Free-standing alumina nanobottles and nanotubes pre-integrated into nanoporous alumina membranes

A novel interfacial structure consisting of long (up to 5 μm), thin (about 300 nm), highly-ordered, free-standing, highly-reproducible aluminum oxide nanobottles and long tubular nanocapsules attached to a rigid, thin (less than 1 μm) nanoporous anodic alumina membrane is fabricated by simple, fast, catalyst-free, environmentally friendly voltage-pulse anodization. A growth mechanism is proposed based on the formation of straight channels in alumina membrane by anodization, followed by neck formation due to a sophisticated voltage control during the process. This process can be used for the fabrication of alumina nanocontainers with highly controllable geometrical size and volume, vitally important for various applications such as material and energy storage, targeted drug and diagnostic agent delivery, controlled drug and active agent release, gene and biomolecule reservoirs, micro-biologically protected platforms, nano-bioreactors, tissue engineering and hydrogen storage.

Active corrosion protection of AA2024 by sol-gel coatings with corrosion inhibitors

A indústria aeronáutica utiliza ligas de alumínio de alta resistência para o fabrico dos elementos estruturais dos aviões. As ligas usadas possuem excelentes propriedades mecânicas mas apresentam simultaneamente uma grande tendência para a corrosão. Por esta razão essas ligas necessitam de protecção anticorrosiva eficaz para poderem ser utilizadas com segurança. Até à data, os sistemas anticorrosivos mais eficazes para ligas de alumínio contêm crómio hexavalente na sua composição, sejam pré-tratamentos, camadas de conversão ou pigmentos anticorrosivos. O reconhecimento dos efeitos carcinogénicos do crómio hexavalente levou ao aparecimento de legislação banindo o uso desta forma de crómio pela indústria. Esta decisão trouxe a necessidade de encontrar alternativas ambientalmente inócuas mas igualmente eficazes. O principal objectivo do presente trabalho é o desenvolvimento de prétratamentos anticorrosivos activos para a liga de alumínio 2024, baseados em revestimentos híbridos produzidos pelo método sol-gel. Estes revestimentos deverão possuir boa aderência ao substrato metálico, boas propriedades barreira e capacidade anticorrosiva activa. A protecção activa pode ser alcançada através da incorporação de inibidores anticorrosivos no prétratamento. O objectivo foi atingido através de uma sucessão de etapas. Primeiro investigou-se em detalhe a corrosão localizada (por picada) da liga de alumínio 2024. Os resultados obtidos permitiram uma melhor compreensão da susceptibilidade desta liga a processos de corrosão localizada. Estudaram-se também vários possíveis inibidores de corrosão usando técnicas electroquímicas e microestruturais. Numa segunda etapa desenvolveram-se revestimentos anticorrosivos híbridos orgânico-inorgânico baseados no método sol-gel. Compostos derivados de titania e zirconia foram combinados com siloxanos organofuncionais a fim de obter-se boa aderência entre o revestimento e o substrato metálico assim como boas propriedades barreira. Testes industriais mostraram que estes novos revestimentos são compatíveis com os esquemas de pintura convencionais actualmente em uso. A estabilidade e o prazo de validade das formulações foram optimizados modificando a temperatura de armazenamento e a quantidade de água usada durante a síntese. As formulações sol-gel foram dopadas com os inibidores seleccionados durante a primeira etapa e as propriedades anticorrosivas passivas e activas dos revestimentos obtidos foram estudadas numa terceira etapa do trabalho. Os resultados comprovam a influência dos inibidores nas propriedades anticorrosivas dos revestimentos sol-gel. Em alguns casos a acção activa dos inibidores combinou-se com a protecção passiva dada pelo revestimento mas noutros casos terá ocorrido interacção química entre o inibidor e a matriz de sol-gel, de onde resultou a perda de propriedades protectoras do sistema combinado. Atendendo aos problemas provocados pela adição directa dos inibidores na formulação sol-gel procurou-se, numa quarta etapa, formas alternativas de incorporação. Na primeira, produziu-se uma camada de titania nanoporosa na superfície da liga metálica que serviu de reservatório para os inibidores. O revestimento sol-gel foi aplicado por cima da camada nanoporosa. Os inibidores armazenados nos poros actuam quando o substrato fica exposto ao ambiente agressivo. Numa segunda, os inibidores foram armazenados em nano-reservatórios de sílica ou em nanoargilas (halloysite), os quais foram revestidos por polielectrólitos montados camada a camada. A terceira alternativa consistiu no uso de nano-fios de molibdato de cério amorfo como inibidores anticorrosivos nanoparticulados. Os nano-reservatórios foram incorporados durante a síntese do sol-gel. Qualquer das abordagens permitiu eliminar o efeito negativo do inibidor sobre a estabilidade da matriz do sol-gel. Os revestimentos sol-gel desenvolvidos neste trabalho apresentaram protecção anticorrosiva activa e capacidade de auto-reparação. Os resultados obtidos mostraram o elevado potencial destes revestimentos para a protecção anticorrosiva da liga de alumínio 2024.

