Carbon Nanotube based Composite Fibers for Strain Sensing, Signal Processing and Computing

Carbon nanotubes dispersed in polymer matrix have been aligned in the form of fibers and interconnects and cured electrically and by UV light. Conductivity and effective semiconductor tunneling against reverse to forward bias field have been designed to have differentiable current-voltage response of each of the fiber/channel. The current-voltage response is a function of the strain applied to the fibers along axial direction. Biaxial and shear strains are correlated by differentiating signals from the aligned fibers/channels. Using a small doping of magnetic nanoparticles in these composite fibers, magneto-resistance properties are realized which are strong enough to use the resulting magnetostriction as a state variable for signal processing and computing. Various basic analog signal processing tasks such as addition, convolution and filtering etc. can be performed. These preliminary study shows promising application of the concept in combined analog-digital computation in carbon nanotube based fibers. Various dynamic effects such as relaxation, electric field dependent nonlinearities and hysteresis on the output signals are studied using experimental data and analytical model.

Microwave absorbers designed from PVDF/SAN blends containing multiwall carbon nanotubes anchored cobalt ferrite via a pyrene derivative

Lightweight and flexible electromagnetic shielding materials were designed by selectively localizing multiwall carbon nanotubes (MWNTs) anchored magnetic nanoparticles in melt mixed co-continuous blends of polyvinylidene fluoride (PVDF) and poly(styrene-co-acrylonitrile) (SAN). In order to facilitate better dispersion, the MWNTs were modified using pyrenebutyric acid (PBA) via pi-pi stacking. While one of the two-targeted properties, i.e., high electrical conductivity, was achieved by PBA modified MWNTs, high magnetic loss was accomplished by introducing nickel (NF) or cobalt ferrites (CF). Moreover, the attenuation by absorption can be tuned either by using NF (58% absorption) or CF (64% absorption) in combination with PBA-MWNTs. More interestingly, when CF was anchored on to MWNTs via the pyrene derivative, the minimum reflection loss attained was -55 dB in the Ku band (12-18 GHz) frequency and with a large bandwidth. In addition, the EM waves were blocked mostly by absorption (70%). This study opens new avenues in designing flexible and lightweight microwave absorbers.

La estructura y propiedades magnéticos de las nanopartículas de Fe50Ni50 obtenidas mediante el método de explosión eléctrica de hilo

[Es]Actualmente ninguna área científica es ajena a la revolución de la nanociencia; las nanopartículas atraen el interés de muchos investigadores desde el punto de vista de la ciencia fundamental y para sus aplicaciones tecnológicas. Las nanopartículas ofrecen la posibilidad de fabricar sensores que sean capaces de detectar desde un virus hasta concentraciones de substancias patógenas que no pueden ser detectadas por los métodos convencionales. Hoy en día existes 82 tratamientos contra el cáncer basadas en la utilización de nanopartículas y los materiales composite con nanopartículas se utilizan como medio de protección frente la radiación del rango de microondas. En la rama de ciencias ambientales, las nanopartículas metálicas sirven como materiales anticontaminantes. En este trabajo se ha estudiado la estructura y las propiedades magnéticas de las nanopartículas de FeNi preparadas mediante el método de explosión eléctrica de hilo. Con la técnica de Rayos–X(DRX) se ha determinado que las nanopartículas se cristalizan en un sistema cúbico FCC con un parámetro de celda de 3.596 Å, también, se ha obtenido el tamaño de dominio coherente que es de 35 nm. La muestra se ha sometido a un programa de temperatura controlada para seguir la evolución de la estructura cristalina y del tamaño del cristal, tanto en atmósfera oxidante como en vacío. Para el aprendizaje de los microscopios utilizados en este trabajo, se ha asistido al curso “Fundamentos de microscopia electrónica de barrido y microanálisis” impartido por SGIker de la UPV/EHU. Se han empleado los microscopios electrónicos SEM y TEM para obtener imágenes de gran resolución de la muestra y analizar su contenido elemental. Partiendo de las imágenes sacadas por el SEM se ha calculado el valor medio del tamaño de las partículas de la muestra, 58 nm. Mediante el Mastersizer 2000 se ha medido el tamaño de las partículas y/o agregados por método de difracción láser, disgregando la muestra todo lo posible hasta conseguir el tamaño medio que se aproxime al de una sola partícula, 100nm. Por último, para la caracterización magnética se ha servido del VSM que mide el momento magnético de una muestra cuando ésta vibra en presencia de un campo magnético estático, consiguiendo una imanación de saturación de 125 emu/g. Hemos fabricado y caracterizado las nanopartículas magnéticas de hierro-níquel y los resultados obtenidos han sido enviados a un congreso especializado de ciencia de materiales (ISMANAM - 2013, Italia).

