Kontrolle der Grenzflächeneigenschaften anorganischer Nanopartikel mittels amphiphiler Polymere

Im Rahmen dieser Arbeit wurden amphiphile Co- und Terpolymere verwendet, um die Grenzflächeneigenschaften anorganischer Nanopartikel zu kontrollieren. Es wurde eine effiziente und vielseitige Methode entwickelt, mit der in-situ hydrophobierte, formanisotrope ZnO-, CdS- und Au-Nanopartikel sowie poröse TiO2-Nanopartikel hergestellt werden konnten. Diese Technik basierte auf der Fällung anorganischer Nanopartikel in einer inversen Emulsion mittels kombinierten Einsatzes zweier maßgeschneiderter amphiphiler Polymere. Ein Copolymer ermöglichte sowohl die Stabilisierung der Emulsion als auch die Hydrophobierung der Partikel, und ein weiteres Struktur-dirigierendes Agens (SDA) kontrollierte den Kristallisationsprozess. Infolge ihrer Form zeigten die Nanopartikel von sphärischen Teilchen abweichende Lagen der Oberflächenplasmonenresonanz und der Bandlücke. Aufgrund der hervorragenden Hydrophobierung dieser Kolloide mittels amphiphiler Copolymere konnten diese homogen in polymere Materialien eingearbeitet werden. Dies erlaubte es die speziellen Eigenschaften von nicht-sphärischen Kolloiden auf Nanokompositmaterialien zu übertragen. Darüber hinaus wurden amphipolare Copolymere genutzt, um superhydrophobe Oberflächen zu generieren. Hierzu wurden Filme bestehend aus rauen SiO2-Nanopartikeln mit fluorierten Emulgatoren beschichtet. In einem dritten Schwerpunkt dieser Arbeit wurden amphiphile Co- und Terpolymere verwendet, um anorganische Nanopartikel zu hydrophilieren. Durch Variation der Emulgatorzusammensetzung konnten die Ladung und Ladungsdichte auf der Partikeloberfläche gezielt gesteuert werden. Darüber hinaus konnte die Partikelhülle zusätzlich mit Farbstoffmolekülen funktionalisiert werden, was den erfolgreichen Einsatz der Kolloide in Zellaufnahmeexperimenten ermöglichte.

A new class of bragg stacks and its principle application

This work is focused on the development of high quality nanoporous 1D photonic crystals –so called Bragg stacks – made by spin-coating of approximately 25 nm large SiO2 and TiO2 nanoparticles bearing interparticle voids large enough to infiltrate reactive species. Therefore, the first part of this work describes the synthesis of well-dispersed TiO2 nanoparticles in this size range (the corresponding SiO2 nanoparticles are commercially available). In the second part, a protocol was developed to prepare nanoporous Bragg stacks of up to 12 bilayers with high quality and precision. Tailor-made Bragg stacks were prepared for different applications such as (i) a surface emitting feedback laser with a FWHM of only 6 nm and (ii) an electrochromic device with absorption reversibly switchable by an external electrical bias independently of the Bragg reflection. In the last chapter, the approach to 1D photonic crystals is transferred to 1D phononic crystals. Contrast in the modulus is achieved by spin-coating SiO2 and PMMA as high and low moduli material. This system showed a band gap of fg = 12.6 GHz with a width of Dfg/fg = 4.5 GHz.

Generation and characterization of stable, highly concentrated titanium dioxide nanoparticle aerosols for rodent inhalation studies

The intensive use of nano-sized titanium dioxide (TiO2) particles in many different applications necessitates studies on their risk assessment as there are still open questions on their safe handling and utilization. For reliable risk assessment, the interaction of TiO2 nanoparticles (NP) with biological systems ideally needs to be investigated using physico-chemically uniform and well-characterized NP. In this article, we describe the reproducible production of TiO2 NP aerosols using spark ignition technology. Because currently no data are available on inhaled NP in the 10–50 nm diameter range, the emphasis was to generate NP as small as 20 nm for inhalation studies in rodents. For anticipated in vivo dosimetry analyses, TiO2 NP were radiolabeled with 48V by proton irradiation of the titanium electrodes of the spark generator. The dissolution rate of the 48V label was about 1% within the first day. The highly concentrated, polydisperse TiO2 NP aerosol (3–6 × 106 cm−3) proved to be constant over several hours in terms of its count median mobility diameter, its geometric standard deviation, and number concentration. Extensive characterization of NP chemical composition, physical structure, morphology, and specific surface area was performed. The originally generated amorphous TiO2 NP were converted into crystalline anatase TiO2 NP by thermal annealing at 950 °C. Both crystalline and amorphous 20-nm TiO2 NP were chain agglomerated/aggregated, consisting of primary particles in the range of 5 nm. Disintegration of the deposited TiO2 NP in lung tissue was not detectable within 24 h.

