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Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15392号 / 工博第3271号 / 新制||工||1492(附属図書館) / 27870 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 垣内 隆, 教授 江口 浩一, 教授 安部 武志 / 学位規則第4条第1項該当

The thesis constitutes an investigation into the production of floating photocatalytic particles (FPP) as a low cost, low carbon footprint and chemical-free wastewater treatment. It is anticipated that this approach would be particularly attractive for developing countries where it could reduce incidences of disease and pollution. The particles were manufactured from cocoa butter (CB), and contained either photocatalytic nanoparticle titanium dioxide TiO2 (P25) or silver-doped TiO2 (0.5% w/w). The photocatalytic activity of the particles was evaluated by means of the decolourisation of the dye indigo carmine (IC). Three arrangements were used; small scale treatment using Petri dishes, an 1800 ml batch-recirculation photoreactor and an 8 litre UV contactor. Membrane emulsification (ME) was the technique used here to generate particles of controlled size. The particles were in effect what are known as Pickering emulsions in which the solid fat core (CB) was stabilised by TiO2 nanoparticles, resulting in composite particles that float easily and can receive incident light to generate highly reactive free radical species. The FPPs were characterised by FEGSEM and EDs mapping analysis, and the images obtained displayed a spherical structure with a rough outer surface, and the EDs showed a good coverage of TiO2 on the surface of at a maximum loading of 10% w/w. Tests were conducted to assess the stability of the particles when used in repeated cycles. Reuse of the particles caused a significant drop of photodegradation activity after four cycles to 42% of that of freshly prepared particles. The correlation of photocatalytic activity with silver dosage was also investigated. The highest photocatalytic activity was achieved at 0.5 wt. % of silver doped TiO2 and was some 10% greater than for un- doped particles. The organic carbon release resulted from TOC analysis for the FPPs that were exposed to UV light for 8.5 hr in water was less than 1 wt. %. First order reaction kinetics were exhibited during decolourisation of IC dye with respect to the initial dye concentration, radiation intensity, percentage coverage of the liquid surface by the FPPs, and the catalytic loading. For a static system (i.e. no forced convection), the most effective surface coverage was identified as being in the range of 60 to 80%. A linear source spherical emission model (LSSE) was adopted to estimate the intensity of the incident radiation on the surface of the FPP layer in the photoreactor and validated. In addition, a preliminary kinetic model to describe of the effect of the photocatalytic active surface concentration of TiO2 as well as the efficient intensity flux in the kinetic model was developed for the FPP layer photoreactor.

Ce travail porte sur la description et la compréhension de l’inversion de phase catastrophique utilisée pour l’émulsification de produits visqueux, à travers l’analyse des effets de formulation et de procédé sur la fraction de phase dispersée à laquelle le processus se produit et sur les mécanismes mis en jeu. Les suivis rhéologique et conductimétrique simultanés in situ de l’émulsification ont permis, du point de vue procédé, de mettre en avant l’influence du débit d’addition de la phase aqueuse sur la formation d’émulsions multiples du type e/H/E lesquelles, en augmentant notablement la fraction de phase dispersée apparente, sont responsables de l’inversion dès de faibles fractions de phase dispersée ajoutée. Au niveau formulation, l’augmentation de la viscosité de l’huile induit de manière remarquable la tendance de cette phase à devenir le milieu dispersé, conduisant à une inversion pour de très faibles fractions de phase aqueuse et donc à des émulsions finales très concentrées (de 80 à 95% en volume). Le suivi au microscope du phénomène d’inversion de phase par l’intermédiaire d’un écoulement de type « squeezing flow », a permis d’établir les conditions et les mécanismes conduisant à une inversion complète ou seulement partielle. La viscosité relative des phases aqueuse et huileuse est responsable d’une inversion catastrophique suivant un mécanisme de type agglomération – coalescence plutôt que de type inclusion/fuite tel que généralement admis. L’établissement