Wide-angle Powder X-ray Diffraction Research Articles

Facile synthesis of ordered mesoporous γ-alumina monoliths via polymerization-based gel-casting

Porous γ-alumina monoliths with hexagonal mesoporous structures were prepared starting from well-ordered mesoporous alumina powders which were firstly synthesized by the self-assembly of aluminum isopropoxide and a triblock copolymer in the presence of nitric acid. The alumina powders were fused together to form alumina monoliths by the integration of polymer gel-casting together with the calcination at different temperatures in air. The powdery and monolithic products were investigated using transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), small-angle X-ray scattering (SAXS), powder wide-angle X-ray diffraction (WA-XRD) and the nitrogen adsorption–desorption isotherm measurements. As results, the as-prepared powdery alumina possesses ordered p6 mm hexagonal mesoporosity, high BET surface area and narrow pore-size distribution. After high-temperature calcination, the obtained alumina monoliths still exhibit ordered mesoporosity with hexagonal symmetry, which is very similar to that of the original powdery sample except for the reduced pore volume and specific surface area. The method can be extended to prepare other porous metal oxide monoliths when appropriate powdery metal oxides with a connected pore system are applied.

Preparation and Characterization of Biodegradable Electrospun Polyanhydride Nano/Microfibers

The biodegradable polyanhydride copolymers P(CPP-SA) composed of p-carboxyhenoxy propane (CPP) and sebacic acid (SA) at weight ratios of 20:80, 35:65 and 50:50 were polymerized by a melt polycondensation process without catalyst. The copolymers were characterized by fourier transform infrared spectroscopy (FT-IR), 1H-nuclear magnetic resonance (1H-NMR), Ubbelohde viscometer, differential scanning calorimetry (DSC) and wide angle X-ray powder-diffraction (XRD). P(CPP-SA) nano/microfibers were the first time to be fabricated by electrospinning. The copolymers hold an excellent fibre-forming performance and the diameter range of 80-3,200 nm can be obtained. The in vitro degradation of the polyanhydride copolymers was evaluated in form of the nano/microfibers by investigating the change of fibrous morphology, weight loss and pH change of degradation medium. The experimental results showed that degradation rate was fast in the fist day and slow in the following period, furthermore the degradation rate decreased with the increase of the content of CPP in copolymers. Therefore, the electrospun polyanhydride nano/microfibers exhibited strong potential as drug delivery vehicle and tissue engineering scaffold.

Preparation and Anticorrosion Property of Polyaniliane/Organo-Clay Nanocomposite Coatings: Comparative Studies of Different Intercalating Agent

In this study, we present the first systematically comparative studies for the effect of intercalating agent on the property of polyaniline (PANI) -clay nanocomposite (PCN) materials. First of all, (4-carboxybutyl) triphenyl-phosphonium bromide (PC-4) and dodecyltriphenyl-phosphonium bromide (PC-12) were used as intercalation agent, separately, for the preparation of organophilic clay through cationic exchange reactions with Na+-montmorillonite (Na+-MMT) clay. Subsequently, organophilic clay was blending with aniline monomers followed by performing in-situ conventionally oxidative polymerization to give series of PCN materials. Subsequently, the as-prepared materials were characterized by Fourier-Transformation infrared (FTIR) spectroscopy, wide-angle powder X-ray diffraction (WXRD), and transmission electron microscopy (TEM). It should be noted that Na+-MMT modified with PC12 was found to reveal better dispersion than that of PC4-modified clay existed in polymer matrix based on studies of WAXRD and TEM. It should be noted that the PCN coatings containing PC12-modified clay platelets was found to reveal better corrosion protection than that of containing PC4-modified clay based on series of electrochemical corrosion measurements in saline. Effect composition on the electrical conductivity, optical and molecular weight of PANI of as-prepared PCN materials was also investigated by four-point probe technique, UV-visible absorption spectroscopy and gel permeation chromatography (GPC), respectively.

The change in characteristics of microcrystalline cellulose during wet granulation using a high-shear mixer.

