Página 8 dos resultados de 18179 itens digitais encontrados em 0.011 segundos

Paclitaxel-loaded PLGA nanoparticles: preparation, physicochemical characterization and in vitro anti-tumoral activity

Fonseca, Cristina; Simões, Sérgio; Gaspar, Rogério
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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The main objective of this study was to develop a polymeric drug delivery system for paclitaxel, intended to be intravenously administered, capable of improving the therapeutic index of the drug and devoid of the adverse effects of Cremophor® EL. To achieve this goal paclitaxel (Ptx)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (Ptx-PLGA-Nps) were prepared by the interfacial deposition method. The influence of different experimental parameters on the incorporation efficiency of paclitaxel in the nanoparticles was evaluated. Our results demonstrate that the incorporation efficiency of paclitaxel in nanoparticles was mostly affected by the method of preparation of the organic phase and also by the organic phase/aqueous phase ratio. Our data indicate that the methodology of preparation allowed the formation of spherical nanometric (<200 nm), homogeneous and negatively charged particles which are suitable for intravenous administration. The release behaviour of paclitaxel from the developed Nps exhibited a biphasic pattern characterised by an initial fast release during the first 24 h, followed by a slower and continuous release. The in vitro anti-tumoral activity of Ptx-PLGA-Nps developed in this work was assessed using a human small cell lung cancer cell line (NCI-H69 SCLC) and compared to the in vitro anti-tumoral activity of the commercial formulation Taxol®. The influence of Cremophor® EL on cell viability was also investigated. Exposure of NCI-H69 cells to 25 [mu]g/ml Taxol® resulted in a steep decrease in cell viability. Our results demonstrate that incorporation of Ptx in nanoparticles strongly enhances the cytotoxic effect of the drug as compared to Taxol®...

Characterization of insulin-loaded alginate nanoparticles produced by ionotropic pre-gelation through DSC and FTIR studies

Sarmento, Bruno; Ferreira, Domingos; Veiga, Francisco; Ribeiro, António
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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Insulin-loaded nanoparticles were prepared by ionotropic pre-gelation of alginate with calcium chloride followed by complexation between alginate and chitosan. The influence of the pH and stoichiometry relationship between polyelectrolytes providing individual particles with a nano-scale size was assessed by photon correlation spectroscopy (PCS) and scanning electron microscopy (SEM). Insulin-polyelectrolyte interactions at varying pH and polyelectrolytes stoichiometry were assessed by differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) studies. Individual and smaller sizing nanoparticles, around 800 nm, were obtained at pH 4.7 with an alginate:chitosan mass ratio of 6:1. Thermograms of insulin-loaded nanoparticles originated shifts on same unloaded nanoparticle peaks and suggested polyelectrolytes-protein interactions at pH around 4.5-5.0. FTIR spectra of insulin-loaded nanoparticles showed amide absorption bands characteristic of protein spectra and revealed the formation of new chemical entities.; http://www.sciencedirect.com/science/article/B6TFD-4JKYTNH-1/1/f2878177436b8ca802aa251efe948a9f

Quantification of MgO surface excess on the SnO(2) nanoparticles and relationship with nanostability and growth

GOUVEA, Douglas; PEREIRA, Gilberto J.; GENGEMBRE, Leon; STEIL, Marlu C.; ROUSSEL, Pascal; RUBBENS, Annick; HIDALGO, Pilar; CASTRO, Ricardo H. R.
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
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In this work, we experimentally showed that the spontaneous segregation of MgO as surface excess in MgO doped SnO(2) nanoparticles plays an important role in the system`s energetics and stability. Using Xray fluorescence in specially treated samples, we quantitatively determined the fraction of MgO forming surface excess when doping SnO(2) with several different concentrations and established a relationship between this amount and the surface energy of the nanoparticles using the Gibbs approach. We concluded that the amount of Mg ions on the surface was directly related to the nanoparticles total free energy, in a sense that the dopant will always spontaneously distribute itself to minimize it if enough diffusion is provided. Because we were dealing with nanosized particles, the effect of MgO on the surface was particularly important and has a direct effect on the equilibrium particle size (nanoparticle stability), such that the lower the surface energy is, the smaller the particle sizes are, evidencing and quantifying the thermodynamic basis of using additives to control SnO(2) nanoparticles stability. (C) 2010 Elsevier B.V. All rights reserved.; Brazilian agency FAPESP