d’un modèle mathématique basé sur les bilans de population et le caractère fractal du phénomène a permis de décrire l’évolution de la taille des gouttes multiples ainsi que la fraction de phase dispersée ajoutée à laquelle l’inversion se produit / This study deals with the description and understanding of catastrophic phase inversion during high viscous oil emulsification, through the analysis of the effects of formulation and process variables on the dispersed phase fraction at which the inversion is triggered and on the involved mechanisms. The simultaneous follow – up in situ of viscosity and conductivity measurements allowed, from a process point of view, to emphasize on the effect that the aqueous phase addition rate has on the formation of multiple w/O/W emulsions. Due to the formation of w/o/W emulsions, the volume of the effective dispersed phase greatly increases while at the same time, if the aqueous phase is added by very small fractions inversion of the w/o/W system can occur. In relation with formulation, an increase in oil viscosity greatly increased the tendency of the oily phase to become the dispersed phase. At the same time, it promoted the formation of highly concentrated emulsions (about 80 to 95 % in volume) after the inversion had occurred. The microscopical follow-up of emulsion morphology by means of squeezing flow, allowed us to establish the conditions and mechanisms that lead to partial or complete inversion. Even though literature sources lead us believe that inversion will occur through the “inclusion/escape” mechanism, experimental results showed that the relative viscosity between the phases promoted inversion through the mechanism of “agglomeration – coalescence” rather than “inclusion/escape”. A mathematical model based on population balances and on the fractal nature of multiple emulsions allowed us to describe the multiples drop size and effective dispersed phase evolution until inversion phenomena

The performance of membranes in various processes is largely dependent on their morphological properties. Thus, membrane structure has been continuously optimised for different applications. Anodic alumina membranes (AAMs) exhibit self-ordered pore structure and the pore size can be tuned in the sub-micrometre range. The aim of this PhD project is to propose and develop AAMs for the applications of membrane filtration and emulsification with potential for scale-up. In the project, the AAMs were initially fabricated in flat sheet form to optimise the process parameters to obtain membranes with a high quality of pore structure. The membrane pore diameter can be readily controlled by the anodization voltage. While AAMs are normally symmetric, by manipulating the anodization voltage, asymmetric AAMs consists of stem pores and active pores have been successfully made. After that, the flat AAMs with symmetric and homogeneous structure were used as a platform to study for surface modification and fluid transport in nano-channels. The surface chemistry and wettability of the membranes has been altered by grafting of silane molecules and carbon coating by chemical vapour deposition. Fluid flow measurement through pristine AAMs with pore diameter in the 20 nm to 100 nm range shows flow enhancement effect, experimentally for the first time, can occur in hydrophilic materials. Subsequently, tubular AAMs were fabricated using aluminium alloy tubes, to be assessed for ultrafiltration and membrane emulsification processes. The pore structure of the tubular AAMs was analogous to flat membranes. Despite the reduced pore circularity and hexagonal arrangement originated from the presence of impurities in the starting materials, the narrow pore size distribution was not compromised. In a selectivity-permeability analysis, the asymmetric tubular AAMs outperformed most of the commercial ceramic membranes but their flux was very low when compared to polymeric membranes. A bovine serum albumin filtration test showed that complete pore blocking-cake filtration model can be used to describe the fouling behaviour. Finally, symmetric tubular membranes were used to study dead-end and cross-flow emulsification processes. The resulting emulsions show low polydispersity. Using a membrane with 25 nm average pore diameter, the obtained average droplet size was as low as 120 nm during a cross-flow emulsification. This is by far the smallest achieved average droplet size by cross-flow membrane emulsification.

