Добірка наукової літератури з теми "NANOPARTICULATE FILLER"

Abstract Nylon composites are of evolving interest due to their good strength, toughness, and low coefficient of friction. Various fillers like micro- and nanoparticulates of metals and metal compounds were used to enhance the mechanical and tribological properties of nylons for many years by researchers. In this paper, an overall understanding of composites, filler materials, especially particulate filler materials, application areas of polymer composites, wear of polymers, and the effect of various fillers on tribo-mechanical properties of nylons have been discussed. The detailed review is limited to micro- and nanoparticulate fillers and their influence on the mechanical and tribological properties of various nylon matrices.

Acrylate polymer-based bone cements constitute the most popular bonding agents used in regenerative surgery. Due to their inferior biocompatibility, however, these materials are often enriched with ceramic additives including hydroxyapatite (HAp). The aim of this paper was to perform a comparative study of the acrylate cements filled with different content (3–21%) of nano- and microscale hydroxyapatite. The work concerns a comparison of times and temperatures of the cross-linking reaction, as well as morphology, glass transition temperature, and principal mechanical properties of the resulting composites. Before being used as a filler, both HAp forms were subjected to an in-depth characterization of their morphology, specific surface area, pore size distribution, and wettability as well as chemical composition and structure. For that purpose, such analytical techniques as scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, tensiometry, Brunauer–Emmett–Teller surface area analysis, differential scanning calorimetry, Shore D hardness test, and Charpy impact test were used. The results indicated a drop of cross-linking temperature and an extension of setting time with the addition of µHAp. The µHAp-filled acrylate composites were characterized by a globular surface morphology, higher glass transition temperature, and lower hardness and impact strength compared to nHAp-filled materials. This relationship was evident at higher nHAp concentrations.

The objective of this research was to study the feasibility of producing biodegradable thermoplastic starch rice-husk composites. The effect of different types of mineral fillers on the various properties of thermoplastic starch composites filled with rice-husk flour, an agricultural waste residue, was studied. The mineral fillers aluminum trihydrate (ATH), magnesium dihydroxide (MDH), nanoparticulate MDH, and nanoclay were studied. It was found that the addition of the mineral fillers and especially nanofillers improved the dimensional stability and the mechanical properties of the composites, while decreasing their biodegradability. The thermogravimetric analysis (TGA) showed that substituting mineral fillers for some part of the lignocellulosic component increased the extents of weight-loss in the first and second steps, but decreased the weight-loss in the last step. This substitution also led to a slight decrease in the thermal decomposition temperatures at the curve peaks.

This study had as its main objective to evaluate the flexural properties (strength and modulus) and degree of conversion of a dimethacrylate resin containing different amounts of nanoparticulated clay Montomorillonite (MMT) as filler. A series of composites containing similar amounts (in volume) of barium glass particles was also tested as control data. Eight formulations with polymeric matrix-based BisGMA/TEGDMA (Bisphenol A Bis(2-hydroxy-3 methacryloxypropyl)Ether/Triethyleneglycol Dimethacrylate), four added with MMT and four added with barium glass in the volume concentration of 20, 30, 40 and 50 vol% were studied. The degree of conversion was determined using near-IR spectroscopy. Elastic modulus and flexural strength were determined by the three-point bending test. The dispersion of MMT nanoparticles was determined by means of X-ray diffraction and transmission electron microscopy analysis. The fillers montomorillonite and barium glass interacted with polymer matrix-based BisGMA/TEGDMA in a distinct manner. Although the addition of montomorillonite nanoparticles resulted in similar degree of conversion and higher elastic modulus values at all concentrations tested, only at the 20 vol% the flexural strength was statistically higher, compared to the control groups filled with barium glass. This could be related to the need of concentration optimization of montomorillonite for each type of polymer matrix in order to adjust or improve mechanical properties. The addition of low concentrations (<l 20% vol) of montomorillonite nanoparticles in dental composites resins – such as additive or hybrid filler – should be studied, aiming to the reduction of polymerization shrinkage, better mechanical properties and improvement of a new technology for future applications.

