In der heutigen chemisch-pharmazeutischen Industrie sind Biokatalysen nicht mehr wegzudenken. Abhängig von der zu realisierenden Biotransformation, wurden signifikante Limitationen vor allem bei der Umwandlung von hydrophoben Substraten identifiziert. Wässrige und organische Einphasenreaktionssysteme treffen hier sehr schnell an ihre Grenzen, sodass nur geringe Ausbeuten realisierbar sind. Eine Alternative stellen mehrphasige Reaktionssysteme dar, wobei hier grundlegend klassische 2-Phasensysteme und Emulsionen unterschieden werden können. Mit Hilfe dieser alternativen Systeme können die bereits genannten Limitationen überwunden werden. Pickering Emulsionen stellen einen Spezialfall der klassischen Tensid stabilisierten Emulsion dar, wobei hier Nano- und Mikropartikel als Stabilisatoren die Tenside an der Tröpfchengrenzfläche ersetzen. Pickering Emulsionen stellen hoch dynamische Systeme dar und trotz kontinuierlicher Forschung auf diesem Gebiet bleiben bisher grundlegende Frage ungeklärt: Welche Parameter für bioaktive w/o Pickering Emulsionen wie Lösungsmittelkomposition, deren Phasenverhältnis, Partikelcharakteristika und -menge, Dispergierverfahren, als auch die Biokatalysatorkonzentration haben auf die Dispersität und Stabilität der Pickering Emulsionen den größten Effekt? Lässt sich eine Vielzahl von Biokatalysatoren in diesem Reaktionssystem einsetzen? Kurzum, eignen sich Wasser in Öl (w/o) Pickering Emulsionen als universelle Reaktionssysteme für effiziente Biokatalysen und stellen somit eine Plattformtechnologie dar? In dieser Studie konnte gezeigt werden, nahezu alle organischen Lösungsmittel, insbesondere leicht wassermischbare Vertreter, können w/o Pickering Emulsionen ausbilden. Ebenso ist eine Stabilisierung sowohl durch Naturstoffpartikel als auch durch hydrophobe und hydrophile Silicon-Compositpartikel realisierbar. In einer umfassenden Charakterisierung der typischen Stellräder für Emulsionen wurden kommerziell erhältliche Lipasen als bioaktive Komponenten zugesetzt, da diese die meistgenutzten Biokatalysatoren in diesem System darstellen. Die Veränderungen der Emulsionsstabilität und Tröpfchengrößen, als Maß der Dispersität, wurden über 24 Stunden erfasst. Hierbei wurde ein maßgebender Einfluss der Proteinkomponente gegenüber allen anderen Parametern wie Partikelmenge, Phasenverhältnis und Dispersionsgeschwindigkeit festgestellt. Proteine mit ihrer amphiphilen Oberflächenbeschaffenheit sind somit nicht nur als Biokatalysatoren, sondern auch als zusätzliche Nanopartikel zu betrachten, die gemeinsam mit hydrophoben Partikeln einen synergetischen und normalisierenden Effekt auf Tröpfchengrößen und Emulsionsstabilität ausüben. Jedoch waren durch Proteinzugabe auch negative Effekte wie Nicht-Etablierung der Emulsion oder eine Phasenumkehr im zeitlichen Verlauf auslösbar, wenn eine Grenzkonzentration überschritten wurde. Hinsichtlich der (bio)chemischen Charakterisierung von enzymbeladenen w/o Pickering Emulsionen konnte deutlich gezeigt werden, kleinere Tröpfchendurchmesser führen zu erhöhten Enzymaktivitäten und besseren Ausbeuten. Im moderat gerührten Batchreaktor wurde die volumetrische Raum-Zeit-Ausbeute um 500% bis 1100% gegenüber dem konventionellen 2 Phasen- und mikroaquatischen Reaktionssystem verbessert. Beim Einsatz von ganzen Zellen im Vergleich zum freien Enzym wurde mit normierter Biokatalysatoraktivität eine Verbesserung auf 130% bis 220% erzielt. Als beste Herstellungsmethodiken konnten das Dispergieren über Schütteln und Zahnkranzdispergierer ermittelt