Ultrastructural characterization of CD133(+) stem cells bound to superparamagnetic nanoparticles: possible biotechnological applications

PAVON, L. F.; GAMARRA, L. F.; MARTI, L. C.; AMARO JUNIOR, E.; MOREIRA-FILHO, C. A.; CAMARGO-MATHIAS, M. I.; OKAMOTO, O. K.
Fonte: BLACKWELL PUBLISHING Publicador: BLACKWELL PUBLISHING
Tipo: Artigo de Revista Científica
ENG
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CD133 antigen is an integral membrane glycoprotein that can bind with different cells. Originally, however. this cellular surface antigen was expressed in human stem cells and in various cellular progenitors of the haematopoietic system. Human cord blood has been described as an excellent source of CD133(+) haematopoietic progenitor cells with a large application potential. One of the main objectives of the present study is to describe for the first time the ultrastructural characteristics of CD133(+) stem cells using transmission electronic microscopy. Another objective of the manuscript is to demonstrate through transmission electronic microscopy the molecular image of magnetic nanoparticles connected to the stein cells of great biotechnological importance, as well as demonstrating the value of this finding for electronic paramagnetic resonance and its related nanobioscientific value. Ultrastructural results showed the monoclonal antibody anti-CD133 bound to the superparamagnetic nanoparticles by the presence of electrondense granules in cell membrane, as well as in the cytoplasm, revealing the ultrastructural characteristics of CD133(+) cells, exhibiting a round morphology with discrete cytoplasmic projections, having an active nucleus that follows this morphology. The cellular cytoplasm was filled up with mitochondrias...

Magnetic coupled electrochemistry: Exploring the use of superparamagnetic nanoparticles for capturing, transporting and concentrating trace amounts of analytes

CONDOMITTI, Ulisses; ZUIN, Andre; NOVAK, Miguel A.; ARAKI, Koiti; TOMA, Henrique Eisi
Fonte: ELSEVIER SCIENCE INC Publicador: ELSEVIER SCIENCE INC
Tipo: Artigo de Revista Científica
ENG
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We propose the use of functionalized superparamagnetic nanoparticles for capturing, and transporting analytes, in association with an external miniature magnet to deposit such nanocarrier species at the electrode surface. This approach can be employed for the electroanalytical determination of chemical species capable of interacting with the nanoparticles, or in the opposite case, to block their response at the electrode surface. The concept was successfully demonstrated by using aminofunctionalized nanoparticles to block the discharge of hexacyanoferrate(II) ions, and to enhance the signals of aquapentacyanoferrate(II) ions via coordination to the surface amino groups. Selective analysis was also performed for silver ions, surpassing the stripping methods in terms of versatility and usefulness. (C) 2010 Elsevier B.V. All rights reserved.

Femtosecond laser induced synthesis of Au nanoparticles mediated by chitosan

Ferreira, P. H. D.; Vivas, M. G.; De Boni, Leonardo; dos Santos, D. S., Jr.; Balogh, Déborah Teresia; Misoguti, Lino; Mendonca, Cleber Renato
Fonte: OPTICAL SOC AMER; WASHINGTON Publicador: OPTICAL SOC AMER; WASHINGTON
Tipo: Artigo de Revista Científica
ENG
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This paper reports the synthesis of Au nanoparticles by 30-fs pulses irradiation of a sample containing HAuCl4 and chitosan, a biopolymer used as reducing agent and stabilizer. We observed that it is a multi-photon induced process, with a threshold irradiance of 3.8 x 10(11) W/cm(2) at 790 nm. By transmission electron microscopy we observed nanoparticles from 8 to 50 nm with distinct shapes. Infrared spectroscopy indicated that the reduction of gold and consequent production of nanoparticles is related to the fs-pulse induced oxidation of hydroxyl to carbonyl groups in chitosan. (C) 2011 Optical Society of America; Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP); Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq); Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)

Magnetic nanohydrometallurgy: A promising nanotechnological approach for metal production and recovery using functionalized superparamagnetic nanoparticles

