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The dissolution of bubbles confined in porous media is relevant to subsurface engineering applications, such as soil remediation, carbon sequestration, and hydrogen storage. Controlling these processes require the understanding of the collective evolution of bubbles (e.g., entrapment, mobilisation, dissolution, growth) in partially saturated porous media. In the simplest case, a bubble grows or dissolves due to mass transfer across its interface. This process is driven by the gradient between a concentration proportional to the bubble's Laplace pressure and the concentration of the dissolved solute in the liquid. When considering a cluster of bubbles, the interdependence between solute transport and bubble dissolution processes becomes substantially more complex to predict. One of the main reasons for this is that the dissipation rate of dissolved solute is affected by the development of a local concentration field around each bubble. In this regard, the presence of a porous medium introduces unique challenges. The tortuosity of the pore space effectively reduces the diffusive solute transport rate relative to diffusion in bulk liquid, while the local connectivity of pores affects the mixing of solute. This thesis presents the development and implementation of a pore-network model (PNM) and microfluidic experiments to investigate the diffusion-driven collective evolution of bubble clusters in porous media, focusing on the relationship between solute transport and dissolution processes. The predictions of the PNM demonstrate that a wide variety of collective dissolution behaviors can be obtained depending on the initial solute concentration, the size distribution of bubbles, and the connectivity of the pore network. The latter controls the intensity of the collective effects with respect to that observed in bulk liquid. The experimental results presented in this work provide direct evidence of these effects. For instance, a bubble that undergoes periods of growth and dissolution alternately in a small bubble cluster is the manifestation of the interplay between differing diffusion fluxes (across the gas-liquid interface and between neighboring pore bodies). In interpreting the experiments, the PNM can be further exploited to predict the solute concentration field in the medium, which is otherwise very challenging to obtain experimentally. The findings of this work establish the pore network's critical role in modulating the relationship between solute transport and the growth/dissolution of bubbles in porous media. The application of the PNM to estimate statistical measures that describe the collective behavior of bubbles, such as the average dissolution rate and an effective diffusion coefficient, may prove very useful in the context of applications dominated by the presence of a so-called residual gas phase consisting of disconnected bubbles that are immobilized by capillary forces.

For over forty decades, the notion of diaspora has been discussed in the context of global processes of de-territorialisation, transnationalism, and hybridity. Thus, 'homeland' became de-emphasised by postmodern critics questioning ideas of rootedness and homeland orientation. However, the Armenian diaspora has been discussed predominantly as an example of a classical or 'victim' diaspora, where the memory of exile, trauma, and eventual return are its key characteristics. Yet, memory is not static, nor are diasporic groups or the 'homeland'. Multiple migratory journeys, repatriation, 'homeland'-'hostland' relations, conflicts, inter-group dynamics, and memory preservation play a significant role in how homeland is perceived, re-created, and experienced. This is particularly the case for the Armenian diaspora due to intertwined historical and socio-political reasons including not only the Genocide and loss of ancestral homeland, but also over a century of diasporisation, multiple migrations, assimilation, Sovietisation, the Nagorno-Karabakh (Artsakh) conflict, and the difficult socio-economic situation of the current Republic. These factors are of particular interest for this research, which explores the notion of the homeland for second and successive generations of diaspora Armenians in its multidimensionality - the homeland viewed as a physical space, shaped by dynamics of belonging and longing, affect and experiences, and the role these play in the negotiation of 'dislocated identities'. Data were collected in the UK and the Republic of Armenia employing semistructured interviews as the main method of data collection. In addition, multi-sited field visits in Armenia and the UK were conducted, and diaspora and repatriate virtual spaces were explored. The data highlights the complexities of diasporic experiences in the 'hostland' and the 'homeland', the shifting nature of diasporic engagement, group dynamics of 'otherness'. Focusing on the Velvet Revolution of 2018 and the Artsakh (Nagorno-Karabakh) war of 2020, this study explores diasporans' and repatriates' engagement in 'homeland' politics and conflicts.