Droplet based microfluidics is a developing technology with great potential towards improving large scale combinatorial studies that require high throughput and accurate metering of reagents. Each droplet can be thought of as a miniature microreactor where complex reactions can be performed on the micro-scale by mixing, splitting and combining droplets. This thesis investigates the operation and control of droplet microfluidic devices operating using constant pressure sources to pump fluids where feedback from the droplets influences the overall performance of the device. For this purpose, a model system consisting of a single T-junction droplet generator and a single network node is used to understand how pressure source control effects droplet generation and transport through microfluidic networks. The first part of this thesis focuses on the generation of Newtonian liquid-liquid droplets from a microfluidic T-junction operating within the squeezing-to-transition regime with stable flow rates. An experimental study was performed to characterize the effects of geometry (height/width ratio, channel width ratio) and flow parameters (Capillary number, flow rate ratio, viscosity ratio) on the droplet size, spacing and rate of production. Three stages of droplet formation were identified (lag, filling and necking), including the newly defined lag stage that appears at the beginning of the formation cycle once the interface pulls back after a droplet detaches. Based on the experimental observations, a model was developed to describe the formation process which incorporates a detailed geometric description of the drop shape with a force balance in the filling stage and a control volume analysis of the necking stage. The model matches well with the experimental results as data falls within 10% of the predicted values. Subsequently, the effect of surfactants on the formation process was investigated. Surfactant transport occurs on a timescale comparable to the production rate of droplets resulting in dynamic interfacial tension effects. This causes strong coupling between the mass transport of surfactants and the drop production process. Using the previously defined force balance, the apparent interfacial tension at the end of the filling stage was measured. The results show that there is a significant deviation from the equilibrium interfacial tension at normal operating conditions for the T-junction generators due to the rapid expansion of the interface. A model was developed to calculate the dynamic interfacial tension for pre and post micellar solutions, which was then incorporated into the overall model for droplet formation in T-junction generators. Next, the behaviour of microfluidic droplet generators operating under pressure source control was investigated. Coupling between the changing interface and hydrodynamic resistance of the droplets and the flow rate of the two phases creates fluctuations in the output of the droplet generator. Oscillations were found to occur over the short term (one droplet formation cycle) and long term (many formation cycles). Two metrics were developed to quantify these oscillations. Short term oscillations were quantified by tracking droplet speed in the output channel and long term oscillation were quantified by measuring changes in droplet spacing. Analysis of experimental and numerical data shows that long term oscillations have a periodicity that matches the residence time of droplets in the system. A simple model is developed to determine the influence of Laplace pressure, droplet resistance, T-junction generator design and network architecture on the magnitude of these oscillations. From the model a set of design rules are developed to improve the overall operation of T-junction generators using pressure driven flow. The final part of this thesis studies the transport of droplets through a single microchannel junction under various geometric and flow conditions applied to the two outlet channels. Droplets alter the hydrodynamic resistance of the channel they travel within which creates a feedback effect where the decision of preceding droplets influences the trajectory of subsequent droplets. Multifaceted behaviour occurs where sometimes the trajectory of droplets follows a repeatable pattern and other times it is chaotic. As part of this work, a discrete analytical model was developed that predicts droplet transport through the junction including transitions between filtering and sorting, bifurcation in the patterns, composition of the patterns, and an estimation of when patterns will disintegrate into chaos. The model was validated by comparing it to compact numerical simulations and microfluidic experiments with good agreement.The complex behaviour of a simple junction emphasizes the challenge that remains for more highly integrated droplet microfluidic networks operating with pressure driven flow.