Effect of external electric field on hydrogen adsorption over activated carbon separated by dielectric materials

Energy crisis and worldwide environmental problem make hydrogen a prospective energy carrier. However, storage and transportation of hydrogen in large quantities at small volume is currently not practical. Lots of materials and devices have been developed for storage hydrogen, but to today none is able to meet the DOE targets. Activated carbon has been found to be a good hydrogen adsorbent due to its high surface area. However, the weak van der Waals force between hydrogen and the adsorbent has limited the adsorption capacity. Previous studies have found that enhanced adsorption can be obtained with applied electric field. Stronger interaction between the polarized hydrogen and the charged sorbents under high voltage is considered as the reason. This study was initiated to investigate if the adsorption can be further enhanced when the activated carbon particles are separated with a dielectric coating. Dielectric TiO2 nanoparticles were first utilized. Hydrogen adsorption measurements on the TiO2-coated carbon materials, with or without an external electric field, were made. The results showed that the adsorption capacity enhancement increased with the increasing amount of TiO2 nanoparticles with an applied electric field. Since the hydrogen adsorption capacity on TiO2 particles is very low and there is no hydrogen adsorption enhancement on TiO2 particles alone when electric field is applied, the effect of dielectric coating is demonstrated. Another set of experiments investigated the behavior of hydrogen adsorption over TiO2-coated activated carbon under various electric potentials. The results revealed that the hydrogen adsorption first increased and then decreased with the increase of electric field. The improved storage was due to a stronger interaction between charged carbon surface and polarized hydrogen molecule caused by field induced polarization of TiO2 coating. When the electric field was sufficient to cause considerable ionization of hydrogen, the decrease of hydrogen adsorption occurred. The current leak detected at 3000 V was a sign of ionization of hydrogen. Experiments were also carried out to examine the hydrogen adsorption performances over activated carbon separated by other dielectric materials, MgO, ZnO and BaTiO3, respectively. For the samples partitioned with MgO and ZnO, the measurements with and without an electric field indicated negligible differences. Electric field enhanced adsorption has been observed on the activated carbon separated with BaTiO3, a material with unusually high dielectric constant. Corresponding computational calculations using Density Functional Theory have been performed on hydrogen interaction with charged TiO2 molecule as well as TiO2 molecule, coronene and TiO2-doped coronene in the presence of an electric field. The simulated results were consistent with the observations from experiments, further confirming the proposed hypotheses.

Production of nanoTiC–graphite composites using Ti-doped self-sintering carbon mesophase powder

This work reports the synthesis of nanoTiC–graphite composites using mesophase pitch containing titanium as TiC or TiO2 nanoparticles. NanoTiC–graphite composites have been prepared using Ti-doped self-sintering mesophase powders as starting materials without using any binders or a metal carbide-carbon mixing stage. The effect of manufacture variables on the graphite compacts properties was studied. Graphites were characterised using XRD and Raman spectroscopy, SEM and TEM, as well as by their mechanical, electrical and thermal properties. The presence of TiC promotes graphitisation producing materials with larger crystal sizes. The kind of titanium source and mesophase content of the starting pitch affects to the final properties. Mesophase pitch with higher amount of mesophase content produces graphites with higher degree of graphitisation. The incorporation of TiC nanoparticles to the graphites composites improved thermal conductivity more than four times, and mechanical properties are not significantly modified by the presence of TiC.