Condomitti, Ulisses; Zuin, Andre; Silveira, Alceu T.; Araki, Koiti; Toma, Henrique E.
Fonte: ELSEVIER SCIENCE BV; AMSTERDAM Publicador: ELSEVIER SCIENCE BV; AMSTERDAM
Tipo: Artigo de Revista Científica
ENG
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We report on a new, promising nanotechnological approach for hydrometallurgy based on recyclable, chemically functionalized superparamagnetic nanoparticles. In this process, the metal ions (e.g. Cu2+) are captured by the nanoparticles and confined at the electrode surface by means of an external magnet. Due to the pre-concentration effect the electrodeposition process is greatly improved, yielding the pure metal in a much shorter time in comparison with the conventional electrodeposition process. After the electrolysis, the magnetic nanoparticles are ready to return to the process. The proposed strategy can advantageously be incorporated in hydrometallurgy, reducing the number of steps associated with complexation, organic solvent extraction, metal release and diffusional electroprocessing, leading to a more sustainable technology. (C) 2012 Elsevier B.V. All rights reserved.; FAPESP; FAPESP; CNPq; CNPq; PETROBRAS; PETROBRAS

Polymeric Nanoparticles as Oral Delivery Systems for Encapsulation and Release of Polyphenolic Compounds: Impact on Quercetin Antioxidant Activity & Bioaccessibility

Pool, Hector; Quintanar, David; Dios Figueroa, Juan de; Bechara, Etelvino Jose Henriques; McClements, David Julian; Mendoza, Sandra
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
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A delivery system containing polymeric (Eudragit) nanoparticles has been developed for encapsulation and controlled release of bioactive flavonoids (quercetin). Nanoparticles were fabricated using a solvent displacement method. Particle size, morphology, and charge were measured by light scattering, electron microscopy and zeta-potential. Encapsulation efficiency (EE) and release profiles were determined using electrochemical methods. Molecular interactions within the particle matrix were characterized by X-ray diffraction, differential scanning calorimetry, and infrared spectroscopy. Antioxidant properties of free and encapsulated quercetin were analyzed by TBARS and fluorescence spectroscopy. Bioaccessibility of quercetin was evaluated using an in vitro digestion model. Relatively small (d a parts per thousand aEuro parts per thousand 370 nm) anionic polymeric nanoparticles were formed containing quercetin in a non-crystalline form (EE a parts per thousand aEuro parts per thousand 67 %). The main interaction between quercetin and Eudragit was hydrogen bonding. Encapsulated quercetin remained stable during 6 months storage and maintained its antioxidant activity. Quercetin bioaccessibility within simulated small intestinal conditions was improved by encapsulation. The knowledge obtained from this study will facilitate the rational design and fabrication of polymeric nanoparticles as oral delivery systems for encapsulation...

Effects of precursor on the morphology and size of ZrO2 nanoparticles, synthesized by sol-gel method in non-aqueous medium

Siddiqui,Mohammed Rafiq Hussain; Al-Wassil,Abdulaziz Ibrahim; Al-Otaibi,Abdullah Mohmmed; Mahfouz,Refaat Mohamad
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2012 EN
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Pure zirconium oxide (ZrO2) nanoparticles with diameters 10-25 nm were synthesized from ZrOCl2.8H2O and Zr(SO4)2.H2O with benzyl alcohol as non-aqueous solvent medium using sol-gel method. Sodium lauryl sulfate was added as surfactants to control the particle size. The synthesized ZrO2 nanoparticles have a mixture of tetragonal and monoclinic structure. The XRD showed the purity of obtained ZrO2 nanoparticles with tetragonal and monoclinic phase and the crystallite size for ZrOCl2.8H2O precursor was estimated to be 18.1 nm and that from Zr(SO4)2.H2O was 9.7 nm. The transmission electron microscopy and scanning electron microscopic studies also shows different sizes of nanoparticles and different morphology depending on the precursor used for the synthesis of ZrO2 nanoparticles