Addition of a cheap, nanoparticulate, hypercrosslinked polymer “sponge” to the high-free-volume glassy polymer PIM-1 gives mixed matrix membranes with enhanced permeability and improved aging behaviour.

The aim of this study was to determine the hardness and the elasticity modulus of the two composite resins base of BISGMA with different inorganic particles: a nanoparticulated with a ceramic withload, (Filtek Z350XT-3M) with and without thermal activation and a microhybrid with no ceramic load (Opallis-FGM). The samples were prepared and subjected to the tests of Vickers hardness (Shimadzu HMV) and acoustic excitation pulse (Sonelastic ®). The samples were divided into three groups: G1-Filtek Z350 XT; G2-Filtek Z350XT MO (subject to further polymerization microwave) and G3-Opallis. The results showed that the hardness of G2 was significantly higher than the groups G1 and G3. The elastic modulus was higher than the G2 to G1 and G3. One can conclude that the resins filled with inorganic ceramic filler showed higher hardness and elastic modulus. The thermal activation increased the hardness and the elasticity modulus of the resin with ceramic load.

In this study, new composite coatings are fabricated and investigated for their applications as the metal coating. The studied coatings consist of two-layered composites with various nanoparticulates as fillers in a polymeric matrix (styrene acrylic). The first layer bonded to the steel plate uses a combination of zinc particles, multi-walled carbon nanotubes, and graphene nanoplatelets. For the second layer, hexagonal boron nitride with high electrical insulation properties is added to the matrix. The morphology of the nanoparticulates is conducted using a scanning electron microscope. The coefficient of thermal expansion, cathodic disbondment resistance, gas penetration, and scratch resistance of the coatings are evaluated. The corroded area on the cathodic disbondment test specimens reduced down up to 90% for the composite with zinc (20 wt%), multi-walled carbon nanotubes (2 wt%), and graphene nanoplatelets (2 wt%), compared to a specimen coated with a pure polymer. It is seen that the presence of nanoparticulates decreased gas permeation and thermal expansion of the matrix by 75% and 65%, respectively. The addition of nanoparticulates also enhanced scratch resistance of the coating composites.

Polymer composites based on poly(vinyl alcohol) filled with silver nanoparticles containing biocompatible fillers, such as silica and hydroxyapatite, have been prepared and tested for potential antimicrobial application. An effect of silver content on the properties of prepared polymer composites was evaluated. The results show that defined bactericidal activity of the elaborated materials was observed silver nanoparticles concentration of  61 ppm. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35421

Thesis (Ph.D.)--City University of Hong Kong, 2005.
"Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy" Includes bibliographical references.

