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This thesis builds on recent innovations in multi-phase emulsion droplet design to demonstrate that emulsion morphologies enable a useful variety of dynamic optical phenomena. Despite the highly dynamic nature of fluid morphologies and their utility for stimuli-responsive, dynamic optical materials and devices, fluid matter is underrepresented in optical technology. Using bi-phase emulsion droplets as refractive micro-optical components, this thesis realizes micro-scale fluid compound lenses with optical properties that vary in response to changes in chemical concentrations, structured illumination, and thermal gradients. Theoretical considerations of emulsions as optical components are used to explain a previously unrecognized total internal reflection-enabled light interference phenomenon in emulsion droplets that results in rich structural coloration. While this work is focused on the fundamental optics of emulsion droplets, it also facilitates the use of light-emitting emulsion morphologies as chemo-optical transducers for early-stage food-borne pathogen detection. This thesis beautifully demonstrates the virtue of fundamental interdisciplinary exploration of unconventional material systems at the interface of optics, chemistry, and materials science, and the benefits arising from translation of the acquired knowledge into specific application scenarios.
This book provides a comprehensive account on the design, materials chemistry, and application aspects behind these novel stimuli-responsive materials.
Complex fluids are of increasing interest because of their ability to provide a unique environment for the exploration of interfacial phenomena. Emulsions, which are mixtures of immiscible liquids, allow for separation of reagents whilst simultaneously providing a liquid-liquid interface wherein reactants can be easily transported, and reactions are able to readily occur. Thus, utilizing complex emulsions as dynamic materials is potentially important to understand localized reaction pathways and kinetics in a controllable and predictable manner. However, a significant limitation of fluid droplets for long-term applications is their eventual breakdown over time. Elucidating approaches by which to enhance droplet stability while simultaneously maintaining their reconfigurability and responsive character is therefore essential. This dissertation, thus, exists in three main sections: first, it aims to investigate a surfactant-free gelation pathway to form oil-core hydrogel capsules to stabilize complex droplets; secondly, it examines the non-equilibrium partitioning of amphiphilic surfactants into biphasic emulsions of miscible oils to dynamically and controllably induce phase separation; and, finally, it attempts to explore the reconfigurable complex droplet as a responsive soft material which can be used to easily manipulate chemical reactions at the oil-water interface. One approach to enhanced stabilization of droplets is by encapsulation, where a shell, often a polymer, encases the liquid droplet to prevent coalescence and limit exchange of droplet contents with the continuous phase. A common approach to droplet encapsulation is interfacial polymerization, where monomers dissolved in immiscible phases react to form capsules localized at the interface. Hydrogels, which are composed of crosslinked, charged polymers swollen in water, are highly permeable to molecules in the aqueous phase and would permit the diffusion of surfactants or other analytes to the droplet surface to trigger a response in droplet configuration. In the first major project of this work, we utilized a Pickering complex droplet intermediate to localize hydrogel formation at the droplet-continuous phase interface. Enhanced stability of droplets with both ionically and covalently crosslinked capsules was observed, with a complete spectrum of reconfigurability possible upon addition of droplet-internal fluorosurfactant, Capstone FS-30. The next major work examines the partitioning of surfactant molecules across the droplet oil-water interface. In general, the partitioning of chemicals across interfaces and their subsequent concentration into droplets and coacervates is important in many fields of study, including organic reaction chemistry and in mimicking individual properties of natural systems, such as living cells. When considering partitioning occurring within emulsions, the dynamics and relative concentration of all components--oil, water, and surfactant--are critical to understanding the behavior of non-equilibrium systems. We became interested in the dynamics and degree of surfactant partitioning while examining the behavior of two-component oil droplets in aqueous surfactant. We produced microscale droplets containing two oils, which in bulk at room temperature are miscible in all proportions. Upon preparing this emulsion, we expected that the droplets would remain in a single phase during their lifetime when undergoing micellar solubilization; however, we noticed phase separation occurring within the droplets. To confirm the partitioning of surfactant into these droplets, we developed a protocol for the LCMS analysis of single microscale droplets. Furthermore, we have shown that, upon addition of ionic surfactant, we can controllably and dynamically induce phase separation through various stimuli. In the last major project of this work, we examine reaction rates at oil-water interfaces and within surfactant micelles. Reactions occurring at the interface of immiscible fluids are important for a variety of different fields, largely due to the separation of reagents into distinct phases only to be reacted specifically and controllably at the interface. This allows unique opportunity to tune reaction kinetics, location, and pathways. Studies have previously been conducted observing reaction kinetics at the oil-water interfaces of emulsions, therefore exploring reactions at interfaces in complex droplets should then allow for an even more specific morphology-dependent, tunable reaction environment.
Complex emulsions are dispersions of kinetically stabilized multiphasic emulsion droplets comprised of two or more immiscible liquids that provide a novel material platform for the generation of active and dynamic soft materials. In recent years, the intrinsic reconfigurable morphological behavior of complex emulsions, which can be attributed to the unique force equilibrium between the interfacial tensions acting at the various interfaces, has become of fundamental and applied interest. As such, particularly biphasic Janus droplets have been investigated as structural templates for the generation of anisotropic precision objects, dynamic optical elements or as transducers and signal amplifiers in chemo- and bio-sensing applications. In the present thesis, switchable internal morphological responses of complex droplets triggered by stimuli-induced alterations of the balance of interfacial tensions have been explored as a universal building block for the design of multiresponsive, active, and adaptive liquid colloidal systems. [...].
