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Avaliação das propriedades mecânicas e microestrutura de um ionómero de vidro experimental reforçado com nano partículas

Silva, Joel Batoca da
Fonte: [s.n.] Publicador: [s.n.]
Tipo: Dissertação de Mestrado
Publicado em //2013 POR
Relevância na Pesquisa
36.82%
Projeto de Pós-Graduação/Dissertação apresentado à Universidade Fernando Pessoa como parte dos requisitos para obtenção do grau de Mestre em Medicina Dentária; Os cimentos de ionómero de vidro são materiais restauradores que possuem um alto potencial de proteção do complexo dentina-polpa dado pela sua capacidade de libertação de flúor associado ao selamento marginal resultante de uma adesão química às estruturas dentárias. Entretanto, apresentam pobres propriedades físico-mecânicas quando comparado com as mais recentes resinas compostas. Este trabalho teve como principal objectivo melhorar as propriedades mecânicas do cimento de ionómero de vidro pela incorporação de nano partículas de alumina e/ou zircónia à composição de um ionómero de vidro comercialmente disponível no mercado. Foi realizado um estudo experimental in vitro com 9 grupos (n = 10) de amostras cilíndricas (6 x 4 mm) de cimento de ionómero de vidro modificado com resina (Vitremer, 3M, USA) com diferentes conteúdos de nano-partículas de alumina e/ou zircónia. Uma resina composta nano-híbrida (GrandioSO, VOCO, Germany) foi usada para estabelecer uma comparação com os cimentos de ionómero de vidro reforçados pela incorporação de nano partículas. Foi feita a caracterização das amostras por testes de compressão axial...

Interação de pontos quânticos com fotossensibilizadores orgânicos na presença de estruturas nano-organizadas; Interaction of quantum dots with organic photosensitizers in the presence of nano-organized structures

Parra, Gustavo Gimenez
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 19/01/2015 PT
Relevância na Pesquisa
36.74%
O sucesso de tratamento de câncer depende do seu diagnóstico e tratamento nas etapas iniciais da doença. Isso estimula a busca de novos métodos de diagnóstico e de tratamento sensíveis e tecnicamente simples. Entre esses métodos, o diagnóstico por fluorescência (DPF) e a fotoquimioterapia (FQT) atraem uma atenção especial, sendo não invasivos, sensíveis e fácil de usar. Os fotossensibilizadores (FS) atualmente utilizados em DPF e FQT são corantes orgânicos, os quais possuem algumas desvantagens, tais como instabilidade fotoquímica e baixa seletividade. Os pontos quânticos (PQ) são candidatos promissores para substituírem os FS clássicos por serem fotoestáveis, apresentarem amplo e intenso espectro de absorção óptica e luminescência com alto rendimento quântico. Contudo a iteração entre FS clássicos e os PQ pode aumentar a eficiência de ambos devido a transferência de energia entre eles. O objetivo geral deste trabalho foi estudar os processos da interação de FS orgânicos (as porfirinas PPh, TMPyP e TPPS4) com PQs (CdTe e CdSe/ZnS), funcionalizados com diferentes grupos, em solução aquosa e na presença de modelos nano-organizados de estruturas biológicas com a finalidade de avaliar seu potencial para aplicação em Fotoquimioterapia e Diagnóstico por Fluorescência. Dedicamos especial atenção aos processos de transferência de energia e de carga entre os PQs e os FS. Os PQs interagem efetivamente com as PPh...

Endothelial cell colonization and angiogenic potential of combined nano- and micro-fibrous scaffolds for bone tissue engineering

Santos, Marina I.; Tuzlakoglu, K.; Fuchs, Sabine; Gomes, Manuela E.; Peters, K.; Piskin, Erhan; Reis, R. L.; Kirkpatrick, C. James; Unger, Ronald E.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /06/2008 ENG
Relevância na Pesquisa
36.78%
Presently the majority of tissue engineering approaches aimed at regenerating bone relies only on postimplantation vascularization. Strategies that include seeding endothelial cells (ECs) on biomaterials and promoting their adhesion, migration and functionality might be a solution for the formation of vascularized bone. Nano/micro-fiber-combined scaffolds have an innovative structure, inspired by extracellular matrix (ECM) that combines a nano-network, aimed to promote cell adhesion, with a micro-fiber mesh that provides the mechanical support. In this work we addressed the influence of this nano-network on growth pattern, morphology, inflammatory expression profile, expression of structural proteins, homotypic interactions and angiogenic potential of human EC cultured on a scaffold made of a blend of starch and poly(caprolactone). The nano-network allowed cells to span between individual micro-fibers and influenced cell morphology. Furthermore, on nano-fibers as well as on micro-fibers ECs maintained the physiological expression pattern of the structural protein vimentin and PECAM-1 between adjacent cells. In addition, ECs growing on the nano/micro-fiber-combined scaffold were sensitive to pro-inflammatory stimulus. Under pro-angiogenic conditions in vitro...

