Materials Science Forum Vols. 636-637

Abstract: This work reports on spectroscopic investigations of interaction of an expanding laser ablated plume of aluminum, zinc, graphite with ambient atmosphere of oxygen and nitrogen gas and the formation of nitrides and oxides. The ambient pressure and fluence dependence on the reactive process occurring in the ablated plume responsible for formation of oxides and nitrides is discussed. Fast photography/imaging technique using intensified charge coupled device (ICCD) is gaining importance as a diagnostic tool for understanding the dynamics of the expanding plasma plume and the gas phase nanoparticle synthesis, thus providing a novel way to understand the transportation of nanoparticles and of control of particle size. Two dimensional images of the expanding plasma plume were captured using ICCD to understand the role of vapor and shock temperature. A comprehensive study done on oxide and nitrides films using pulsed laser deposition technique for possible laser oscillations in UV region of electromagnetic spectrum is presented.

Abstract: The present work describes the synthesis of nitrogen doped multi-walled carbon nanotubes (CNx CNT). The chosen production method was the catalytic pyrolysis of a solid mixture containing [Ni(DMG)2] and melamine (C3H6N6), under an Αr atmosphere. A series of various experiments were performed, using different proportions of the reaction mixture, in order to optimize the production conditions of nitrogen doped carbon nanotubes. Finally, the produced materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), Raman spectroscopy as well as thermogravimetric analysis (TGA). The obtained data from all the above analyses, showed the formation of nitrogen doped carbon nanotubes of various diameters as well as nanofibers surrounded by byproducts such as aggregations of amorphous carbon and metallic catalyst, depending on the proportion of the reaction mixture.

Abstract: The present work deals with the synthesis of carbon nanotube-zeolite composites using as method the catalytic liquid spray pyrolysis. The nanotubes were formed after pyrolysis of toluene on the surface of a zeolite of type ZSM-5, which was used as a catalytic substrate. ZSM-5 zeolite was synthesized using the autoclave process and full characterized. Prior to the pyrolyses, the catalytic substrates were produced by mixing a certain amount of zeolite with a solution of Fe(NO3)3•9H2O of specific concentration. The obtained materials from the spray pyrolysis were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetry-differential analysis (TG-DTA).

Abstract: This work deals with a new class of vanadium pentoxide nanocomposites containing supramolecular iron or manganese tetrapyridyl porphyrins coordinated to four [Ru(bipy)2Cl]+ complexes. Their characterization was carried out by means of X-ray diffraction, SEM, AFM, confocal Raman microscopy, electronic spectroscopy and electrochemistry. According to X-ray diffraction, the original VXG lamellar framework was maintained in the nanocomposite material, but the interlamellar distance increased from 11.6 Å to 18.5 Å, reflecting the intercalation of the porphyrin species into the inorganic matrix. The films generated by direct deposition of the nanocomposite aqueous suspensions onto interdigitated gold electrodes exhibited good electrical and electrochemical performance for application in amperometric sensors.

Abstract: Gracilaria is a red algal genus that biosynthesizes a polymer called agar that is extensively used in the food and pharmaceutical industries as gelling and stabilizing agent. In the last years, many studies have focused on gel properties of this biopolymer; but the agar films and coatings still have few studies reported. The edible film and coating have a protective function, preventing moisture, oxygen and flavour transfers between food and surroundings. The objectives of this work are the production of biodegradable agar films from Gracilaria vermiculophylla, collected in Ria de Aveiro, Portugal, and the study of the effect of glycerol, an hydrophilic plasticizer, on the properties of the films and on subsequent application in edible coating of fresh fruits and vegetables. The agar extraction was carried out at specific optimum parameters determined in previous work (3.5 h pre-treatment duration, 6% NaOH concentration and 2 h extraction time). Agar films were made using the knife coating technique and compared with commercial agar. The physical properties of films such as hygroscopicity, mechanical resistance (Young’s modulus, tensile strength and elongation), and permeability to water vapour and oxygen were characterized. As expected, the plasticizer addition revealed and increase on elongation and decrease on tensile strength. The films were transparent and optically clear, showing good properties similar to the commercial agar films. The potential application of the agar/glycerol solution to fresh vegetable preservation was tested. Model fruits and vegetables were coated with the biopolymer/plasticizer solution and compared with a control sample in terms of colour, firmness, weight loss and shelf life. Considering on one hand the abundance of the raw algal material which is actually an invasive species, and the properties of the agar films and coatings obtained on the other hand, commercial use of G.vermiculophylla from Ria de Aveiro is well justified.