The objective of this study was to investigate the mechanism of hard granule formation and to demonstrate the applicability of X-ray diffraction methods for studying the polymeric pharmaceutical excipients. Using a high-shear mixer, microcrystalline cellulose (MCC) was granulated with water as the granulating liquid. The hardness of the MCC granules increased with granulation time and the amount of water added. The specific surface area measured by the N2 adsorption method was reduced during the process. Crystallite size of cellulose, calculated by Scherrer's equation adapted for wide angle X-ray diffraction method, decreased with granulation time and with increasing amounts of water added. Debye plots for X-ray small scattering patterns suggested that the average magnitude of the continuous solid region in MCC granules became significantly greater, whereas the specific surface area of the MCC granules, calculated from Debye plots, became smaller in comparison with that of intact MCC. These findings suggested that the long-chain structures in MCC were disrupted, resulting in smaller units with shorter chain lengths due to the strong shear force of the impeller. These smaller units then form a network within the granules. Thus, MCC granules are strengthened with longer granulation time and greater amounts of water, resulting in a more intricate network. The change in MCC chain length and physical structure can be experimentally detected using the small-angle X-ray scattering and wide-angle powder X-ray diffraction methods.

Facile synthesis of blocky styrene(1,3)-butadiene copolymers having stereoregular monomeric sequences

Half titanocenes (CpCH2CH2O)TiCl2 1 and (CpCH2CH2 OCH3)TiCl3 2, activated by methylaluminoxane are tested in styrene–1,3-butadiene copolymerization. The titanocene 1 is able to copolymerize styrene and 1,3-butadiene, with a facile procedure, to give products with high molecular weight. The analysis of microstructure by 13C-NMR reveals that the styrene homosequences in copolymers are in syndiotactic arrangement, while the butadiene homosequences are, prevailingly, in 1,4-cis configuration, according with behavior of 1 in the homopolymerizations of styrene and 1,3-butadiene, respectively. The reactivity ratios of copolymerization are estimated by diad composition analysis. All obtained copolymers have r1 × r2 values much larger than 1, indicating blocky nature of homosequences. The structural characterization by wide-angle X-ray powder diffraction and differential scanning calorimetry indicates that all copolymers are crystalline, with Tm varying from 171 to 239 °C, depending on the styrene content. The titanocene 2 did not succeed in styrene–1,3-butadiene copolymerization, giving rise to a blend of homopolymers. Compounds 1 and 2 were also tested in the polymerization of several conjugated dienes, and the obtained results were very useful to rationalize the behavior of both catalysts in the copolymerization of styrene and butadiene. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 815–822, 2010

Self-assembled TiO2 nanoparticles: mesoporosity, optical and catalytic properties

Herein, we explore the idea of self-assembly of nearly monodisperse nanoparticles as uniform building blocks to design highly crystalline mesoporous TiO(2) nanoparticles, through evaporation-induced self-assembly (EISA) and hydrothermal methods by using non-ionic Pluronic F127 and anionic surfactant SDS, respectively as structure directing agents. The small- and wide-angle powder X-ray diffraction and transmission electron microscopy (TEM) are used to characterize the mesophases. N(2) adsorption-desorption studies and high-resolution TEM results further reveal that mesopores are formed by the arrangement of the nanoparticles of size ca. 4.0-5.0 nm for SDS-templated and 8.0-9.0 nm for F127-templated TiO(2) nanoparticles with broad interparticle pore size distribution. Optical properties of these nanomaterials are studied by UV-visible diffuse-reflectance spectroscopy, photoluminescence (PL) and time-resolved fluorescence (TCSPC). These nanostructured titania exhibited excellent catalytic activity in the photodegradation of ecologically abundant dyes Methylene blue and Rose Bengal under UV-visible light irradiation.

SBA-15-Supported Mixed-Metal Oxides: Partial Hydrolytic Sol−Gel Synthesis, Adsorption, and Structural Properties

