Processible nanomaterials with high conductivity and magnetizability. Preparation and properties of maghemite/polyaniline nanocomposite films

A versatile process employing anionic surfactants has been developed for the preparation of processible nanocomposite films with electrical conductivity and magnetic susceptibility. Maghemite (g-Fe2O3) nanoclusters (similar to 10 nm in size) are coated with 4-dodecyl- benzenesulfonic acid, and polyaniline (PAn) chains are doped with 10-camphorsulfonic acid. The coated nanoclusters and doped polymers are soluble in common solvents, and casting the solutions readily gives free-standing nanocomposite films with nanocluster contents as high as similar to 50 wt %. The g-Fe2O3/PAn nanocomposites show high conductivity (82-337 S cm(-1)) and magnetizability (up to similar to 35 emu/g g-Fe2O3).

TG-DTA properties of new nonlinear optical materials: K(2)Ln(NO3)(5)center dot 2H(2)O (Ln = La, Ce, Pr, Nd, Sm)

Single crystals of K(2)Ln(NO3)(5). 2H(2)O (KLnN) (Ln = La, Ce, Pr, Nd, Sm) were grown from aqueous solution. The thermogravimetric analysis and differential thermal analysis curves of KLnN demonstrate that the processes of dehydration, melting, irreversible phase transformation and decomposition of NO3- take place in sequence in the heating processes (except KCN). There are three stages in the decomposition of NO3- in KLnN (Ln = La, Nd, Sm) while two in KLnN (Ln = Ce, Pr). K(2)Ln(NO3)(5) is formed at about 225 degrees C by the reaction of KNO3 and Ln(NO3)(3). nH(2)O (Ln = La, Ce, Pr, Nd). (C) 2000 Elsevier Science Ltd. All rights reserved.

Toughening PA1010 with a functionalized saturated polyolefin elastomer

Polyamide (PA)1010 is blended with a saturated polyolefin elastomer, ethylene-cu-olefin copolymer (EOCP). To improve the compatibility of PA1010 with EOCP, different grafting rates of EOCP with maleic anhydride (MA) are used. The reaction between PA1010 and EOCP-g-MA during extrusion is verified through an extraction test. Mechanical properties, such as notched Izod impact strength, elongation at break, etc., are examined as a function of grafting rate and weight fraction of elastomer. It was found that in the scale of grafting rate (0.13-0.92 wt %), 0.51 wt % is an extreme point for several mechanical properties. Elastomer domains of PA1010/ EOCP-g-MA blends show a finer and more uniform dispersion in the matrix than that of PA1010/EOCP blends. For the same grafting rate, the average sizes of elastomer particles are almost independent on the contents of elastomer, but for different grafting rates, the particle sizes are decreased with increasing grafting rate. The copolymer formed during extrusion strengthens the interfacial adhesion and acts as an emulsifier to prevent the aggregation of elastomer in the process of blending. (C) 2000 John Wiley & Sons, Inc.

Circular dichroism and resonance Raman comparative studies of wild type cytochrome c and F82H mutant

The UV-visible, circular dichroism (CD), and resonance Raman (RR) spectra of the wild type yeast iso-1-cytochrome c (WT) and its mutant F82H in which phenylalanine-82 (Phe-82) is substituted with His are measured and compared for oxidized and reduced forms. The CD spectra in the intrinsic and Soret spectral region, as well as RR spectra in high, middle, and low frequency regions, are discussed. From the analysis of the spectra, it is determined that in the oxidized F82H the two axial ligands to the heme iron are His-18 and His-82 whereas in the reduced form the sixth ligand switches from His-82 to Met-80 providing the coordination geometry similar to that of WT. Based on the spectroscopic data, the conclusion is that the porphyrin macrocycle is less distorted in the oxidized F82H compared to the oxidized WT. Similar distortions are present in the reduced form of the proteins. Frequency shifts of Raman bands, as well as the decrease of the or-helix content in the CD spectra, indicate more open conformation of the protein around the heme. (C) 2000 John Wiley & Sons, Inc.

Sintering of nanopowders of amorphous silicon nitride under ultrahigh pressure

Nanopowders of amorphous silicon nitride were densified and sintered without additives under ultrahigh pressure (1.0-5.0 GPa) between room temperature and 1600 degrees C. The powders had a mean diameter of 18 nm and contained similar to 5.0 wt% oxygen that came from air-exposure oxidation, Sintering results at different temperatures were characterized in terms of sintering density, hardness, phase structure, and grain size. It was observed that the nanopowders can be pressed to a high density (87%) even at room temperature under the high pressure. Bulk Si3N4 amorphous and crystalline ceramics (relative density: 95-98%) were obtained at temperatures slightly below the onset of crystallization (1000-1100 degrees C and above 1420 degrees C, respectively. Rapid grain growth occurred during the crystallization leading to a grain size (>160 nm) almost 1 order of magnitude greater than the starting particulate diameters, With the rise of sintering temperature, a final density was reached between 1350 and 1420 degrees C, which seemed to be independent of the pressure applied (1.0-5.0 GPa), The densification temperature observed under the high pressure is lower by 580 degrees C than that by hot isostatic pressing sintering, suggesting a significantly enhanced low-temperature sintering of the nanopowders under a high external pressure.