Abstract: In this work, the method of Fourier transform infrared was used to study the recrystallization phenomenon in cassava starch films containing different plasticizers content and type. The films were obtained by conventional casting method and then, conditioned for several periods in desiccators containing saturated water-NaBr solution and also, in desiccators containing silica gel. From the results, the main changes occurred in the fingerprint region, and were attributed to new interactions arising between the polymeric chains and the plasticizer. The changes in the peak amplitude located near 1015 cm-1 were associated to the formation of semi crystalline junctions in the film matrix, as affected by the plasticizer and moisture content in the films. The slight changes in peak positions were attributed to the modifications in the intermolecular forces in the film matrix. The semi crystallinity nature of films was checked by X-ray diffraction. At macroscopic scale, the flexibility of the films increased, which could favor the reorientation of the macromolecules.

Abstract: The effect of glycerol content on the physical properties of gelatin-based edible films was studied in this work, on the basis of the interactions between the plasticizer and polymeric matrix. In this work, some non-usual techniques were used to characterize edible films. For dielectric measurements and infrared spectroscopy, these films were conditioned in silica gel in order to minimize the water effect. For other analysis, the films were conditioned in NaBr. Infrared spectroscopy showed no apparent changes in the position peaks, suggesting an absence of new interactions between the plasticizer and film matrix. It seems that the plasticizers only occupy some specific regions between the polymeric matrix, increasing their distance, and thus, affecting their mobility, which results in more flexible films. Dielectric constant of the films increased with plasticizer content, and decreased over silica gel conditioning. The polarizability was found to arise mainly from water molecules present in the film. Microwave response was found to be also sensitive to water content in the films, due to plasticizer hydrophilic nature. According to the diffractograms, gelatin films presented essentially an amorphous nature, independently of the glycerol content. The results suggest, therefore, that the glycerol induces no chemical modifications in the films.

Abstract: Photografting of bifunctional photolinker on biocompatible amphiphilic copolymers, such as PCL-b-PEGs and PLGA-b-PEGs, has been developed as a practical and versatile strategy for the materials functionalisation. Depending on the copolymer nature (block length, % of crystallinity) and the experimental conditions we could selectively direct the grafting on the hydrophilic PEG segments. The resulting copolymers were further derivatized with molecules of interest (RGD-peptides, LDV-peptides, “home-made”peptidomimetics, mannose derivatives,…) by substitution of the O-succinimidyl ester of the photolinker. The derivatization rates were controlled by radiolabelling, colorimetric assay and XPS spectroscopy. The functionalized copolymers were used in the formulation of nanoparticles displaying the ligands on their outer-shell. This nanoparticulate system was successfully employed for the oral vectorisation of antigen and for the targeted delivery of an anticancer drug.

Abstract: Magnetorheological elastomers (MREs) were obtained by mixing soft polyurethane and carbonyl-iron particles. The effect of the volume fraction of the ferromagnetic particles on the MREs microstructure and properties, as well as their arrangement in relation to the external magnetic field were investigated. As a ferromagnetic component carbonyl–iron powder, with particle size from 6-9µm, was used. The amount of the carbonyl iron particles was varied from 1.5 to 33.0 %(v/v). The samples were produced with randomly dispersed and aligned carbonyl iron particles. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The rheological properties (G’, G’’ and tan δ) of the MRE were tested without and with the application of the magnetic field. It was found that the microstructure of MREs, particularly the amount and arrangement of the carbonyl-iron particles, has a significant influence on their rheological and damping properties.

Abstract: The present work evaluates the combination effect of hindered amine light stabilizers (HALS) and ultraviolet absorbers (UVA) on the ultraviolet (UV) stability of acrylonitrile-butadiene-styrene (ABS). Thus, two types of light stabilizers, Tinuvin P and Chimassorb 119 FL, were used to improve the ABS endurance against UV. Stabilized ABS samples were submitted to accelerated weathering in a Xenontest 150 S chamber, according to standard methods, in order to predict copolymer lifetime within a commercially acceptable time period. Infrared spectroscopy with attenuated total reflectance accessory (FTIR-ATR) was used to follow chemical modifications that occur on the material surface as a consequence of degradation process. While non-stabilized ABS samples loose the butadiene component in the first 22 h of exposure, in stabilized samples submitted to same accelerated conditions this component only disappears after 150 h of exposure. Non-stabilized and stabilized ABS samples present a similar yellowing behavior, a gradually increase with exposure time. Nevertheless, as expected, color modifications are less pronounced for stabilized ABS samples. The results obtained suggest that a better performance was achieved for stabilized ABS samples with Tinuvin P and Chimassorb 119 FL, which is very important to extend the copolymer lifetime.