Effects of nano CuO on aquatic decomposers : from community to cellular responses

Pradhan, Arunava; Seena, Sahadevan; Helm, Stefan; Gerth, katharina; Krauss, Gerd-Joachim; Wesenberg, Dirk; Schlosser, Dietmar; Pascoal, Cláudia; Cássio, Fernanda
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /05/2012 ENG
Relevância na Pesquisa
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Acknowledgement: FEDER-POFC-COMPETE, DAAD and FCT supported this work (PEst-C/BIA/UI4050/2011, FCT-DAAD-2010-2011, NANOECOTOX-PTDC/AAC-AMB/121650/2010) and A. Pradhan (SFRH/BD/45614/2008).; ntensive use of metal nanoparticles increases the chance of their release into freshwaters that may pose risk to biota and associated ecological processes. In streams, microbes play a key role in detritus foodwebs transferring carbon and energy from plant litter to invertebrate shredders. Here, we investigated the effects of nano CuO (<50 nm, nanopowder, Sigma) on aquatic detritus foodwebs by examining i) leaf-litter decomposition by bacterial and fungal communities, ii) cellular damage and physiological responses of fungal populations collected from non-polluted and metal-polluted streams, and iii) survival, growth and leaf consumption by an invertebrate shredder. Results were compared with those obtained with ionic copper. Stream-dwelling microbial communities were obtained by immersion of leaves in a non- polluted stream (Portugal). Microbial communities were exposed in microcosms to nano CuO (≤ 500 mg L-1) and Cu2+ (≤ 30 mg L-1). Leaf decomposition decreased with increasing concentrations of nano and ionic copper. Both copper forms reduced biomass of bacteria and fungi...

Betões de elevado desempenho com nano-partículas de TiO2 e cinzas volantes : resistência mecânica, durabilidade e custo

Martins, Tiago Manuel da Rocha; Aguiar, J. L. Barroso de; Jesus, Carlos M. G.; Torgal, Fernando Pacheco
Fonte: Universidade do Minho. Departamento de Engenharia Civil Publicador: Universidade do Minho. Departamento de Engenharia Civil
Tipo: Artigo de Revista Científica
Publicado em 29/03/2014 POR
Relevância na Pesquisa
36.74%
Os betões de elevado desempenho apresentam vantagens várias sobre os betões correntes nomeadamente elevada resistência e durabilidade. Estes materiais permitem a execução de estruturas com menor quantidade de aço e com uma vida útil superior, fatores cruciais para a eco-eficiência daquelas. Apesar disso as publicações sobre betões com nano-partículas são escassas, representando apenas 1% do total de publicações em revista internacional sobre estes materiais. As publicações sobre betões de elevado desempenho com nano-partículas são ainda mais reduzidas. O presente artigo apresenta resultados de uma investigação experimental sobre a resistência mecânica e a durabilidade de betões de elevado desempenho contendo nano-partículas de TiO2 e cinzas volantes. Os parâmetros de durabilidade foram avaliados com recurso a ensaios de absorção de água por imersão e por capilaridade, ensaios de ultra-sons, resistividade elétrica, difusão de cloretos e resistência ao ataque químico. Os resultados mostram que betões com um teor crescente de nano-partículas de TiO2 evidenciam uma redução da durabilidade. Mostram também que betões com 1% de nano-partículas de TiO2 e substituição parcial de cimento Portland por 30% de cinzas volantes apresentam uma elevada resistência mecânica (C55/C67) a par de uma elevada durabilidade. Contudo as nano-partículas de TiO2 agravam de forma muito significativa o custo dos betões.