Revestimentos antirrefletores no vidro tem sido objeto de estudo de grande parcela da comunidade científica e tecnológica para obtenção de alta transmitância óptica em sistemas ópticos e, sobretudo para melhorar a eficiência em muitas aplicações, tais como painéis de células solares, telas de exibição de vídeo, pára-brisas de automóveis, óculos e janelas de edifícios. Mais recentemente, superhidrofobicidade tem apresentado crescente interesse para diversas áreas, tais como roupas repelentes a água, superfícies metálicas e microfluido. Neste trabalho, combinamos superhidrofobicidade e antirreflexão à autolimpeza e transparência. Essas propriedades são obtidas pela combinação em multiescala de topologia de superfície baseada na deposição de nanopartículas de sílica (SNPs), revestimentos de índice gradual e revestimentos interferométricos, utilizando politetrafluoroetileno (PTFE), em três rotas. Na primeira rota com apenas uma camada (vidro/SNPs), as amostras apresentaram um ângulo de contato (WCA) de 161°±2° com alto valor de histerese angular e pouca antireflexão. Na segunda rota com duas camadas (vidro/SNPs/PTFE), as amostras apresentaram um WCA de 169°±2° com baixo valor de histerese angular e com melhor antireflexão. Na terceira rota, composta por três camadas (vidro/SNPs/aerogel/PTFE), as amostras apresentaram um WCA de 158°±2° com baixo valor de histerese angular (<5°) e uma transmitância em incidência normal acima de 99%, com decréscimo de menos de 2% para incidência oblíqua a 20°. Estes resultados mostram a obtenção simultânea propriedades antirrefletoras e autolimpantes em vidro, devido à combinação de efeitos de revestimentos interferométricos e de índice gradual, na região do visível e do infravermelho.
Anti-reflective coatings on glass have been subject of great technological and scientific attention for low-loss transmission optical systems, and particularly they enhance efficiency in many applications, such as solar panels and cells, video display screens, automobile windscreens, eyeglasses and windows of buildings. More recently, superhydrophobicity has found increasing interest for other diverse areas, such as waterrepellent clothing, metallic surfaces and microfluidics. In this work, we combine superhydrophobicity and anti-reflection with regard to self-cleaning and transparency. These properties are pursued by combination of multi-scale surface topology based on silica nanoparticles (SNPs), index grading and interference coating, as well as Polytetrafluoroethylene (PTFE) self-assembly, using three approaches. In the first, onelayer approach (glass/SNPs), the resulting samples presented water contact angle (WCA) of 161o ± 2o with high angular hysteresis and some antireflection. In the second, two-layer approach (glass/SNPs/PTFE), the resulting samples presented a WCA of 169o ± 2o with very low hysteresis, as well as significant antireflection. The third, three-layer approach (glass/SNPs/silica aerogel/PTFE), produced surfaces with WCA of 158o ± 2o with also very low hysteresis (<5o), in addition to normal transmittance of 99% or higher, which decreased less than 2% at 20o incidence. These results show that proper structure-coated glass, with a combination of interference and graded-index effects, may provide simultaneous self-cleaning and wide-angle antireflection properties, in the visible and infrared spectra.

Este trabalho apresenta a produção e a caracterização de filmes finos produzidos a partir da técnica de RF Magnetron Sputtering. Foram produzidos filmes finos sobre substrato de silício a partir de alvos vítreos de germânio de GeO2-PbO preparados com e sem os reagentes AgNO3 e Cu2O. Foi desenvolvida metodologia adequada para a obtenção de nanopartículas em filmes finos por meio de tratamento térmico. Os filmes foram caracterizados por técnicas de perfilometria, elipsometria, Microscopia de Força Atômica (AFM), Rutherford Backscattering (RBS), Microscopia Eletrônica de Transmissão (TEM) e medidas elétricas para a obtenção das curvas de capacitância e corrente em função da tensão. Os valores dos índices de refração medidos ficaram em torno de 1,9, isto é, próximo do valor do alvo vítreo utilizado para as deposições. Através do AFM foi observado que a rugosidade vale-pico variou de 2 a 4 nm. Através de TEM verificou-se em todos os filmes a presença de nanopartículas metálicas e também facetas cristalinas formadas pelos próprios elementos da matriz. Pelas medidas elétricas, foram obtidos os resultados das constantes dielétricas que variaram com o tratamento térmico. Os valores variaram de 8 a 15 superando o valor do SiO2 que é de 3,9. Com todos os resultados elétricos, foi notado que o filme preparado com o reagente CU2O foi o que apresentou maior estabilidade com o tratamento térmico o que é adequado para o preparo de dispositivos MOS. Neste caso o valor obtido para a constante dielétrica foi de 14.
This work presents the production and characterization of thin films produced by the RF Magnetron Sputtering technique. There were produced thin films on silicon substrate from vitreous targets of GeO2-PbO prepared with and without AgNO3 and Cu2O reagents. It was developed adequate methodology to obtain metallic nanoparticles in thin films by means of heat treatment. The films were characterized using perfilomitry, ellipsometry, Atomic Force Microscopy (AFM), Rutherford Backscattering (RBS), Transmission Electron Microscopy (TEM) techniques and electrical measurements in order to obtain the curves of current and capacitance as a function of the voltage. The values of refractive indices were measured around 1.9 next to the value of the vitreous target used for the deposition. Through the AFM, it was observed that the valley-peak roughness varied from 2 to 4 nm. Through TEM, it was observed in all films the presence of metallic nanoparticles and also some crystalline faces formed by the elements of the matrix. With the electrical measurements, there were obtained the dielectric constants that varied with the heat treatment. The values ranged from 8 to 15 surpassing the value of SiO2 which is 3.9. With all the electric results, it was noted that the film prepared with copper was the one that presented the highest stability with the heat treatment that is appropriate for the preparation of MOS devices.