Surface Functionalization of Monodisperse Magnetic Nanoparticles

Lattuada, Marco; Hatton, T. Alan
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 11308 bytes; application/pdf
EN
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We present a systematic methodology to functionalize magnetic nanoparticles through surface-initiated atom-transfer radical polymerization (ATRP). The magnetite nanoparticles are prepared according to the method proposed by Sun et al. (2004), which leads to a monodisperse population of ~ 6 nm particles stabilized by oleic acid. The functionalization of the nanoparticles has been performed by transforming particles into macro-initiators for the ATRP, and to achieve this two different routes have been explored. The first one is the ligand-exchange method, which consists of replacing some oleic acid molecules adsorbed on the particle surface with molecules that act as an initiator for ATRP. The second method consists in using the addition reaction of bromine to the oleic acid double bond, which turns the oleic acid itself into an initiator for the ATRP. We have then grown polymer brushes of a variety of acrylic polymers on the particles, including polyisopropylacrylamide and polyacrylic acid. The nanoparticles so functionalized are water soluble and show responsive behavior: either temperature responsive behavior when polyisopropylacrylamide is grown from the surface or PH responsive in the case of polyacrylic acid. This methodology has potential applications in the control of clustering of magnetic nanoparticles.; Singapore-MIT Alliance (SMA)

Desenvolvimento e caracterização de nanopartículas lipídicas contendo topotecano; Development and characterization of lipid nanoparticles containing topotecan

SOUZA, Leonardo Gomes
Fonte: Universidade Federal de Goiás; BR; UFG; Mestrado em Ciências Farmacêuticas; Ciências da Saúde - Farmácia Publicador: Universidade Federal de Goiás; BR; UFG; Mestrado em Ciências Farmacêuticas; Ciências da Saúde - Farmácia
Tipo: Dissertação Formato: application/pdf
POR
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Topotecan (TPT), hydrophilic semisynthetic analogue of camptothecin, is a topoisomerase I inhibitor anticancer agent. Encapsulation of TPT in nanocarriers can protect him from inactivation on plasmatic pH and P-glycoprotein (P-gp) mediated resistance. In this study, solid lipid nanoparticles (SLN) were produced by three different methods: cold high pressure homogenization (CHPH), double emulsion prepare (DEMP) and microemulsion dilution (MMD). Derivative systems from NLS, nanostructured lipid carriers (NLC) were produced only by MMD. Temperature proved to be a limiting factor in producing nanoparticles loaded TPT and must be strictly controlled. Nanoparticles produced by MMD (SLN and NLC) presented best encapsulation efficiency, drug loading and particle size distribution. These particles presented 150 nm average diameter, 0.2 PdI and -45 mV average zeta potential. Despite the hydrophilic drugs encapsulation to be a hard work, lipid nanoparticles loaded TPT presented 6% drug loading and an encapsulation efficiency biggest then 95%. Encapsulation of TPT in lipid nanoparticles sustained drug release by 12 hours and protected the drug from degradation at pH 7,4 at 37°C. Drug nanoencapsulation also increased his citotoxicity on K562 leucemic cells at 2 and 24 hours. There weren t differences between NLC and SLN on release...

Mesoporous silica nanoparticles act as a self-adjuvant for ovalbumin model antigen in mice

Mahony, D.; Cavallaro, A.; Stahr, F.; Mahony, T.; Qiao, S.; Mitter, N.
Fonte: Wiley - VCH Verlag GmbH & Co KGaA Publicador: Wiley - VCH Verlag GmbH & Co KGaA
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
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Immunization to the model protein antigen ovalbumin (OVA) is investigated using MCM-41 mesoporous silica nanoparticles as a novel vaccine delivery vehicle and adjuvant system in mice. The effects of amino surface functionalization and adsorption time on OVA adsorption to nanoparticles are assessed. Amino-functionalized MCM-41 (AM-41) shows an effect on the amount of OVA binding, with 2.5-fold increase in binding capacity (72 mg OVA/g AM-41) compared to nonfunctionalized MCM-41 (29 mg OVA/g MCM-41). Immunization studies in mice with a 10 μg dose of OVA adsorbed to AM-41 elicits both antibody and cell-mediated immune responses following three subcutaneous injections. Immunizations at a lower 2 μg dose of OVA adsorbed to AM-41 particles results in an antibody response but not cell-mediated immunity. The level of antibody responses following immunization with nanoformulations containing either 2 μg or 10 μg of OVA are only slightly lower than that in mice which receive 50 μg OVA adjuvanted with QuilA, a crude mixture of saponins extracted from the bark of the Quillaja saponaria Molina tree. This is a significant result, since it demonstrates that AM-41 nanoparticles are self-adjuvanting and elicit immune responses at reduced antigen doses in vivo compared to a conventional delivery system. Importantly...

