Numerical investigation of graphene and graphene-polymer nanocomposites

This thesis is a comprehensive and deep investigation on graphene and graphene-polymer nanocomposites. It explores the strong structure-property relationships in both graphene and graphene-based polymeric nanocomposites. A number of significant conclusions, including failure mechanism in graphene, interfacial load transfer and thermal transport mechanisms in graphene-polymer nanocomposites, have been drawn through both atomistic simulations and theoretical analysis. These results can provide direct guidelines for development of new graphene-based materials and devices.

Preparação de novos nanobiocompósitos comestíveis ativos contendo nanoemulsão de canela e pectina

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Design of nanoparticle systems with antimicrobial properties

Infektiöse Komplikationen im Zusammenhang mit Implantaten stellen einen Großteil aller Krankenhausinfektionen dar und treiben die Gesundheitskosten signifikant in die Höhe. Die bakterielle Kolonisation von Implantatoberflächen zieht schwerwiegende medizinische Konsequenzen nach sich, die unter Umständen tödlich verlaufen können. Trotz umfassender Forschungsaktivitäten auf dem Gebiet der antibakteriellen Oberflächenbeschichtungen ist das Spektrum an wirksamen Substanzen aufgrund der Anpassungsfähigkeit und Ausbildung von Resistenzen verschiedener Mikroorganismen eingeschränkt. Die Erforschung und Entwicklung neuer antibakterieller Materialien ist daher von fundamentaler Bedeutung.rnIn der vorliegenden Arbeit wurden auf der Basis von Polymernanopartikeln und anorganischen/polymeren Verbundmaterialien verschiedene Systeme als Alternative zu bestehenden antibakteriellen Oberflächenbeschichtungen entwickelt. Polymerpartikel finden Anwendung in vielen verschiedenen Bereichen, da sowohl Größe als auch Zusammensetzung und Morphologie vielseitig gestaltet werden können. Mit Hilfe der Miniemulsionstechnik lassen sich u. A. funktionelle Polymernanopartikel im Größenbereich von 50-500 nm herstellen. Diese wurde im ersten System angewendet, um PEGylierte Poly(styrol)nanopartikel zu synthetisieren, deren anti-adhesives Potential in Bezug auf P. aeruginosa evaluiert wurde. Im zweiten System wurden sog. kontakt-aktive kolloide Dispersionen entwickelt, welche bakteriostatische Eigenschaften gegenüber S. aureus zeigten. In Analogie zum ersten System, wurden Poly(styrol)nanopartikel in Copolymerisation in Miniemulsion mit quaternären Ammoniumgruppen funktionalisiert. Als Costabilisator diente das zuvor quaternisierte, oberflächenaktive Monomer (2-Dimethylamino)ethylmethacrylat (qDMAEMA). Die Optimierung der antibakteriellen Eigenschaften wurde im nachfolgenden System realisiert. Hierbei wurde das oberflächenaktive Monomer qDMAEMA zu einem oberflächenaktiven Polyelektrolyt polymerisiert, welcher unter Anwendung von kombinierter Miniemulsions- und Lösemittelverdampfungstechnik, in entsprechende Polyelektrolytnanopartikel umgesetzt wurde. Infolge seiner oberflächenaktiven Eigenschaften, ließen sich aus dem Polyelektrolyt stabile Partikeldispersionen ohne Zusatz weiterer Tenside ausbilden. Die selektive Toxizität der Polyelektrolytnanopartikel gegenüber S. aureus im Unterschied zu Körperzellen, untermauert ihr vielversprechendes Potential als bakterizides, kontakt-aktives Reagenz. rnAufgrund ihrer antibakteriellen Eigenschaften wurden ZnO Nanopartikel ausgewählt und in verschiedene Freisetzungssysteme integriert. Hochdefinierte eckige ZnO Nanokristalle mit einem mittleren Durchmesser von 23 nm wurden durch thermische Zersetzung des Precursormaterials synthetisiert. Durch die nachfolgende Einkapselung in Poly(L-laktid) Latexpartikel wurden neue, antibakterielle und UV-responsive Hybridnanopartikel entwickelt. Durch die photokatalytische Aktivierung von ZnO mittels UV-Strahlung wurde der Abbau der ZnO/PLLA Hybridnanopartikel signifikant von mehreren Monaten auf mehrere Wochen verkürzt. Die Photoaktivierung von ZnO eröffnet somit die Möglichkeit einer gesteuerten Freisetzung von ZnO. Im nachfolgenden System wurden dünne Verbundfilme aus Poly(N-isopropylacrylamid)-Hydrogelschichten mit eingebetteten ZnO Nanopartikeln hergestellt, die als bakterizide Oberflächenbeschichtungen gegen E. coli zum Einsatz kamen. Mit minimalem Gehalt an ZnO zeigten die Filme eine vergleichbare antibakterielle Aktivität zu Silber-basierten Beschichtungen. Hierbei lässt sich der Gehalt an ZnO relativ einfach über die Filmdicke einstellen. Weiterhin erwiesen sich die Filme mit bakteriziden Konzentrationen an ZnO als nichtzytotoxisch gegenüber Körperzellen. Zusammenfassend wurden mehrere vielversprechende antibakterielle Prototypen entwickelt, die als potentielle Implantatbeschichtungen auf die jeweilige Anwendung weiterhin zugeschnitten und optimiert werden können.

