′-dihydroxybiphenyl (DAHP) in dimethylacetamide (DMAc) solvent to prepare the precursor poly(amic acid) (PAA) solution for the PI. Various proportions of tetraethoxysilane (TEOS) were mixed with PAA to prepare PI-silica hybrids through sol-gel process. The structure and morphology of these hybrids were investigated with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), optical surface profilometery, and Fourier transform infrared (FTIR) spectroscopy and compared with the one in which the matrix was prepared from PMDA and ODA with no pendant hydroxyl functionalities. Formation of silica lean and silica rich phases (SLP and SRP) as a result of formation of nano-sized silica clusters with diffused boundaries, dispersed in the matrix and their agglomerates, respectively, along with totally different morphology suggest a strong influence of hydroxyl groups in controlling the morphology of PI-silica hybrids. A model namely “Retain and React” has been introduced to explain observed structure.     

Selective Solid‐Liquid Interface Sulfidation Growth of Hierarchical Copper Sulfide and Its Hybrid Nanoflakes for Superior Lithium‐Ion Storage

Two‐dimensional metal sulfides and their hybrids are emerging as promising candidates in various areas. Yet, it remains challenging to synthesize high‐quality 2D metal sulfides and their hybrids, especially iso‐component hybrids, in a simple and controllable way. In this work, a low‐temperature selective solid‐liquid sulfidation growth method has been developed for the synthesis of CuS nanoflakes and their hybrids. CuS nanoflakes of about 20 nm thickness and co‐component hybrids CuO_x/CuS with variable composition ratios derived from different sulfidation time are obtained after the residual sulfur removal. Besides, benefiting from the mild low‐temperature sulfidation conditions, selective sulfidation is realized between Cu and Fe to yield iso‐component FeO_x/CuS 2D nanoflakes of about 10–20 nm thickness, whose composition ratio is readily tunable by controlling the precursor. The as‐synthesized FeO_x/CuS nanoflakes demonstrate superior lithium storage performance (i. e., 707 mAh g^?1 at 500 mA g^?1 and 627 mAh g^?1 at 1000 mA g^?1 after 450 cycles) when tested as anode materials in LIBs owing to the advantages of the ultrathin 2D nanostructure as well as the lithiation volumetric strain self‐reconstruction effect of the co‐existing two phases during charging/discharging processes.     

The Role of Fe in the Thermal Stabilization of Ormosils

The thermal stability of organically modified silicates (Ormosils) is limited by that of their organic constituent. In the case of the polydimethylsiloxane (PDMS)-silica hybrids, degradation of the PDMS begins around 250°C, which restricts their range of applications. Several strategies have been used to stabilize PDMS, such as substitution of the methyl groups by phenyl groups. Another strategy is the addition of very small amounts (typically about 1 wt%) of iron. This technique has been used successfully in the stabilization of liquid silicones. In the case of PDMS-SiO₂ hybrids, this small dopant concentration has a very significant effect on the thermal stability, increasing it by up to 200°C. However, very little is known of the mechanism of stabilization. In the present work we carry out an investigation of the materials in order to explain the mechanisms involved. The materials were investigated by liquid and solid state ²⁹Si NMR, BET, SEM, TGA and DMA. The data indicates that Fe plays a most significant role at the solution stage already. The structures of the hybrids with and without Fe are very different. In other words, the thermal stabilization mechanism appears to be due not so much a direct redox process taking place in the solid state (as in the case of liquid silicones) but rather, to differences in chemical structures induced by Fe in the liquid. Specifically, PDMS chain cleavage and increased cross-linking to SiO₂ appear to be the cause of the thermal stabilization.     