Green synthesis and characterization of silver nanoparticles produced using 'Arbutus Unedo' leaf extract

Kouvaris, P; Delimitis, A; Zaspalis, V; Papadopoulos, D; Tsipas, Sophia Alexandra; Michailidis, N
Fonte: Elsevier Publicador: Elsevier
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article
Publicado em /06/2012 ENG
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Metallic nanoparticles have received great attention from chemists, physicists, biologists and engineers who wish to use them for the development of a new generation of nanodevices. In the present study silver nanoparticles were synthesized from aqueous silver nitrate through a simple and eco-friendly route using leaf broth of Arbutus unedo, which acted as a reductant and stabilizer simultaneously. The aqueous silver ions when exposed to the leaf broth were reduced and stabilized over long periods of time resulting in the green synthesis of surface functionalized silver nanoparticles. The bio-reduced silver nanoparticles were appropriately characterized. The results revealed the formation of single crystalline Ag nanoparticles with a narrow size distribution for each sample. The particles, although discrete, were predominately coated with the organic leaf extract forming small aggregates, which makes them stable over long time periods and highly appropriate for coatings or biotechnology applications.

Uptake studies in rat Peyer's patches, cytotoxicity and release studies of alginate coated chitosan nanoparticles for mucosal vaccination

Borges, Olga; Cordeiro-da-Silva, Anabela; Romeijn, Stefan G.; Amidi, Maryam; Sousa, Adriano de; Borchard, Gerrit; Junginger, Hans E.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
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The design of particulate vaccine delivery systems, particularly for mucosal surfaces, has been a focus of interest in recent years. In this context, we have previously described the development and the characterization of a new nanosized delivery system, consisting of a model antigen adsorbed to chitosan particles and coated with sodium alginate. In the present work the ovalbumin release profiles from these coated nanoparticles in different pH buffers were investigated and compared to those of the uncoated particles. Cytotoxicity of the polymers and nanoparticles was assessed using the MTT assay. Finally, particle uptake studies in rat Peyer's patches were performed. It was demonstrated that the coating of the nanoparticles with sodium alginate not only avoided a burst release observed with uncoated particles but also increased the stability of the particles at pH 6.8 and 7.4 at 37 °C. At neutral pH, the release was lower than 5% after 3.5 h incubation in a low ionic strength buffer. For both, chitosan and alginate polymers, and for the nanoparticles, comparable cell viability data close to 100%, were obtained. Additionally, based on confocal laser scanning microscopy observations, it was shown that alginate coated nanoparticles were able to be taken up by rat Peyer's patches...

Produção de sistemas híbridos à base de hidrogel de Pluronic e nanopartículas porosas de sílica para aplicação antitumoral; Production of hybrid systems based on Pluronic hydrogel and porous silica nanoparticles for anticancer application

Camila Pedroso Silveira Bueno
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 03/03/2015 PT
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Um dos principais problemas da quimioterapia, atualmente, é o uso de fármacos extremamente citotóxicos, cuja falta de especificidade acarreta na ação sob todos os tipos de células, incluindo as saudáveis, gerando efeitos colaterais intensos, que prejudicam a terapia em si. Nesse sentido, os nanomateriais oferecem uma opção terapêutica valiosa, pois podem conjugar especificidade e liberação sustentada do fármaco, prevenindo-o de ser degradado prematuramente e permitindo o uso de menores doses. A fim de desenvolver um sistema do tipo drug depot que servisse como plataforma para a liberação sustentada de fármacos, foram produzidas, neste trabalho, formulações baseadas em nanopartículas mesoporosas de sílica e hidrogel de Pluronic F-127, associadas a dois fármacos individualmente: doxorrubicina e sildenafila. As nanopartículas mesoporosas de sílica são boas alternativas para uso médico, pois são biocompatíveis e possuem grande volume de poros, atuando como carreadoras, promovendo a liberação sustentada do fármaco. O Pluronic F-127 atua como agente gelificante e promove uma liberação prolongada das nanopartículas e do fármaco incorporado, uma vez que é um polímero termo-reversível que permite a formação de um hidrogel à temperatura ambiente. A doxorrubicina é um antibiótico antitumoral de largo espectro...