Micro/nanoreservoirs for controlled release of active species in smart functional coatings

This work reports one possible way to develop new functional coatings used to increase the life time of metallic structures. The functionalities selected and attributed to model coatings in the frame of this work were corrosion protection, self-sensing and prevention of fouling (antifouling). The way used to confer those functionalities to coatings was based on the encapsulation of active compounds (corrosion inhibitors, pH indicators and biocides) in micro and nanocontainers followed by their incorporation into the coating matrices. To confer active corrosion protection, one corrosion inhibitor (2-mercaptobenzothiazole, MBT) was encapsulated in two different containers, firstly in silica nanocapsules (SiNC) and in polyurea microcapsules (PU-MC). The incorporation of both containers in different models coatings shows a significant improvement in the corrosion protection of aluminum alloy 2024 (AA2024). Following the same approach, SiNC and PU-MC were also used for the encapsulation of phenolphthalein (one well known pH indicator) to introduce sensing properties in polymeric coatings. SiNC and PU-MC containing phenolphthalein acted as corrosion sensor, showing a pink coloration due to the beginning of cathodic reaction, resulting in a pH increase identified by those capsules. Their sensing performance was proved in suspension and when integrated in coatings for aluminium alloy 2024 and magnesium alloy AZ31. In a similar way, the biocide activity (antifouling) was assigned to two polymeric matrices using SiNC for encapsulation of one biocide (Dichloro-2-octyl-2H-isothiazol-3-one, DCOIT) and also SiNC-MBT was tested as biocide. The antifouling activity of those two encapsulated compounds was assessed through inhibition and consequent decrease in the bioluminescence of modified E. coli. That effect was verified in suspension and when incorporated in coatings for AISI 1008 carbon steel. The developed micro and nanocontainers presented the desired performance, allowing the introduction of new functionalities to model coatings, showing potential to be used as functional additives in the next generation of multifunctional coatings.

Détermination de l’effet protecteur des liposomes non phospholipidiques à haute teneur en cholestérol

Nous démontrons qu'il est possible de former des bicouches fluides non phospholipides en milieu aqueux avec un mélange d'acide palmitique (PA), cholestérol (Chol) et sulfate de cholestérol (Schol) avec une proportion molaire de 30/28/42. Ces liposomes non phospholipidiques peuvent maintenir un gradient de pH (pHinterne 8 / pHexterne 6) sur une période 100 fois plus longue que les liposomes faits de 1-palmitoyl-2-oléoyl-sn-glycéro-3-phosphocholine (POPC) et de cholestérol (60/40 mol/mol). De plus, ces LUV non phospholipidiques protègent l'acide ascorbique d'un milieu oxydant (1 mM de fer (III)). Une fois piégé dans les liposomes, l'acide ascorbique présente une vitesse de dégradation similaire à celle obtenue en l'absence de fer(III). Ces performances illustrent la perméabilité exceptionnellement limitée de ces liposomes, ce qui implique qu'ils peuvent présenter des avantages comme nanocontenants pour certaines applications. D'autre part, des vésicules unilamellaires géantes (GUV pour Giant Unilamellar Vesicles) ont été formées à partir d'un mélange d'acide palmitique et de cholestérol (30/70 mol/mol). Ces GUV sont stables sur l'échelle de temps de semaines, elles ne s'agrègent pas et elles sont sensibles au pH. Afin d'établir la formation des GUV, l'imagerie par microscopie confocale à balayage laser a été utilisée. Deux sondes fluorescentes ont été utilisées: le rouge du Nile, une sonde hydrophobe qui s'insère dans le cœur hydrophobe des bicouches lipidiques, et la calcéine, une sonde hydrophile qui a été emprisonné dans le réservoir interne des GUV. Cette approche a permis l'observation des parois des GUV ainsi que de leur contenu. Ces résultats montrent la possibilité de former de nouveaux microcontenants à partir d'un mélange d'un amphiphile monoalkylé et de stérol.