Cette étude porte sur la filtration des particules métalliques contenues dans les fumées de métallisation. Des retours d'expériences spécifiques aux dépoussiéreurs filtrants les fumées de métallisation témoignent d'un colmatage des filtres très rapide ainsi que de l'inefficacité des techniques de décolmatage pneumatique habituellement utilisées. Il en résulte une durée de vie des éléments filtrants très réduite. L'objectif de cette étude est de caractériser le colmatage puis le décolmatage afin d'améliorer les performances des dépoussiéreurs à cartouches filtrantes vis-à-vis des fumées de métallisation. Trois axes de recherches ont été exploré sur un banc pilote spécialement équipé : - la caractérisation des fumées de métallisation. Elle a permis de qualifier la structure spatiale de la particule par la dimension fractale et le facteur de forme dynamique grâce au couplage série DMA-ELPI et à une méthodologie originale d'analyse des données validée sur différents aérosols. Les caractéristiques obtenues expliquent les propriétés colmatantes des fumées de métallisation. - La caractérisation du dépôt engendré au cours de la phase de filtration (ou de colmatage). Elle montre une structure incompressible dans la gamme de filtration habituellement pratiquée en industrie. Ces travaux ont permis d'estimer la porosité expérimentale du dépôt formé par les fumées de métallisation. - L'étude sur le décolmatage. Elle décrit et explique l'inefficacité des décolmatages utilisés en industrie. Il ressort que seule une très faible surface du média plissé est décolmatée. L'alternative du precoating se révèle très efficace mais seulement en mode off-line
This study deals with the filtration of metallic particles contained in the metallization fumes. Experience feedback specific to the filtration of metallization fumes by dust collectors report a rapid clogging of filters and the inefficiency of pneumatic cleaning techniques commonly used. This leads to a high reduction in filters lifetime. The objective of this study is characterize clogging then unclogging in order to improve the performance of dust cartridge filter against metallization fumes. Three research axes were explored on a dedicated bench : - Metallization fumes characterization. It allows describing the spatial structure of the particle by the fractal dimension and the dynamic shape factor with the DMA-ELPI serial coupling and thanks to an original data analysis methodology validated on various aerosols. The characteristics obtained explain the clogging properties of metallization fumes. - Characterization of the cake generated during the filtration phase (or clogging). It shows a incompressible structure in the velocities filtration range of industry. The experimental porosity of the cake formed by filtering metallization fumes is estimated thanks to these studies. - Study on cleaning. It describes and explains the inefficiency of pneumatic cleaning techniques employed in industry. It appears that only a very small surface of the pleated media is unclogged. The precoating alternative is shown to be very efficient provided that it is combined with off-line cleaning procedures