Controllable synthesis of functionalized CdS nanocrystals and CdS/PMMA nanocomposite hybrids

We reported controllable synthesis of CdS nanocrystal-polymer transparent hybrids by using polymethylmethacrylate (PMMA) as a polymer matrix. In a typical run, the appropriate amounts of cadmium chloride (CdCl₂) and sodium sulfide (Na₂S) in the presence of 2-mercaptoethanol (ME) as the organic ligand are well dispersed in H₂O/DMF solution without any aggregation. From a combination of transmission electron microscopy (TEM) and a computing method of Brus’s model according UV-vis absorption spectra, the particle size of as-prepared hydroxyl-coated CdS nanocrystal was determined to be about 5 nm. Then, with the surface treatment with methacryloxypropyltrimethoxysilane (MPS), CdS-PMMA hybrids were obtained via free radical polymerization in situ. FT-IR characterization indicates the formation of robust bonding between CdS nanocrystals and the organic ligand and the formation of double-bond functional CdS nanocrystals. The TGA measurement displays CdS-PMMA hybrids possess better thermal stability compared with pure PMMA polymer. The fluorescence measurement shows that CdS nanocrystals and CdS-PMMA hybrids exhibit good optical properties. Also, the luminescent photographs taken under ultraviolet light prove the luminescence properties.     

Silica hybrid nanocomposites

In this work we present experimental results about the formation, properties and structure of sol — gel silica based biocomposite containing Calcium alginate as an organic compound. Two different types of silicon precursors have been used in the synthesis: tetramethylortosilicate (TMOS) and ethyltrimethoxysilane (ETMS). The samples have been prepared at room temperature. The hybrids have been synthesized by replacing different quantitis of the inorganic precursor with alginate. The structure of the obtained hybrid materials has been studied by XRD, IR Spectroscopy, EDS, BET and AFM. The results proved that all samples are amorphous possessing a surface area from 70 to 290 m²/g. It has also been established by FT IR spectra that the hybrids containing TMOS display Van der Walls and Hydrogen bonding or electrostatic interactions between the organic and inorganic components. Strong chemical bonds between the inorganic and organic components in the samples with ETMS are present. A self-organized nanostructure has been observed by AFM. In the obtained hybrids the nanobuilding blocks average in size at about 8–14 nm for the particles.     

聚苯胺/贵金属复合纳米材料的可控合成及催化应用

导电高分子/贵金属复合纳米材料因其在催化、传感、表面增强拉曼、光热治疗等诸多领域的应用前景而受到广泛关注.本文主要介绍我们课题组近年来利用可控合成策略制备的负载型和包埋型两种结构聚苯胺/贵金属复合纳米材料,以及利用复合纳米材料的结构和功能特性,对其在多相催化领域的应用、结构与催化性能之间构效关系的探索.     

Effect of alkyl chain length in the terminal ester group on mesomorphic properties of new chiral lactic acid derivatives

Two series of new liquid crystalline lactic acid derivatives with a terminal ester group have been synthesised. The effect of this ester unit and the length of its alkyl chain on the mesomorphic and dielectric properties of the compounds exhibiting a broad temperature range of chiral smectic phases have been studied. We found that the mesomorphic behaviour and phase transition temperatures are strongly affected by the molecular architecture. Depending on the alkyl chain length in the terminal ester unit, the studied materials exhibited paraelectric smectic A*, ferroelectric tilted smectic C* and antiferroelectric smectic C_A* phases over a broad temperature range. The physical properties of the compounds have been studied by optical polarising microscopy, differential scanning calorimetry, electro-optic measurements, small-angle X-ray scattering and dielectric spectroscopy. Furthermore, the homologues with short terminal alkyl chains showed a very small layer shrinkage at the transition from the orthogonal SmA* to the tilted SmC* phase, which is a characteristic feature of ‘de Vries-type’ behaviour.     

The helical structure of highly ordered smectic phases

Optical studies of smectic phases have been performed in homogeneously oriented samples of chiral 4-(2'-methylbutyl) phenyl-4'-n-octylbiphenyl-4-carboxylate (CE8). The helix structure has been found in smectic phases C, I and J, but not in the smectic G phase. Two chiral phases have been found between S_I* and S_G phases. Up to now one of them has not been observed. The pitch of the helix has been measured in all of the twisted smectic phases, including the S_J* phase. The existence of the helix in this phase suggests that the correlations between smectic layers are not very strong.     