Vibrational spectroscopic studies of laboratory scale polymer melt processing : application to a thermoplastic polyurethane nanocomposite

A laboratory scale twin screw extruder has been interfaced with a near infrared (NIR) spectrometer via a fibre optic link so that NIR spectra can be collected continuously during the small scale experimental melt state processing of polymeric materials. This system can be used to investigate melt state processes such as reactive extrusion, in real time, in order to explore the kinetics and mechanism of the reaction. A further advantage of the system is that it has the capability to measure apparent viscosity simultaneously which gives important additional information about molecular weight changes and polymer degradation during processing. The system was used to study the melt processing of a nanocomposite consisting of a thermoplastic polyurethane and an organically modified layered silicate.

Studies on the Tracking and Erosion Resistance of RTV Silicone Rubber Nanocomposite

One of the problems associated with outdoor polymeric insulators is tracking and erosion of the weathershed which can directly influence the reliability of the power system. Flame retardants are added to the base material to enhance its tracking and erosion resistance. Hydroxide fillers are regarded as the best flame retardants. This paper deals with studies related to nano - sized magnesium dihydroxide (MDH) and micron-sized Alumina Trihydrate (ATH) fillers as flame retardants in RTV silicone rubber. Tracking and erosion resistance studies were carried out on MDH and ATH silicone rubber composites using an inclined plane tracking and erosion (IPT) resistance tester. The MDH filled (5% by wt) composites performed much better than ATH composites in terms of eroded mass, depth of erosion, width and length of erosion. The eroded mass of MDH composite is 49.8 % that of ATH composite which can be attributed to high surface area and higher thermal stability of MDH nanofillers.

Polyelectrolyte/silver nanocomposite multilayer films as multifunctional thin film platforms for remote activated protein and drug delivery

We demonstrate a nanoparticle loading protocol to develop a transparent, multifunctional polyelectrolyte multilayer film for externally activated drug and protein delivery. The composite film was designed by alternate adsorption of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on a glass substrate followed by nanoparticle synthesis through a polyol reduction method. The films showed a uniform distribution of spherical silver nanoparticles with an average diameter of 50 +/- 20 nm, which increased to 80 +/- 20 nm when the AgNO3 concentration was increased from 25 to 50 mM. The porous and supramolecular structure of the polyelectrolyte multilayer film was used to immobilize ciprofloxacin hydrochloride (CH) and bovine serum albumin (BSA) within the polymeric network of the film. When exposed to external triggers such as ultrasonication and laser light the loaded films were ruptured and released the loaded BSA and CH. The release of CH is faster than that of BSA due to a higher diffusion rate. Circular dichroism measurements confirmed that there was no significant change in the conformation of released BSA in comparison with native BSA. The fabricated films showed significant antibacterial activity against the bacterial pathogen Staphylococcus aureus. Applications envisioned for such drug-loaded films include drug and vaccine delivery through the transdermal route, antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A critical review on in situ reduction of graphene oxide during preparation of conducting polymeric nanocomposites

