Background optimization of powder electron diffraction for implementation of the e-PDF technique and study of the local structure of iron oxide nanocrystals.

The local structural characterization of iron oxide nanoparticles is explored using a total scattering analysis method known as pair distribution function (PDF) (also known as reduced density function) analysis. The PDF profiles are derived from background-corrected powder electron diffraction patterns (the e-PDF technique). Due to the strong Coulombic interaction between the electron beam and the sample, electron diffraction generally leads to multiple scattering, causing redistribution of intensities towards higher scattering angles and an increased background in the diffraction profile. In addition to this, the electron-specimen interaction gives rise to an undesirable inelastic scattering signal that contributes primarily to the background. The present work demonstrates the efficacy of a pre-treatment of the underlying complex background function, which is a combination of both incoherent multiple and inelastic scatterings that cannot be identical for different electron beam energies. Therefore, two different background subtraction approaches are proposed for the electron diffraction patterns acquired at 80 kV and 300 kV beam energies. From the least-square refinement (small-box modelling), both approaches are found to be very promising, leading to a successful implementation of the e-PDF technique to study the local structure of the considered nanomaterial.

Visualization of the Final Stage of Sintering in Nanoceramics with Atomic Resolution.

The deep understanding of the sintering mechanism is pivotal to optimizing denser ceramics production. Although several models explain the sintering satisfactorily on the micrometric scale, the extrapolation for nanostructured systems is not trivial. Aiming to provide additional information about the particularities of the sintering at the nanoscale, we performed in situ experiments using high-resolution transmission electron microscopy (HRTEM). We studied the pore elimination process in a ZrO2 thin film and identified a high anisotropic pore elimination. Interestingly, there is a redistribution of the atoms from the rough surface in the solid-gas surface, followed by the atom attachment in a faceted surface. Finally, we found evidence of the pore acting as a pin, reducing the GB mobility. These findings certainly can contribute to enhance the kinetic models to describe the densification process of systems at the nanoscale.

Pair Distribution Function from Electron Diffraction in Cryogenic Electron Microscopy: Revealing Glassy Water Structure.

In recent years, cryogenic electron microscopy (Cryo-EM) has revolutionized the structure determination of wet samples and especially that of biological macromolecules. The glassy-water medium in which the molecules are embedded is considered an almost in vivo environment for biological samples. The local structure of amorphous ice is known from neutron- and X-ray-diffraction studies, techniques appropriate for much larger volumes than those used in cryo-EM. We here present a first study of the pair-distribution function g(r) of glassy water under cryo-EM conditions using electron diffraction data. We found g(r) to be between that of low-density amorphous ice and that of supercooled water. Under electron exposure, cubic-ice regions were found to nucleate in thicker glassy-water samples. Our work enables to obtain quantitative structural information using g(r) from cryo-EM.

PU nanocomposites from bifunctional nanoparticles: impact of liquid interphase on mechanical properties.

The Fe3O4@Poly(1,4-butanediol)/polyurethane nanocomposite is a highly interphase-dependable material with unique characteristics. Firstly, the nanoparticle's organic shell allows simple fabrication of very well dispersed nanocomposites and the incorporation of extremely high amounts of nanoparticles (NP) into the polymer matrix. Secondly, both chemical and physical aspects of the nanoparticles determine the material's mechanical behavior. The chemical functionality of the organic layer - free hydroxyl groups at the end of the tethered chains - ensures the material's stiffening through covalent bonds with the matrix, while being at molten state provides high flexibility and deformability yet maintaining mechanical resistance. As a result, nanocomposites at the low concentration region show increased elastic modulus and tensile strength and slight increase in total strain, while highly concentrated nanocomposites show reduction of elastic modulus and tensile strength and roughly double the total strain. The combination of the chemical and physical functionalities ensures high compatibility between nanoparticles and matrix and allows the production of highly concentrated - above 90% in weight - nanocomposites as a cohesive and flexible material, instead of a brittle wafer. This bifunctionality effect is unprecedented and the results open a wide range of new possibilities in the tailoring of functional nanomaterials for all sorts of applications in materials science.

Correction: Nanocrystals self-assembled in superlattices directed by the solvent-organic capping interaction.

Correction for 'Nanocrystals self-assembled in superlattices directed by the solvent-organic capping interaction' by Cleocir José Dalmaschio et al., Nanoscale, 2013, 5, 5602-5610.

Nanocrystals self-assembled in superlattices directed by the solvent-organic capping interaction.