Comportamento mecânico de compósitos de fibra de vidro/epoxy nano-reforçados

Silva, Henrique
Fonte: Instituto Politécnico de Viseu Publicador: Instituto Politécnico de Viseu
Tipo: Tese de Doutorado
Publicado em 22/12/2014 POR
Relevância na Pesquisa
36.74%
Os materiais compósitos laminados de matriz polimérica têm propriedades vantajosas tendo por isso uma ampla variedade de aplicações. Estes materiais são porém suscetíveis de sofrerem delaminações que podem debilitar consideravelmente as estruturas. Na direção da espessura do laminado as fibras não funcionam como um reforço efetivo, pelo que a resistência entre camadas é sempre menor que a resistência no plano. Neste trabalho estudam-se compósitos de fibra de vidro do tipo E, costurada sob a forma de tecido equilibrado tri-direcional e matriz epoxídica modificada com nano-argila montmorilonita organicamente modificada (OMMT) ou nanotubos de carbono de parede múltipla (MWCNT). A adição destes nanomateriais pretende melhorar as propriedades interfaciais e assim contribuir para melhorar o comportamento mecânico destes materiais. No fabrico dos compósitos trifásicos foi utilizado o processo de moldagem assistida a vácuo a partir do empilhamento de dez camadas de fibra de vidro previamente impregnadas com resina nano-modificada. Para caracterizar e comparar a Tenacidade à Fratura Interlaminar dos compósitos, fibra de vidro/epóxido foram realizados ensaios de Fratura Interlaminar, com solicitações de carga em Modo I...

Nano-structured alloy and composite coatings for high temperature applications

Gao,Wei; Li,Zhengwei
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/03/2004 EN
Relevância na Pesquisa
36.76%
Nano-structured materials often possess special properties that materials with identical compositions but ordinary grain size do not have. This paper reports our work on the surface nano-crystallisation and nano-structured alloy and composite coatings. A number of processing methods including magnetron sputtering, thermal spray and pulse electro-spark deposition have been used to produce surface nano-crystalline structure. The compositions and microstructures can be well controlled by using different targets or electrodes, nano-structured composites and adjusting processing parameters. Surface nano-structured coatings can provide special chemical, mechanical and electronic properties such as high temperature corrosion and corrosive wear resistance. It has potential applications such as turbine blades, engine parts for petrochemical, aerospace and electronic device industries. This paper is focused on the study of the interrelations between processing, microstructure and properties. Physical models have been established to explain the effects of nano-crystalline structure on the properties.

Fabrication and corrosion resistance of Mg-Zn-Y-based nano-quasicrystals alloys

Wang,Zhifeng; Zhao,Weimin; Qin,Chunling; Cui,Yan
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2012 EN
Relevância na Pesquisa
36.74%
A wedge-shaped copper mold was used to fabricate micro quasicrystals(QCs). Stable Mg-Zn-Y-based nano-QCs were directly synthesized through this simple route instead of crystallization from metallic glasses or complicated forming processes at high temperature. The study showed that on the tips of the wedge-shaped ingots, the minimum diameter of nano-QCs approach to 4~6 nm. The main size of nano-QCs is about 10~30 nm. The maximum microhardness of QCs has been dramatically improved to about HV440 which increased by about 280% compared with that of the petal-like QCs fabricated under common cast iron mold cooling conditions. Possessing a certain negative enthalpy of mixing and existence of Frank-Kasper-type phases determined the formation of Mg-Zn-Y-based nano-QCs. The further electrochemical studies showed that Mg71Zn26Y2Cu1 nano-QC alloy possess high corrosion resistance in simulated seawater and its corrosion resistance is much better than those of the Mg72Zn26Y2 and Mg71Zn26Y2Cu0.5 Ni0.5 nano-QC alloys.