Photogeneration of Hydrogen from Water by Hybrid Molybdenum Sulfide Clusters Immobilized on Titania

Two new hybrid molybdenum(IV) Mo3S7 cluster complexes derivatized with diimino ligands have been prepared by replacement of the two bromine atoms of [Mo3S7Br6]2− by a substituted bipyridine ligand to afford heteroleptic molybdenum(IV) Mo3S7Br4(diimino) complexes. Adsorption of the Mo3S7 cores from sample solutions on TiO2 was only achieved from the diimino functionalized clusters. The adsorbed Mo3S7 units were reduced on the TiO2 surface to generate an electrocatalyst that reduces the overpotential for the H2 evolution reaction by approximately 0.3 V (for 1 mA cm−2) with a turnover frequency as high as 1.4 s−1. The nature of the actual active molybdenum sulfide species has been investigated by X-ray photoelectron spectroscopy. In agreement with the electrochemical results, the modified TiO2 nanoparticles show a high photocatalytic activity for H2 production in the presence of Na2S/Na2SO3 as a sacrificial electron donor system.

Argamassas de auto-limpeza : da formulação às aplicações

Atualmente assiste-se a um grave problema de salubridade visual das cidades, designadamente no espaço edificado/ construído. A sujidade é uma ameaça que, junto com os graffitis, tem contribuído para a degradação precoce dos espaços urbanos. A fim de se enfrentar este problema, que tem vindo a proliferar nas cidades, um pouco por todo o mundo, a presente dissertação de mestrado ambiciona contribuir para a sistematização da informação existente sobre a produção e caracterização de argamassas de auto-limpeza. As argamassas de auto-limpeza são produzidas por uma de duas formas: com a adição de nanopartículas de dióxido de titânio (TiO2) na sua matriz ou com a aplicação de um filme fino à base de TiO2 na sua superfície. Esta segunda é apontada como a técnica mais eficaz e económica. Salienta-se o facto do TiO2 ser um dos nanomateriais mais utilizados na construção pelas suas propriedades fotocatalíticas que o capacitam como um dos mais exímios fotocatalisadores, aquando da fotocatálise heterogénea. É graças ao processo de fotodegradação química da fotocatálise, que na presença de luz solar e da ação da água, que o TiO2 é ativado, desencadeando reações químicas que aumentam a eficácia e eficiência fotocatalítica. Analisou-se um conjunto de trabalhos de investigação recentes que comprovam que o uso das argamassas de auto-limpeza é adequado e benéfico em intervenções em edifícios novos como em obras de conservação e reabilitação de edifícios antigos. Além de reduzirem os investimentos em obras de limpeza, manutenção/conservação e reabilitação, prolongam a conservação das fachadas e melhoram os níveis da qualidade do ar. Apesar do crescente número de patentes pedidas e concedidas nesta área, as normas aplicáveis ainda não se encontram uniformizadas. Nesse sentido, a experiência do Japão deve ser tida como exemplo para que os restantes países desenvolvam de forma consensual as suas próprias normas e patentes, permitindo, futuramente, conferir maior credibilidade, segurança no uso dos nanomateriais e uma maior permeabilidade no setor da construção. Elencam-se alguns nano-produtos à base de nano TiO2 comercializados que têm vindo a ser aplicados sobretudo na China, Japão e na Alemanha.

Determinants of biological activity of nanomaterials in innate immunity cells: the role of aspect ratio, environmental contaminants and protein corona

