Depuis quelques années, notre laboratoire développe des nanoparticules lipidiques bicompartimentées originales produites par homogénéisation haute pression, un procédé transposable à grande échelle, à partir d’excipients pharmaceutiques validés par différentes pharmacopées (Eur., USP, JP). Ces particules appartiennent ainsi à la famille des nano-objets Janus puisqu’elles sont organisées en deux sous-structures juxtaposées : une moitié est constituée d’une gouttelette huileuse alors que l’autre moitié est composée d’une structure vésiculaire et renferme un cœur aqueux délimité par une bicouche phospholipidique. En plus de la biocompatibilité intrinsèque des lipides constituants, un tel système représente un outil potentiellement très intéressant et valorisable du point de vue pharmaceutique et biomédical capable d’incorporer séparément et de co-véhiculer des substances hydrophiles et lipophiles aux activités distinctes, par exemple un agent d’imagerie médical et un principe actif pour coupler diagnostique et thérapie. Ici, nous nous sommes intéressés à charger les nanoparticules Janus avec un fluide magnétique composé de nanocristaux d’oxyde de fer (ferrofluide, FF), actif en tant qu’agent de contraste efficace en IRM, étant magnétiquement contrôlable et permettant d’envisager un traitement par hyperthermie. Tour à tour, des FF hydrophiles ou lipophiles compatibles avec le procédé de production ont été développés en étudiant différentes voies de stabilisation des nanocristaux en fonction du compartiment d’encapsulation. / In recent years, our team has developed original compartmented lipid nanometer-sized particles produced by high pressure homogenization, a scalable process, with pharmaceutically approved excipients. The particles actually belong to the family of Janus nano-objects as they are organized in two juxtaposed substructures : one half is a droplet of liquid-state lipids while the other half is vesicle-like and encloses an aqueous core delimited by a phospholipid-containing bilayer shell. Added to the intrinsic biocompatibility of the constituting lipids, such a system provides a potentially very valuable tool in pharmaceutical and biomedical fields, able to separately incorporate and co-convey hydrophilic and lipophilic substances with distinct activities, for example, a medical imaging agent and a drug for coupling diagnosis and therapy. Here, we are interested in loading Janus nanoparticles with a magnetic fluid composed of superparamagnetic iron oxide nanocrystals (ferrofluid, FF), indeed as efficient contrast agent for MRI, being magnetically targetable and providing ability for hyperthermia treatment. Alternately, hydrophilic or lipophilic FF compatible with the production process have been developed by investigating different stabilization pathways of the nanocrystals depending on the encapsulation compartment.

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The Temple of Janus was an important and symbolic temple in Rome. The doors served as an index for peace and war and were either opened or closed accordingly. The only contemporary depiction of the temple is the Neronian coins that were struck in 64/5 CE in both Rome and Lugdunum in celebration of Nero’s defeat of the Parthians. This coin type is the only evidence that we have left of the Temple of Janus since the temple is lost and has no remains left. Therefore, it is necessary to analyze the depictions of the temple on these coins to discover the most reliable and accurate representation of the Temple of Janus since they are the only evidence left of its appearance. By discovering the exact order of striking and observing how the appearance of the temple changed over time in the earliest Neronian sestertii, I will attempt to uncover the most accurate depiction of the Temple of Janus. The architectural features present on the earliest dies, which will be discovered by means of a die study, will be further analyzed by un-manipulating its numismatic representation; this is because die engravers had certain working methods that they would use to manipulate the appearance in order to depict a large monument on such a small medium. I will then undo these changes made to the depiction of the temple in order to discover the true architectural features of the temple and therefore reconstruct the lost Temple of Janus and uncover its original appearance. / Thesis / Master of Arts (MA)