Weatherability and Leach Resistance of Wood Impregnated with Nano-Zinc Oxide

Clausen, Carol A; Green, Frederick; Nami Kartal, S
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 15/06/2010 EN
Relevância na Pesquisa
36.74%
Southern pine specimens vacuum-treated with nano-zinc oxide (nano-ZnO) dispersions were evaluated for leach resistance and UV protection. Virtually, no leaching occurred in any of the nano-ZnO–treated specimens in a laboratory leach test, even at the highest retention of 13 kg/m3. However, specimens treated with high concentrations of nano-ZnO showed 58–65% chemical depletion after 12 months of outdoor exposure. Protection from UV damage after 12 months exposure is visibly obvious on both exposed and unexposed surfaces compared to untreated controls. Graying was markedly diminished, although checking occurred in all specimens. Nano-zinc oxide treatment at a concentration of 2.5% or greater provided substantial resistance to water absorption following 12 months of outdoor exposure compared to untreated and unweathered southern pine. We conclude that nano-zinc oxide can be utilized in new wood preservative formulations to impart resistance to leaching, water absorption and UV damage of wood.

The role of particle size of particulate nano-zinc oxide wood preservatives on termite mortality and leach resistance

Clausen, Carol A; Kartal, S Nami; Arango, Rachel A; Green, Frederick
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 15/06/2011 EN
Relevância na Pesquisa
36.74%
Historically most residential wood preservatives were aqueous soluble metal formulations, but recently metals ground to submicron size and dispersed in water to give particulate formulations have gained importance. In this study, the specific role nano-zinc oxide (ZnO) particle size and leach resistance plays in termite mortality resulting from exposure to particulate ZnO-treated wood was investigated. Southern yellow pine (SYP) sapwood impregnated with three concentrations of two particle sizes (30 and 70 nm) of ZnO were compared to wood treated with soluble zinc sulphate (ZnSO4) preservative for leach resistance and termite resistance. Less than four percent leached from the particulate nano-ZnO-treated specimens, while 13 to 25% of the zinc sulphate leached from the soluble treated wood. Nano-ZnO was essentially non-leachable from wood treated with 5% formulation for the 30-nm particle size. In a no-choice laboratory test, eastern subterranean termites (Reticulitermes flavipes) consumed less than 10% of the leached nano-ZnO-treated wood with 93 to 100% mortality in all treatment concentrations. In contrast, termites consumed 10 to 12% of the leached ZnSO4-treated wood, but with lower mortality: 29% in the 1% treatment group and less than 10% (5 and 8%...

Resonant frequency of gold/polycarbonate hybrid nano resonators fabricated on plastics via nano-transfer printing

Dechaumphai, Edward; Zhang, Zhao; Siwak, Nathan P; Ghodssi, Reza; Li, Teng
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 17/01/2011 EN
Relevância na Pesquisa
36.84%
We report the fabrication of gold/polycarbonate (Au/PC) hybrid nano resonators on plastic substrates through a nano-transfer printing (nTP) technique, and the parametric studies of the resonant frequency of the resulting hybrid nano resonators. nTP is a nanofabrication technique that involves an assembly process by which a printable layer can be transferred from a transfer substrate to a device substrate. In this article, we applied nTP to fabricate Au/PC hybrid nano resonators on a PC substrate. When an AC voltage is applied, the nano resonator can be mechanically excited when the AC frequency reaches the resonant frequency of the nano resonator. We then performed systematic parametric studies to identify the parameters that govern the resonant frequency of the nano resonators, using finite element method. The quantitative results for a wide range of materials and geometries offer vital guidance to design hybrid nano resonators with a tunable resonant frequency in a range of more than three orders of magnitude (e.g., 10 KHz-100 MHz). Such nano resonators could find their potential applications in nano electromechanical devices. Fabricating hybrid nano resonators via nTP further demonstrates nTP as a potential fabrication technique to enable a low-cost and scalable roll-to-roll printing process of nanodevices.

Fabrication and Properties of Porphyrin Nano- and Micro-particles with Novel Morphology