Polyimide-Silica Hybrids: Spectroscopy,Morphology and Mechanical Properties

Polyimide/silica hybrids were prepared by a sol-gel process and were evaluated in terms of curing behaviour, morphology and mechanical properties. The spectroscopic examination showed that the presence of the inorganic phase accelerates the imidization of the polyamic acid. Two types of morphology for the silica phase were obtained by tailoring the composition of the precursor solution mixture. The mechanical properties were found to be strongly dependent on the system morphology. The largest increase in rigidity and strength properties were achieved when the two phases were co-continuous.     

PMMA Based Nanocomposites Filled with Modified CaCO3 Nanoparticles

PMMA based nanocomposites filled with calcium carbonate nanoparticles (CaCO₃) have been prepared by in situ polymerization approach. In order to improve inorganic nanofillers/polymer compatibility, PBA chains have been grafted onto CaCO₃ nanoparticle surface. Morphological analysis performed on nanocomposite fractured surfaces has revealed that the CaCO₃ modification induces homogeneous and fine dispersion of nanoparticles into PMMA as well as strong interfacial adhesion between the two phases. Mechanical tests have shown that both unmodified and modified CaCO₃ are responsible for an increase of the Young's Modulus, whereas only PBA-grafted nanoparticles allow to keep unchanged impact strength, strongly deteriorated by adding unmodified CaCO₃. Finally, the presence of CaCO₃ nanoparticles significantly improves the abrasion resistance of PMMA also modifying its wear mechanism.     

Micellar Solubilization of Proteins in Aprotic Solvents and their Spectroscopic Characterisation

The quaternary ammonium salt methyl-trioctylammonium chloride enables the transfer of α-chymotrypsin, trypsin, pepsin and glucagone from water to cyclohexane. Reversed micelles, whose polar core solubilizes both protein and water, are probably formed in the apolar phase. The influence of various parameters on the phase transfer (concentration, pH, solvent, temperature, etc.) has been investigated. Absorption, fluorescence and circular dichroism studies of the biopolymers in the cyclohexane system have been carried out. For trypsin and chymotrypsin, the CD. signal in the 200 nm region is very similar in water and in cyclohexane, which suggests that the polypeptide folding is not substantially different in the two phases. The fluorescence quantum yield is always much larger in the cyclohexane phase than in water. The longer wavelength region of the UV. absorption spectrum is slightly red-shifted relative to water, and a band at 225 nm, probably arising from the aromatic chromophore, is apparent in the organic phase. Reasons for these spectral perturbations are discussed. The enzymes transferred from water into cyclohexane phases can be continuously retransferred into a second water phase. The possible relevance of this ‘double transfer’ as a model for the vectorial transport of biopolymers or a separation technique is discussed.     

Many-electron self-interaction and spin polarization errors in local hybrid density functionals

Errors for systems with noninteger occupation have been connected to common failures of density functionals. Previously, global hybrids and pure density functionals have been investigated for systems with noninteger charge and noninteger spin state. Local hybrids have not been investigated for either of those systems to the best of our knowledge. This study intends to close this gap. We investigate systems with noninteger charge to assess the many-electron self-interaction error and systems with noninteger spin state to assess the spin polarization error of recently proposed local hybrids and their range-separated variants. We find that long-range correction is very important to correct for many-electron self-interaction error in cations, whereas most full-range local hybrids seem to be sufficient for anions, where long-range-corrected density functionals tend to overcorrect. On the other hand, while all hitherto proposed long-range-corrected density functionals show large spin polarization errors, the Perdew-Staroverov-Tao-Scuseria (PSTS) functional performs best of all local hybrids in this case and shows an outstanding behavior for the dependence of the energy on the spin polarization.     