O demorado tratamento térmico, comum no preparo de fotocatalisadores e sua imobilização em substratos, foi contornado nesta tese, em que se investigaram duas estratégias de modificação de eletrodos de ouro com TiO2 P25. A primeira consiste em promover a formação de uma nanocamada pela simples exposição do metal por 1 min à suspensão aquosa de TiO2 (10 g L-1 em HCl 0,1 mol L-1); na segunda, deposita-se uma pequena alíquota (5 ou 8 µL) da suspensão diretamente no substrato (drop coating) para secá-lo em seguida por irradiação com lâmpada incandescente (60 W a 20 cm), obtendo-se bons resultados de uma a três camadas depositadas. Comprovou-se grande aumento da estabilidade da suspensão aquosa e duplicação da atividade fotocatalítica do nanofilme de TiO2 em decorrência da repulverização de P25 comercial em almofariz, melhoria inalcançável por sonicação da suspensão. O tamanho de partícula médio obtido por DLS para o TiO2 disperso em meio de HCl 0,1 mol L-1 atingiu 103±3 nm, enquanto que o filme depositado na superfície do ouro (observado por MEV e caracterizado por EDS) não ultrapassou 100 nm de espessura, sendo dominado por partículas de diâmetro de 20 (anatase) a 30 nm (rutilo), observadas por MET. A estabilidade da suspensão é susceptível ao ânion do ácido utilizado, sendo que resultados igualmente satisfatórios foram obtidos com HCl e HclO4 0,1 mol L-1, enquanto que para a mesma concentração de H2SO4 o TiO2 sofreu sedimentação rápida e o eletrodo preparado com a suspensão apresentou fotoatividade 10x menor. Filmes de espessuras bastante distintas (100 nm e 2 m) depositados a partir de suspensão 10 g L-1 por contato e drop coating com gota de 5,0 µL, respectivamente, foram comparados em relação à sua capacidade de transporte de elétrons e resposta eletroquímica ao Fe(CN)6 3 1,0 mmol L-1, sendo que a carga líquida formal de oxidação do EDTA 1,0 mmol L-1 é apenas 50 % maior para o filme 20x mais espesso, além de gerar distorções consideráveis nas ondas voltamétricas do sistema-sonda reversível em relação ao filme nanométrico e à superfície polida. Com eletrodos modificados pelo protocolo otimizado de drop coating (8,0 µL de TiO2 2 g L-1), testou-se o efeito da presença de diferentes eletrólitos de suporte (ácidos 0,1 mol L-1) em processos anódicos de fotooxidação em geral. A curva de decaimento da fotocorrente iph com o tempo pode ser descrita por uma equação de decaimento exponencial duplo iph = i0 + A1 exp(k1t) + A2 exp( k21t), permitindo distinguir as contribuições da fotocorrente de oxidação da água (i0) e de termos referentes a dois tipos de sítio superficiais, sendo um de cinética rápida e outro de cinética lenta. A seguinte ordem foi determinada para a fotocorrente total inicial (iph0 total) dos eletrólitos: HNO3 > HClO4 > HCl > H1SO4 > H3PO4 e as explicações propostas para tal se embasam na adsortividade dos ânions no TiO2 e na reatividade dos respectivos traps formados. O mesmo modelo de ajuste matemático foi utilizado para avaliar a fotoatividade do eletrodo modificado pela sua irradiação sucessiva e repetida em HNO3 0,1 mol L-1 (sem EDTA), sendo observada redução significativa principalmente nos parâmetros relativos aos sítios de reação e, assim, sugere-se um impedimento dos mesmos através, p. ex., da formação de peróxidos superficiais. Na presença também de EDTA, a carga líquida total despendida na sua fotooxidação se mantém relativamente constante nas sucessivas irradiações. Por fim, os experimentos de fotooxidação do EDTA sob varredura de potencial revelaram uma região de relação linear entre a fotocorrente e o potencial aplicado ao eletrodo modificado com TiO2 que se estende até a região de saturação de fotocorrente ser atingida, comportamento compatível com filmes nanoparticulados porosos não-dopados. A inclinação da região linear aumenta em função da [EDTA], como se os valores de condutância (di/dE) se elevassem dependendo da reação interfacial. Ajuste de modelo matemático hiperbólico correlacionando a (foto)resistência do filme em função da fotocorrente de saturação R = R0 + kIsph1, fornece resistência ôhmica do filme R0 de 5,0 kΩ e uma constante atrelada ao fotopotencial de 237 mA Ω. Já a curva monotônica de fotocorrente de saturação (Isph) com a [EDTA] apresenta comportamento linear até cerca de 0,7 mmol L-1, sugerindo-se que nessa região o controle por transporte de massa é a etapa limitante do processo global. Acima dessa concentração o coeficiente angular diminui gradualmente à medida que a reação de cinética de captura das lacunas passa a ser o determinante até um limite máximo (aparentemente 5,0 mmol L-1 de EDTA, nas condições do experimento) onde a disponibilidade de lacunas fotogeradas passa a governar.