Li, Xiangqing; Zhang, Line; Mu, Jin; Qiu, Jinlong
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 21/05/2008 EN
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36.74%
New types of porphyrin nano- and micro-particles composed of J- and H-heteroaggregates were prepared by electrostatic self-assembly of two oppositely charged porphyrins, tetrakis(4-trimethylammoniophenyl)porphyrin (H2TAPP4+) and tetrakis(4-sulfonatophenyl)porphyrin cobalt(II) (CoTPPS4−), in aqueous solutions. Transmission electron microscopy (TEM) images showed novel morphology and size distribution of porphyrin particles fabricated under different experimental conditions. The assembly process of the nano- and micro-particles was monitored by UV–Vis spectra. Fluorescence spectra and UV–Vis spectra provided optical information on the formation of the nano- and micro-particles. Cyclic voltammograms of the porphyrin particles indicated that the electron gain and loss of the H2TAPP4+ion were restrained, and the electron transfer of the CoTPPS4−ion was promoted in the J- and H-type porphyrin heteroaggregates within the particles. The stability and constitution of the nano- and micro-particles were confirmed by UV-light irradiation, heat-treatment, and pH and ionic strength changes. Photoelectrochemical measurements showed that the photoelectron transfer of TiO2modified with the particles was more efficient than that of TiO2sensitized by either monomers. The photoelectronic and photocatalytic properties of the products indicated that the pyramidal or spherical configuration of the nano- and micro-particles was favorable for the absorption and transfer of the energy. It can be found that TiO2sensitized by the porphyrin nano- and micro-particles exhibits significant improvement in energy conversion and photocatalytic activity with reference to pure TiO2.

Facile fabrication of super-hydrophobic nano-needle arrays via breath figures method

Kim, Jiseok; Lew, Brian; Kim, Woo Soo
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em 06/12/2011 EN
Relevância na Pesquisa
36.78%
Super-hydrophobic surfaces which have been fabricated by various methods such as photolithography, chemical treatment, self-assembly, and imprinting have gained enormous attention in recent years. Especially 2D arrays of nano-needles have been shown to have super-hydrophobicity due to their sharp surface roughness. These arrays can be easily generated by removing the top portion of the honeycomb films prepared by the breath figures method. The hydrophilic block of an amphiphilic polymer helps in the fabrication of the nano-needle arrays through the production of well-ordered honeycomb films and good adhesion of the film to a substrate. Anisotropic patterns with water wettability difference can be useful for patterning cells and other materials using their selective growth on the hydrophilic part of the pattern. However, there has not been a simple way to generate patterns with highly different wettability. Mechanical stamping of the nano-needle array with a polyurethane stamp might be the simplest way to fabricate patterns with wettability difference. In this study, super-hydrophobic nano-needle arrays were simply fabricated by removing the top portion of the honeycomb films. The maximum water contact angle obtained with the nano-needle array was 150°. By controlling the pore size and the density of the honeycomb films...

Preparation, assessment, and comparison of α-chitin nano-fiber films with different surface charges

Zhang, Yan; Jiang, Jie; Liu, Liang; Zheng, Ke; Yu, Shiyuan; Fan, Yimin
Fonte: Springer US Publicador: Springer US
Tipo: Artigo de Revista Científica
Publicado em 21/05/2015 EN
Relevância na Pesquisa
36.76%
Chitin nano-fibers with positive and negative charges have been, respectively, produced from partially deacetylated and 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidized α-chitin. The average diameters and lengths of the TEMPO-oxidized chitin nano-fibers (TOChN) were 14 ± 4.3 and 190 ± 140 nm, respectively, and the average diameters and lengths of the partially deacetylated chitin nano-fibers (DEChN) were 6 ± 1.7 and 320 ± 105 nm, respectively. A partially deacetylated chitin nano-fiber film (DEChN-F), a TEMPO-mediated and oxidized chitin nano-fiber film (TOChN-F), and a composite film (DE-TO-ChN-F) consisting of a combination of the two were prepared by drying the dispersions at 40 °C. The DEChN-F, TOChN-F, and DE-TO-ChN-F all have similar tensile strengths of approximately 90 MPa; however, the chitosan film (Chitosan-F) had a tensile strength of approximately 30 MPa. In addition, TOChN-F and DE-TO-ChN-F have a thermal weight loss at 210 °C, and DEChN-F has a thermal weight loss at 280 °C. DEChN-F was found to have antimicrobial activity with regards to Escherichia coli. Finally, the chitin nano-fiber films could be slightly degraded by cellulase, which provided a novel biological performance of the chitin nano-material.