Study on a novel polyimide precursor prepared by a modified polymerization of monomeric reactants (MPMR) procedure

A novel polyimide precursor based on the dimethyl ester of 3,3',4,4'-biphenyltetracarboxylic acid, 4,4'-methylene dianiline and the monomethyl ester of 5-norbornene-2,3-dicarboxylic acid (BPDE/MDA/NE) was prepared by a modified polymerization of monomeric reactants (PMR) approach (MPMR). The composition of the precursor was quantitatively characterized by means of FTIR, HPLC and GC. The fractions of imide, amic ester and amic acid units in the precursor, typically prepared by refluxing in 1,4-dioxane for 2 h, were 33.7, 30.8 and 1.1 mol-%, respectively. The portion of free MDA was 3.34 wt.-% as determined by HPLC.

Effect of compatibilization on the properties of HIPS/PA1010 blends

Blends consisting of high-impact polystyrene (HIPS) as the matrix and polyamide 1010 (PA1010) as the dispersed phase were prepared by mixing. The grafting copolymers of HIPS and maleic anhydride (MA), the compatibilizer precursors of the blends, were synthesized. The contents of the IMA in the grafting copolymers are 4.7 wt % and 1.6 wt %, and were assigned as HAM and LMA, respectively. Different blend morphologies were observed by scanning electron microscopy (SEM); the domain size of the PA1010 dispersed phase in the HIPS matrix of compatibilized blends decreased comparing with that of uncompatibilized blends. For the blend with 25 wt % HIPS-g-MA component, the T-c of PA1010 shifts towards lower temperature, from 178 to 83 degrees C. It is found that HIPS-g-MA used as the third component has profound effect on the mechanical properties of the resulting blends. This behavior has been attributed to the chemical reaction taking place in situ during the mixing between the two components of PA1010 and HIPS-g-MA. (C) 2000 John Wiley & Sons, Inc.

Confined crystallization behavior of PEO in silica networks

Poly(ethylene oxide) (PEO) and silica (SiO2) organic-inorganic hybrid materials have been synthesized by sol-gel approach. The crystallization behavior of PEO in silica networks has been investigated by differential scanning calorimeter (DSC) and scanning electron micrograph (SEM). The degree of PEO crystallinity in PEO/SiO2 hybrid networks reduces with the increase of SiO2. PEO is in amorphous state when the concentration of PEO is lower than 50 wt% in the hybrid materials. The melting points of PEO in the networks are lower than that of pure PEG, but the melting point of PEO in the networks almost has the same melting point. WAXD and SEM results show that the crystalline behavior of PEO in PEO/SiO2 hybrid system is sternly confined. (C) 1999 Elsevier Science Ltd. All rights reserved.

Morphology of conductive blend fibers of polyaniline and polyamide-11

Polyaniline (PANI), a member of the intrinsically conducting polymer (ICPs) family, was blended with polyamide-11 (polyco-aminoundecanoyle) in concentrated sulfuric acid. The above solution was used to spin conductive PANI/polyamide-11 fibers by wet-spinning technology. Scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to study the two-phase morphology of the conductive PANI/polyamide-11 fibers. The micrographs of the cross-section, the axial section and the surface of the monofilament demonstrated that the two blend components were incompatible. The morphology of PANI in the fibers was of fibrillar form, which was valuable for producing conducting channels. The electrical conductivity of the fibers was from 10(-6) to 10(-1) S/cm with the different PANI fraction and the percolation threshold was about 5 wt.%. By comparing the two blend systems of PANI/Polyamide-11 fibers and carbon black filled poly(ethylene terephthalate) (PET) fibers, it was shown that the morphology of the conductive component had an influence on electrical conductivity, The former had higher conductivity and lower percolation threshold than the latter. (C) 2001 Elsevier Science B.V. All rights reserved.

Conductive polyaniline/silica hybrids from sol-gel process

A hybrid material with a conductive organic network in an inorganic matrix has been prepared by in-situ hydrolysis/polycondensation of TEOS in an aqueous solution of a solubilized polyaniline. Due to intense hydrogen bonding (indicated by Si-29 NMR and FTIR) the conductive polymer is very well dispersed in the silica matrix. The Figure shows SEM images of a 46/54 wt.-% hybrid at two temperatures (left 20 degreesC, right 100 degreesC).