Síntese e caracterização de microesferas poliméricas reticuladas à base de poli(ácido metacrílico) contendo nanopartículas magnéticas de ferritas de manganês

As nanopartículas de ferritas de manganês (MnFe2O4) tem sido de grande interesse por causa de suas notáveis propriedades magnéticas doces (baixa coercividade e moderada magnetização de saturação) acompanhada com boa estabilidade química e dureza mecânica. A formação de materiais híbridos/compósito estabiliza as nanopartículas magnéticas (NPMs) e gera funcionalidades aos materiais. Entretanto, não foi encontrada na literatura uma discussão sobre a síntese e as propriedades de polímeros polares reticulados à base de ácido metacrílico contendo ferritas de manganês na matriz polimérica. Assim, o objetivo desta Dissertação foi produzir partículas esféricas poliméricas reticuladas, com boas propriedades magnéticas, à base de ácido metacrílico, estireno, divinilbenzeno e ferritas de manganês. Neste trabalho, foram sintetizados compósitos de ferrita de manganês (MnFe2O4) dispersa em copolímeros de poli(ácido-metacrílico-co-estireno-co-divinilbenzeno), via polimerização em suspensão e em semi-suspensão. Foram variados os teores de ferrita (1% e 5%) e a concentração do agente de suspensão (0,2% e 5%). Além disso, foram testadas sínteses contendo a fase orgânica pré-polimerizada, e também a mistura da ferrita na fase orgânica (FO), antes da etapa da polimerização em suspensão. Os copolímeros foram analisados quanto as suas morfologias - microscopia óptica; propriedades magnéticas e distribuição das ferritas na matriz polimérica - VSM, SEM e EDS-X; propriedades térmicas TGA; concentração de metais presentes na matriz polimérica absorção atômica. As ferritas foram avaliadas quanto à cristalografia XRD. A matriz polimérica foi avaliada pela técnica de FTIR. As amostras que foram pré-polimerizadas e as que além de pré-polimerizadas foram misturadas as ferritas de manganês na FO, apresentaram as melhores propriedades magnéticas e uma incorporação maior da ferrita na matriz polimérica. Essas rotas sintéticas fizeram com que os copolímeros não apresentassem aglomeração, e também minimizou a presença de ferritas na superfície das microesferas. Em geral, todos os copolímeros obtidos apresentaram as características de materiais magneticamente doces além do superparamagnetismo. Foi constatado que o aumento da concentração do PVA e a diminuição da concentração da ferrita fazem com que os diâmetros das microesferas decresçam. Os resultados de TGA e DTG mostraram que ao misturar as ferritas na FO, a concentração de material magnético na matriz polimérica aumenta cerca de 10%. Entretanto, somente a amostra PM2550, pré-polimerizada e com as ferritas misturadas na FO (5% de ferrita e 0,2% de PVA), apresentou potencial aplicação. Isso porque as ferritas não ficaram expostas na superfície das microesferas, ou seja, o material magnético fica protegido de qualquer ação externa

Microwave Resonant and Zero-Field Absorption Study of Doped Magnetite Prepared by a Co-Precipitation Method

Fe3O4 and ZnxFe3-xO4 pure and doped magnetite magnetic nanoparticles (NPs) were prepared in aqueous solution (Series A) or in a water-ethyl alcohol mixture (Series B) by the co-precipitation method. Only one ferromagnetic resonance line was observed in all cases under consideration indicating that the materials are magnetically uniform. The shortfall in the resonance fields from 3.27 kOe (for the frequency of 9.5 GHz) expected for spheres can be understood taking into account the dipolar forces, magnetoelasticity, or magnetocrystalline anisotropy. All samples show non-zero low field absorption. For Series A samples the grain size decreases with an increase of the Zn content. In this case zero field absorption does not correlate with the changes of the grain size. For Series B samples the grain size and zero field absorption behavior correlate with each other. The highest zero-field absorption corresponded to 0.2 zinc concentration in both A and B series. High zero-field absorption of Fe3O4 ferrite magnetic NPs can be interesting for biomedical applications.