Droplet based microfluidics is a developing technology with great potential towards improving large scale combinatorial studies that require high throughput and accurate metering of reagents. Each droplet can be thought of as a miniature microreactor where complex reactions can be performed on the micro-scale by mixing, splitting and combining droplets. This thesis investigates the operation and control of droplet microfluidic devices operating using constant pressure sources to pump fluids where feedback from the droplets influences the overall performance of the device. For this purpose, a model system consisting of a single T-junction droplet generator and a single network node is used to understand how pressure source control effects droplet generation and transport through microfluidic networks. The first part of this thesis focuses on the generation of Newtonian liquid-liquid droplets from a microfluidic T-junction operating within the squeezing-to-transition regime with stable flow rates. An experimental study was performed to characterize the effects of geometry (height/width ratio, channel width ratio) and flow parameters (Capillary number, flow rate ratio, viscosity ratio) on the droplet size, spacing and rate of production. Three stages of droplet formation were identified (lag, filling and necking), including the newly defined lag stage that appears at the beginning of the formation cycle once the interface pulls back after a droplet detaches. Based on the experimental observations, a model was developed to describe the formation process which incorporates a detailed geometric description of the drop shape with a force balance in the filling stage and a control volume analysis of the necking stage. The model matches well with the experimental results as data falls within 10% of the predicted values. Subsequently, the effect of surfactants on the formation process was investigated. Surfactant transport occurs on a timescale comparable to the production rate of droplets resulting in dynamic interfacial tension effects. This causes strong coupling between the mass transport of surfactants and the drop production process. Using the previously defined force balance, the apparent interfacial tension at the end of the filling stage was measured. The results show that there is a significant deviation from the equilibrium interfacial tension at normal operating conditions for the T-junction generators due to the rapid expansion of the interface. A model was developed to calculate the dynamic interfacial tension for pre and post micellar solutions, which was then incorporated into the overall model for droplet formation in T-junction generators. Next, the behaviour of microfluidic droplet generators operating under pressure source control was investigated. Coupling between the changing interface and hydrodynamic resistance of the droplets and the flow rate of the two phases creates fluctuations in the output of the droplet generator. Oscillations were found to occur over the short term (one droplet formation cycle) and long term (many formation cycles). Two metrics were developed to quantify these oscillations. Short term oscillations were quantified by tracking droplet speed in the output channel and long term oscillation were quantified by measuring changes in droplet spacing. Analysis of experimental and numerical data shows that long term oscillations have a periodicity that matches the residence time of droplets in the system. A simple model is developed to determine the influence of Laplace pressure, droplet resistance, T-junction generator design and network architecture on the magnitude of these oscillations. From the model a set of design rules are developed to improve the overall operation of T-junction generators using pressure driven flow. The final part of this thesis studies the transport of droplets through a single microchannel junction under various geometric and flow conditions applied to the two outlet channels. Droplets alter the hydrodynamic resistance of the channel they travel within which creates a feedback effect where the decision of preceding droplets influences the trajectory of subsequent droplets. Multifaceted behaviour occurs where sometimes the trajectory of droplets follows a repeatable pattern and other times it is chaotic. As part of this work, a discrete analytical model was developed that predicts droplet transport through the junction including transitions between filtering and sorting, bifurcation in the patterns, composition of the patterns, and an estimation of when patterns will disintegrate into chaos. The model was validated by comparing it to compact numerical simulations and microfluidic experiments with good agreement.The complex behaviour of a simple junction emphasizes the challenge that remains for more highly integrated droplet microfluidic networks operating with pressure driven flow.

Many daily life products consist of mixtures of oil and water. When an immiscible material is dispersed an interface in-between the two phases is created which gives rise to rheological phenomena which can be exploited for product formulation; this is the case in products such as hand-creams and food products. Furthermore emulsions are used to transport hydrophobic materials, for example, many pharmaceuticals are injected as emulsions into the bloodstream. The performance of such products depends on their microstructure, which is determined by its formulation and how its constituents are mixed together; therefore the microstructure depends on the properties of the dispersed phases, the emulsifier used, the equipment used and its processing conditions. Emulsified products are seldom mono-dispersed due to the complex drop breakup mechanism in the turbulent fields inside the equipment in which the phases are forced together. The chaotic breakup mechanism of highly viscous dispersed phases yield complex and broad drop size distributions (DSD) as a result of the dominating viscous cohesive stresses inside the parent drop. Former studies have used the Sauter mean diameter and/or the size of the largest drop as the characteristic measure of central tendency of the DSD to correlate their results and to prove mechanistic or phenomenological models; however these parameters in isolation are insufficient to characterise the whole DSD of highly polydisperse emulsions. In this dissertation a vast amount of silicon oils of different viscosity were used as dispersed phase to study the effect of various processing conditions and formulations on the resulting DSD. The effect of several formulation and processing parameters were studied for two different mixing devices: stirred vessels and in-line high-shear mixers. (1) For stirred vessels, the effect of stirring speed, continuous phase viscosity and dispersed phase volume fraction were studied in combination with the viscosity of the dispersed phase for steady-state systems. (2) For in-line high-shear mixers a model that links batch and multi-pass continuous emulsification for multimodal DSD was derived from a transient mass balance. Processing parameters such as time and volume, flow rate and number of passes through the mixer, and stirring speed were studied for a wide dispersed phase viscosity range. The analytical methodology implemented included the use of one or more probability density functions to describe the shape of the DSD. The models proposed gave reasonable approximations of the Sauter mean diameter and allowed to study the drop size changes and the relative amount of different types of drops resulting from different breakup mechanisms.