Structural, Spectroscopic (NMR, IR, and Raman), and DFT Investigation of the Self-Assembled Nanostructure of Pravastatin-LDH (Layered Double Hydroxides) Systems

Layered double hydroxide (LDH) nanocontainers, suitable as carriers for anionic drugs, were intercalated with Pravastatin drug using magnesium-aluminum and zinc-aluminum in a M-II/Al molar ratio equal 2 and different Al3+/Pravastatin molar ratios. Postsynthesis treatments were used in order to increase the materials crystallinity. Hybrid materials were characterized by a set of physical chemical techniques: chemical elemental analysis, X-ray diffraction (XRD), mass coupled thermal analyses, vibrational infrared and Raman spectroscopies, and solid-state C-13 nuclear magnetic resonance (NMR). Results were interpreted in light of computational density functional theory (DFT) calculations performed for Sodium Pravastatin in order to assign the data obtained for the LDH intercalated materials. XRD peaks of LDH-Pravastatin material and the one-dimensional (1D) electron density map pointed out to a bilayer arrangement of Pravastatin in the interlayer region, where its associated carboxylate and vicinal hydroxyl groups are close to the positive LDH. The structural organization observed for the stacked assembly containing the unsymmetrical and bulky monoanion Pravastatin and LDH seems to be promoted by a self-assembling process, in which local interactions are maximized and chloride ion cointercalation is required. It is observed a high similarity among vibrational and C-13 NMR spectra of Na-Pravastatin and LDH-Pravastatin materials. Those features indicate that the intercalation preserves the drug structural integrity. Spectroscopic techniques corroborate the nature of the guest species and their arrangement between the inorganic layers. Changes related to carboxylate, alcohol, and olefinic moieties are observed in both vibrational Raman and C-13 NMR spectra after the drug intercalation. Thus, Pravastatin ions are forced to be arranged as head to tail through intermolecular hydrogen bonding between adjacent organic species. The thermal decomposition profile of the hybrid samples is distinct of that one observed for Na-Pravastatin salt, however, with no visible increase in the thermal behavior when the organic anion is sequestrated within LDH gap.

Synthese und Analytik von sauer katalysiert dargestellten Polyorganosiloxan-Nanokugeln mit Kern-Schale-Architektur