Several bimetallic mixed oxides−silica nanocomposites were prepared using SBA-15 as a support and suitable metal-containing reagents. The oxide precursors were obtained by reacting two metal alkoxides, namely, titanium(IV) isopropoxide [Ti(OiPr)4], zirconium propoxide [Zr(OPr)4], and aluminum isopropoxide [Al(OiPr)3], or one of these alkoxides with a solution of nickel nitrate hexahydrate [Ni(NO3)2·6H2O] in isopropyl alcohol (iPrOH). The final condensation of the bimetallic species was achieved by a partial hydrolytic sol−gel route in the pores of SBA-15 silica using small amounts of HCl with concomitant slow evaporation of the solvent. High loadings of these oxides were deposited after several deposition cycles. The as-prepared nanocomposites were characterized by thermogravimetric analysis, whereas nitrogen adsorption at −196 °C was measured for the materials calcined at 300 and 600 °C. Nitrogen adsorption isotherms and the calculated pore-size distributions showed that the deposition of large amounts of the aforementioned oxides in SBA-15 occurred according to an “island-type” mechanism, resulting in the formation of pore constrictions but without damaging the ordered structure of SBA-15. Small-angle X-ray diffraction (XRD) analysis provided additional evidence for the presence of these oxides in the ordered mesopores after thermal treatment below 300 °C and for the diffusion of these species to the external surface of SBA-15 after calcination above 600 °C. Changes in the Al coordination in these oxides with an increase in the temperature of calcination were monitored by Al27 MAS NMR, showing the existence of surface, framework, and oxygen-deficient Al3+ sites. After consecutive depositions, the resulting composites were calcined at higher temperatures (600−800 °C) and characterized by wide-angle powder XRD, which revealed the existence of nanoparticles of double and single oxide phases formed in the aforementioned temperature range. The crystallite size of these nanoparticles estimated using the Scherrer formula were, in general, larger than the silica pore widths, suggesting the surface diffusion of these oxides and sintering of small nanoparticles during thermal treatment.

Thermoplastic Cellulose-graft-poly(l-lactide) Copolymers Homogeneously Synthesized in an Ionic Liquid with 4-Dimethylaminopyridine Catalyst

An effective method for grafting L-lactide (LA) from unmodified cellulose by ring-opening polymerization (ROP) in homogeneous mild conditions is presented. By using 4-dimethylaminopyridine (DMAP) as an organic catalyst, cellulose-graft-poly(L-lactide) (cellulose-g-PLLA) copolymers with a molar substitution (MS(PLLA)) of PLLA in a range of 0.99-12.28 were successfully synthesized in ionic liquid 1-allyl-3-methylimidazolium chloride (AmimCl) at 80 degrees C. The amount and length of grafted PLLA in cellulose-g-PLLA copolymers were controlled by adjusting the molar ratios of LA monomer to cellulose. The structure and thermal properties of cellulose-g-PLLA copolymers were characterized by (1)H NMR, (13)C NMR, wide-angle X-ray powder diffraction (WAXD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and optical microscopy. The DSC results revealed that the copolymers exhibited a single glass transition temperature, T(g), which sharply decreased with the increase of MS(PLLA) up to MS(PLLA) = 8.28 (DS(PLLA) = 2.19) and increased a little with a further increase of the lactyl content. When MS(PLLA) was above 4.40, the graft copolymers exhibited thermoplastic behavior, indicating the intermolecular and intramolecular hydrogen bonds in cellulose molecules had been effectively destroyed. By using a conventional thermal processing method, fibers and disks of cellulose-g-PLLA copolymers were prepared.

Autoclave and β-Amylolysis Lead to Reduced in Vitro Digestibility of Starch

In this study, a combination of autoclave and beta-amylolysis was used to modulate the digestibility of normal corn starch (NCS) and wheat starch (WS). The modification procedure comprised three cycles of autoclave at 35% moisture content and 121 degrees C, beta-amylolysis, and one additional cycle of autoclave. Starch materials were sampled at each stage and characterized. The fine structure of starch was determined using high-performance size-exclusion chromatography, the micromorphology of starch dispersion was imaged using cryo-SEM, the crystalline pattern was evaluated using wide-angle X-ray powder diffraction, and the digestibility was measured using Englyst assay. After beta-amylolysis, amylose was enriched (from 25.4 to 33.2% for NCS and from 27.5 to 32.8% for WS) and the branch density was increased (from 5.2 to 7.7% for NCS and from 5.3 to 7.9% for WS). Cryo-SEM images showed that the autoclave treatment led to the formation of a low-swelling, high-density gel network, whereas beta-amylolysis nearly demolished the network structure. The loss of A-type crystalline structure and the formation of B- and V-type structures resulted from autoclave, which suggests the formation of amylose-based ordered structure. Englyst assay indicated that, due to beta-amylolysis, the resistant starch (RS) content was increased to 30 from 11% of native NCS and to 23 from 9% of native WS. In contrast, autoclave showed only minor impact on RS levels. The increase of RS observed in this study is associated with enhanced branch density, which is different from the four types of RS commonly defined.