In the modern world, the scale of industrial production within all sectors has reached unprecedented levels due to ever-growing demand and consumption of various products. A vast majority of industrial processes exploits the benefits brought by the multiphase flows whose complex dynamics are governed by the concoction of fundamental physics. Probing the details of such flows, experimentally and/or theoretically provides an ability to develop and optimise the needs of industrial applications. Yet, this progression is gradual as it depends on the advancement of measurement technologies that enable the investigation of the complex behaviour and topologies of many different possible combinations of phases utilised in industry. Use of the novel optical diagnostic techniques coupled with bespoke capacitance probes in the present study enables us to explore uncharted territory of two-phase gas-liquid annular flows in vertically orientated pipes. In the present study, a recently developed variant of laser-induced fluorescence (LIF) technique, termed structured-planar laser-induced fluorescence (S-PLIF), is used which allows us to eliminate biases commonly encountered during film-thickness measurements of gas-liquid flows due to refraction and reflection of the light at the interface. In parallel, a bespoke capacitance probe is also employed which permits us to conduct film thickness measurements with high temporal resolution along the perimeter of the pipe. Simultaneous application of these two measurement techniques provides an opportunity to study the subtle differences found in thin annular film structures caused not only by the function of liquid and gas flow rates, but also by the surface-active agents which are widely known to cause drastic changes in flow behaviour due to surface tension gradients. The flow characteristics are studied in terms of mean film thickness, roughness, probability density functions, time-scales of the flows, and gas entrainment in the liquid film. The analysis of the data reveals important changes in the flow characteristics due to the presence of soluble surfactant. Firstly, it is observed that surfactant promotes thinning of annular films at nearly all flow conditions investigated herein, hinting at its influence on the turbulence within the bulk flow. The behaviour of interfacial waves was also found to be notably altered by the surfactant where the film roughness and the time-scale of the waves increase in gas-sheared film flows with low to moderate turbulence and low gas entrainment. This corresponds to flows not in the 'regular wave' regime. A decrease in both characteristics then follows upon an increase in turbulence to a sufficiently high level of the two phases. The high gas-shear rate not only limits the highest attainable wave amplitude downstream, but also results in high agitation of air and water phases, and thus, high gas and liquid entrainment. Ultimately, this smooths the base film populated with small-amplitude waves and substantially reduces the amplitude of large interfacial waves. Generally, good agreement with relevant literature correlations is found. The estimated time-scales of the wave dynamics and Marangoni flow showed that the surfactant plays an increasingly important role on waves with lower amplitudes. The sizes of the bubbles entrained in the surfactant-free liquid film are found to exhibit log-normal distributions that become flatter with a decrease in the gas Reynolds number, while this distribution is maintained for surfactant-laden flows. On the other hand, wider distributions in the bubble sizes are found for the surfactant-laden flows at the highest gas-shear rate for all liquid Reynolds numbers. The normalised location of the bubbles (quantified as the relative entrainment depth, i.e., distance of the bubble from the local air-water film height in the wall-normal direction divided by the local film thickness) follows a Gaussian distribution, where the majority of the bubbles accumulate in the middle of the thin film. Understanding the need for further development of the multiphase flows that involves the use of surfactants, motivated us to develop a method to prepare water soluble fluorescent surfactant, which is described in the present work. Furthermore, a detailed characterisation of the fluorescent surfactant is also provided, which may encourage further experimental and modelling investigations of the relevant surfactant-laden multiphase dynamics found in small- and large-industrial scale applications.

This research explores how a religion 'on the move' responds to the challenges of diasporic conditions and the tensions between continuity and change. It provides an understanding of how migrant religions articulate and orient their ritual universe and social and organisational structures within the new spatial settings of diaspora. Alevism, forming the second-largest religious movement in Turkey, has recently adopted a transnational scope as a consequence of international migration. Migration has transformed the oppressed Alevis into a migrant faith community with the freedom to practise their collective rituals openly and, to some extent, have become 'recognised' in the host society, while the Alevi claim for recognition is still an ongoing struggle in Turkey. During three decades of diasporic journey, Alevis have had significant community developments, intensifying their activism in the national and transnational spheres. Political and economic developments in the UK have also shaped their homeland engagements. Besides newly built migrant houses, cemevis (Alevi community centres) began to spread into rural areas, funded by diaspora remittances. Such diasporic spatial markers have multiple effects on the homeland's changing rural landscape. A multi-sited ethnography, including interviews and observations in London and villages of British Alevis in Turkey, is used to gain insights into the remaking of religion and rebuilding of identity and community in the diaspora. It examines the diasporic experience of the Alevi community in the UK through territorialisation, the rebuilding of community and identity and reproduction of culture, and their impact on the changing rural homeland landscape. Intergenerational transmission and the Alevi claim for visibility and recognition are the central motivations shaping the diasporic rebuilding process, in particular placemaking performances. As a result, diasporic Alevism has become more institutionalised, organised and spatialised. Such diasporic developments have also involved ritual transformation. The religious structures established through historical processes have encountered many challenges and have been updated and re-oriented in the diaspora setting. This thesis demonstrates that the diasporic experience has profoundly transformed ritualised Alevi culture.