In dieser Arbeit wurden zwei Wege zur sauer katalysierten Synthese von Polyorganosiloxan-Kern-Schale-Nanopartikeln mit monomodaler Größenverteilung erarbeitet. Zum einen führt eine Erhöhung der Rührergeschwindigkeit auf 14000 rpm unter Verwendung eines Ultrathorax, während der ersten Stunde der Kondensation des Kernes zu Nanokugeln mit einer monomodalen Größenverteilung mit einem hydrodynamischen Radius von 33.1 nm +/- 22%. Zum anderen eröffnete die Reduktion des Flottenverhältnisses S, d.h. des Verhältnisses von Tensid- zu Monomermenge, von S=0.02 auf S=0.001 einen zweiten Weg zur Synthese von Nanokugeln mit monomodaler Größenverteilung. Der Radius dieser Kugeln beträgt 54.2 nm +/- 20%. Durch diese beiden Synthesewege sind Polyorganosiloxan-Nanokugeln in zwei verschiedenen Größen zugänglich. Durch 29Si-NMR-Messungen der Kerndispersion konnte gezeigt werden, dass die Ursache der bimodalen Größenverteilung der Polyorganosiloxan-Nanokugeln in der Synthese der Kerndispersion zu finden ist. Aus den hieraus ermittelten Ergebnissen geht hervor, dass sich während der sauer katalysierten Kondensation von Diethoxydimethylsilan neben den PDMS-Ketten auch zyklische Kondensationsprodukte bilden. Die während der Reaktion fortschreitende Bildung von Zyklen - insbesondere von Vierringen - bewirkt eine Phasenseparation der Dispersion. Dies führt zur beobachteten Bildung der bimodalen Größenverteilung der Polyorganosiloxan-Nanokugeln. Wird die Rührergeschwindigkeit auf 14000 rpm während der ersten Stunde der Kondensation des Kernes erhöht, wird eine verminderte Ringbildung gefunden. Der erhöhte Energieeintrag und die damit verbundene bessere Durchmischung der Dispersion während der ersten Stunde der Kondensation des Kerns führt bevorzugt zum Kettenwachstum, so dass die Tendenz zur Ringbildung verringert wird. Es tritt keine Phasenseparation auf, wodurch die beobachtete monomodale Größenverteilung der Nanokugeln erklärt wird. Wird das Flottenverhältnis reduziert und somit der pH-Wert der Lösung erhöht, werden bevorzugt offenkettige PDMS-Produkte gebildet. Die Bildung von Vierringen erfolgt nicht, Ringe höherer Ordnung werden nur in untergeordneter Menge gebildet. Es erfolgt keine Phasenseparation der Dispersion und eine monomodale Größenverteilung der Polyorganosiloxan-Nanokugeln wird erhalten. Die durch Erniedrigung des Flottenverhältnisses synthetisierten Polyorganosiloxan-Nanokugeln zeigten in AFM-Experimenten interessante Eigenschaften. So ist es möglich, die Nanokugeln auf einer Mica-Oberfläche mittels der AFM-Spitze zu manipulieren, ohne sie hierbei sie degradieren. Die sauer katalysierte Synthese ermöglicht die Einführung von basenlabilen Hydridgruppen in die Polyorganosiloxan-Nanokugeln. Ausgehend von in organischen Lösungsmitteln redispergierbaren Polyorganosiloxan-Nanokugeln, deren Oberfläche mit Hydridgruppen funktionalisiert wurde, konnten durch Hydrosilylierung mit allylterminiertem Polyethylenoxid wasserlösliche potentielle Nanokontainer synthetisiert werden.