The lengthy thermal treatment is a common step during the preparation and immobilization of photocatalysers on substrates, which by the way, was overcome in this thesis by the investigation of two strategies of modification of gold electrodes with P25 TiO2. The first one consists in promoting the formation of a nanolayer by the simple exposure of the metal surface to an aqueous suspension of TiO2 (10 g L-1 on 0.1 mol L-1 HCl) during 1 min; the second involves the deposition of a small drop (5 or 8 L) of the suspension on the gold substrate (drop coating) and its drying by irradiation with an incandescent lamp (60 W at 20 cm far), with worthy results also for two or three deposited layers. The stability of this aqueous suspension was appreciably improved by the repulverization of commercial P25 in a grinding mortar. As a consequence the photocatalytic activity conferred to the electrode by the formation of the TiO2 nanofilm doubled. Such improvements cannot be attained by bath sonication of the suspension. The average particle size determined by DLS for the TiO2 dispersed in 0.1 mol L-1 HCl was 103±3 nm, while the film deposited on the surface of gold consisted of particles of 20 nmn (anatase) and 30 nm (rutile) characterized by TEM and barely achieved a thickness of 100 nm (characterized by SEM and EDS). The stability of the modifying suspension is susceptible to the type of anion of the electrolyte. Good results were found with 0.1 mol L-1 HCl and HClO4, but not with 0.1 mol L-1 H2SO4. This last medium causes fast sedimentation of TiO2 and generates electrodes with one tenth of the photoactivity achieved with the other acids. The effect of film thickness on the photoactivity was evaluated for films with 100 nm and 2.0 µm prepared from a 10 g L-1 TiO2 suspension by the contact and drop coating (5 µL) strategies, respectively. The electron transport across both films and the electrochemical response for the 1.0 mmol L-1 Fe(CN) 63- probe was compared. The formal net charge for the 1.0 mmol L-1 EDTA oxidation was only 50 % higher for the 20x thicker film that also considerably distorts the voltammetric waves of the aforementioned reversible probe. The effect of different supporting electrolytes (0.1 mol L-1 acids) on the anodic photooxidation processes in general was tested with electrodes modified by an optimized drop coating protocol (8.0 µL of 2 µg L-1 TiO2). The curve describing the photocurrent decay in function of time might be ascribed to an equation of double exponential decay iph = i0 + A1 exp(k1t) + A2 exp (k2t), which allows the distinction of the contribution of water oxidation (i0) from terms of two types of surface sites: a kinetically fast site and a slow one. The total initial photocurrent (iph0 total) of the following electrolytes decays in the order: HNO3 > HClO4 > HCl > H2SO4 > H3PO4; explanations comprise the adsorbability of each respective anion on TiO2 and the reactivity of the corresponding traps formed. Similar curve fitting applied to the data of photoactivity of the gold electrode during successive irradiations of its surface in 0.1 mol L-1 HNO3 (absence of EDTA) revealed that sites reactivities underwent considerable reduction. It is suggested that during repetitive experiments the sites are impaired by the formation of surface peroxides. However, in the presence of 1.0 mmol L-1 of EDTA, the formal net charge of oxidation of the organic species remains almost unaltered. Ultimately, the experiments concerning the photooxidation of EDTA under linear potential scan revealed a region of linear relation between the photocurrent and the potential applied to the electrode modified with a TiO2 film (nanometric or micrometric), which holds until the saturation photocurrent is attained. This behavior is typical for porous non-doped nanoparticulate electrodes. The slope of the linear region increase somewhat with the EDTA concentration, as though the conductance values (di/dE) were raised depending on the interfacial reaction rate. The fitting of a hyperbolic model R = R0 + kIsph-1 for the correlation of the (photo)resistence (R) of the film with the photocurrent of saturation (Isph) allows the estimation of an ohmic resistance of 5.0 kΩ, and a photopotential related constant of 237 mA Ω. The curve of correlation between Isph and the [EDTA] is linear fit until 0.7 mmol L-1, suggesting that in this initial region the mass transport to the interface is the limiting step of the global process. Above that concentration, the slope of the curve is gradually reduced as the kinetic of capture of the holes becomes the determining step and from 5.0 mmol L-1 on an asymptotic Isph is reached (under the conditions of the experiments), where the holes photogeneration might start governing.