Síntese e avaliação de hidrogéis à base de alginato e nanopartículas magnéticas preparadas in situ para remoção de Mn(II) e Ni(II) de efluente industrial

Esta Dissertação teve como objetivo,a síntese de hidrogéis à base de alginato e nanopartículas magnéticas (maghemita) preparadas in situ. Os hidrogéis foram preparados em diferentes concentrações de alginato de sódio (2 e 3% m/v), FeSO4 (0,3 e 0,5 mol L-1) e CaCl2 (0,1 e 0,3 mol L-1). As propriedades físico-químicas dos hidrogéis foram analisadas e, posteriormente, foram avaliados quanto à capacidade de remoção de íons Ni2+ e Mn2+ de soluções aquosas. Para caracterização das amostras foram utilizadas diversas técnicas de análises, tais como, análise granulométrica, microscopia óptica (OM), microscopia eletrônica de varredura (SEM), microscopia eletrônica de transmissão (TEM), magnetometria de amostra vibrante (VSM), espectroscopia na região do infravermelho por transformada de Fourier (FTIR), difratometria de raios-X (XRD), espectroscopia Mössbauer, e análise termogravimétrica (TGA). Foram preparados hidrogéis com morfologia predominantemente esférica e dimensões micrométricas (500 a 850 m), com átomos de Fe e Ca dispersos uniformemente em sua estrutura. Os hidrogéis apresentaram boa resistência térmica e comportamento superparamagnético. As amostras foram intumescidas em água deionizada durante um intervalo de tempo a fim de avaliar o grau de intumescimento (Q) para determinar a amostra com a melhor resposta para posterior aplicação em solução aquosa contendo íons metálicos (Ni2+ e Mn2+). Os resultados revelaram que a amostra cuja concentração de 3% m/v de alginato de sódio, 0,3 mol L-1 de FeSO4 e 0,3 mol L-1 de CaCl2 obteve maior Q (50%). Em consequência deste resultado, optou-se por utilizar estaamostra, na remoção de metais pesados presentes em soluções aquosas e em efluentes industriais. Vários parâmetros,tais como: tempo de contato,pH, concentração inicial do íon e massa de hidrogel foram estudados.Os resultados, para efluente sintético, revelaram que o tempo de equilíbrio foi de 60 minutos; a capacidade de remoção dos metais melhora com o aumento de pH (3 a 9), sendo máxima em pH 7;quanto menor a concentração inicial da solução iônica (50 a 500 mg L-1), maior a capacidade de remoção, 52% de Ni2+ e 49% de Mn2+ (concentração inicial de 50 mg L-1). No efluente industrial, a remoção foi de 61% de Ni2+ e 57% de Mn2+(300 mg de hidrogel). Os resultados encontrados revelaram que os hidrogéis magnéticos produzidos à base de alginato têm potencial uso no tratamento de efluentes industriais contaminados com metais pesados