Magnetic and elastic anisotropy in magnetorheological elastomers using nickel-based nanoparticles and nanochains

Landa, Romina Ailín; Antonel, Paula Soledad; Ruiz, Mariano Manuel; Pérez, Oscar E.; Butera, Alejandro Ricardo; Jorge, Guillermo Antonio; Oliveira, Cristiano; Negri, Martín
Fonte: Amer Inst Physics Publicador: Amer Inst Physics
Tipo: info:eu-repo/semantics/article; info:ar-repo/semantics/artículo; info:eu-repo/semantics/publishedVersion Formato: application/pdf
ENG
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Nickel (Ni) based nanoparticles and nanochains were incorporated as fillers in polydimethylsiloxane (PDMS) elastomers and then these mixtures were thermally cured in the presence of a uniform magnetic field. In this way, macroscopically structured-anisotropic PDMS-Ni based magnetorheological composites were obtained with the formation of pseudo-chains-like structures (referred as needles) oriented in the direction of the applied magnetic field when curing. Nanoparticles were synthesized at room temperature, under air ambient atmosphere (open air, atmospheric pressure) and then calcined at 400 °C (in air atmosphere also). The size distribution was obtained by fitting SAXS experiments with a polydisperse hard spheres model and a Schulz-Zimm distribution, obtaining a size distribution centered at (10.0 - 0.6) nm with polydispersivity given by sigma= (8.0 ± 0.2) nm. The SAXS, XRD and TEM experiments are consistent with single crystal nanoparticles of spherical shape (average particle diameter obtained by TEM: (12 ± 1) nm). Nickel-based nanochains (average diameter: 360 nm; average length: 3 mm, obtained by SEM; aspect ratio=length/diameter ~10) were obtained at 85 ºC and ambient atmosphere (open air, atmospheric pressure). The magnetic properties of Ni-based nanoparticles and nanochains at room temperature are compared and discussed in terms of surface and size effects. Both Ni-based nanoparticles and nanochains were used as fillers for obtaining the PDMS structured magnetorheological composites...

Experimental study of the structural and magnetic properties of -Fe2O3 nanoparticles

Yusuf, S. M.; Teresa, José María de; Ibarra, M. Ricardo
Fonte: American Physical Society Publicador: American Physical Society
Tipo: Artículo Formato: 259768 bytes; application/pdf
ENG
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11 pages, 4 tables, 13 figures.-- et al.; Structural and magnetic properties of -Fe2O3 nanoparticles annealed at 200 and 250 °C have been studied by using high resolution transmission electron microscopy (TEM), electron energy loss spectroscopy, x-ray diffraction, neutron diffraction, polarized small angle neutron scattering (SANS) and dc magnetization techniques. Here we have dealt with an important problem of the symmetry of crystal structure of -Fe2O3 nanoparticles with cation vacancy distribution. Present study also correlates various structural and magnetic results that have been obtained for -Fe2O3 nanoparticles using various experimental techniques. Analysis of x-ray and neutron diffraction data shows cation vacancies at the octahedral site, consistent with the space group P43 3 2. A log-normal distribution of particle size for both the samples has been found. A good crystallinity has been found from TEM, x-ray diffraction and neutron diffraction studies. Neutron diffraction study at room temperature confirms a ferrimagnetic ordering of tetrahedral and octahedral site moments with a net moment of ~1.58 and 1.83 µB per formula unit for the samples annealed at 200 and 250 °C, respectively. SANS data analysis is consistent with a mass fractal spatial arrangement of these nanoparticles with a fractal dimension of 1.25. The SANS results are consistent with the same form factor for both the chemical particle size and the magnetic particle size indicating the absence of any observable shell with disordered spins. Superparamagnetic behavior of noninteracting nanoparticles with a log-normal distribution of blocking temperature (with a particle moment of ~28 000 µB for the sample annealed at 200 °C) is found in our dc magnetization study at room temperature.; Financial support from Paul Scherrer Institute by the NMI3 project and the Spanish Ministry of Science (through the projects SAB2003-0255...