Thermodynamics of PMMA/SAN blends: Application of the Sanchez-Lacombe lattice fluid theory

Polymer blends of poly(methyl methacrylate) (PMMA) and poly(styrene-co-acrylonitrile) (SAN) with an acrylonitrile content of about 30 wt % were prepared by means of solution-casting and characterized by virtue of pressure-volume-temperature (PVT) dilatometry. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalpy of the mixing, the volume change of the mixing, and the combinatorial and vacancy entropies of the mixing for the PMMA/SAN system. A new volume-combining rule was used to evaluate the close-packed volume per mer, upsilon*, of the PMMA/SAN blends. The calculated results showed that the new and the original volume-combining rules had a slight influence on the FH interaction parameter, the enthalpy of the mixing, and the combinatorial entropy of the mixing. Moreover, the spinodals and the binodals calculated with the SL theory by means of the new volume-combining rule could coincide with the measured data for the PMMA/SAN system with a lower critical solution temperature, whereas those obtained by means of the original one could not.

Study on polymer micelles of hydrophobically modified ethyl hydroxyethyl cellulose using single-molecule force spectroscopy

Individual hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC) molecules under different conditions were elongated using a new atomic force microscope (AFM) based technique-single-molecule force spectroscopy (SMFS). The critical concentration of HM-EHEC for micelle-like clusters at a solid/liquid interface was around 0.8 wt %, which is lower than that in solution. The different mechanical properties of HM-EHEC below and above the critical concentration were displayed on force-extension curves. Through a comparison with unmodified hydroxyethyl cellulose, substituent-induced effects on nanomechanical features of HM-EHEC were investigated. Because of hydrophobic interactions and cooperative binding with the polymer, surfactants such as sodium dodecyl sulfate (SDS) dramatically influence the elastic properties of HM-EHEC below the critical concentration, and further addition of SDS reduces the interactions between the hydrophobic groups and the surfactant.

Reaction and formation of crystalline silicon oxynitride in Si-O-N systems under solid high pressure

Oxidized amorphous Si3N4 and SiO2 powders were pressed alone or as a mixture under high pressure (1.0-5.0 GPa) at high temperatures (800-1700 degreesC). Formation of crystalline silicon oxynitride (Si(2ON)2) was observed from amorphous silicon nitride (Si3N4) powders containing 5.8 wt% oxygen at 1.0 GPa and 1400 degreesC, The Si2ON2 coexisted with beta -Si3N4 with a weight fraction of 40 wt%, suggesting that all oxygen in the powders participated in the reaction to form Si2ON2. Pressing a mixture of amorphous Si3N4 of lower oxygen (1.5 wt%) and SiO2 under 1.0-5.0 GPa between 1000 degrees and 1350 degreesC did not give Si2ON2 phase, but yielded a mixture of alpha,beta -Si3N4, quartz, and coesite (a high-pressure form of SiO2). The formation of Si2ON2, from oxidized amorphous Si3N4 seemed to be assisted by formation of a Si-O-N melt in the system that was enhanced under the high pressure.

Preparation of polyimide-BaTiO3 hybrid films by a dispersion process and their microstructure

Barium titanate (BaTiO3) powders with particle sizes of 30 similar to 50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO3 nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO3 content was less than 1 wt%. Highly loaded hybrid film containing 30 wit % BaTiO3 was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide.

Effects of rubber content and temperature on unstable fracture behavior in ABS materials with different particle sizes

The fracture behavior of ABS materials with a particle diameter of 110 nm and of 330 nm was studied using instrumented Charpy impact tests. The effects of rubber content and temperature on fracture behavior, deformation mode, stable crack extension, plastic zone size, J-integral value, and crack opening displacement were investigated. In the case of a particle size of 110 nm, the material was found to break in a brittle manner, and the dominant crack mechanism was unstable crack propagation. Fracture toughness increases with increasing rubber content. In the case of a particle size of 330 nm, brittle-to-tough transition was observed. The J-integral value first increases with rubber content, then levels off after the rubber content is greater than 16 wt %. The J-integral value of a particle diameter of 330 nm was found to be much greater than that of 110 nm. The J-integral value of both series first increased with increasing temperature until reaching the maximum value, after which it decreased with further increasing temperature. The conclusion is that a particle diameter of 330 nm is more efficient than that of 110 nm in toughening, but for both series the effectiveness of rubber modification decreases with increasing temperatures higher than 40 degreesC because of intrinsic craze formation in the SAN matrix at temperatures near the glass transition of SAN. (C) 2000 John Wiley & Sons, Inc.