As defined by the European Union, “ ’Nanomaterial’ (NM) means a natural, incidental or manufactured material containing particles, in an unbound state or as an aggregate or agglomerate, where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm-100 nm ” (2011/696/UE). Given their peculiar physico-chemical features, nanostructured materials are largely used in many industrial fields (e.g. cosmetics, electronics, agriculture, biomedical) and their applications have astonishingly increased in the last fifteen years. Nanostructured materials are endowed with very large specific surface area that, besides making them very useful in many industrial processes, renders them very reactive towards the biological systems and, hence, potentially endowed with significant hazard for human health. For these reasons, in recent years, many studies have been focused on the identification of toxic properties of nanostructured materials, investigating, in particular, the mechanisms behind their toxic effects as well as their determinants of toxicity. This thesis investigates two types of nanostructured TiO2 materials, TiO2 nanoparticles (NP), which are yearly produced in tonnage quantities, and TiO2 nanofibres (NF), a relatively novel nanomaterial. Moreover, several preparations of MultiWalled Carbon Nanotubes (MWCNT), another nanomaterial widely present in many products, are also investigated.- Although many in vitro and in vivo studies have characterized the toxic properties of these materials, the identification of their determinants of toxicity is still incomplete. The aim of this thesis is to identify the structural determinants of toxicity, using several in vitro models. Specific fields of investigation have been a) the role of shape and the aspect ratio in the determination of biological effects of TiO2 nanofibres of different length; b) the synergistic effect of LPS and TiO2 NP on the expression of inflammatory markers and the role played therein by TLR-4; c) the role of functionalization and agglomeration in the biological effects of MWCNT. As far as biological effects elicited by TiO2 NF are concerned, the first part of the thesis demonstrates that long TiO2 nanofibres caused frustrated phagocytosis, cytotoxicity, hemolysis, oxidative stress and epithelial barrier perturbation. All these effects were mitigated by fibre shortening through ball-milling. However, short TiO2 NF exhibited enhanced ability to activate acute pro-inflammatory effects in macrophages, an effect dependent on phagocytosis. Therefore, aspect ratio reduction mitigated toxic effects, while enhanced macrophage activation, likely rendering the NF more prone to phagocytosis. These results suggest that, under in vivo conditions, short NF will be associated with acute inflammatory reaction, but will undergo a relatively rapid clearance, while long NF, although associated with a relatively smaller acute activation of innate immunity cells, are not expected to be removed efficiently and, therefore, may be associated to chronic inflammatory responses. As far as the relationship between the effects of TiO2 NP and LPS, investigated in the second part of the thesis, are concerned, TiO2 NP markedly enhanced macrophage activation by LPS through a TLR-4-dependent intracellular pathway. The adsorption of LPS onto the surface of TiO2 NP led to the formation of a specific bio-corona, suggesting that, when bound to TiO2 NP, LPS exerts a much more powerful pro-inflammatory effect. These data suggest that the inflammatory changes observed upon exposure to TiO2 NP may be due, at least in part, to their capability to bind LPS and, possibly, other TLR agonists, thus enhancing their biological activities. Finally, the last part of the thesis demonstrates that surface functionalization of MWCNT with amino or carboxylic groups mitigates the toxic effects of MWCNT in terms of macrophage activation and capability to perturb epithelial barriers. Interestingly, surface chemistry (in particular surface charge) influenced the protein adsorption onto the MWCNT surface, allowing to the formation of different protein coronae and the tendency to form agglomerates of different size. In particular functionalization a) changed the amount and the type of proteins adsorbed to MWCNT and b) enhanced the tendency of MWCNT to form large agglomerates. These data suggest that the different biological behavior of functionalized and pristine MWCNT may be due, at least in part, to the different tendency to form large agglomerates, which is significantly influenced by their different capability to interact with proteins contained in biological fluids. All together, these data demonstrate that the interaction between physico-chemical properties of nanostructured materials and the environment (cells + biological fluids) in which these materials are present is of pivotal importance for the understanding of the biological effects of NM. In particular, bio-persistence and the capability to elicit an effective inflammatory response are attributable to the interaction between NM and macrophages. However, the interaction NM-cells is heavily influenced by the formation at the nano-bio interface of specific bio-coronae that confer a novel biological identity to the nanostructured materials, setting the basis for their specific biological activities.

Development of a Lab-on-a-Chip Device for Rapid Nanotoxicity Assessment In Vitro

Increasing useof nanomaterials in consumer products and biomedical applications creates the possibilities of intentional/unintentional exposure to humans and the environment. Beyond the physiological limit, the nanomaterialexposure to humans can induce toxicity. It is difficult to define toxicity of nanoparticles on humans as it varies by nanomaterialcomposition, size, surface properties and the target organ/cell line. Traditional tests for nanomaterialtoxicity assessment are mostly based on bulk-colorimetric assays. In many studies, nanomaterials have found to interfere with assay-dye to produce false results and usually require several hours or days to collect results. Therefore, there is a clear need for alternative tools that can provide accurate, rapid, and sensitive measure of initial nanomaterialscreening. Recent advancement in single cell studies has suggested discovering cell properties not found earlier in traditional bulk assays. A complex phenomenon, like nanotoxicity, may become clearer when studied at the single cell level, including with small colonies of cells. Advances in lab-on-a-chip techniques have played a significant role in drug discoveries and biosensor applications, however, rarely explored for nanomaterialtoxicity assessment. We presented such cell-integrated chip-based approach that provided quantitative and rapid response of cellhealth, through electrochemical measurements. Moreover, the novel design of the device presented in this study was capable of capturing and analyzing the cells at a single cell and small cell-population level. We examined the change in exocytosis (i.e. neurotransmitterrelease) properties of a single PC12 cell, when exposed to CuOand TiO2 nanoparticles. We found both nanomaterials to interfere with the cell exocytosis function. We also studied the whole-cell response of a single-cell and a small cell-population simultaneously in real-time for the first time. The presented study can be a reference to the future research in the direction of nanotoxicity assessment to develop miniature, simple, and cost-effective tool for fast, quantitative measurements at high throughput level. The designed lab-on-a-chip device and measurement techniques utilized in the present work can be applied for the assessment of othernanoparticles' toxicity, as well.