Close-packed arrays of ZrO2 nanocrystals (NCs) have been self-assembled from a colloidal solution in a withdrawal dip coating process. A benzyl alcohol route was used to obtain NCs of narrowly controlled size, and then the capping layer was replaced by oleate using solvothermal treatment. The oleate solubility was explored in chloroform, hexane and toluene to prepare thin films of NCs using a dip coating process. From TEM images, the final structures show that increasing the solvent polarity improved self-assembly to prepare mono- and multi-layer superlattices, during solvent evaporation in a short time. The entangled organic chain in the NC surface offsets the limitations of the faceted NCs, improving the assembly quality, allowing the NC assembly to approach the formation of a hard sphere model, resulting in a FCC close-packed structure. Furthermore, the low interaction of chloroform with the capping layer reduces the shrinkage effect during the solvent evaporation preserving the array in the final self-assembled structure. Molecular dynamics simulations with soft potentials supported the conclusion that hexane interacts with the organic capping ligand, increasing the apparent radius of each NC and stabilizing the colloidal suspension, whereas chloroform is partially removed from the capping layer during the aggregation process, forming an array of nanoparticles.

Impact of the colloidal state on the oriented attachment growth mechanism.

In the last five years, several excellent reviews about oriented attachment (OA) have evidenced the advances achieved in this research area, detailing the growth mechanism and the kinetic models. The main focus of this review is to examine the dependence of the OA mechanism on the colloidal state and to demonstrate how the colloidal state modifies the OA mechanism. Basically, we can define two main possible approaches to achieve self-organization or mutual orientation of adjacent nanocrystals. One is the effective collision of particles with mutual orientation controlled by the number of collisions. This type of growth occurs in a well dispersed colloidal suspension and results in a statistical growth process. The second way is through coalescence induced by particle rotation. This mechanism must be dominant in a weakly flocculated colloidal state in which there is significant interaction among particles. This type of process leads to the formation of complex structures.

Oxide surface modification: synthesis and characterization of zirconia-coated alumina.

Four aluminas were used as supports for impregnation with a zirconium oxide with the aim to achieve a coating, without phase separation, between support and modifier. The supports were impregnated with different concentrations of zirconium aqueous resin, obtained through the polymeric precursor method. After impregnation the samples were calcined and then characterized by XRD, which led to identification of crystalline zirconia in different concentrations from each support used. Using a simple geometric model the maximum amount of surface modifier oxide required for the complete coating of a support with a layer of unit cells was estimated. According to this estimate, only the support should be identified below the limit proposed and crystalline zirconium oxide should be identified above this limit when a complete coating is reached. The results obtained from XRD agree with the estimated values and to confirm the coating, the samples were also characterized by EDS/STEM, HRTEM, XPS, and XAS. The results showed that the zirconium oxide on the surface of alumina support reached the coating in the limit of 15 Zr nm(-2), without the formation of the ZrO(2) phase.

Nanostructured alumina-coated implant surface: effect on osteoblast-related gene expression and bone-to-implant contact in vivo.

PURPOSE: The use of nanotechnology to enhance endosseous implant surfaces may improve the clinical control of interfacial osteoblast biology. This study investigated the influence of a nanostructure-coated implant surface on osteoblast differentiation and its effects on bone-to-implant contact (BIC) and removal torque values. MATERIALS AND METHODS: Titanium disks were machined (M) or machined and subsequently treated by acid etching (Ac) or by dipping in an aluminum oxide solution (Al2O3). Surfaces were characterized by scanning electron microscopy, atomic force microscopy, and x-ray microanalysis. For the in vitro experiment, rat mesenchymal stem cells (rMSCs) were grown in osteogenic supplements on the disk surfaces for 3 days. Real-time polymerase chain reaction (PCR) was used to measure mRNA levels of several gene products (bone sialoprotein, osteocalcin, osteopontin, and RUNX-2). For the in vivo experiment, titanium implants were placed in rat tibiae and harvested after 3 to 21 days for measurement of bone-specific mRNA levels by real-time PCR. Removal torque and BIC were measured 3 to 56 days after placement. RESULTS: Average height deviation (Sa, in nm) values for M, Ac, and Al2O3 implants were 86.5, 388.4, and 61.2, respectively. Nanostructured Al2O3 topographic features applied to machined implants promoted MSC commitment to the osteoblast phenotype. Greater bone-specific gene expression was observed in tissues adjacent to Al2O3 implants, and associated increases in BIC and torque removal were noted. CONCLUSION: Nanostructured alumina may directly influence cell behavior to enhance osseointegration.