Synthesis and Characterisation of Polyaniline/Montmorillonite Nanocomposites

A series of polyaniline / montmorillonite clay (PANI-MMT) composites has been synthesised by solution polymerisation in the presence of hydrochloric acid and a substoichiometric amount of ammonium persulfate (APS). For a preferred molar ratio of monomer to oxidant of 2:1, the aniline was polymerised and largely incorporated into the MMT. The PANI-MMT composites were characterised and compared by Fourier-transform infrared (FTIR) spectroscopy, wide-angle powder X-ray diffraction and scanning electron microscopy (SEM). The effect of loading with the conducting polymer on the nanocomposites’ DC electrical conductivity was studied, and the maximum conductivity (pressed powder compact) was found to be 4.73 × 10 1 S.cm-1, comparable with that of pure polyaniline in the same form. The conductivity followed quite well the temperature-dependence relationship □(T) = □0.exp[-To/T)1/2], characteristic of one-dimensional variable-range hopping (1-D VRH).

Structural and magnetic properties of inverse opal photonic crystals studied by x-ray diffraction, scanning electron microscopy, and small-angle neutron scattering

The structural and magnetic properties of nickel inverse opal photonic crystal have been studied by complementary experimental techniques, including scanning electron microscopy, wide-angle and small-angle diffraction of synchrotron radiation, and polarized neutrons. The sample was fabricated by electrochemical deposition of nickel in voids in a colloidal crystal film made of 450 nm polystyrene microspheres followed by their dissolving in toluene. The microradian small-angle diffraction of synchrotron radiation was used to reveal the opal-like large-scale ordering proving its tendency to the face-centered-cubic fcc structure with the lattice constant of 65010 nm. The wide-angle x-ray powder diffraction has shown that nanosize fcc nickel crystallites, which form an inverse opal framework, have some texture prescribed by principal directions in inverse opal on a macroscale, thus showing that the atomic and macroscopic structures are correlated. The polarized small-angle neutron scattering is used on the extreme limit of its ability to detect the transformation of the magnetic structure under applied field. Different contributions to the neutron scattering have been analyzed: the nonmagnetic nuclear one, the pure magnetic one, and the nuclear-magnetic interference. The latter in the diffraction pattern shows the degree of the spatial correlation between the magnetic and nuclear reflecting planes and gives the pattern behavior of the reversal magnetization process for these planes. The field dependence of pure magnetic contribution shows that the three-dimensional geometrical shape of the structure presumably leads to a complex distribution of the magnetization in the sample.

Mesoporous TiO2/α-Fe2O3: Bifunctional Composites for Effective Elimination of Arsenite Contamination through Simultaneous Photocatalytic Oxidation and Adsorption

Bifunctional mesoporous TiO2 (meso-TiO2)/α-Fe2O3 composites are successfully synthesized by impregnation of Fe3+ into meso-TiO2 followed by calcination at 300 °C. The composites are characterized by wide-angle X-ray powder diffraction, small-angle X-ray diffraction, and transmission electron microscopy. The “bifunctional” means that the composites possess synergy of the photocatalytic ability of meso-TiO2 for oxidation of As (III) to As (V) and the adsorption performance of α-Fe2O3 for As (V). Experimental results show that the meso-TiO2/α-Fe2O3 composites can oxidize higher toxic As (III) to lower toxic As (V) with high efficiency at various pH values in the photocatalysis reaction. At the same time, As (V) is effectively removed by adsorption onto the surface of composites. In addition, As (V) can be easily desorbed from the composites by heat treatment in alkali solution. After reusage for several times, the composites still present comparable catalysis and adsorption performance with that of first use, indicating the excellent stability of the bifunctional composites. The reasonable mechanism for the formation of meso-TiO2/α-Fe2O3 composites, the photocatalytic oxidation of As (III) to As (V) and simultaneous removal of As (V) are also presented in this paper. The bifunctional composites are expected to have significant applications in treating water contamination.