This thesis summarizes the use of interfacial reactions, responsive surfactants, and specific tuning of interfacial tensions to discover novel ways to manufacture and manipulate dynamic double emulsion systems. In Chapter 1, we introduce emulsions and surfactants. We describe the fabrication of emulsions and creating stimuli responsive systems. Finally, we explore the relatively recent research into dynamic double emulsions, which is explored further in this thesis. In Chapter 2, we demonstrate the use of selective, interfacial imine formation at emulsion interfaces for the in situ formation of surfactants for novel manufacturing of emulsions and biosensors, dynamic morphology changes through perturbing imine equilibria, and the destruction of emulsions with imine formation at the emulsion-solid interface. In Chapter 3, we introduce surfactants that localize at the internal interface of double emulsions, which enables the incorporation of liquid crystals into dynamically reconfigurable complex emulsions. Further, we demonstrate that isomerization of a photo-responsive azobenzene surfactant at the internal interface of liquid crystal double emulsions results in reversible morphology change. In addition, isomerization of the azobenzene internal surfactant results in overall droplet movement, both orientational and translational. In Chapter 4, we describe that interfacial confinement of magnetic nanoparticles to emulsions interfaces, accomplished through interfacial imine formation, imparts ferromagnetic behavior to dynamic double emulsion comprising isotropic solvents. Further, we demonstrate liquid crystal double emulsions enable precise assembly of magnetic nanoparticles at the emulsion interface and can produce droplets movement and reorganization of the director field. In Chapter 5, we synthesize nucleophile-responsive surfactants with Michael acceptor functionalities to create responsive single and double emulsions. We demonstrate the emulsion systems are responsive to both small nucleophiles and polymeric nanoassemblies. Further, we describe the use of an unrelated stimuli, light, to trigger a cascade that results in emulsion responses.
Microgels by Precipitation Polymerization: Synthesis, Characterization, and Functionalization, by A. Pich and W. Richtering * Hydrogels in Miniemulsions, by K. Landfester and A. Musyanovych * Nano- and Microgels Through Addition Reactions of Functional Oligomers and Polymers, by K. Albrecht, M. Moeller, and J. Groll * Synthesis of Microgels by Radiation Methods, by F. Krahl and K.-F. Arndt * Microgels as Nanoreactors: Applications in Catalysis, by N. Welsch, M.s Ballauff, and Y. Lu
Emulsions occur either as end products or during the processing of products in a huge range of areas including the food, agrochemical, pharmaceuticals, paints and oil industries. As end products, emulsions allow to avoid organic solvent in processing hydrophobic coatings. Emulsion technology is a suitable approach to vehicle viscous phases. It is also a remarkable mean of targeting actives or capturing specific species. The range of applications of emulsions progresses and their manufacturing becomes more and more sophisticated. Besides this broad domain of technological interest, emulsions are raising a variety of fundamental questions at the frontier between physic and chem istry. Indeed, as a class of soft colloidal materials, emulsions science is linked to various aspects of these disciplines: phase transitions, surface forces and wetting, metastability and hydrodynamic instabilities, mechanical properties and flow. The aim of this book is to review the main important concepts governing emulsion science. In Chapter 2, repulsive interactions between liquid films are discussed as well as adhesive interaction related to wetting. In Chap ter 3, consequences of weak and strong attractions are presented, related to the well accepted liquid solid transition analogy. In Chapter 4, the basics of both bulk compressibility and shear elasticity are presented, the role of disorder being the most important aspect of the elastic behavior of these soft systems. In Chapter 5 the central question of the emulsion lifetime related to metastability is discussed.
This open access book, published in the Soft and Biological Matter series, presents an introduction to selected research topics in the broad field of flowing matter, including the dynamics of fluids with a complex internal structure -from nematic fluids to soft glasses- as well as active matter and turbulent phenomena. Flowing matter is a subject at the crossroads between physics, mathematics, chemistry, engineering, biology and earth sciences, and relies on a multidisciplinary approach to describe the emergence of the macroscopic behaviours in a system from the coordinated dynamics of its microscopic constituents. Depending on the microscopic interactions, an assembly of molecules or of mesoscopic particles can flow like a simple Newtonian fluid, deform elastically like a solid or behave in a complex manner. When the internal constituents are active, as for biological entities, one generally observes complex large-scale collective motions. Phenomenology is further complicated by the invariable tendency of fluids to display chaos at the large scales or when stirred strongly enough. This volume presents several research topics that address these phenomena encompassing the traditional micro-, meso-, and macro-scales descriptions, and contributes to our understanding of the fundamentals of flowing matter. This book is the legacy of the COST Action MP1305 “Flowing Matter”.
A general and introductory survey of foams, emulsions and cellular materials. Foams and emulsions are illustrations of some fundamental concepts in statistical thermodynamics, rheology, elasticity and the physics and chemistry of divided media and interfaces. They also give rise to some of the most beautiful geometrical shapes and tilings, ordered or disordered. The chapters are grouped into sections having fairly loose boundaries. Each chapter is intelligible alone, but cross referencing means that the few concepts that may not be familiar to the reader can be found in other chapters in the book. Audience: Research students, researchers and teachers in physics, physical chemistry, materials science, mechanical engineering and geometry.
Polymers are one of the most versatile and important materials used for capsule preparation despite various others available. Suitably formulated capsules can securely protect ingredients, deliver them to targeted sites, and release them expeditiously, improving functions and minimizing adverse effects. New polymers are constantly being explored to develop more efficient capsules as they are routinely used in pharmaceuticals, consumer healthcare products, nutrients, and food. This book focuses on the current state of the art of polymer-based capsules and delivery systems. It describes the formulation processes of capsules developed from redox-responsive polymers and polymer-functionalized carbon nanotubes, in addition to shedding light on coacervation of polymers for encapsulation. It reviews different active ingredients that can be used with polymer capsules in various products, encapsulation of essential oils using such capsules, and development of polymer capsules of cells and bacteriophages.