Les élastomères chargés sont des matériaux nanocomposites présentant un compromis de propriétés unique exploité notamment dans les bandes de roulement des pneumatiques. Ils comprennent une charge renforçante, silice ou noir de carbone, qui doit présenter un module élevé, des dimensions nanométriques, et avoir la capacité de se disperser et de former des liaisons fortes avec la matrice. La nanocellulose est caractérisée par une morphologie anisotrope avec une section de l'ordre de 10 nm, et une structure cristalline avec un module d'environ 150 GPa. L'objectif de la thèse est d'évaluer si ce substrat peut être employé comme charge renforçante. Les travaux se divisent ainsi en trois parties portant successivement sur l'obtention d'aérogels de haute surface spécifique, la modification de leur surface, puis leur emploi comme renfort. La mise au point d'un protocole de lyophilisation de suspensions de nanocellulose, et d'un procédé d'estérification par voie gaz des aérogels obtenus, a permis d'obtenir des charges avec une haute surface spécifique et une interface avec un agent hydrophobe ou un agent de couplage. Une attention particulière a été accordée à la topochimie de la réaction dont le suivi a été réalisée par RMN du solide. Ces charges ont ensuite été incorporées au sein d'un élastomère, puis les matériaux obtenus ont été caractérisés par MET et par des tests mécaniques. Dans le cas d'un aérogel de nanocellulose avec une haute surface spécifique et un agent de couplage, les propriétés des matériaux obtenus sont alors caractéristiques du comportement d'un élastomère chargé.