L’objectif de ce projet était l’étude systématique des interactions, de la microstructure et de la dynamique de suspensions de colloïdes qui imitent les mouvements de systèmes auto-propulsés (actifs), au moyen de techniques de diffusion : diffusion des rayons X aux (ultra) petits angles (USAXS/SAXS) et spectroscopie de corrélation de photons X (XPCS).À la différence des colloïdes passifs conventionnels (particules browniennes), les colloïdes actifs sont des systèmes hors équilibre faits d’objets auto-propulsés. Ces systèmes montrent une dynamique fascinante qui s’apparente aux mouvements de volée d'oiseaux, d’essaim d’insectes, etc.Les micro-organismes mobiles sont des exemples types de colloïdes actifs, notamment certaines variétés de bactéries, ou les colloïdes de type Janus caractérisé par une composition asymétrique de leur surface qui peux engendrer une propulsion, l’auto-diffusiophorèse. Les thèmes principaux de cette thèse sont les interactions inter-particule, les interactions particule-solvant et les dynamiques phorétiques des systèmes actifs.En premier lieu, la structure et la mobilité de la bactérie Escherichia coli ont été étudiées au moyen de SAXS/USAXS . Comme projet secondaire, l’obtention de données couvrant une très large gamme de vecteur de diffusion (q) a permis de dériver un modèle structural multi-échelle de la bactérie, en combinant les caractéristiques de colloïdes (corps cellulaire), de membranes (enveloppe cellulaire) et de polymères (flagelles). Ce modèle a été affiné au moyen de mesures complémentaires de diffusion de neutrons aux petits angles (SANS) sur des suspensions de la bactérie E. coli en variant le contraste externe (remplacement isotopique partielle du solvant) afin d’aboutir à une détermination quantitative de la densité électronique des membranes et des distances entre membranes.Ces bactéries ont ensuite été utilisées comme éléments actifs en mélange avec des colloïdes passifs de silice de taille sub-micrométrique, pour comprendre comment la présence de bactéries actives mobiles affecte les interactions effectives et la dynamique des colloïdes passifs. Des mesures USAXS et XPCS simultanées ont permis de déduire les propriétés statiques et hydrodynamiques de ces colloïdes passifs. Les données suggèrent que les bactéries actives se comportent comme un fluidifiant pour les colloïdes passifs, en réduisant leurs interactions attractives et en augmentant leur dynamique ; réciproquement, ces derniers sont affectés par la solution tampon et par la présence de bactéries augmente la viscosité environnante effective.Enfin, les mouvements phorétiques de colloïdes de silice et de type Janus (silice partiellement recouvert de nickel) suspendus dans un mélange de 3-methylpyridine (3MP) + eau/eau lourde pendant la séparation de phase liquide-liquide ont été investigués par USAXS et XPCS. Les mouvements des colloïdes sont fortement corrélés à la dynamique de la séparation de phase du fait de l’absorption préférentielle de 3MP à la surface de silice. Les colloïdes de silice montrent une dynamique advective avec une diffusion amélioré en direction des microdomaines riches en 3MP, évoquant la dynamique des systèmes auto-propulsés, jusqu’à l’aboutissement de la séparation de phase. Les suspensions de colloïdes de type Janus ont un comportement beaucoup plus complexe, la dynamique étant fortement corrélée aux interactions asymétriques avec le solvant. Cette dynamique est soit augmentée soit supprimée en fonction de la concentration en 3MP qui modifie aussi la micro-structure du système. Au lieu que les colloïdes de silice migrent vers la phase riche en 3MP, les colloïdes de type Janus agissent comme des tensioactifs en se plaçant à l’interface.Cette thèse démontre l’intérêt des techniques de diffusion pour explorer les propriétés des systèmes actifs et examiner leur comportement en thermodynamique hors équilibre afin de compléter les informations obtenues par observations microscopique. / This project aimed to systematically investigate the interactions, microstructure and dynamics in suspensions of colloidal particles that mimic active motions, using (Ultra) Small- Angle X-ray Scattering (USAXS/SAXS) and X-ray Photon Correlation Spectroscopy (XPCS). As opposed to the conventional passive colloids (Brownian particles), active colloids are non-equilibrium systems consisting of self-propelled particles that display many fascinating dynamics, such as streaming, swarming, flocking, etc. in appropriate media. Practical examples of active systems are motile microorganisms, such as some species of bacteria, or synthetic Janus colloids – characterized by an asymmetric chemical composition of their surface – that can induce a propulsion mechanisms, like self-diffusiophoresis. The foci of this thesis are on interparticle interactions, particle-medium interactions and the phoretic dynamics in active systems.Firstly, the structure and motility of Escherichia coli bacteria were investigated by combined USAXS and SAXS methods. As an offshoot, the scattering data spanning a broad scattering vector (q)-range permitted the derivation of a multiscale structural model by combining colloidal (cell-body), membrane (cell-envelope) and polymer (flagella) features. This model was further refined by contrast-variation Small Angle Neutron Scattering (SANS) measurements on E. coli suspensions at three match points and the full contrast which allowed the determination of the membrane electron-density and the inter-membrane distances on a quantitative scale.These bacteria were then used as active component in a mixture with micron-sized passive silica colloids, with the aim of investigating how the effective interactions and dynamics of passive colloids are affected by the presence and the motility of active E. coli. Both static and hydrodynamic information were obtained via the simultaneous use of USAXS and XPCS techniques. Data suggested active bacteria act as a fluidizing agent in such systems, reducing attractive interactions and enhancing the dynamics of passive colloids, which, at the same time, are affected by the buffer and more viscous environment due to the bacterial presence.Finally, the phoretic motions of micron-sized silica colloids and half-coated silica/nickel Janus colloids suspended in a mixture of 3-methylpyridine (3MP) and water/heavy water undergoing liquid-liquid phase separation were investigated using USAXS and XPCS. Due to the preferential wetting of 3MP on the silica surface, the motion of the colloids is strongly correlated to the dynamics of phase separation.Silica colloids displayed advective motion with enhanced diffusion toward the 3MP-rich phase reminiscent of self-propelled motion until the phase separation is completed. Suspensions of Janus colloids showed a much richer scenario, where colloid dynamics are strongly influenced by the asymmetric interactions with the solvent. The dynamics of Janus colloids were either enhanced or suppressed depending on the 3MP concentration, which, concurrently, affected the microstructure of the system. As opposed to the partitioning in 3MP-rich phase in the case of silica colloids, Janus particles behave like surfactants at the interface.The thesis demonstrates the ability of studying active systems by means of scattering methods and probe their behaviour in the thermodynamic limit and complement the information derived from direct microscopy observations.

Ph. D.--Leiden--Rijksuniversiteit, 1997. / Bibliogr. p. 581-595. Index.

Thesis (Ph. D.)--University of Pennsylvania, 1913. / Bibliography: p. [73]-75.

Janus particles, named after the two faced Roman god Janus, possess unique asymmetry and combine two distinct functions at their opposite sides, allowing them to target complex self-assembled architectures and materials inaccessible for homogeneous building blocks. In this study, three areas regarding the topic of Janus particles were explored: the synthesis of Janus particles, their (self-) assembly, and applications. In the first part of the work, we have drawn our attention to the optimization of the synthetic procedures concerning the preparation of Janus particles and to the extending of the current Janus particle library by adding new geometries to the list. In the case of spherical Janus particles, we have developed an easy approach to tailor the Janus ratio of the resulting particles, thus, extending the possibilities of the Pickering emulsion approach for the creation of a variety of Janus particle architectures. Additionally, a new methodology was employed to measure directly and in situ the position/contact angle of the prepared Janus particles with different Janus ratios at a water-oil interface. It was further concluded that having simply two different functionalities on a particle surface does not necessarily imply amphiphilic behavior: only in the case of large wettability contrasts our particles were in a true Janus regime. In the case of platelet-like Janus particles, we have developed a completely new approach for their large-scale synthesis, which involved a reduced number of steps compared to the spherical Janus particles. In the second part of the work, the assembly behavior of various kinds of functional spherical Janus particles was investigated depending on the nature of the Janus particles and the surrounding media conditions. Oppositely charged, uncharged amphiphilic, and charged amphiphilic Janus particles were fabricated comprising different responsive polymers on their surface, and their assembly was investigated depending on the pH value of the dispersion, the ionic strength, or the solvent. It was found that, under specific conditions, the Janus particles formed hierarchical chain-like structures in solutions, which were not observed in the case of the homogeneous particle mixtures. The obtained results indicate that the fundamental understanding of the Janus particle assembly mechanisms is crucial for the programmed formation of desired structures. In the third part of the work, we have focused on the applications of our developed hybrid hairy Janus particles and proposed two main directions that would benefit from the unique properties or architecture of the Janus particles. The first direction is based on the exploitation of the superior interfacial activity of the Janus particles and their use for interfacial catalysis. The second proposed direction for the application of Janus particles is based on their use as building blocks for functional structured surfaces. The prepared surfaces were thoroughly characterized and tested for their performance toward anti-icing as well as anti-fouling applications. Ultimately, the developed functional surfaces based on Janus particles as building blocks are very promising for their future application in the coating technology.

Janus particles, named after the two faced Roman god Janus, possess unique asymmetry and combine two distinct functions at their opposite sides, allowing them to target complex self-assembled architectures and materials inaccessible for homogeneous building blocks. In this study, three areas regarding the topic of Janus particles were explored: the synthesis of Janus particles, their (self-) assembly, and applications. In the first part of the work, we have drawn our attention to the optimization of the synthetic procedures concerning the preparation of Janus particles and to the extending of the current Janus particle library by adding new geometries to the list. In the case of spherical Janus particles, we have developed an easy approach to tailor the Janus ratio of the resulting particles, thus, extending the possibilities of the Pickering emulsion approach for the creation of a variety of Janus particle architectures. Additionally, a new methodology was employed to measure directly and in situ the position/contact angle of the prepared Janus particles with different Janus ratios at a water-oil interface. It was further concluded that having simply two different functionalities on a particle surface does not necessarily imply amphiphilic behavior: only in the case of large wettability contrasts our particles were in a true Janus regime. In the case of platelet-like Janus particles, we have developed a completely new approach for their large-scale synthesis, which involved a reduced number of steps compared to the spherical Janus particles. In the second part of the work, the assembly behavior of various kinds of functional spherical Janus particles was investigated depending on the nature of the Janus particles and the surrounding media conditions. Oppositely charged, uncharged amphiphilic, and charged amphiphilic Janus particles were fabricated comprising different responsive polymers on their surface, and their assembly was investigated depending on the pH value of the dispersion, the ionic strength, or the solvent. It was found that, under specific conditions, the Janus particles formed hierarchical chain-like structures in solutions, which were not observed in the case of the homogeneous particle mixtures. The obtained results indicate that the fundamental understanding of the Janus particle assembly mechanisms is crucial for the programmed formation of desired structures. In the third part of the work, we have focused on the applications of our developed hybrid hairy Janus particles and proposed two main directions that would benefit from the unique properties or architecture of the Janus particles. The first direction is based on the exploitation of the superior interfacial activity of the Janus particles and their use for interfacial catalysis. The second proposed direction for the application of Janus particles is based on their use as building blocks for functional structured surfaces. The prepared surfaces were thoroughly characterized and tested for their performance toward anti-icing as well as anti-fouling applications. Ultimately, the developed functional surfaces based on Janus particles as building blocks are very promising for their future application in the coating technology.

Thesis (Ph.D.)--University of Alabama at Birmingham, 2008. / Title from first page of PDF file (viewed on June 8, 2009). Includes bibliographical references.

Submitted by Etelvina Domingos (etelvina.domingos@ufpe.br) on 2015-03-12T18:05:01Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO Thaises Brunelle de Lima.pdf: 2138377 bytes, checksum: 3d7f6e7b30968db5465114bb99e5b693 (MD5) / Made available in DSpace on 2015-03-12T18:05:01Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DISSERTAÇÃO Thaises Brunelle de Lima.pdf: 2138377 bytes, checksum: 3d7f6e7b30968db5465114bb99e5b693 (MD5) Previous issue date: 2014 / CNPq / Partículas com caráter Janus são aquelas que apresentam características distintas em cada um de seus hemisférios. Esse tipo de partículas tem atraído muita atenção em áreas de pesquisas diversas. Neste trabalho preparamos nanopartículas de dióxido de titânio (TiO2) com característica Janus através de um método simples, chamado método de emulsão de Pickering. Estas partículas foram caracterizadas através de microscopia eletrônica de varredura. Como aplicação destas partículas, elas foram utilizadas em dispositivos fotovoltaicos orgânicos de heterojunção de volume, que consiste em uma camada ativa de materiais interpenetrados e colocados entre os eletrodos. A camada ativa era composta pelo polímero condutor Poli (1 - metoxi-4-(2-etil-hexiloxi)-p-fenilenovinileno) (MEHPPV), que funciona como doador de elétrons, e nanotubos de carbono de múltiplas camadas (MWCNT) foram usados como aceitadores de elétrons. Os dispositivos preparados foram analisados através da caracterização elétrica, onde realizamos medidas de fotocondutividade com o intuito de comparar os sistemas com camada ativa pura, com adição de nanopartículas de TiO2 e com adição das nanopartículas de TiO2 com características Janus.