Graphene oxide (GO), prepared by chemical oxidation of graphite, serves as a building block for developing polymeric nanocomposites. However, their application in electrical conductivity is limited by the fact that the oxygen sites on GO trap electrons and impede charge transport. Conducting nanocomposites can be developed by reducing GO. Various strategies have been adopted to either reduce GO ex situ, before the composite preparation, or in situ during the development of the nanocomposites. The current state of research on in situ reduction of GO during the preparation of conducting polymeric nanocomposites is discussed in this review. The mechanism and the efficiency of reduction is discussed with respect to various strategies employed during the preparation of the nanocomposite, the type of polymer used, and the processing conditions employed, etc. Its overall effect on the electrical conductivity of the nanocomposites is also discussed and the future outlook in this area is presented.

Novel nanocomposite fibres for technical textile applications : synthesis and characterisation of poly(m-xylene adipamide) montmorillonite nanocomposites

Technical textiles, based on advanced polymeric materials, are an important segment of the synthetic textile market. This area has seen considerable growth in recent times, now accounting for almost 25% of all manufactured synthetic fibres, and has driven the recent development of a range of specialist high performance polymer fibres that are stronger, lighter or have improved heat and fire resistance. However, the increasing size of the market has highlighted the need for materials that have improved performance whilst maintaining low manufacturing costs. These factors have resulted in a change in how new specialty fibres are developed and the emphasis in this field is now on the upgrading or improving of the properties of commodity (conventional) fibres by modifying their properties to suit specific applications.

This paper will describe our work on preparing novel polymer nanocomposite fibres by the addition of clay nanoparticles during melt extrusion. The effect of the nanoparticles on the processing of the fibres and the result on the physical morphology and mechanical properties will be described.

Novel nanocomposite fibres for technical textile applications

Technical textiles, based on advanced polymeric materials, are an important segment of the synthetic textile market. This area has seen considerable growth in recent times, now accounting for almost 25% of all manufactured synthetic fibres, and has driven the recent development of a range of specialist high performance polymer fibres that are stronger, lighter or have improved heat and fire resistance. However, the increasing size of the market has highlighted the need for materials that have improved performance whilst maintaining low manufacturing costs. These factors have resulted in a change in how new specialty fibres are developed and the emphasis in this field is now on the upgrading or improving of the properties of commodity (conventional) fibres by modifying their properties to suit specific applications.

This paper will describe our work on preparing novel polymer nanocomposite fibres by the addition of clay nanoparticles during melt extrusion. The effect of the nanoparticles on the processing of the fibres and the result on the physical morphology and mechanical properties will be described.

A controllable simple method for production of polymeric nanofiberous composite via single nozzle jet electrospinning

A special Micro-Nano fiberous composite structure composed of nano- and micro-scale fiber of Polycaprolactone (PCL) and Gelatin produced by using single nozzle electrospinning instrument. By controlling the solution (polymer concentration and polymer composition percent) and processing parameters of electrospinning (feed rate and electrostatic field), different portion of nano and micro fibers in the structure is achieved. This method can result a one-stage method of fabrication of Micro-Nano fiberous composite structure instead of previously used twostage process or using additional facility to produce structure near-similar to this composite structure. The resulting materials finely mingle nano- and micro fibers together, rather than simply juxtaposing them, as is commonly found in the literature. The results obtained from SEM, Flow Porosimetry, and DMA led the authors to confirm that the structure has very versatile and improved properties for many applications like cell culture scaffolds. These favourable mechanical and structural properties can provide easier opening of spaces for cell penetration to deeper levels of the scaffold and withstand to tensions during to clinical handling.

Barrier and Mechanical Properties of Clay-Reinforced Polymeric Nanocomposites

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Comparison of the nanoparticles performance in the photocatalytic degradation of a styrene-butadiene rubber nanocomposite

Much has been talking about the advantages of polymeric nanocomposites, but little is known about the influence of nanoparticles on the stability of these materials. In this sense, we studied the influence of both oxides of zirconium and titanium, known to have photocatalytic properties, as well as the influence of synthetic clay Laponite on the photodegradation of styrene-butadiene rubber (SBR). SBR nanocomposites were prepared by the colloidal route by mixing commercial polymer lattices and nanometric anatase TiO2, monoclinic ZrO2 or exfoliated Laponite clays colloidal suspensions. To better understand the degradation mechanisms that occur in these nanocomposites, the efficiency of different photocatalysts under ultraviolet radiation was monitored by FT-IR and UV-vis spectroscopies and by differential scanning calorimetric. It was observed that TiO2 and ZrO2 nanoparticles undoubtedly acted as catalysts during the photodegradation process with different efficiencies and rates. However, when compared to pure SBR samples, the polymer degradation mechanism was unaffected. Unlike studies with nanocomposites montmorillonite, exfoliated laponite clay effectively acts as a photostabilizer of polymer UV photodegradation. Copyright © 2012 Wiley Periodicals, Inc.