Investigation of adsorption of dyes onto modified titanium dioxide

Titanium dioxide (TiO2) nanoparticles with different sizes and crystalloid structures produced by the thermal method and doped with silver iodide (AgI), nitrogen (N), sulphur (S) and carbon (C) were applied as adsorbents. The adsorption of Methyl Violet (MV), Methylene Blue (MB), Methyl Orange (MO) and Orange II on the surface of these particles was studied. The photocatalytic activity of some particles for the destruction of MV and Orange II was evaluated under sunlight and visible light. The equilibrium adsorption data were fitted to the Langmuir, Freundlich, Langmuir-Freundlich and Temkin isotherms. The equilibrium data show that TiO2 particles with larger sizes and doped with AgI, N, S and C have the highest adsorption capacity for the dyes. The kinetic data followed the pseudo-first order and pseudo-second order models, while desorption data fitted the zero order, first order and second order models. The highest adsorption rate constant was observed for the TiO2 with the highest anatase phase percentage. Factors such as anatase crystalloid structure, particle size and doping with AgI affect the photocatalytic activity significantly. Increasing the rutile phase percentage also decreases the tendency to desorption for N-TiO2 and S-TiO2. Adsorption was not found to be important in the photocatalytic decomposition of MV in an investigation with differently sized AgI-TiO2 nanoparticles. Nevertheless C-TiO2 was found to have higher adsorption activity onto Orange II, as the adsorption role of carbon approached synchronicity with the oxidation role.

Development of a lab-on-a-chip device for rapid nanotoxicity assessment in vitro

Increasing useof nanomaterials in consumer products and biomedical applications creates the possibilities of intentional/unintentional exposure to humans and the environment. Beyond the physiological limit, the nanomaterialexposure to humans can induce toxicity. It is difficult to define toxicity of nanoparticles on humans as it varies by nanomaterialcomposition, size, surface properties and the target organ/cell line. Traditional tests for nanomaterialtoxicity assessment are mostly based on bulk-colorimetric assays. In many studies, nanomaterials have found to interfere with assay-dye to produce false results and usually require several hours or days to collect results. Therefore, there is a clear need for alternative tools that can provide accurate, rapid, and sensitive measure of initial nanomaterialscreening. Recent advancement in single cell studies has suggested discovering cell properties not found earlier in traditional bulk assays. A complex phenomenon, like nanotoxicity, may become clearer when studied at the single cell level, including with small colonies of cells. Advances in lab-on-a-chip techniques have played a significant role in drug discoveries and biosensor applications, however, rarely explored for nanomaterialtoxicity assessment. We presented such cell-integrated chip-based approach that provided quantitative and rapid response of cellhealth, through electrochemical measurements. Moreover, the novel design of the device presented in this study was capable of capturing and analyzing the cells at a single cell and small cell-population level. We examined the change in exocytosis (i.e. neurotransmitterrelease) properties of a single PC12 cell, when exposed to CuOand TiO2 nanoparticles. We found both nanomaterials to interfere with the cell exocytosis function. We also studied the whole-cell response of a single-cell and a small cell-population simultaneously in real-time for the first time. The presented study can be a reference to the future research in the direction of nanotoxicity assessment to develop miniature, simple, and cost-effective tool for fast, quantitative measurements at high throughput level. The designed lab-on-a-chip device and measurement techniques utilized in the present work can be applied for the assessment of othernanoparticles' toxicity, as well.^

Peptide-based low molecular weight gelators for the preparation of self-assembled materials