Nanocapsules for self-healing materials

Im Rahmen dieser Arbeit wurden neue Ansätze für das Konzept der kapselbasierten Selbstheilungsmaterialien untersucht. Die Verkapselung von Selbstheilungsreagenzien in funktionellen Nanokapseln wurde dabei mittels drei verschiedener Herstellungsmethoden in Miniemulsion durchgeführt. Zunächst wurde die Synthese von Kern-Schale-Partikeln mit verkapselten Monomeren für die Ringöffnungs-Metathese-Polymerisation über freie radikalische Polymerisation in Miniemulsionstropfen beschrieben. Durch orthogonale Reaktionen wurden dabei verschiedene chemische Funktionalisierungen in die Schale eingebracht. Die Rolle des Tensides, das Verhältnis von Kernmaterial zu Monomer sowie die Variation der Lösungsmittelqualität hatte dabei einen Einfluss auf die Struktur der Kolloide. Die Heilungsreagenzien blieben auch nach der Verkapselung aktiv, was durch erfolgreich durchgeführte Selbstheilungsexperimente gezeigt werden konnte. Im zweiten Abschnitt wurde die Synthese von Silica-Nanocontainern für Selbstheilungsmaterialien über Hydrolyse und Polykondensation von Alkoxysilanen an der Grenzfläche der Miniemulsionstropfen beschrieben. Dieser Ansatz ermöglichte die effiziente Verkapselung sowohl von Monomeren als auch von Lösungen der Katalysatoren für die Metathese-Polymerisation in einem Einstufenprozess. Die Größe der Kapseln, die Dicke der Schale und der Feststoffgehalt der Dispersionen konnte dabei in einem weiten Bereich variiert werden. Anhand von erfolgreich durchgeführten Selbstheilungsreaktionen, die über Thermogravimetrie und 13C-NMR-Spektroskopie verfolgt wurden, konnte gezeigt werden, dass die Selbstheilungsreagenzien nach der Verkapselung aktiv blieben. Das dritte Konzept behandelte die Herstellung von polymeren Nanokapseln mittels Emulsions-Lösungsmittelverdampfungstechnik, welche eine milde Methode zur Verkapselung darstellt. Es wurde eine allgemeine und einfache Vorgehensweise beschrieben, in der Selbstheilungsreagenzien in polymeren Nanokapseln unter Verwendung von kommerziell erhältlichen Polymeren als Schalenmaterial verkapselt wurden. Zudem wurden Copolymere aus Styrol und verschiedenen hydrophilen Monomeren über freie radikalische Polymerisation sowie über polymeranaloge Reaktionen hergestellt. Diese statistischen Copolymere waren ebenso wie Blockcopolymere zur Herstellung von wohldefinierten Kern-Schale-Nanopartikeln mittels Emulsions-Lösungsmittelverdampfungsprozess geeignet. rnrnDes Weiteren wurde ein neues Konzept für die Synthese von pH-responsiven Nanokapseln aus tensidfreien Emulsionen unter Verwendung von Copolymeren aus Styrol und Trimethylsilylmethacrylat beschrieben. Der vorgeschlagene synthetische Ansatz ermöglicht dabei die erste Synthese von Nanokapseln über den Emulsions-Lösungsmittelverdampfungsprozess in Abwesenheit eines Tensides. Eine vollständig reversible Aggregation ermöglichte eine leichte Trennung der Nanokapseln von der kontinuierlichen Phase sowie eine Erhöhung der Konzentration der Nanokapseldispersionen auf das bis zu fünffache. Darüber hinaus war es möglich, Selbstheilungsreagenzien in stabilem Zustand zu verkapseln. Abschließend wurde die elektrochemische Abscheidung von mit Monomer gefüllten Nanokapseln in eine Zinkschicht zur Anwendung im Korrosionsschutz behandelt.

Smart magnetic dispersions - from switchable release to well-defined hybrid nanofibers

The synthesis, characterization and application of aqueous dispersions of superparamagnetic/polymer hybrid nanoparticles and capsules is described. Implementation of the superparamagnetic moiety into the polymer matrix enables a response of the nanomaterials towards an external magnetic field. Application of the external field is used for two main purposes: i) As heat generator, when an alternating magnetic field is applied. ii) As structuring agent to self-assemble superparamagnetic nanoparticles in the external field.rnIn the first part, superparamagnetic nanoparticles were used as heat generators in order to achieve a magnetic field induced release of an active compound from nanocontainers. To achieve such a release in remote-controlled fashion, the encapsulation of superparamagnetic nanoparticles into polymer nanocapsules was combined with the integration of a thermolabile compound into the shell of the nanocontainers. The magnetic nanoparticles acted as generators for heat, which decomposed the thermolabile compound. Pores were created in the degrading shell and an active substance was released.rn Additionally, the self-assembly of polymer nanoparticles, which were labeled with a superparamagnetic moiety as structuring agent, could be demonstrated. A combination of a magnetic field induced self-assembly and a sintering of neighboring particles upon an increase in temperature above the glass transition temperature of the polymer was used to form stable architectures. Various structures with tunable periodicity could be obtained ranging from smooth linear nanofibers to zigzag fibers. Besides solely creating linear architectures, the frugal process additionally allowed the creation of arrangements in analogy to more complex polymer architectures: By the introduction of defined junction points, the generation of branched structures and networks was demonstrated. Additionally, by tailoring the interaction of differently sized particles, the preparation of nanoparticle arrangements in statistical or block copolymer fashion was shown. Moreover, a reversible linear assembly and linkage of the nanoparticles was demonstrated following a lock/unlock mechanism. Therefore, the particles were locked in their linear assembly by a stable iron(III) hydroxamato-complex and unlocked by addition of a reducing agent and formation of a less stable iron(II)-complex.Further, in various projects with collaboration partners, nanoparticles and nanocapsules were labeled with a superparamagnetic moiety for their use as contrast agents in magnetic resonance imaging or as magnetically separable dispersions.