Nano Hydroxyapatite/Collagen, Nano Hydroxyapatite and Anodic Oxides on Titanium - Preparation, Characterization and Biological Responses -; Nano Hydroxyapatite/Kollagen, Nano Hydroxyapatite und Anodische Oxide auf Titanium - Präparationen, Charakterisierungen and Biologische Antworten -

Zhu, Xiaolong
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
36.92%
Aim The purpose of the present study is to develop, characterize and biologically evaluate a new surface for titanium implants to optimize osseointegration at the bone-implant interface. Materials and Metholds After pretreatment procedure, rectangular cp titanium specimens were anodized in a galvanostatic mode with a current density of 70 A/m2 till different voltages using either 0.2 M H3PO4 solution or a mixture of 0.03 M calcium glycerophosphate (Ca-GP) and 0.15 M calcium acetate (CA) as electrolyte. Surface characterization were performed including morphology, roughness, wettability, chemical compositions and states of elements. UV-irradiation was performed for 1 hours under two 254 nm UV-light bulbs. Nano HA was synthesized and its structure was analyzed by XRD and TEM. Collagen type I (calf skin) was homogeneously mixed with nano HA sol, and then the mixture was coated on the Ti surfaces. In vitro studies including cytotoxicity, cell attachment and spreading, cell proliferation and alkaline phosphatase activity were investigated into anodic oxides, nano HA and nano HA/collagen surfaces by cell culture and evaluation with the SaOS-2 human osteoblast-like cell line, derived from a human osteosarcoma. Results With an increase of anodizing voltages...

Comportamento mecânico de compósitos de fibra de vidro/epoxy nano-reforçados

Silva, Henrique Pereira da
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Tese de Doutorado
POR
Relevância na Pesquisa
36.84%
Os materiais compósitos laminados de matriz polimérica têm propriedades vantajosas tendo por isso uma ampla variedade de aplicações. Estes materiais são porém suscetíveis de sofrerem delaminações que podem debilitar consideravelmente as estruturas. Na direção da espessura do laminado as fibras não funcionam como um reforço efetivo, pelo que a resistência entre camadas é sempre menor que a resistência no plano. Neste trabalho estudam-se compósitos de fibra de vidro do tipo E, costurada sob a forma de tecido equilibrado tri-direcional e matriz epoxídica modificada com nano-argila montmorilonita organicamente modificada (OMMT) ou nanotubos de carbono de parede múltipla (MWCNT). A adição destes nanomateriais pretende melhorar as propriedades interfaciais e assim contribuir para melhorar o comportamento mecânico destes materiais. No fabrico dos compósitos trifásicos foi utilizado o processo de moldagem assistida a vácuo a partir do empilhamento de dez camadas de fibra de vidro previamente impregnadas com resina nano-modificada. Para caracterizar e comparar a Tenacidade à Fratura Interlaminar dos compósitos, fibra de vidro/epóxido foram realizados ensaios de Fratura Interlaminar, com solicitações de carga em Modo I...

DEVELOPMENT AND APPLICATION OF NON-TAPERED ELECTROSPRAY EMITTERS FOR NANO-ESI MASS SPECTROMETRY

Su, Shuqin
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 3222183 bytes; application/pdf
EN; EN
Relevância na Pesquisa
36.76%
Nano-ESI mass spectrometry is an attractive analytical technique due to its high sensitivity and small sample consumption, which is especially important for research areas such as proteomics. However, current nano-ESI emitters become a bottleneck for nano-ESI to be widely applied because of problems such as clogging, poor robustness, large flow resistance, and poor spray efficiency for highly aqueous solutions. The objective of this thesis study is to address the problems associated with tapered emitters and provide alternative solutions by developing advanced nano-ESI emitters. Two strategies that were explored to improve the clogging resistance and robustness while maintaining comparable electrospray performances include the development of emitters with larger apertures and multiple channels. Following these strategies, five types of emitters were fabricated without tapering either internal or external diameters, which include a roughened open tubular emitter, a porous membrane-assisted emitter, a microstructured multiple channel photonic crystal fiber (MSF) emitter, a packed ODS bead emitter, and an entrapped ODS bead emitter. The successful transformation of MSF fibers to nanoelectrospray emitters demonstrates a new practical approach to expand the application of nano-ESI because of its availability...