The life of nanoparticles in contact with biological media and entities

Tran Thi Thanh, Ngoc; Pascual i Gainza, Jordi
Fonte: [Barcelona] : Universitat Autònoma de Barcelona, Publicador: [Barcelona] : Universitat Autònoma de Barcelona,
Tipo: Tesis i dissertacions electròniques; info:eu-repo/semantics/doctoralThesis; info:eu-repo/semantics/publishedVersion Formato: application/pdf
Publicado em //2015 ENG
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Para contribuir al creciente requerimiento de una caracterización rigurosa de los materiales utilizados en el campo de nanotoxicología, el estudio de los problemas de toxicidad y seguridad de los nanomateriales, esta tesis tiene como objetivo describir la evolución de la identidad de las nanopartículas (capítulos 2 y 3), centrándose en la plata, un material muy comercializado, cuando se expone a entornos biológicos. Esta identidad completa puede ser el resultado de procesos individuales, incluyendo la agregación, la aglomeración, la adsorción de proteínas (o biomoléculas), la corrosión y la disolución, o todos ellos a la vez. La reactividad química de las nanopartículas, lo que hace de ellas unos materiales muy útiles para muchos productos, puede ser, al mismo tiempo, motivo de preocupación sobre el efecto nocivo para la salud. Esta preocupación puede ser abordada mediante el aumento de la persistencia de las nanopartículas. Sin embargo, también hay que considerar la posibilidad de perder la reactividad deseada debido al aumento de la persistencia. Por lo tanto, es importante controlar y equilibrar estas dos propiedades. En tales circunstancias, esta tesis también tiene como objetivo investigar la reactividad química y la persistencia de las nanopartículas de plata (AgNPS) en medios biológicos...

Microstructural characterization of L10 FePt/MgO nanoparticles with perpendicular anisotropy

Zhang, Y.; Wan, J.; Skumryev, Vassil; Stoyanov, S.; Huang, Y.; Hadjipanayis, G. C.; Weller, D.
Fonte: Universidade Autônoma de Barcelona Publicador: Universidade Autônoma de Barcelona
Tipo: Artigo de Revista Científica Formato: application/pdf
Publicado em //2004 ENG
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L10 FePt nanoparticles with perpendicular magnetic anisotropy were fabricated on a heated MgO substrate by using an atomic deposition technique. The microstructure of the FePt nanoparticles was studied by transmission electron microscopy and high resolution transmission electron microcopy. The as-made L10 FePt nanoparticles are isolated and have a faceted morphology with a bimodal distribution of particle size as small as 2.5 nm. A semicoherent atomic interface between the FePt nanoparticles and the MgO substrate is observed. The room temperature coercivity of these FePt nanoparticles was measured via both superconducting quantum interference device and magneto-optical Kerr effect techniques and found to be as high as 6.7 kOe.

Dichloro(bis[diphenylthiourea])cadmium complex as a precursor for HDA-capped CdS nanoparticles and their solubility in water

Shumbula,Poslet M.; Moloto,Makwena J.; Tshikhudo,Tshinyadzo R.; Fernandes,Manuel
Fonte: South African Journal of Science Publicador: South African Journal of Science
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2010 EN
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A single-source precursor route has been explored by using the diphenylthiourea cadmium complex as the source of cadmium sulphide (CdS) nanoparticles. The reaction was carried out using hexadecylamine (HDA) as the solvent and stabilising agent for the particles. The phenylthiourea complex was synthesised and characterised by means of a combination of spectroscopic techniques, microanalysis and X-ray crystal structural analysis. The diphenylthiourea complex was thermolysed in HDA at 120 ºC for 1 h to produce CdS nanoparticles. The CdS nanoparticles prepared were made water-soluble via a ligand exchange reaction involving the use of pyridine to displace HDA. The pyridine was, in turn, replaced by glucose and glucuronic acid. The absorption and emission spectra showed the typical features of quantum confinement for the nanoparticles for both HDA-capped and glucose- or glucuronic acid-capped CdS nanoparticles. The change in the capping groups, from HDA to glucose and glucuronic acid, resulted in absorption and emission features that were almost similar, with only slight red-shifting and tailing.