The influence of the film thickness of nanostructured alpha-Fe2O3 on water photooxidation.

The present work shows the influence of the film thickness in the optical and photoelectrochemical properties of nanostructured alpha-Fe(2)O(3) thin film. We found that the film thickness has a strong influence on the optical absorption and the results here reported can help in the design of nanostructured alpha-Fe(2)O(3) with superior performance for water photo-oxidation. The results show that the optical property of the hematite film is affected by the film thickness, probably due to the stress induced by the strong interaction between film and substrate. This stress generates defects in the crystal lattice of the hematite film, increasing the (e(-))-(h(+)) recombination process.

Effects of the solvent evaporation technique on the degree of conversion of one-bottle adhesive systems.

This study evaluated the effect of four methods of solvent evaporation on the degree of conversion (DC) of seven one-bottle adhesive systems: Excite (EX), ONE-STEP (OS), Optibond Solo Plus (OB), Prime&Bond 2.1 (PB), Prime&Bond NT (NT), Single Bond (SB) and Single Bond Plus (SP) using Fourier Transform Infrared Analysis (FTIR). Adhesive resins were: 1) applied to KBr pellet surfaces and left undisturbed for 30 seconds (condition 1), 2) left undisturbed for 30 seconds and air-dried with an air stream for 10 seconds (condition 2), 3) left undisturbed for 60 seconds (condition 3) and 4) left undisturbed for 60 seconds and air-dried for 10 seconds (condition 4) before curing. FTIR spectra were obtained and the DC was calculated by comparing the ratio of aliphatic/aromatic double carbon bonds before and after light-activation for 10 seconds (XL 3000, 3M). The results of each product were analyzed by one-way repeated measure ANOVA and post-hoc Tukey's test (p<0.05). The DC of PB, NT, OB and SP adhesives was not affected by the four evaporation conditions, while the DC of EX, OS and SB changed according to the evaporation method. The results suggested that the DC of some adhesives was similar regardless of the evaporation method when no water from dentin or rinsing was involved. Other bonding agents showed higher DC after specific conditions of solvent evaporation.

Degree of conversion of adhesive systems light-cured by LED and halogen light.

This study evaluated the effect of blue light emitting diode (LED) and quartz tungsten halogen (QTH) on the degree of conversion (DC) of an etch-and-rinse Single Bond adhesive system (SB) and a mixture composed of primer solution and resin bond from Clearfil SE Bond self-etching adhesive system (CB) using Fourier transform infrared analysis (FTIR). Adhesives were applied to potassium bromide pellet surfaces and FTIR analyses were performed before and after photo-activation for 10 s with either LED (Freelight 1 - 400 mw/cm(2)) or QTH (XL 3000 - 630 mw/cm(2)) light-curing units (n=8). Additional FTIR spectra were obtained from photo-activated samples stored in distilled water for 1 week. The DC was calculated by comparing the spectra obtained from adhesive resins before and after photo-activation. The results were analyzed by two-way split-plot ANOVA and Tukey's test (p<0.05). Both adhesive systems exhibited low DC (%) immediately after photo-activation (SB/QTH: 18.7 +/- 3.9; SB/LED: 13.5 +/- 3.3; CF/QTH: 13.6 +/- 1.9; CF/LED: 6.1 +/- 1.0). The DC of samples light-cured with LED was lower than DC of those light-cured with QTH, immediately after light curing and after 1 week (SB/QTH: 51.3 +/- 6.6; SB/LED: 50.3 +/- 4.8; CF/QTH: 56.5 +/- 2.9; CF/LED: 49.2 +/- 4.9). The LED curing unit used to photo-activate the adhesive resins promoted lower DC than the QTH curing unit both immediately after light curing and 1 week after storage in water.

Degree of conversion of adhesive systems light-cured by LED and halogen light

This study evaluated the effect of blue light emitting diode (LED) and quartz tungsten halogen (QTH) on the degree of conversion (DC) of an etch-and-rinse Single Bond adhesive system (SB) and a mixture composed of primer solution and resin bond from Clearfil SE Bond self-etching adhesive system (CB) using Fourier transform infrared analysis (FTIR). Adhesives were applied to potassium bromide pellet surfaces and FTIR analyses were performed before and after photo-activation for 10 s with either LED (Freelight 1 - 400 mw/cm²) or QTH (XL 3000 - 630 mw/cm²) light-curing units (n=8). Additional FTIR spectra were obtained from photo-activated samples stored in distilled water for 1 week. The DC was calculated by comparing the spectra obtained from adhesive resins before and after photo-activation. The results were analyzed by two-way split-plot ANOVA and Tukey's test (p<0.05). Both adhesive systems exhibited low DC ( percent) immediately after photo-activation (SB/QTH: 18.7 ± 3.9; SB/LED: 13.5 ± 3.3; CF/QTH: 13.6 ± 1.9; CF/LED: 6.1 ± 1.0). The DC of samples light-cured with LED was lower than DC of those light-cured with QTH, immediately after light curing and after 1 week (SB/QTH: 51.3 ± 6.6; SB/LED: 50.3 ± 4.8; CF/QTH: 56.5 ± 2.9; CF/LED: 49.2 ± 4.9). The LED curing unit used to photo-activate the adhesive resins promoted lower DC than the QTH curing unit both immediately after light curing and 1 week after storage in water.

Este estudo avaliou a influência de sistemas de fotoativação no grau de conversão (GC) de sistemas adesivos por meio da análise infravermelha transformada de Fourier (FTIR). Os sistemas adesivos Single Bond (SB) e Clearfil SE Bond (CF) foram aplicados em pastilhas de brometo de potássio e fotoativados com luz halógena (XL 3000 - 630 mw/cm²) (QTH) e LED (Elipar Freelight 1 - 400 mw/cm²) por 10 s (n=8). Foram obtidos espectros de FTIR antes e imediatamente após a fotoativação, e tambem após 1 semana de armazenamento em água destilada. Calculou-se o GC comparando-se a razão entre os picos das bandas dos espectros, antes e após a fotoativação. Os resultados de GC foram submetidos à ANOVA e ao teste de Tukey (p<0,05). Para ambos os sistemas adesivos, o GC ( por cento) obtido imediatamente após a fotoativação com LED foi inferior ao obtido utilizando-se QTH (SB/QTH: 18,7 ± 3,9; SB/LED: 13,5 ± 3,3; CF/QTH: 13,6 ± 1,9; CF/LED: 6,1 ± 1,0). Após uma semana foi observado um aumento significativo no GC de todos os grupos, porém os valores dos grupos fotoativados com LED mantiveram-se inferiores aos obtidos com QTH (SB/QTH: 51,3 ± 6,6; SB/LED: 50,3 ± 4,8; CF/QTH: 56,5 ± 2,9; CF/LED: 49,2 ± 4,9). O GC dos adesivos fotoativados com LED foi inferior ao observado após fotoativação com QTH, imediatamente após fotoativação como após 1 semana de armazenamento em água.

Growth of SnO nanobelts and dendrites by a self-catalytic VLS process.

This article reports on the growth of SnO nanobelts and dendrites by a carbothermal reduction process. The materials were synthesized in a sealed tube furnace at 1210 degrees C and at 1260 degrees C for 2 h, in a dynamic nitrogen atmosphere of 40 sccm. After synthesis, gray-black materials were collected downstream in the tube and the samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDX). The results showed that the gray-black materials were composed of nanobelts, which grew in the [110] direction of the orthorhombic structure of SnO. Some of the belts also presented dendritic growth. The dendrites grew in the (110) planes of the SnO structure, and no defects were observed at the junction between the nanobelts and the dendrites. A self-catalytic vapor-liquid-solid (VLS) process was proposed to explain the growth of the SnO nanobelts and dendrites.

Influence of curing accelerator for cyanoacrylate glues on physical properties of adhesive resins

The objectives of this study were to evaluate the effect of a curing accelerator (CA) on the ultimate tensile strength (UTS) and degree of conversion (DC) of two adhesive systems, Single Bond and Clearfil SE Bond, as well as to identify the composition of the CA hour-glass adhesive resin samples with a cross sectional area of 0,8 mm² at the "neck" were tested in tension using a Universal Testing Machine. Fourier transform infrared spectroscopy (FTIR) was used to analyse thin films of each adhesive resin. All samples were stored in the dark for 24 hours before they were tested. During the UTS and FTIR analyses, the contact of the CA with samples was either avoided or not. The gas chromatography mass spectrocopy (GC-MS) and the nuclear magnetic resonance (NMR) analyses determined the molecular weight and structure of the CA. UTS and DC were analyzed by ANOVA and Tukey's test at 95% of confidence. The use of the CA did not affect the UST (p=0.5996) but increased the DC of the samples (p<0.0001). The compound identified by GC-MS and NMR was N-dimethyl p-toluidine. The application of CA in microtensile bond strength methodology raises concern regarding its effects on poorly polymerized adhesive systems.