Nano-emulsions

Solans, Conxita; Izquierdo, P.; Nolla Anguera, Jordi; Azemar Sazatornil, Nuria; García-Celma, M. J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
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9 pages, 5 figures.-- Printed version published Oct 2005.; The formation, properties and applications of nano-emulsions (also referred to as miniemulsions, ultrafine emulsions, submicron emulsions) are reviewed and summarized. Nano-emulsion droplet sizes fall typically in the range of 20–200 nm and show narrow size distributions. Although most of the publications on either oil-in-water (O/W) or water-in-oil (W/O) nano-emulsions report their formation by dispersion or high-energy emulsification methods, an increased interest is observed in the study of nano-emulsion formation by condensation or low-energy emulsification methods (based on the phase transitions that take place during the emulsification process). Phase behaviour studies have shown that the size of the droplets is governed by the surfactant phase structure (bicontinuous microemulsion or lamellar) at the inversion point induced by either temperature or composition. Studies on nano-emulsion formation by the phase inversion temperature (PIT) method have shown a relation between minimum droplet size and complete solubilization of the oil in a microemulsion bicontinuous phase independently of whether the initial phase equilibria is single or multiphase. Due to their small droplet size nano-emulsions possess stability against sedimentation or creaming with Ostwald ripening forming the main mechanism of nano-emulsion breakdown. The main application of nano-emulsions is the preparation of nanoparticles using a polymerizable monomer as the disperse phase (the so-called miniemulsion polymerization method) where nano-emulsion droplets act as nanoreactors. Novel complex polymeric materials as well as hybrid organic/inorganic materials...

Formation and stability of nano-emulsions

Tadros, Tharwat F.; Izquierdo, P.; Esquena, Jordi; Solans, Conxita
Fonte: Elsevier Publicador: Elsevier
Tipo: Artículo Formato: 22195 bytes; application/pdf
ENG
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16 pages, 18 figures, 3 tables.-- PMID: 15072948 [PubMed].-- Available online Dec 16, 2003.-- Issue title: "Emulsions, From Fundamentals to Practical Applications" (3rd World Congress on Emulsions, Lyon, France, Sep 2002).; This review describes the principles of formation and stability of nano-emulsions. It starts with an introduction highlighting the main advantages of nano-emulsions over macroemulsions for personal care and cosmetic formulations. It also describes the main problems with lack of progress on nano-emulsions. The second section deals with the mechanism of emulsification and the dynamic light scattering technique for measurement of the droplet size of nano-emulsions. This is followed by a section on methods of emulsification and the role of surfactants. Three methods are described for nano-emulsion preparation, namely high energy emulsification (using homogenisers), low energy emulsification whereby water is added to an oil solution of the surfactant and the principle of the phase inversion temperature (PIT). A section is devoted to steric stabilisation and the role of the adsorbed layer thickness. The problem of Ostwald ripening (which is the main instability process of nano-emulsions) is described in some detail. The methods that can be applied to reduce Ostwald ripening are briefly described. This involves the addition of a second less soluble oil phase such as squalene and/or addition of a strongly adsorbed and water insoluble polymeric surfactant. The last part of the review gives some examples of nano-emulsions that are prepared by the PIT method as well as using high pressure homogeniser. A comparison of the two methods is given and the rate of Ostwald ripening is measured in both cases. The effect of changing the alkyl chain length and branching of the oil was investigated using decane...

Unique carbon-nano-structure for high quality electron-emitter to be employed in a variety of applications

Hiraki,Akio; Hirak,Hirohisa
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/11/2008 EN
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There have been many trials to employ nano-carbon materials, such as carbon-nano-tubes and nano-diamond films, as electron-emitter. Several reasons exist why the nano-carbon materials are good for the emitter. They are, in addition to (a) unique morphological shapes of the materials good for the emitter- the high aspect ratio of the carbon-nano-tube is a good example-, (b) sturdiness(they can even be formed in a plasma), (c) high thermal conductivity (current density in the electron-emitting-nano-structure is high, thus it is vital to provide effective Joule-heat dissipation), and (d) easiness of the fabrication of the electron-emitting carbon materials. In order to fabricate good electron emitters, we have long been trying to employ a variety of fabrication CVD methods and fabricating conditions (starting CVD gas, pressure, temperature, substrate materials and so on).Then recently our emitters have shown a world-top-ranking property: very low turn-on- voltage(0.5V/µm induce 10µA/cm² of emission current) and high current at low applied voltage with gap distance of 1mm(1mA/cm² at 1.1V/µm and 100/ at 2V/µm). This excellent property comes from a carbon-nano-structure which we call CNX(Carbon-Nano-eXit). In addition, these emitter can be formed on a variety of substrates(Ni...