基于功能化磁性纳米材料的高灵敏聚离子选择性电极

聚离子如肝素和鱼精蛋白等在临床医学领域有着广泛的应用。快速准确地检测其浓度 对安全有效地使用聚离子具有指导意义。然而现有的检测手段已经不能满足人们的需要， 开发新的能够直接检测聚离子的传感器已成为迫切的需要。 聚离子电极的出现使人们找到了一种能够快速简便地检测聚离子的手段。利用掺杂了 合适的离子交换剂的聚合物膜，电极能够对聚离子产生明显的电位响应。这种响应的机理 是聚离子通过萃取从样品溶液进入有机相，与有机相中的离子交换剂形成离子对，从而导 致膜电位的变化。理论表明，通过加快萃取过程，电极的灵敏度能够得到显著提高。实验 证明，利用旋转圆盘电极可以有效降低扩散层厚度并增强传质，从而使电极的灵敏度得到 提高。然而旋转圆盘电极的装置比较复杂且容易产生信号噪音。 功能化的纳米粒子能够均匀分散在样品溶液中从而促进纳米粒子上功能基团与样品 分析物之间的反应，这是因为其粒径较小能够降低扩散层厚度增强传质。在众多的纳米粒 子中，磁性纳米粒子具有磁响应的特性，在许多方面具有潜在的应用价值。本文中我们报 道一种利用磁性纳米粒子快速灵敏检测聚离子的电位型分析方法。 实验中采用共沉淀法合成了磁性纳米粒子，并采用油酸钠作为分散剂。功能化磁性纳 米粒子通过蒸发溶剂，利用长链分子的非共价结合力修饰。透射电镜照片显示磁性纳米粒 子粒径均匀，平均粒径约为25 nm。X 射线衍射证明磁性纳米粒子为四氧化三铁，且无其 它杂质存在，用德拜-休克尔公式计算得纳米粒子粒径约为25 nm，与透射电镜表征的结果 相符。红外光谱的结果表明，磁性纳米粒子表面成功地包覆了油酸分子以及离子交换剂与 增塑剂，从而使磁性纳米粒子表面功能化。最后通过对离子交换剂用量的考察，得到了最 佳的功能化磁性四氧化三铁纳米粒子。 将功能化磁性纳米粒子与聚合物膜电极结合，开发了一种新的聚离子电极，并在 0.05-50 μg mL-1 的浓度范围内检测鱼精蛋白。考察了聚合物敏感膜组成与反应时间的影响， 得到了最优的检测条件。使用最大电位变化速率对鱼精蛋白浓度的对数作图，得到了在 0.05-5 μg mL-1 的浓度范围内的线性关系，建立了标准工作曲线，其检出限为0.033 μg mL-1。 控制实验说明，只有在磁场与功能化磁性纳米粒子都存在的条件下，电极才会产生明显的 电位变化。利用此电

Hermetically-coated superparamagnetic Fe2O3 particles with SiO2 nanofilms

Magnetic nanoparticles are frequently coated with SiO2to improve their functionality and bio-compatibility in a range of biomedical and polymer nanocomposile applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coaled with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis (FSP) of iron acelylacetonale in xylene/acetonitrile solutions, and the resulting aerosol was in situ coaled with SiO2 by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3, particle properties and the thickness of their silica coaling film. This ensures that the non-magnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe2O3 coated with about 2 nm thin SiO2 layers was nearly identical lo that of uncoated, pure Fe2O3 nanoparlicles.

Hermetically coated superparamagnetic Fe2O3 particles with SiO2 nanofilms

Magnetic nanoparticles are frequently coated with SiO2 to improve their functionality and biocom-patibility in a range of biomedical and polymer nanocomposite applications. In this paper, a scalable flame aerosol technology is used to produce highly dispersible, superparamagnetic iron oxide nanoparticles hermetically coated with silica to retain full magnetization performance. Iron oxide particles were produced by flame spray pyrolysis of iron acetylacetonate in xylene/acetonitrile solutions and the resulting aerosol was in situ coated with silicon dioxide by oxidation of swirling hexamethlydisiloxane vapor. The process allows independent control of the core Fe2O3 (maghemite) particle properties and the thickness of their silica coating film. This ensures that the nonmagnetic SiO2 layer can be closely controlled and minimized. The optimal SiO2 content for complete (hermetic) encapsulation of the magnetic core particles was determined by isopropanol chemisorption. The magnetization of Fe 2O3 coated with about 2 nm thin SiO2 layers was nearly identical to that of uncoated, pure Fe2O3 nanoparticles. © 2009 American Chemical Society.