Organisations are increasingly employing databases on a large scale to store critical data that is essential for their functioning. Malicious access and modifications of the databases may lead to adverse financial and legal implications. In recent years, security researchers have focused on detecting abuse of access privileges by the employees of an organisation. Identifying threats from insiders is hard because they are aware of the organisation of the database in addition to having authorised access privileges. Therefore, an intrusion detection system(IDS) collects data from a computer system, analyses it for security faults, and reports the results to the administrator. Most of the current systems are not sufficient in properly classifying the users based on their access privileges and often end up flagging the legitimate users as intruders. These systems based on dependency mining rely on hard-coded values of sensitivity parameters which makes the system prone to a decrease in accuracy over time due to changes in user behaviour. On the other hand, the techniques that rely purely on unsupervised learning methods and data mining generally suffer from a higher false positive rate and supervised learning methods have proven to be ineffective against novel attacks. Majority of the techniques suffer from low recall because of their sensitivity towards changing user access patterns. Thus, there exists a need for a hybrid approach that caters to the pitfalls of both the topologies while retaining their benefits. To overcome the above problems, we propose novel approaches to integrate the benefits of various mining and metaheuristic techniques for reducing the high false positive rate. The thesis first addresses a new data mining-based approach namely ‘The Fuzzy Asso ciation Data Dependency Rule Miner (FADDRM) for identifying malicious transactions in databases by mining data dependencies between data items. Our method focuses on extracting association rules using fuzzy association rule mining in combination with Fuzzy Connected Clustering (FCC) and the rules are used to classify the transactions as 3 malicious or non-malicious. In the second part, we discuss a novel database intrusion detection system (DIDS) based on Expectation Maximisation Clustering and Sequential Pattern Mining (EMSPM). This method relies on the database pre-existing logs and the data dependency rules that are obtained by mining user information access patterns using modified PrefixSpan algo rithm. The Expectation Maximisation clustering algorithm assigns role profiles based on the database user’s behaviours. These clusters and patterns are then processed into an algorithm that prevents generation of unwanted rules as well as malicious transactions. In the third part, we present a BIDE and modified Particle Swarm Optimization clus tering based malicious query detection (BPSOMQD) approach.This method incorporates frequent closed sequential pattern mining which forms the basis for generation of data dependency rules. Further to recognise anomalous user activity, modified Particle Swarm Optimization algorithm is proposed which is used to generate role profiles associated with the transaction. To classify a transaction as malicious or non-malicious, a combination of Multilevel Rule Similarity Score (MRSS) between data dependency rules, incoming transactions and Cluster Similarity Index (CSI) with created role profiles is used. In the fourth part, we propose a Frequent Sequential Pattern mining and a modified metaheuristic hybrid clustering of Grey Wolf and Whale optimization algorithm (FPG WWO) to identify malicious transactions in RBAC and non-RBAC supervised databases. We use the CM-SPADE mining algorithm to extract database dependency rules that are used to detect outsider threats. Insider threats are detected by comparing user activities to previously determined role profiles that are assigned using the modified metaheuristic clustering from the past user behaviour. During the learning phase, transactions are la belled malicious on the basis of novel similarity threshold, i.e., the “congruity index”. If the transaction is found to be malicious, an alarm is triggered and the database executes a rollback.During the detection phase, a role matcher authenticates role clusters for the incoming transaction. If the role profile is not matched, the transaction is labelled as malicious and aborted. In the fifth part, we propose Trust factor based analysis of user behaviour using se 4 quential pattern mining for detecting intrusive transactions in databases (TFUBID) to prevent misuse of access privileges by insiders of an organisation. Since, groups of users access the organisational database for similar purposes, we cluster user behaviour vectors using fuzzy clustering and define a class of Integral Data Attributes using sequential pat tern mining to model trust factor based behavioural patterns of employees accessing the database assigning higher weight to critical elements and Directly Correlated Attributes. Modified Jensen-Shannon distance is used to give weights to data attributes and avoid the curse of dimensionality in dissimilarity calculation.The idea of an “incredulity score” is introduced which quantifies the degree of anomalous behaviour exhibited by each user based on his previous transactions. Finally, we propose Outlier based Intrusion Detection in Databases for User Behaviour Analysis using Weighted Sequential Pattern Mining (OIUWSPM) ,a novel method for detecting malicious transactions that follows a sequential flow that begins with outlier detection and continues with various behavioural checks at the role induced rule mining component and user level feature extraction. The idea of Dynamic Sensitivity is used distinctively at role level which complements the access counts of each attribute. We introduce the notion of Coherence Count computed by the application of Longest Common Subsequence(LCS) and the utilisation of Levenshtein distance for calculating Divergence between the user level Relation access paths. We analyse user behaviour by registering user level Relation access path reinforced on user transactions. Comprehensive implementation of the above models reveal that their performance is better and more efficient than other models.

High performance coatings of pipelines should possess properties such as high adhesion to the substrate, low gas permeability, high corrosion resistance, etc. In this study, novel nanocomposite materials are studied for coating of steel plates. The coatings consist of two-layer composites with different nanoparticulates. Zinc particles, multi-walled carbon nanotubes (MWCNT), and graphene nanoplatelets (GNP) are used for the base layer bonded to the steel. Zinc particles are used as a filler and act as sacrificial anode against corrosion (cathodic protection). Hexagonal boron nitride (hBN) is added to the matrix for the second layers. Adhesion of the coatings is studied through pull-off tests. To examine the corrosion protection capabilities, cathodic disbondment tests are conducted on the coated steel plates. The gas permeability of the coatings is evaluated through a standard testing technique. Results show that addition of Zinc particulates could enhance corrosion protection. The addition of GNP and hBN nanoparticulates resulted in lower gas penetration. Results of this research will contribute to the development of advanced pipeline coatings.