Polypyrrole-Based Nitrogen-Doped Carbon Replicas of SBA-15 and SBA-16 Containing Magnetic Nanoparticles

Polypyrrole-based ordered mesoporous carbons (OMCs) were synthesized via chemical vapor infiltration of pyrrole into pores of the SBA-15 and SBA-16 silica templates containing iron(III) chloride catalyst (FeCl3). After carbonization of polypyrrole at 800 °C and etching of the silica templates with hydrofluoric acid solution, nitrogen-doped and graphitic OMCs with incorporated magnetic nanoparticles were obtained. These materials were analyzed by CHNS elemental analysis, thermogravimetry (TG), nitrogen adsorption, small and wide angle powder X-ray diffraction (XRD), Raman spectroscopy, scanning, and transmission electron microscopy (TEM). The resulting carbon replicas retained the crystallographic symmetry of the silica templates: namely, P6mm in the case of the SBA-15 template, and Im3m in the case of the SBA-16 template. The uniformity, size, and volume of ordered mesopores in the carbon replicas were affected by structural properties of the templates used as shown by analysis of nitrogen adsorption isotherms and pore size distributions. A better infiltration of carbon precursor was achieved for the templates with larger pores, which resulted in the carbon replicas of improved adsorption and structural properties. Elemental analysis revealed the presence of nitrogen in the carbon replicas studied in the range of 3−8 wt %, whereas TG analysis of the replica samples in air gave about 2−5% residue, which was identified as hematite (Fe2O3). The presence of graphitic domains was confirmed by characteristic TG oxidation profile above 400 °C, the D and G bands on the Raman spectra, and the intense reflections on the wide angle XRD patterns. Powder XRD also showed the presence of extra-framework magnetic iron (α-Fe) and iron carbide (Fe3C) nanoparticles having crystallite size in the ranges of 40−80 and 20−40 nm, respectively. TEM images also revealed that these nanoparticles were larger than the carbon rods and pore widths of the SBA-15 carbon replica, which is in good agreement with the XRD-based estimation. The in situ EDS analysis of carbon rods and spheres showed that iron was present in the carbonaceous framework, which does not exclude the existence of much smaller nanoparticles, below 5 nm.

Comparative studies for the effect of intercalating agent on the physical properties of epoxy resin-clay based nanocomposite materials

In this study, a series of comparative studies for the effect of intercalating agent on the physical properties of the epoxy resin-clay based nanocomposite materials were performed. First, the quaternary alkylphosphonium and alkylammonium salt were both used as the intercalating agents separately for the preparation of organophilic clay through the cationic exchange reactions with Na +-montmorillonite clay. Subsequently, the organophilic clay was blent into the epoxy resin through in-situ thermal ring-opening polymerizations to prepare a series of polymer-clay nanocomposite (PCN) materials. The as-synthesized PCN materials were subsequently characterized by Fourier-Transformation infrared (FTIR) spectroscopy, wide-angle powder X-ray diffraction (WXRD), and transmission electron microscopy (TEM). It should be noted that the quaternary alkylphosphonium salt (Φ 3P +-C 12)-modified clay was found to show better dispersion capability than that of quaternary alkylammonium salt (Me 3N +-C 16)-modified clay existed in the polymer matrix based on the studies of WXRD and TEM. The better dispersion of (Φ 3P +-C 12)-modified clay in epoxy resin was found to lead more effectively enhanced physical property such as corrosion protection, gas barrier, mechanical strength, thermal stability, and flame retardant properties of polymers than that of (Me 3N +-C 16)-modified clay, in the form of coating and membrane, based on the measurements of a series of electrochemical corrosion parameters, gas permeability analysis (GPA), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and limiting oxygen index (LOI), respectively. Effect of material composition on the physical properties of as-prepared materials was also investigated.

Synthesis and magnetic properties of antiferromagnetic Co 3O 4 nanoparticles

Antiferromagnetic Co 3O 4 nanoparticles with diameter around 30 nm have been synthesized by a solution-based method. The phase identification by the wide-angle X-ray powder diffraction indicates that the Co 3O 4 nanoparticle has a cubic spinel structure with a lattice constant of 0.80843(2) nm. The image of field emission scanning electron microscope shows that the nanoparticles are assembled together to form nanorods. The magnetic properties of Co 3O 4 fine particles have been measured by a superconducting quantum interference device magnetometer. A deviation of the Néel temperature from the bulk is observed, which can be well described by the theory of finite-size scaling. An enhanced coercivity as well as a loop shift are observed in the field-cooled hysteresis loop. The exchange bias field decreases with increasing temperature and diminishes at the Néel temperature. The training effect and the opening of the loop reveal the existence of the spin-glass-like surface spins.