Particles adsorbed at fluid-fluid interfaces confer stability to dispersed systems such as foams and emulsions. The emergent properties associated with the interfacial microstructure underpins the creation of functional materials. In the design, synthesis and application of such materials, it is essential to understand the dynamic behaviour of structured interfaces at deformation timescales that are relevant in practical scenarios. In this experiment-driven study, a bubble is used as a probe to understand the stability mechanisms and dynamics of fluid-fluid interfaces coated with particles. First, in a model wax-based oil foam, or oleofoam, bubble dissolution time, under controlled conditions, is used as a parameter to assess the bulk and interfacial rheological contributions responsible for the remarkable stability observed. Focus is then drawn to interfacial phenomena, by removing bulk effects, through microscopic observations of crystal-coated bubbles undergoing deformation due to either bubble dissolution or ultrasound-driven volumetric oscillations. In this way phenomena at two extreme timescales, 10,000 s and 0.0001 s, are observed and interpreted. Finally, the effect of unsteady, fast deformation on a complex interface is systematically studied using a well characterised model interface, comprising of bubbles coated with optically resolvable, monodisperse latex microspheres. The bubbles are subjected to acoustic forcing, leading to the rapid cyclic compression and expansion of the colloidal monolayer. Effects of pressure amplitude, particle size and surface coverage on bubble excursions are studied. The results signify the importance of local mesoscopic phenomena in explaining the stability of oleofoams, where invoking macroscopic rheological reasoning alone is somewhat inadequate. Experimental timescales strongly influence the nature, integrity and response of complex interfaces to imposed stresses. Further, a bubble driven by ultrasound has potential in studying time-dependent interfacial mechanics.

Ultrasound contrast agent microbubbles are central to biomedical ultrasound field, from diagnostic imaging to therapeutic applications. In diagnostic imaging, microbubbles provide an enhanced contrast compared to the surrounding blood pool and tissue. More recently, advanced surface engineering has allowed microbubbles to be used as effective tools for localised drug and gene delivery. Microbubble dynamics can be precisely controlled by the driving ultrasound waves, allowing for drug payload to be remotely released in the region of interest. Microbubble behaviour, when confined inside the vasculature, is affected by the vessel dimensions and its mechanical properties. In therapeutic applications, microbubbles can also be found outside of the vasculature, surrounded by biological tissue. Microbubble dynamics are influenced by the viscoelastic properties of the surrounding tissues. In order to accurately predict the microbubble behaviour, it is important to understand these changes in the microbubble dynamics. For drug delivery applications, microbubbles can facilitate drug uptake. One of the mechanisms thought responsible, is the microstreaming flow generated by an oscillating bubble. This flow has been studied for non-biomedically relevant bubbles, however experimental data for the flow induced by ultrasound contrast agent microbubbles is lacking. This Thesis investigates microbubble behaviour inside tissue mimicking phantoms. The resonance behaviour of the microbubbles is explored when they are placed in biologically relevant scenarios: embedded inside the phantoms and inside channels of various properties. Microbubbles were embedded inside hydrogel phantoms of different viscoelastic properties, which were used to study the effect of the changing viscoelastic properties on the bubble behaviour. Additionally, from the bubble dynamics, the viscoelastic properties of the phantoms were extracted in the kHz range. These values were compared to the values measured using a conventional rheometer in the low frequency range of a few Hz. In order to investigate the resonance behaviour of microbubbles near viscoelastic boundaries, channels of different dimensions and viscoelastic properties were used. Bubbles were injected into the channels and their resonance behaviour was characterised as a function of changing viscoelastic properties and confinement ratios of the said channels. Lastly, the streaming flow generated by an oscillating ultrasound contrast agent microbubble is studied to help understand this phenomenon and its possible importance in drug delivery. A complex phantom was designed to provide a side-view of the microstreaming events which enabled the visualisation of the streaming patterns. The extent of microstreaming range was examined as a function of the forcing acoustic pressure. The results obtained in this Thesis provide an insight into the change of microbubble dynamics, which can be translated to biomedical microbubbles. The microstreaming flow produced by a contrast agent microbubble has a potential to be translated into biological settings to help elucidate the role of microstreaming in drug delivery.