纳米水基磁性液体在肿瘤治疗领域的研究进展

结合作者在纳米磁性液体方面的研究经历，介绍了生物医学应用领域纳米磁性粒子的组成结构及特点，指出高分子改性纳米磁性粒子具有生物相容性好、稳定性强、载药量高的优点，并对目前高分子改性纳米四氧化三铁颗粒的制备方法及特点进行了对比分析。指出进一步研制磁响应性强、载药量高、粒度分布均匀的纳米磁性粒子，使之对癌细胞具有亲和作用，尽量避免对毛细血管网状内皮系统的清除，是未来肿瘤治疗领域纳米磁性粒子的研发目标，并对目前制备方法中存在的不足提出了改进的建议。

Sensing H2O2 with layer-by-layer assembled Fe3O4-PDDA nanocomposite film

It was found that Fe3O4 nanoparticles (Fe3O4 NPs) possess intrinsic enzyme mimetic activity similar to that found in natural peroxidase. Here, we applied Fe3O4 NPs to the construction of efficient electrochemical sensor to detect the concentration of hydrogen peroxide. The sensor was fabricated with layer-by-layer assembly of Fe3O4 NPs and poly(diallyldimethylammonium chloride) (PDDA) through the electrostatic interaction, and the multilayer film was characterized with UV-vis absorption spectra, atomic force microscopy, and cyclic voltammetry.

Luminescence functionalization of mesoporous silica with different morphologies and applications as drug delivery systems

Ordered mesoporous silica (MCM-41) particles with different morphologies were synthesized through a simple hydrothermal process. Then these silica particles were functionalized with luminescent YVO4:EU3+ layers via the Pechini sol-gel process. The obtained YVO4:Eu3+ and MCM-41 composites, which maintained the mesoporous structure of MCM-41 and the red luminescence property of YVO4:Eu3+ were investigated as drug delivery systems using ibuprofen (IBU) as model drug. The physicochemical properties of the samples were characterized by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N-2 adsorption, and photoluminescence (PL) spectra, respectively.

Fabrication of Iron Oxide Core/Gold Shell Submicrometer Spheres with Nanoscale Surface Roughness for Efficient Surface-Enhanced Raman Scattering

A method to synthesize Fe3O4 core/Au shell submicrometer structures with very rough surfaces on the nanoscale is reported. The Fe3O4 particles were first modified with uniform polymers through the layer-by-layer technique and then adsorbed a lot of gold nanoseeds for further Au shell formation. The shell was composed of a large number of irregular nanoscale An particles arranged randomly, and there were well-defined boundaries between these Au nanoparticles. The Fe3O4 core/Au shell particles showed strong plasmon resonance absorption in the near-infrared range, and can be separated quickly from solution by an external magnet.

Nanoreactor of Fe3O4@SiO2 Core-Shell Structure with Nanochannels for Efficient Catalysis

We introduced a new nanoreactor system consisting of nanochannel-filled Fe3O4 core and SiO2 shell. Different morphologies of Fe3O4@SiO2 Core-shell nanostructures could be obtained through simple HCI etching of the magnetic cores. The outer silica shells were permeable and the Fe3O4 cores were accessible to the reactants. Therefore, the present nanoreactor system was applied to catalyze the reduction of H2O2, and it showed outstanding catalytic activity compared with bare Fe3O4 or Fe3O4@SiO2 core-shell nanoparticles.

A General Route to Construct Diverse Multifunctional Fe3O4/Metal Hybrid Nanostructures

We have developed a simple, efficient, economical, and general approach to construct diverse multifunctional Fe3O4/metal hybrid nanostructures displaying magnetization using 3-aminopropyltrimethoxysilane (APTMS) as a linker. High-density Au nanoparticles (NPs) could be supported on the surface of superparamagnetic Fe3O4 spheres and used as seeds to construct Au shell-coated magnetic spheres displaying near-infrared (NIR) absorption., which may make them promising in biosensor and biomedicine applications. High-density flower-like Au/Pt hybrid NPs could be supported on the surface of Fe3O4 spheres to construct multifunctional hybrid spheres with high catalytic activity towards the electron-transfer reaction between potassium ferricyanide and sodium thiosulfate. High-density Ag or Au/Ag core/shell NPs could also be supported on the surface of Fe3O4 spheres and exhibited pronounced surface-enhanced Raman scattering (SERS), which may possibly be used as an optical probe with magnetic function for application in high-sensitivity bioassays.