Stimuli-responsive materials for self-healing in corrosion protection

The corrosion of metallic materials is a crucial issue on an economical and ecological scale. Corrosion protection becomes then necessarily needed. The main focus of the thesis is to develop stimuli-responsive nanocontainers for self-healing in corrosion protection. A nanocontainer is efficient if distinct payloads can be selectively released via different stimuli because unwanted and unspecific release can be avoided. For anti-corrosion, the wanted nanocontainer is the one able to release its self-healing agents or corrosion inhibitors upon change of pH- or/and redox-potential due to the variation of these two signals at the corroded sites. Conducting polymers such as polyaniline (PANI) were chosen for building the shell of capsules due to their important characteristics of being both pH- and redox responsive.

Estudo das propriedades inibidoras de corrosão das imidazolinas oleica e quaternária e seu encapsulamento em partículas inertes.

Entre os inibidores de corrosão clássicos que já são utilizados na indústria do petróleo, foram estudadas a imidazolina oleica e a quaternária através de técnicas eletroquímicas, gravimétrica e analíticas, para avaliar a eficiência de inibição e como esses inibidores atuam em meio ácido. O meio agressivo foi uma solução de NaCl 3,5% em massa acidificada com ácido clorídrico até atingir um pH=2 com o objetivo de simular o ambiente de extração petrolífera. O substrato empregado foi o aço carbono 1020. As técnicas eletroquímicas utilizadas foram: monitoramento do potencial de circuito aberto, medidas de resistência de polarização linear, espectroscopia de impedância eletroquímica (EIE ) e curvas de polarização. Os valores das componentes real e imaginária de impedância indicam uma resistência maior aos processos de transferência de carga com o aumento da concentração dos inibidores e os Diagramas de Bode de ângulo de fase, revelaram a presença de uma camada de inibidor adsorvida sobre o metal com uma constante de tempo em altas frequências observada para a imidazolina oleica e quaternária. Para a imidazolina quaternária, verificou-se que só para tempos maiores de imersão é que o filme se adsorve de forma eficiente demonstrando uma cinética mais lenta de adsorção. Nos ensaios gravimétricos, os resultados de taxa de corrosão em m/ano foram decrescentes com o tempo após período de imersão de 30 dias, para ambas as imidazolinas. O uso das técnicas analíticas foi necessário a fim de se compreender melhor o comportamento das imidazolinas sobre o aço no meio estudado. Os resultados da análise de íons férricos em solução, por emissão atômica, foram obtidos durante várias amostragens durante o período do ensaio de perda de massa, e foi possível verificar um processo de inibição da corrosão até doze dias de imersão do metal, depois disto ocorre um disparo na quantidade de ferro liberado em solução, sugerindo que pode estar ocorrendo uma degradação do inibidor após 12 dias de imersão. Para esclarecer esse ponto, análises por espectroscopia Raman dos produtos de fundo formados durante os ensaios de perda de massa indicaramm que a degradação pode realmente estar ocorrendo. Foi confirmado, também por espectroscopia Raman sobre a superfície do aço após imersão prévia em solução contendo a imidazolina oleica, que há uma película adsorvida que protege o metal do meio agressivo. Técnica de microscopia eletrônica de varredura foi utilizada para caracterizar os corpos de prova na ausência e presença do inibidor, depois dos ensaios eletroquímicos e foi possível caracterizar, através dessa técnica a maior eficiência inibidora do filme de imidazolina quaternária. Dois tipos de nanoconatiners foram avaliados para o encapsulamento das duas imidazolinas estudadas: nanocontainers a base do argilomineral haloiista e sílica mesoporosa tipo SBA 15. Resultados de impedância eletroquímica mostraram a liberação dos inibidores de corrosão encapsulados com o tempo de imersão. Análise na região do infravermelho por sonda de fibra ótica foi utilizada para comprovar química e qualitativamente a liberação do inibidor a partir dos nanorreservatórios, no meio agressivo.