This thesis investigates ways of constructing parental roles and ethnic identities by Polish migrants in the UK. It is based on data obtained through a qualitative, small-scale study that used in-depth interviews in combination with participant observations. The research was carried out with Polish migrant parents living in the South East of England and in London, who moved to the UK after 2004. The context for the research is the shift from communism to democracy in Poland in 1989. This changed the influence of a romantic paradigm that previously encouraged parents to transmit nationalistic and Catholic ideologies to children. This cultural shift prompted uncertainty about what it means to be a 'good mother or father' in Poland and in the Polish diaspora. My research concerns the ways the post EU accession cohort of Polish migrants raise their children. I consider this through exploring religious rituals, food practices and language use. I also explore how gendered parental roles are negotiated in this migration situation through everyday family practices. In taking child-rearing as the lens to explore the experience of migration, this research extends investigation of home-making in the diaspora. Home-making is understood here as practices through which migrants negotiate belonging. I explore religious rituals, language use and food practices to consider this process. This investigation builds upon recent discussions within diaspora and transnationalism studies that consider how parents negotiate social norms and values around childrearing in the host country. It also draws on the debates within parenting culture studies highlighting new modes of 'intensive parenting' (Hays 1996; Lee 2008) and it makes use of investigations into the origins of national and religious discourses in Poland that consider how motherhood and fatherhood have been historically constructed in Poland and the transformation of gendered parental roles. Following a discussion of methodology, I demonstrate across three analytical chapters the importance of diasporic resources and links with Poland for parents at various levels, including symbolic, financial and emotional. I highlight a plurality of meanings given to Polishness, which I illustrate by exploring religious rituals, language use and food practices. The improvement of their children, rather than advancement of the nation, emerges as the main concern for participants, which I address through attaching meaning through the Polish culture. The argument advanced overall recognizes a need for acknowledging diversity in parenting practices among transnational families. This thesis demonstrates a range of decisions and negotiations that migrant parents abroad have to make during the childrearing process and recognizes a need for acknowledging diversity in parenting practices in research about contemporary transnational families.

Capsules are employed in a range of industries as essential vehicles for the storage and delivery of drugs, biologically active species, surfactants, and personal care formulations. Key performance aspects are dictated by the capsule's overall shape and dimensions, porosity and internal microstructure. Various approaches are employed in the fabrication of capsules with precise size and shape control. This work focuses on the formation of capsules by the selective removal of solvent from monodisperse solution droplets - produced using microfluidics - upon immersion in an external solvent. The microfluidic generation of microporous polymer capsules using an ex-situ phase inversion process is presented and the effect of various process parameters on capsule structure and internal microstructure examined. These include polymer concentration, droplet size and non-solvent quality. Further, the effect of ternary solution thermodynamics on the microstructure of the capsules is explored, and precise control over pore size and distribution is demonstrated. Building on these findings and polymer-colloid phase behaviour, the fabrication of nanocomposite capsules, generated from polymer-nanoparticle mixtures, is reported and a well-defined external and internal morphology diagram established. These include nucleated and bicontinuous microstructures, as well as isotropic and non-isotropic external shapes. Upon dissolution, rapid and modulated, pulsed, release of the nanoparticle clusters over timescales ranging seconds to hours is demonstrated. The release profile is found to be dependent on capsule morphology, and a systematic study of the role of extraction solvent and kinetics on capsule gradient structure is presented; this provides an effective strategy to decouple demixing and coarsening timescales from the capsule solidification time, and is exploited to controllably design capsules with varied internal microstructures: hollow, core-shell, bicontinuous and compact domains. Overall, the work presents a robust and facile microfluidic approach for the design and fabrication of microcapsules, exhibiting a wide range of internal and external morphologies, by exploiting solution/mixture thermodynamics, solvent exchange kinetics, and phase inversion.

Colloidal particles at fluid interfaces are used as precursors in many applications and for the manufacture of novel material, principally because they give outstanding stability to foams and emulsions. The stability is attributed to the large decrease in energy associated with the adsorption of a particle at a fluid-fluid interface, of the order of a million times the thermal energy kT for micrometric particles. In some applications, particle removal from fluid-fluid interfaces is needed, for example, when reactions use expensive colloidal particles, or to achieve phase separation. However, because of the strong attachment, particle removal from fluid-fluid interfaces is challenging. There is a need for new techniques for particle removal that can be controlled and precisely triggered. We study the destabilisation of particle-coated bubbles using two external fields: temperature and pressure. We choose particle-coated bubbles because they are the paradigm of stabilisation by particles. The destabilisation via temperature is triggered by cooling the external liquid. Cooling the external phase results in an enhanced gas diffusion. In this way, we obtained a steady delivery of all the adsorbed particles. The destabilisation via pressure is achieved by applying ultrasound waves to bubbles to drive them into ultrafast volumetric oscillations. These oscillations cause strong interfacial deformations capable of delivering particles in under a millisecond. The techniques developed to manipulate coated bubbles and trigger desorption are remotely triggered and scaleable, with relevance to various applications such as controlled particle delivery and recovery.