Effects of Homochiral Molecules of (S)-(+)-Ibuprofen and (S)-(−)-Sodium Ibuprofen Dihydrate on the Crystallization Kinetics of Racemic (R,S)-(±)-Sodium Ibuprofen Dihydrate

The aim of this paper is to identify the effects of homochiral molecules such as (S)-(+)-ibuprofen and (S)-(−)-sodium ibuprofen dihydrate on the crystallization kinetics: the induction period, the crystal growth rate, and the end point of the racemic compound of (R,S)-(±)-sodium ibuprofen dihydrate. Crystallization kinetics of racemic species of sodium ibuprofen dihydrate in the presence of small amounts of homochiral parent molecules of (S)-(+)-ibuprofen and its constituent enantiomers (S)-(−)-sodium ibuprofen dihydrate were studied by electrical conductance, optical microscopy, differential scanning calorimetry, and wide-angle powder X-ray diffraction. Racemic (R,S)-(±)-sodium ibuprofen dihydrate with self-association property was sensitive to processing history and deserved a tight control for reproducibility on scale-up. Crystals grown from a racemic water−acetone solution of sodium ibuprofen dihydrate and vaccuum-dried at 90 °C for 4 h produced racemic species of α-form racemic compounds and γ-form racemic conglomerates having a R:S w/w ratio of about 45:55 (enantiomeric excess of the solids, ee = 10% in S) by the addition of no additives, and 0.02 g of (S)-(+)-ibuprofen or 0.02 g of (S)-(−)-sodium ibuprofen, respectively. Fundamental parameters of the crystallization kinetics of racemic species of sodium ibuprofen dihydrate such as the induction time, τ; the interfacial energy, γ; the Gibbs energetic barrier, ΔG cr; the nucleation rate, J; the critical size of stable nuclei, rc; the crystal mass growth rate, RG; the power number, g; and the end point were evaluated with different initial supersaturation ratios, S0, and compared. In general, τ, ΔG cr, and rc decreased and J increased when S0 increased or homochiral additives were added. γ decreased in the presence of homochiral additives. RG increased as S0 increased in the presence of (S)-(+)-ibuprofen. g ranged from 0.5 to 1.7. The end point decreased in the presence of additives or with the increase in S0. At high S0, the effects of homochiral additives on the induction period, the crystal growth rate and the end point became to diminish. Adoption of such inexpensive, simple, and robust methods as electrical conductance, optical microscopy, and differential scanning calorimetry in common research laboratories offers the opportunity to the pharmaceutical industry to lower manufacturing cycle times and end product variability in a crystallization process that would result in shorter time to market and a reduced likelihood of drug product failures. The addition of configurationally similar homochiral molecules such as the parent acid or the same constituent enantiomer to the racemic solution may have opened a new doorway for the generation of racemic species that cannot be obtained by the addition of other impurities.

Organogelators from self-assembling peptide based dendrimers: structural and morphological features

Two peptide based dendrimers containing l-aspartic acid as the branching unit and succinic acid/terephthalic acid as the core unit were synthesized, characterized, and studied. These dendritic peptides form gels in various organic solvents including n-hexanol, benzene, toluene, chlorobenzene, 1,2-dichlorobenzene, o-xylene, tetralin, and nitrobenzene. Gels were characterized by freeze fracture transmission electron microscopic (FF-TEM), field emission scanning electron microscopic (SEM), transmission electron microscopic (TEM), wide angle X-ray powder diffraction (WAXPD), and variable temperature FTIR (VT-FTIR) studies. The VT-FTIR study indicates that amides and ester groups are involved in intermolecular hydrogen bonding in the gel state. Two transitions have been observed for both the dendrimer gels upon heating: the first one corresponds to the gel to sol transition and corresponds to the breaking of hydrogen bonds between esters and amides; the second one corresponds to the breaking of hydrogen bonds between amides. In the case of dendrimer 1 structural reorganization occurs in the sol state after the first transition, which is absent in the dendrimer 2 in the sol state. FF-TEM observations showed that both dendritic peptides form a platelet structure in gel state. SEM images of these dried gels indicate different geometry in different solvents in their self-assembled gel state.