werden. Grenzflächentoxizität, als oft diskutierter Vorgang in Mehrphasensystemen, spielte auch in bioaktiven w/o Pickering Emulsionen eine wichtige Rolle. Es konnte gezeigt werden, hydrophilere Lösungsmittel, wie 2 Methyltetrahydrofuran, sorgten für eine minimierte Grenzflächendenaturierung der Proteine. Hingegen denaturierten hydrophobere Vertreter wie Cyclopentylmethylether und Cyclooctadien einen erheblichen Anteil des gelösten Proteins an der Grenzfläche. Eine eventuelle Kontamination der organischen Produktphase mit gentechnisch veränderten Enzymen durch assimiliertes Protein wurde ebenfalls untersucht. Es konnten geringe gelöste Proteinmengen festgestellt werden, wobei die Spannweite der gelösten Mengen 1 – 4% der Proteingesamtmenge betrug. Hydrophobere Lösungsmittel nahmen generell weniger Protein auf. Für die Evaluation der Verteilung von Substraten und Produkten zwischen beiden flüssigen und der festen Phase der Pickering Emulsion wurden exemplarisch das hydrophilste Substrat und das hydrophobste Produkt getestet. Es wurde keine signifikante Diffusion der gelösten Stoffe in die wässrige bzw. feste Phase ermittelt, insofern konnte eine dauerhaft hohe Bioverfügbarkeit der Substrate in der organischen Phase angenommen werden. Im gerührten Batch konnte eine Übertragung von Ionen zwischen den Dispersionströpfchen nur mit Hilfe von gelstabilisierten Dispersionströpfchen Einhalt geboten werden. Über derartige Modifikationen kann nun auch der Einsatz von mehreren Biokatalysatoren mit verschiedenen pH-Optima und Puffer-Präferenzen verwirklicht werden. Weiterhin konnte die disperse Phase auch gegen stark eutektische Lösungsmittel ausgetauscht werden, sodass Pickering Emulsionen auch als annähernd wasserfreie Reaktionssysteme nutzbar erschienen. In der Risiko- und Anwendungsanalyse über drei Enzymklassen mit drei als „grüner“ klassifizierten Lösungsmitteln in abgestuften Hydrophobizitäten, erwies sich Cyclopentylmethylether als das Lösungsmittel der Wahl für die Etablierung bioaktiver w/o Pickering Emulsionen. Bei der Anwendung verschiedener Biokatalysator-Phänotypen in verschiedenen Reaktionssystemen und Lösungsmitteln, kristallisierten sich bioaktive w/o Pickering Emulsion in Cyclopentylmethylether als produktivstes System heraus. Jedoch wurden bei allen Versuchen inaktivierende Vorgänge auf die verschiedenen Biokatalysatoren beobachtet, wobei Enzyme mit einer augenscheinlichen Gleichverteilung von hydrophoben und hydrophilen Aminosäureresten auf ihrer Oberfläche deutlich bessere Ergebnisse zeigten. In der Anwendung von freiem Enzym und Ganzzell-Biokatalysator, bei normierter Gesamtaktivität, resultierten für den Einsatz in bioaktiven Pickering Emulsionen die ganzen Zellen als beste Biokatalysator-Formulierung. Es wurde signifikant höhere Produktivität sowie auch 300% kleinere Tröpfchen der dispergierten Phase erreicht. Die Modularisierung von Biokatalysen gegenüber One-Pot-Synthesen zeigte ebenfalls deutliche Vorteile in den Kennzahlen der durchgeführten Biotransformation, wobei der jeweilige Prozessschritt an den Biokatalysator angepasst und so ein Optimum an Effizienz erreicht werden kann. Auf diese Weise können biokatalytische Umwandlungen kombiniert werden, die sich im One-Pot-System durch Inhibierungen der angewandten Biokatalysatoren ausschließen würden.:Vorwort/ Danksagung I Zusammenfassung III Abstract VII Liste der Publikationen XIV Abkürzungsverzeichnis und Symbole XIV 1 Einleitung 1 1.1 Biokatalysatoren – Generelle Aspekte und spezielle Vertreter 1 1.2 Angewandte Biokatalyse in Ein-und Mehrphasen-Reaktionssystemen 6 1.3 Pickering Emulsionen - Stand der Technik 14 1.4 Zielstellung der Arbeit: Optimierte bioaktive w/o Pickering Emulsionen 16 2 Material & Methoden 17 2.1 Material 17 2.1.1 Geräte & Zubehör 17 2.1.2 Chemikalien & Kits 19 2.1.3 Puffer 21 2.1.4 Enzyme 22 2.2 Proteinchemische Methoden 22 2.2.1 Bestimmung der Proteinkonzentration - BCA-Test 22 2.2.2 Bestimmung der Proteingröße und -reinheit - SDS-Polyacrylamidgelelektro- phorese (SDS – PAGE) 23 2.2.3 Photometrische Aktivitätsbestimmungen in wässrigem Milieu 24 2.2.4 Zusammenfassung Enzym-Charakteristika 27 2.3 w/o Pickering Emulsion – Essentielle Komponenten und Modifikationen 29 2.3.1 Definition des w/o PE-Standardsystems 29 2.3.2 Partikel zur Stabilisierung von w/o Pickering Emulsionen 29 2.3.3 Siliconbeschichtung von hydrophilen Partikeln und Bakterien 31 2.3.4 Bestimmung der Morphologie und Tröpfchengrößenverteilung 32 2.3.5 Lösungsmittelscreening 33 2.3.6 Phasen-Migration von Proteinen 34 2.3.7 Verteilungskoeffizienten von Substraten und Produkten im triphasischen Reaktionssystem Pickering Emulsion 34 2.4 Biokatalyse in Pickering Emulsionen 35 2.4.1 Bioaktive w/o PE - Definition des Standard-Reaktionssystems 35 2.4.2 Biokompatibilität „grüner“ Lösungsmittel 36 2.4.3 GC – Analytik 38 2.5 Statistische Auswertung der Experimente 40 2.5.1 Gewichteter Mittelwert, interne und externe Konsistenz 40 2.5.2 Lösungsmittelscreening: statistische Auswertung 41 3 Ergebnisse und Diskussion 42 3.1 Modifizierung von Nano-, Mikro- und Naturstoffpartikeln durch Siliconbeschichtung und Anwendungsscreening in w/o PE 42 3.1.1 Hydrophobizität der Silicon-Polymere 42 3.1.2 Morphologie von anorganischen Partikel-Materialien mit und ohne Silicon- Beschichtung 43 3.1.3 Morphologie von Naturstoff-Partikeln mit und ohne Silicon-Beschichtung 47 3.1.4 Partikel-Aggregation und Gegenmaßnahmen 51 3.1.5 Partikel-Screening 53 3.2 Charakterisierung von w/o Pickering Emulsionen im gerührten Batch 59 3.2.1 Pickering Emulsionen in biokatalytisch relevanten organischen Lösungs- mitteln 59 3.2.2 Bioaktive w/o PE - Auswirkung von Enzym – und Proteinmengen 66 3.2.3 Bioaktive w/o PE - Effekte der eingesetzten Partikelkonzentrationen 68 3.2.4 Bioaktive w/o PE - Einfluss der Phasenverhältnisse 70 3.2.5 Bioaktive w/o PE - Einfluss der angewandten Dispergiergeschwindigkeit 71 3.2.6 Bioaktive w/o PE - Herstellungsverfahren und Einfluss auf das Enzym 73 3.2.7 Vergleich 2-Phasensystem und bioaktive w/o Pickering Emulsion im gerührten Batch 75 3.2.8 Tröpfchengröße und Einfluss auf Produktbildung des PE-Systems 77 3.2.9 Phasen-Migration von Proteinen - Evaluation von Enzymwechselwirkungen mit dem Reaktionssystem 79 3.2.10 Verteilungskoeffizienten von Substraten und Produkten in den Standard– Reaktionssystemen 81 3.2.11 Protonen-Transfer zwischen zwei dispergierten Phasen in w/o Pickering Emulsionen 82 3.2.12 Alternative DES/o Pickering Emulsionen für wasserfreie Systeme 83 3.3 Bioaktive w/o Pickering Emulsion: Einschritt-Synthesen 84 3.3.1 Lipasenkatalysierte Umesterung in wässrigem Milieu 84 3.3.2 Carboligation mittels Benzaldehydlyase 86 3.3.3 Reduktionen via Alkoholdehydrogenasen 95 3.3.4 Transaminase 106 3.4 Bioaktive w/o Pickering Emulsionen: Mehrschritt-Synthesen 112 3.4.1 One-Pot-Biokatalyse gegen modularisierte Mehrschritt-Chemo-Biokatalyse 112 4 Bioaktive w/o Pickering Emulsionen als Reaktionssystem für Biokatalysen: Zusammenfassung & Bewertung 117 5 Plattform w/o Pickering Emulsion: Schlussfolgerung und Ausblick 130 6 Literatur 131 Anhang 150 Versicherung 150 Abbildungsverzeichnis 151 Tabellenverzeichnis 158 Download Datensammlung 164 A3.1.5 TMODS-Silicat-NP-Benchmark 165 A3.2.1-1 Lösungsmittel-Screening: physiko-chemische Eigenschaften 167 A3.2.1-2 Regressionsanalyse: Qualität PE gegen alle physiko-chemischen Eigenschaften 171 A3.2.1-3 Optimierte Regressionsanalyse: Qualität PE gegen Molekulargewicht, Dichte und Dampfdruck 173 A3.2.3 Auswirkungen von Protein- und Enzymmengen 175 A3.2.4 Effekte der eingesetzten Partikelmengen 175 A3.2.5 Einfluss der Phasenverhältnisse 176 A3.2.6 Einfluss der angewandten Dispersionsgeschwindigkeit/ -energie 176 A3.3.1 Lipasenkatalysierte Umesterung 177

[pt] Muitas indústrias, como as de petróleo, cosméticos e farmacêuticos, buscam estabilizar emulsões de forma efetiva e com menor custo. O uso de partículas sólidas como agentes emulsificantes (emulsões Pickering) tem apresentado grandes benefícios, como custo e estabilidade das emulsões, quando comparados aos surfactantes, que são utilizados na emulsão clássica. A eficácia de uma determinada partícula na estabilização de uma emulsão depende das suas propriedades e da sua interação com as fases oleosa e aquosa da emulsão. Essas partículas sólidas adsorvem-se na interface óleo-água criando uma fina camada entre as fases, evitando a coalescência das gotas. Uma forma de estudar a estabilidade de emulsões Pickering é analisar o experimento de coalescência de duas interfaces óleo-água que são forçadas uma contra a outra. A metodologia deste trabalho baseou-se em medições do tempo de coalescência de uma gota de óleo, presente em uma dispersão aquosa de nanopartículas, quando a mesma é forçada contra uma interface óleoágua. Para a correta visualização e registro do momento da coalescência da gota utilizou-se uma câmera de alta velocidade (Photron FastCam SA3). As nanopartículas utilizadas foram: Laponita RD, dióxido de titânio HAc e Aerosil R972. Observou-se tempos de coalescência maiores para testes com dispersões aquosas de Laponita RD 1,0 porcento (m/m) e de Aerosil R972 0,0024 porcento (m/m) do que para testes com água pura (Milli-Q). / [en] Several industries, such as oil and gas, cosmetics, and pharmaceutical, seek to stabilize emulsions more effectively and at a lower cost. As compared to surfactants, which are used in classic emulsions, the use of solid particles as emulsifying agents (Pickering emulsions) has presented great benefits, including lower costs and better emulsion stability. A particle s effectiveness on stabilizing an emulsion is related to its properties, as well as its interaction with the oil and water phases of the emulsion. These solid particles adsorb at the oil-water interface, creating a thin layer between the phases, and thus avoiding the coalescence of the droplets. One method to study the stability of Pickering emulsions is to analyze the coalescence experiment of two oil-water interfaces that are forced against each other. The methodology of this work was based on measurements of the coalescence time of an oil droplet in an aqueous dispersion of nanoparticles, when it is forced against an oil-water interface. A high speed camera (Photron FastCam SA3) was used for the proper visualization and recording of the moment of drop coalescence. The three types of nanoparticles used were: Laponite RD, titanium dioxide HAc, and Aerosil R972. Longer coalescence times were observed for tests with aqueous dispersions of Laponite RD 1.0 percent (w/w) and Aerosil R972 0.0024 percent (w/w) versus tests with plain water (Milli-Q).

In recent years, water-in-oil Pickering emulsions have been introduced as promising reaction systems for multiphase enzyme catalysis, in particular lipase-catalyzed esterification and transesterification. Here, we for the first time gained insight into the effects that the presence of the proteins exert on the fineness and stability of the emulsion system and thus, the catalytic performance. We demonstrated a distinct, concentration-and enzyme-dependent decrease of droplet sizes in the dispersed phase, accompanied by decreasing stability against coalescence. This was due to a probably quantitative adsorption of lipases at the interphase intercalating the solid particles. Destabilization was reduced slightly at increased particle content and increased volume portion of the dispersed phase, respectively. However, the low tolerable lipase concentrations in the reaction system considerably limited its productivity. Thus, our study points at the enzyme content, or rather enzyme location, in Pickering emulsions being the crucial parameter for optimizing catalytic performance.

<div>The House Cricket (Acheta domesticus) is a promising alternative to traditional protein sources, as these insects produce over 12 times the mass of protein for a given mass of food/water when compared to cattle, while also producing lower amounts of greenhouse gases and NH3 emissions (Kim et al. 2017, Hanboonsong, Jamjanya and Durst 2013, Van Huis 2013). Additionally, previous studies have demonstrated significant emulsification and gelling properties of insect flours, such as from cricket, which has been attributed to the functional properties of the protein (Kim et al. 2017). Ground cricket flours contain significant quantities of both protein and fibrous polysaccharides, particularly chitin. Since chitin particles are also capable of preparing emulsions as a Pickering stabilizer, there remains a question on the relative role of the protein and chitin components in crickets for stabilizing emulsion products. Relative contributions of each component was identified by first isolating the water-soluble protein and water-insoluble chitin fractions from ground cricket flour and then determining their interfacial properties and stability of prepared oil-in-water emulsions. Dynamic interfacial tension measurements indicated significant surface activity of the protein fraction, while there was minimal evidence of significant surface pressure development in the presence of 5-10 μm chitin particles. 10 % (w/w) canola oil-in-water emulsions were prepared with 0.5-2% (w/w) of the water-soluble protein fraction and 5.29% (w/w) canola oil-in-water emulsions were prepared with 0.688% of the chitin fraction. Stability of the emulsions against creaming was between 75% and 90% for emulsions stabilized by the protein fraction over three weeks of storage and between 93% and 96% for emulsions stabilized by chitin over 24 hours of storage. Significant fractions of precipitate- and oil-layers found in chitin-stabilized dispersions was attributed to the presence of large chitin particles (79 μm volume weighted mean diameter) and inefficient adsorption to droplet interfaces during homogenization, respectively. Volume-weighted mean diameter of emulsified oil droplets remained at 17-24 μm among protein-stabilized (>1.5 wt%) emulsions over three weeks of storage but only 60 μm over 24 hours among chitin-stabilized emulsions. Light micrographs of emulsion droplets showed successful adsorption of chitin fractions to oil droplets in the emulsion layer, verifying their potential as Pickering stabilizers. These findings demonstrated that both water-soluble protein and chitin particles obtained from ground cricket flours are legitimate emulsion stabilizers, yet the chitin fraction is much less effective without a more intensive approach to reduce their particle size.</div>

Les émulsions stabilisées par des particules solides sont connues et étudiées depuis le début du XXème siècle, dans le but de comprendre les propriétés originales qu'elles présentent. Afin de rationaliser ces systèmes, nous développons un système modèle basé sur l'utilisation de techniques microfluidiques pour la fabrication de gouttes et de nanoparticules de silice onodisperses pour les stabiliser. La première partie de ce travail porte sur 'optimisation et la compréhension de la synthèse diphasique des nanoparticules dans le cadre de la Théorie Classique de la Nucléation. Ces nanoparticules sont ensuite utilisées pour stabiliser des gouttes d'huiles ormées dans une puce microfluidique, ce qui permet de découpler les différents phénomènes conduisant à l'obtention d'une émulsion : création de surface, adsorption des particules, coalescence des gouttes. Les émulsions collectées peuvent être déstabilisées par ajout d'un solvant dans la phase continue, provoquant la formation de gouttes non sphériques ou la séparation totale des eux phases. Enfin, nous examinons les mécanismes permettant d'expliquer la stabilisation ou la déstabilisation provoquée des gouttes par des nanoparticules.

Stimulus-responsive colloidosomes which completely dissolve upon a mild pH change are developed. pH-Responsive nanoparticles that dissolve upon a mild pH increase are synthesized by a nanoprecipitation method and are used as stabilizers for a double water-in-oil-in-water Pickering emulsion. These emulsions serve as templates for the production of pH-responsive colloidosomes. Removal of the middle oil phase produces water-core colloidosomes that have a shell made of pH-responsive nanoparticles, which rapidly dissolve above pH 7. The permeability of these capsules is assessed by FRAP, whereby the diffusion of a fluorescent tracer through the capsule shell is monitored. Three methods for tuning the permeability of the pH-responsive colloidosomes were developed: ethanol consolidation, layer-by-layer assembly and the generation of PLGA-pH-responsive nanoparticle hybrid colloidosomes. The resulting colloidosomes have different responses to the pH stimulus, as well as different pre-release permeability values. Additionally, fundamental studies regarding the role of particle surface roughness on Pickering emulsification are also shown. The pH-responsive nanoparticles were used as a coating for larger silica particles, producing rough raspberry-like particles. Partial dissolution of the nanoparticle coating allows tuning of the substrate surface roughness while retaining the same surface chemistry. The results obtained show that surface roughness increases the emulsion stability of decane-water systems (to almost twice), but only up to a certain point, where extremely rough particles produced less stable emulsions presumably due to a Cassie-Baxter wetting regime. Additionally, in an octanol-water system, surface roughness was shown to affect the type of emulsion generated. These results are of exceptional importance since they are the first controlled experimental evidence regarding the role of particle surface roughness on Pickering emulsification, thus clarifying some conflicting ideas that exist regarding this issue.

This thesis presented a microfluidic preparation of bubbles-templated micro-size materials. In particular, this thesis focused on the microfluidic formation and dissolution of CO2 bubbles. First, this thesis described pH-regulated behaviours of CO2 bubbles in the microfluidic channel. This method opened a new way to generate small (<10 µm in diameter) with a narrow size distribution (CV<5%). Second, the microfluidic dissolution of CO2 bubbles possessed the important feature: the local change of pH on the bubble surface. This allowed us to encapsulate the bubbles with various colloidal particles. The bubbles coated with particles showed a high stability against coalescences and Ostwald ripening. The dimensions and shapes of bubbles with a shell of colloidal particle were manipulated by the hydrodynamic and chemical means, respectively. Third, we proposed a microfluidic method for the generation of small and stable bubbles coated with a lysozyme-alginate shell. The local pH decrease at the periphery of CO2 bubbles led to the electrostatic attraction between lysozyme on the bubble surface and alginate in the continuous phase. This produced the bubbles with a shell of biopolymers, which gave a long-term stability (up to a month, at least) against the dissolution and coalescence. Fourth, we presented a single-step method to functionalize bubbles with a variety of nanoparticles. The bubbles showed the corresponding properties of nanoparticles on their surface. Further, we explored the potential applications of these bubbles as contrast agents in ultrasound and magnetic resonance imaging.

This thesis presented a microfluidic preparation of bubbles-templated micro-size materials. In particular, this thesis focused on the microfluidic formation and dissolution of CO2 bubbles. First, this thesis described pH-regulated behaviours of CO2 bubbles in the microfluidic channel. This method opened a new way to generate small (<10 µm in diameter) with a narrow size distribution (CV<5%). Second, the microfluidic dissolution of CO2 bubbles possessed the important feature: the local change of pH on the bubble surface. This allowed us to encapsulate the bubbles with various colloidal particles. The bubbles coated with particles showed a high stability against coalescences and Ostwald ripening. The dimensions and shapes of bubbles with a shell of colloidal particle were manipulated by the hydrodynamic and chemical means, respectively. Third, we proposed a microfluidic method for the generation of small and stable bubbles coated with a lysozyme-alginate shell. The local pH decrease at the periphery of CO2 bubbles led to the electrostatic attraction between lysozyme on the bubble surface and alginate in the continuous phase. This produced the bubbles with a shell of biopolymers, which gave a long-term stability (up to a month, at least) against the dissolution and coalescence. Fourth, we presented a single-step method to functionalize bubbles with a variety of nanoparticles. The bubbles showed the corresponding properties of nanoparticles on their surface. Further, we explored the potential applications of these bubbles as contrast agents in ultrasound and magnetic resonance imaging.

Carbon dioxide (CO₂) flooding is the second most common tertiary recovery technique implemented in the United States. Yet, there is huge potential to advance the process by improving the volumetric sweep efficiency of injected CO₂. Delivering CO₂ into the reservoir as a foam is one way to do this. Surfactants have traditionally been used to generate CO₂ foams for mobility control; however, the use of nanoparticles as a foam stabilizing agent provides several advantages. Surfactant-stabilized foams require constant regeneration to be effective, and the surfactant is adsorbed onto reservoir rocks and is prone to chemical degradation at harsh reservoir conditions. Nanoparticle-stabilized foams have been found to be tolerant of high temperature and high salinity environments. Their nano size also allows them to be transported through reservoir rocks without blocking pore throats. Stable CO₂-in-water foams were generated using 5 nm silica nanoparticles with a short chain polyethylene glycol surface coating. These foams were generated by the co-injection of CO₂ and a nanoparticle dispersion through both rock matrix and fractures. A threshold shear rate was found to exist for foam generation in both fractured and non-fractured Boise sandstone cores. The ability of nanoparticles to generate foams only above a threshold shear rate is advantageous; in field applications, high shear rates are associated with high permeability zones, where the presence of foam is desired. Reducing CO₂ mobility in these high permeability zones diverts CO₂ into lower permeability regions containing not yet swept oil. Nanoparticles were also found to be able to stabilize CO₂ foams by co-injection through rough-walled fractures in cement cores, demonstrating their ability to stabilize foams without matrix flow. Experiments were conducted on the ability of fly ash, a waste product from burning coal in power plants, to stabilize oil-in-water emulsions and CO₂ foams. The use of fly ash particles as a foam stabilizing agent would significantly reduce material costs for potential tertiary oil recovery and CO₂ sequestration applications. Nano-milled fly ash particles without surface treatment were able to generate stable oil-in-water emulsions when high frequency, high energy vibrations were applied to a mixture of fly ash dispersion and dodecane. Oil-in-water emulsions were also generated by co-injecting fly ash and dodecane, a low pressure analog to CO₂, through a beadpack. Emulsions generated by co-injection, however, were unstable and coalesced within an hour. A threshold shear rate was required for the emulsion generation. Fly ash particles were found to be able to stabilize CO₂ foam in a high pressure batch mixing cell, but not by co-injection through a beadpack. Dispersions of fly ash particles were found to be stable only at low salinities (<1 wt% NaCl). / text

abstract: Liquid-liquid interfaces serve as ideal 2-D templates on which solid particles can self-assemble into various structures. These self-assembly processes are important in fabrication of micron-sized devices and emulsion formulation. At oil/water interfaces, these structures can range from close-packed aggregates to ordered lattices. By incorporating an ionic liquid (IL) at the interface, new self-assembly phenomena emerge. ILs are ionic compounds that are liquid at room temperature (essentially molten salts at ambient conditions) that have remarkable properties such as negligible volatility and high chemical stability and can be optimized for nearly any application. The nature of IL-fluid interfaces has not yet been studied in depth. Consequently, the corresponding self-assembly phenomena have not yet been explored. We demonstrate how the unique molecular nature of ILs allows for new self-assembly phenomena to take place at their interfaces. These phenomena include droplet bridging (the self-assembly of both particles and emulsion droplets), spontaneous particle transport through the liquid-liquid interface, and various gelation behaviors. In droplet bridging, self-assembled monolayers of particles effectively "glue" emulsion droplets to one another, allowing the droplets to self-assembly into large networks. With particle transport, it is experimentally demonstrated the ILs overcome the strong adhesive nature of the liquid-liquid interface and extract solid particles from the bulk phase without the aid of external forces. These phenomena are quantified and corresponding mechanisms are proposed. The experimental investigations are supported by molecular dynamics (MD) simulations, which allow for a molecular view of the self-assembly process. In particular, we show that particle self-assembly depends primarily on the surface chemistry of the particles and the non-IL fluid at the interface. Free energy calculations show that the attractive forces between nanoparticles and the liquid-liquid interface are unusually long-ranged, due to capillary waves. Furthermore, IL cations can exhibit molecular ordering at the IL-oil interface, resulting in a slight residual charge at this interface. We also explore the transient IL-IL interface, revealing molecular interactions responsible for the unusually slow mixing dynamics between two ILs. This dissertation, therefore, contributes to both experimental and theoretical understanding of particle self-assembly at IL based interfaces. / Dissertation/Thesis / Ph.D. Chemical Engineering 2013