Le Cydia pommonella granulovirus (CPGV) est un insecticide naturel des ravageurs des pommes sensible à l’environnement extérieur (UV et dioxygène). Pour le protéger, nous avons encapsulé le CpGV dans des émulsions doubles de type eau dans huile dans eau (E/H/E). Cependant, l’utilisation des émulsions doubles requiert la maitrise de leur stabilité thermodynamique et la compréhension des mécanismes mis en jeu au cours de leur déstabilisation. C’est dans ce contexte que différents paramètres de formulation : procédé d’émulsification, type de stabilisant hydrophile, concentration en stabilisant lipophyle et en gouttelette d’eau, utilisation d’un agent anti-UV ont été testés pour étudier leur influence sur la libération du virus. Chaque formulation a fait l’objet de test d’efficacité sur les vergers et detransposition à l’échelle pilote afin de déterminer la formulation la plus efficace et pouvant être produit industriellement. / Cydia pommonella granulovirus (CpGV) is a natural insecticide pest of apples wich is sensitive to the external environment (UV and oxygen). To protect it, we have encapsulatedthe CpGV in double emulsions of water-in-oil-in-water (W / O / W). However, it’s necessary to understand the mechanisms involved in their destabilizationin order to master their thermodynamic stability. In that context, several various formulation parameters: emulsification processes, hydrophilic stabilizer type, lipophilic stabilizer concentration and water droplet, using a UV stabilizer were tested to study their influence on virus release. Each stable formulation undergoes efficiency tests in fields and pilot scale to determine the most effective formulation which could be industrially produced.

Enteric pathogens form a large part of infectious diseases which contribute to a bulk of the healthcare costs. Enteric infections are usually contracted via the faecal-oral route or through contact with contaminated surfaces. Treatment by antibiotics is becoming increasingly ineffective due to the growing number of antibiotic resistant strains. Anti-microbial resistance poses a serious threat to the future of healthcare worldwide and necessitates the search for alternate forms of therapy. Bacteriophages (phages), are viruses which specifically infect and lyse bacteria. To introduce phages as a viable form of therapy, route of administration needs to be considered carefully. Model phages with broad host ranges are ideal for therapy however oral delivery to the lower gastro-intestinal (GI) poses several challenges. The acidic stomach environment can be detrimental to phages, rendering them inactive during passage. To overcome this challenge and improve the stability of phage during encapsulation and storage, this PhD research has been conducted. pH responsive polymers, Eudragit and alginate were used to develop composite microparticles which protected phage from acidic pH (pH 1-3). A novel method of acidifying oil was developed for crosslinking droplets in vitro to avoid the use of harsh solvent systems that can cause phage inactivation. Platform microfluidic technology was employed for phage encapsulation for the first time. Monodispersed droplets and particles were produced, offering fine-tuning of droplet diameter to tailor the release and pH protection of encapsulated phage. Process scale-up was attempted using membrane emulsification (ME) to produce larger volumes of encapsulated phage. In vitro and in-situ models investigated the efficacy of encapsulated phage-bacterial killing. Industrial scale method of spray drying, and electrospinning were also used to demonstrate the versatility of the formulation. Tableting dry powder phage, showed an effective method for producing solid dosage forms for therapy. Additionally, electrospun phage fibres also showed the potential use of pH responsive formulations in addressing wound infections. Improvement in encapsulated phage storage stability was observed with the addition of trehalose in the formulation. This research underpins the need for testing phage encapsulation for site-specific delivery and offers insight into the potential use of commercially available technologies.