Nanocomposite PAAm/methyl cellulose/montmorillonite hydrogel: Evidence of synergistic effects for the slow release of fertilizers

In this work, we synthesized a novel series of hydrogels composed of polyacrylamide (PAAm), methylcellulose (MC), and calcic montmorillonite (MMt) appropriate for the controlled release of fertilizers, where the components presented a synergistic effect, giving very high fertilizer loading in their structure. The synthesized hydrogel was characterized in relation to morphological, hydrophilic, spectroscopic, structural, thermal, and kinetic properties. After those characterizations, the application potential was verified through sorption and desorption studies of a nitrogenated fertilizer, urea (CO(NH2)2). The swelling degree results showed that the clay loading considerably reduces the water absorption capability; however, the hydrolysis process favored the urea adsorption in the hydrogel nanocomposites, increasing the load content according to the increase of the clay mass. The FTIR spectra indicated that there was incorporation of the clay with the polymeric matrix of the hydrogel and that incorporation increased the water absorption speed (indicated by the kinetic constant k). By an X-ray diffraction technique, good nanodispersion (intercalation) and exfoliation of the clay platelets in the hydrogel matrix were observed. Furthermore, the presence of the montmorillonite in the hydrogel caused the system to liberate the nutrient in a more controlled manner than that with the neat hydrogel in different pH ranges. In conclusion, excellent results were obtained for the controlled desorption of urea, highlighting the hydrolyzed hydrogels containing 50% calcic montmorillonite. This system presented the best desorption results, releasing larger amounts of nutrient and almost 200 times slower than pure urea, i.e., without hydrogel. The total values of nutrients present in the system show that this material is potentially viable for application in agriculture as a nutrient carrier vehicle. © 2013 American Chemical Society.

Development and characterization of a new bio-nanocomposite (bio-NCP) for diagnosis and treatment of breast cancer

Breast cancer is a public health problem throughout the world. Moreover, breast cancer cells have a great affinity for hydroxyapatite, leading to a high occurrence of bone metastasis. In this work we developed a bio-nanocomposite (bio-NCP) in order to use such affinity in the diagnosis and treatment of breast cancer. The bio-NCP consists of magnetic nanoparticles of Mn and Zn ferrite inside a polymeric coating (chitosan) modified with nanocrystals of apatite. The materials were characterized with synchrotron X-ray Powder Diffraction (XPD), Time-of-Flight Neutron Powder Diffraction (NPD), Fourier Transformed Infra-red Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and magnetic measurement with a Physical Property Measurement System (PPMS). We obtained ferrite nanoparticles with a high inversion degree of the spinel structure regarding the Fe and Mn, but with all the Zn in the A site. The coating of such nanoparticles with chitosan had no notable effects to the ferrite microstructure. In addition, the polymeric surface can be easily modified with apatite nanocrystals since the hydration of the bio-NCP during synthesis can be controlled. The resulting bio-NCP presents a spherical shape with a narrow size distribution and high magnetic response at room temperature and is a very promising material for early diagnosis of breast cancer and its treatment. © 2013 Elsevier B.V.

Fabrication and Characterization of PZT-PAni/PVDF Based Nanocomposite

This work presents the preparation and characterization of PZT ceramic obtained by the polymeric precursor method (PPM). The influence of the synthesis method on the grain size and the morphology are also object of study. The fabrication and characterization of composite films with 0-3 connectivity, immersing nanoparticles of PZT into the non-polar poly(vinylidene fluoride) -PVDF as the polymer matrix were presented. For comparison there are results obtained with composite samples made of ceramic particles unrecovered and recovered with a conducting polymer, the polyaniline (PAni).