Highly-ordered mesoporous nanocrystalline yttria-stabilized zirconia synthesized through evaporation-induced self-assembly method

An ordered tetragonal mesoporous 16 mol% yttria-stabilized zirconia (8YSZ) has been successfully prepared by evaporation-induced self-assembly (EISA) using tri-block copolymer Pluronic F127 as a structure-directing agent and inorganic chlorides as precursors in a non-aqueous medium. The arrangement of mesopores was identified by small-angle X-ray diffraction and transmission electron microscopy (TEM). A distinct face-centered tetragonal lattice was able to describe such an ordered mesopore arrangement. The structure and crystallite size of pore-walls were determined by wide-angle X-ray powder diffraction and high-resolution TEM. The well-ordered face-centered tetragonal mesoporous 8YSZ with average pore size of 4.3 nm and high specific surface area of 134 m2/g and the pore-wall is composed of ∼4.8 nm nanocrystalline 8YSZ domains.

Synthesis of biomorphological mesoporous TiO 2 templated by mimicking bamboo membrane in supercritical CO 2

A new approach is presented for preparing biomorphological mesoporous TiO 2 templated by mimicking bamboo inner shell membrane via supercritical CO 2 (SCCO 2) transportation through titanium tetrabutyloxide (TTBO). The analysis of wide-angle X-ray powder diffraction (XRD) showed the prepared TiO 2 in phase of anatase, and the small-angle XRD revealed the presence of mesopores without periodicity. The product exhibited the shape of crinkled films and extended in two dimensions up to centimeters. The electron microscopic observation showed that the TiO 2 films were around 200 nm in thickness, and across the films there were numerous round or ellipse-shaped mesopores, being 10–50 nm in diameter, which were formed by the close packing of TiO 2 particles. High-resolution transmission electron microscope (HRTEM) displayed that the single TiO 2 particle size was about 12.5 nm. The UV–vis absorption spectrum was transparent in the wavelength of 320–350 nm for suspensions of the prepared mesoporous TiO 2 in ethanol at the concentration of 5.0 mg/l. The mesoporous TiO 2 prepared with the aid of SCCO 2 exhibited an obvious blue shift compared with the TiO 2 prepared by sol–gel infiltration. The possible mechanism for the formation of the mesoporous TiO 2 is summarized into a biomimetic mineralization pathway. First, TTBO was transported to the membrane surface via SCCO 2, and then condensed. Hydrolysis reactions between the functional groups of organic membrane and TTBO took place to form the nuclear TiO 2, and the TiO 2 seeds grew around the organic membrane into TiO 2 mesoporous materials. The approach provides a low-cost and efficient route for the production of ceramics nanomaterials with unique structural features, which may have potential application in designing UV-selective shielding devices [S. Zhao, X.H. Wang, S.B. Xin, Q. Jiang, X.P. Liang, Rare Metal Mater. Eng. 35 (2006) 508–510].

Preparation and characterization of poly( o-methoxyaniline)/Na +–MMT clay nanocomposite via emulsion polymerization: Electrochemical studies of corrosion protection

A series of poly( o-methoxyaniline) (PMA)/Na +–montmorillonite (MMT) clay nanocomposite (Na +–PCN) materials have been successfully prepared by in situ emulsion polymerization in the presence of inorganic nanolayers of hydrophilic Na +–MMT clay with DBSA and APS as surfactant and initiator, respectively. The as-synthesized Na +–PCN materials were characterized by Fourier-transformation infrared (FTIR) spectroscopy, wide-angle powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). Na +–PCN materials in the form of coatings with low loading of Na +–MMT clay (e.g., 5 wt.%, CLMA5) on cold rolled steel (CRS) were found much superior in corrosion protection over those of neat PMA based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current and impedance spectroscopy in 5 wt.% aqueous NaCl electrolyte. The molecular weight of PMA extracted from Na +–PCN materials and net PMA were determined by gel permeation chromatography (GPC) with NMP as eluant. Effects of material composition on the optical properties, electrical conductivity, thermal stability and surface morphology of neat PMA and/or a series of Na +–PCN materials, in the form of solution, powder-pressed pellet and fine powder, were also studied by ultraviolet–visible spectra, four-point probe technique, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively.