X-ray Microanalysis Mapping Research Articles

Microscopy as a Powerful Technique to Characterise Polymer Matrix Nanocomposites

Polymer nanocomposites are a recent class of materials that have drawn considerable attention in recent years, due to the significant improvements in several properties. Even though a lot of research has been performed on the preparation of these materials, the homogeneous dispersion of nanoparticles in polymeric matrices, especially in non-polar, is still a difficult task. Thus, frequently nanocomposites exhibited worst properties than conventional polymers that limit their effective application. One way to improve nanoparticles dispersion is by using an in situ sol-gel method, which is based on a reaction between a precursor, containing the inorganic particle, and a polymer followed by hydrolysis-condensation reaction. Therefore, the present work aims to use microscopy techniques to investigate the dispersion of nanoparticles containing aluminium in PP and EVA matrices, prepared by a sol-gel process in the melt.Polypropylene modified with maleic anhydride (PP-g-MA, Polybond 3200) supplied by Crompton and ethylene-vinyl acetate (EVA) with 12 wt.% (EVA12, Escorene Ultra UL 00112) and 27 wt.% (EVA27, Escorene Ultra UL 00328) of vinyl acetate supplied by Exxon Mobil, were used as organic matrices to prepared the nanocomposites. The precursor, aluminium isopropoxide (Al(Pr-i-O)3), used as received in powder state, was supplied by Sigma Aldrich. Nanocomposites with the same composition were prepared by melt mixing in an internal mixer under constant processing conditions, as previously describe by Oliveira. The hybrid nanocomposite (HN) synthesized with PP-g-MA was called HN-Pr, with EVA12 was HNEVA12 and the one synthesized with EVA27 was HNEVA27.Samples characterized by SEM were fractured at low temperature and gold coated. Samples analysed by TEM were sectioned by cryo-ultramicrotomy using a diamond knife at -60 ºC and -140 ºC under liquid nitrogen for EVAs and PP-g-MA nanocomposites, respectively. X-ray microanalysis mapping was performed in 300 μm2, in the same place where SEM analysis was made, with an energy dispersive X-ray Spectrometer (EDS) from Link eXL II from Oxford Instruments attached to the SEM.SEM micrographs presented in Figure 1a, b and c show that while HN-Pr has a homogeneous and rough surface, HNEVA12 and HNEVA27 have homogeneous and smoother surfaces. The presence of nanoparticles agglomerations can not be observed in the micrographs, which indicates a good dispersion and interaction between organic and inorganic components. Therefore, in order to investigate nanoparticles dispersion TEM analysis were performed and the results presented in Figure 2 evidence different degrees of nanoparticles dispersion in polymeric matrices and distinct sizes. The best dispersion was achieved in HN-Pr followed by HNEVA27. The average particle size is 200, 130 and 120 nm for HN-Pr, HNEVA12 and HNEVA27, respectively. The differences in particles dimension can be explained by the extension of the chemical reaction, which in agreement with other techniques, it was higher for EVA27. EDS analysis results presented in Figure 3 render 2.84, 5.07 and 3.49 % of aluminium content in the analysed area of HN-Pr, HNEVA12 and HNEVA27, respectively.In this study, it was observed that reaction extension has a great influence on size and dispersion of the generated nanoparticles. According to SEM and TEM results, the smallest nanoparticles were achieved in EVA27. Moreover, for the three nanocomposites prepared well dispersed nanoparticles were obtained. The EDS spectrum confirmed the presence of aluminium in nanocomposites structure.This work showed that microscopic technics are very powerful on the characterization of new polymer matrix nanocomposites.The authors are grateful to the Portuguese Foundation of Science and Technology (FCT) Project SFRH / BD / 39085 / 2007 for the financial support.

Internal structure, hygroscopic and reactive properties of mixed sodium methanesulfonate-sodium chloride particles

Internal structures, hygroscopic properties and heterogeneous reactivity of mixed CH(3)SO(3)Na/NaCl particles were investigated using a combination of computer modeling and experimental approaches. Surfactant properties of CH(3)SO(3)(-) ions and their surface accumulation in wet, deliquesced particles were assessed using molecular dynamics (MD) simulations and surface tension measurements. Internal structures of dry CH(3)SO(3)Na/NaCl particles were investigated using scanning electron microscopy (SEM) assisted with X-ray microanalysis mapping, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The combination of these techniques shows that dry CH(3)SO(3)Na/NaCl particles are composed of a NaCl core surrounded by a CH(3)SO(3)Na shell. Hygroscopic growth, deliquescence and efflorescence phase transitions of mixed CH(3)SO(3)Na/NaCl particles were determined and compared to those of pure NaCl particles. These results indicate that particles undergo a two step deliquescence transition: first at ∼69% relative humidity (RH) the CH(3)SO(3)Na shell takes up water, and then at ∼75% RH the NaCl core deliquesces. Reactive uptake coefficients for the particle-HNO(3) heterogeneous reaction were determined at different CH(3)SO(3)Na/NaCl mixing ratios and RH. The net reaction probability decreased notably with increasing CH(3)SO(3)Na and at lower RH.

Three‐dimensional nanocomposite scaffolds with ordered cylindrical orthogonal pores

A silica reinforcement can improve the mechanical properties of hydrogels in the rubbery state. A method to prepare a scaffold with a well-ordered array of cylindrical pores is presented in this work, which yields a scaffold with a biphasic matrix of a hybrid nanocomposite: the hydrogel poly(2-hydroxyethyl acrylate) (PHEA) and a silica network obtained by an acid catalyzed sol-gel process of tetraethoxysilane (TEOS). As porogenic template of the scaffold stacked layers of commercial polyamide 6 fabrics were used, which were compressed and sintered. Porosity and dynamic mechanical response of the resulting scaffolds were measured and compared with the bulk properties. Removal of the organic polymer phase of the scaffold by pyrolysis revealed the overall continuity of the silica network; the residue maintained the original cylindrical pore structure of the scaffolds, though slightly shrunk. Atomic force microscopy topography measurements of these pyrolysed residues revealed a silica structure with particle aggregates having sizes around tens of nanometers. The silica distribution was assessed by X-ray microanalysis mapping, showing homogeneity at a micrometer scale.

Cupric ion release controlled by copper/low‐density polyethylene nanocomposite in simulated uterine solution

The Cu2+ release rate of novel copper/low-density polyethylene composites as an intrauterine device material in the simulated uterine solution was investigated for 280 days. The corrosion products of these composites were identified by the X-ray diffraction method. The distributions of the copper phase and the cuprous oxide phase at different corrosion depths in the composites were measured by the internal standard method. For comparison, copper particles of two sizes were embedded in a polyethylene matrix to form composites. The average copper particle diameter of the nanocomposite was 30 nm, while that of microcomposite was 52 microm. Mechanism of Cu2+ release controlled by the nanocomposite revealed that many clusters composed of copper nanoparticles, which were observed by the field emission scanning electron microscopy in the nanocomposite, led to the formation of large amounts of Cu2O and consequently facilitated the Cu2+ steady release. A scanning electron microscope with energy dispersive X-ray microanalysis mapping technique (SEM/EDX) was employed to measure the corrosion depth and to calculate the life span of the nanocomposite. The result that the nanocomposite displayed a near zero-order release after a month of incubation indicated that the Cu2+ release behavior controlled by nanocomposite was remarkably superior to that by microcomposite.

Precipitation of Sr-rich intermetallic particles and their influence on pore formation in Sr-modified A356 alloy

The nature of enhanced pore formation in Sr-modified A356 Al alloy melts has been investigated, leading to the observation of the precipitation of Sr-rich compounds on the wetted side of oxide films. Scanning electron microscopy of casting surfaces showed that the surface oxide film might be a good possible nucleation site of Sr-rich compounds. The observation of internal pores using secondary electron microscopy and X-ray microanalysis mapping showed precipitation of Sr-rich compounds on the wetted side of the oxide films in most pores. The possibility of Sr-rich intermetallics being nucleated on oxide films was assessed by determining their planar disregistry factor; good matching planes were found between Al2Si2Sr intermetallics and γ-Al2O3 and spinel oxide films. The crystallographic alignment revealed in scanning electron microscope (SEM) images also corroborates an epitaxial relationship. Mechanisms by which Sr in Al-Si alloys may contribute to the formation of porosity are discussed.

Powdery mildew of Arabidopsis thaliana: a pathosystem for exploring the role of silicon in plant–microbe interactions

Silicon (Si) has been used in agriculture to protect plants against disease for hundreds of years and its prophylactic effects in monocots and dicots are well documented. The mechanisms by which Si exerts its protective effects in planta, however, are uncertain and presently the subject of debate. In this study, we sought to determine if Arabidopsis thaliana could be used to clarify the role of Si in plant–pathogen interactions. Accordingly, X-ray microanalysis mapping, light microscopy, scanning and transmission electron microscope techniques were used to examine the leaves of Si− fed A. thaliana plants inoculated with the powdery mildew fungus, Erysiphe cichoracearum. The results of this study demonstrate for the first time, that A. thaliana is a species that absorbs Si and that the incidence of powdery mildew disease for Si− fed plants is significantly lower compared to control plants. In particular, treatment with Si appeared to induce the production of an electron-dense, fungitoxic substance that accumulated within and around the collapsed fungal haustoria of infected epidermal cells within the leaves of disease-resistant plants. These results with Arabidopsis corroborate recent observations in other non-related species and support the emerging theory that the mechanisms by which Si imparts resistance to plants are complex and are not entirely explained by the traditionally proposed role of Si as a reinforcer of mechanical resistance. Collectively, the findings of the present study have established the Arabidopsis thaliana- Erysiphe cichoracearum pathosystem as a valid model to investigate the role of Si in plant–microbe interactions.