Preparation, microstructure, and property characterizations of fluorinated polyimide-organosilicate hybrids

Synthesis of organosilicate (orgSiO₂) via sol-gel process utilizing tetraethoxysilane (TEOS) and diethoxydimethylsilane (DEDMS) as precursors was carried out in this work. Various amounts of orgSiO₂ were blended with fluorinated poly(amic acid) (PAA) to form the PAA-orgSiO₂ precursors and the fluorinated polyimide (PI)-orgSiO₂ (i.e., the HR1) thin-film hybrids were prepared via spin coating and curing treatments. The PI-orgSiO₂-AP (i.e., the HR2) hybrids were also prepared by using the PAA-orgSiO₂ precursors containing the amine silane coupling agent, the 3-aminopropyltriethoxysilane (APTEOS). The effects of APTEOS on promoting the crosslinking between organic and inorganic components as well as the network formation were investigated. Fourier-transform infrared spectroscopy (FTIR) showed that the orgSiO₂ particles indeed formed in the hybrids due to the emergence of absorption bands corresponding to SiOSi and OSiO bonds. Nuclear magnetic resonance (NMR) analyses revealed that the Q⁴ units or, the four bridging bond units, dominate the structure of orgSiO₂. Thermal analysis indicated that the implantation of orgSiO₂ in PI matrix may effectively improve the thermal stability of hybrids. Transmission electron microscopy (TEM) revealed the formation of nano-scale orgSiO₂ particles in both hybrids and the sizes of orgSiO₂ are relating to the Si content. In HR1 hybrids, the particles obviously coarsened when Si content was high while, in HR2 hybrids, the addition of APTEOS effectively suppressed the phase separation and the ultrafine orgSiO₂ particles as small as 5 nm could be achieved in the sample with high Si content. Dielectric measurements showed that the lowest values of dielectric constants are 2.40 and 2.20 for HR1 hybrid at intermediate Si content = 0.4 mol and HR2 hybrid with the highest Si content = 0.8 mol, respectively. The suppression of dielectric constants was attributed to the absence of polar SiOH and SiH₂O functional groups as well as the completion of hydrolysis in the hybrids. Formation of silica xerogels in the hybrids should be another cause of dielectric constant decrement, as indicated by the porosity calculation. Experimental results implied that the control of orgSiO₂ size to imply the closed-form silica structure is essential to the low-dielectric constant properties of hybrids. Leakage current density measurement illustrated that no deterioration effect occurs due to the addition of orgSiO₂ nanoparticles in polymeric matrix and satisfactory electrical properties are preserved for the hybrids for advanced low-dielectric applications.     

Mixed ionic-electronic conductivity in phases in the praseodymium oxide system

The praseodymium oxide system contains a series of related phases with very narrow compositional width and unique extended defect structures, rather than the more common isolated point defects. The electrical conductivity of three of these phases has been measured by the use of AC complex impedance and DC methods in the temperature range 75–400 °C. The beta phase, Pr₆O₁₁, exhibits a total conductivity of 6.77×10^–2 S/cm at 400 °C, with an activation energy of 0.52 eV/atom. The conductivity of the epsilon phase, Pr₅O₉, is slightly lower, with an activation energy of 0.51 eV/atom. The iota phase, Pr₇O₁₂, has a very low conductivity. The activation energies for electrical transport in the beta and epsilon phases are in the general range found in a number of mixed conductors based upon LSGM oxides. Electronic Publication     

Solid Acid-Base Control of Inorganic/Organic Hybrids by Inorganic Components for Molecule-Selectivity

Solid acid-base properties of methylsiloxane-based inorganic/organic hybrids were controlled by incorporation of inorganic components other than Si into methylsiloxane networks. The effect of different inorganic components on the solid acid-base properties was estimated by first-principles calculations based on density functional theory (DFT). The deprotonation tends to occur in the order Si < Al < Nb inorganic components, suggesting that the acidity increases in the same order. Methylsiloxane-based hybrids with solid acid-base properties were also synthesized by incorporating inorganic components derived from metal alkoxides. Hammett indicators revealed that the solid acidity increased in the order Si < Al < Nb inorganic components, which was consistent with the results of first-principles calculations. Preliminary experiments revealed that the methylsiloxane-based hybrids also provided a solid basic nature by containing Ca and Y inorganic components derived from metal alkoxides. The acidic hybrids were found to have Brønsted acid sites from the FT-IR experiments of adsorbed pyridine on the hybrids.