Low molecular weight gelators (LMWGs) based on pseudo-peptides are here studied for the preparation of supramolecular materials. These compounds can self-assemble through non-covalent interactions such as hydrogen bonds and π-π stacking, forming fibres and gels. A wide variety of materials can be prepared starting from these building blocks, which can be tuned and functionalised depending on the application. In this work, derivatives of the three aromatic amino acids L-Phenylalanine, L-Tyrosine and L-DOPA (3,4-dihydroxiphenylalanine) were synthesised and tested as gelators for water or organic solvents. First, the optimal gelating conditions were studied for each compound, varying concentration, solvent and trigger. Then the materials were characterised in terms of mechanical properties and morphology. Water remediation from dye pollution was the first focus of this work. Organogels were studied as absorbent of dyes from contaminated water. Hydrogels functionalised with TiO2 nanoparticles and graphene platelets were proposed as efficient materials for the photo-degradation of dyes. An efficient method for the incorporation of graphene inside hydrogels using the gelator itself as dispersant was proposed. In these materials a high storage modulus coexists with good self-healing and biocompatibility. The incorporation of a mineral phase inside the gel matrix was then investigated, leading to the preparation of composite organic/inorganic materials. In a first study, the growth of calcium carbonate crystals was achieved inside the hydrogel, which preserved its structure after crystal formation. Then the self-assembled fibres made of LMWGs were used for the first time instead of the polymeric ones as reinforcement inside calcium phosphate cements (CPCs) for bone regeneration. Gel-to-crystal transitions occurring with time in a metastable gel were also examined. The formation of organic crystals in gels can be achieved in multicomponent systems, in which a second gelator constitutes the independent gel network. Finally, some compounds unable to gelate were tested as underwater adhesives.

Biological behaviour of thin films consisting of Au nanoparticles dispersed in a TiO2 dielectric matrix

In this work it was studied the possible use of thin films, composed of Au nanoparticles (NPs) embedded in a TiO2 matrix, in biological applications, by evaluating their interaction with a well-known protein, Bovine Serum Albumin (BSA), as well as with microbial cells (Candida albicans). The films were produced by one-step reactive DC magnetron sputtering followed by heat-treatment. The samples revealed a composition of 8.3 at.% of Au and a stoichiometric TiO2 matrix. The annealing promoted grain size increase of the Au NPs from 3 nm (at 300 °C) to 7 nm (at 500 °C) and a progressive crystallization of the TiO2 matrix to anatase. A broad localized surface plasmon resonance (LSPR) absorption band (λ = 580–720 nm) was clearly observed in the sample annealed at 500 °C, being less intense at 300 °C. The biological tests indicated that the BSA adhesion is dependent on surface nanostructure morphology, which in turn depends on the annealing temperature that changed the roughness and wettability of the films. The Au:TiO2 thin films also induced a significant change of the microbial cell membrane integrity, and ultimately the cell viability, which in turn affected the adhesion on its surface. The microstructural changes (structure, grain size and surface morphology) of the Au:TiO2 films promoted by heat-treatment shaped the amount of BSA adhered and affected cell viability.

Model catalyst studies of the strong metal-support interaction: Surface structure identified by STM on Pd nanoparticles on TiO2(110)

Model catalysts of Pd nanoparticles and films on TiO2 (I 10) were fabricated by metal vapour deposition (MVD). Molecular beam measurements show that the particles are active for CO adsorption, with a global sticking probability of 0.25, but that they are deactivated by annealing above 600 K, an effect indicative of SMSI. The Pd nanoparticles are single crystals oriented with their (I 11) plane parallel to the surface plane of the titania. Analysis of the surface by atomic resolution STM shows that new structures have formed at the surface of the Pd nanoparticles and films after annealing above 800 K. There are only two structures, a zigzag arrangement and a much more complex "pinwheel" structure. The former has a unit cell containing 7 atoms, and the latter is a bigger unit cell containing 25 atoms. These new structures are due to an overlayer of titania that has appeared on the surface of the Pd nanoparticles after annealing, and it is proposed that the surface layer that causes the SMSI effect is a mixed alloy of Pd and Ti, with only two discrete ratios of atoms: Pd/Ti of 1: 1 (pinwheel) and 1:2 (zigzag). We propose that it is these structures that cause the SMSI effect. (c) 2005 Elsevier Inc. All rights reserved.

Photothermal Study of Two Different Nanofluids Containing SiO2 and TiO2 Semiconductor Nanoparticles

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)