Understanding Behavior Of Particle Stabilized Emulsions And Transformations In Colloidal Systems

There has been much scientific interest in the behaviour of colloidal particles at liquid interfaces. From a research aspect they provide model systems for fundamental studies of condensed matter physics. From a commercial aspect they provide applications for making new materials in the cosmetics, food and paint industries. In many cases of colloidal particles at interfaces, the mechanism of particle interactions is still unknown. Particle-Stabilized Emulsions and Colloids looks at recent studies on the behaviour of particles at liquid interfaces. The book first introduces the basic concepts and principles of colloidal particles at liquid-liquid interfaces including the interactions and conformations. The book then discusses the latest advances in emulsions and bicontinuous emulsions stabilized by both solid and soft particles and finally the book covers applications in food science and oil extraction. With contributions from leading experts in these fields, this book will provide a background to academic researchers, engineers, and graduate students in chemistry, physics and materials science. The commercial aspects will also be of interest to those working in the cosmetics, food and oil industry.

This work uses silica nanoparticles to stabilize oil-in-water and water-in-water emulsions. These emulsions are called Pickering emulsions and have potential use for enhanced oil recovery. There are two challenges with using nanoparticles for subsurface applications which are the high salinities and elevated temperatures of reservoir brines. These conditions are problematic because nanoparticles without surface modification are unstable, because of nanoparticle charge screening, which leads to particle agglomeration. Additionally, much of the current research on particle stabilized emulsions focuses on using nanoparticles modified with hydrophobic molecules or surfactants with the sole intent of getting particles to the oil/water interface. Because of this, many of these particles are not applicable for subsurface applications due to their lack of stability in brine. To address these challenges, I functionalize silica nanoparticles with different concentrations of a hydrophilic silane called (3-glycidyloxypropyl)trimethoxysilane (glymo) and stabilize Pickering emulsions with these particles. Glymo was selected as a nanoparticle surface modifier because of its ability to sterically stabilize particles in brine. I characterized the static stability of different Pickering emulsion formulations by using a centrifuge and by calculating the emulsion demulsification pressure. I correlate a critical demulsification pressure to emulsions that show little change in emulsion drop size while flowing, which I define as dynamically stable. The critical demulsification pressure is applied to several untested Pickering emulsion formulations to verify its applicability as an emulsion pre-screening tool. I perform a rheological characterization on emulsions stabilized with low and high surface coverage glymo-coated particles to establish relationships between nanoparticle bridging and the extent of glymo surface modification with different ionic strength brines. I use cryo-scanning electron microscopy to visually assess the bridging behavior of these different Pickering emulsions. I use fumed silica particles, with different wettabilities, and assess their ability to destabilize a model Pickering emulsion. I determine there is a strong correlation between the wettability of a fumed silica particle and its ability to destabilize a model emulsion. This work is relevant because most of the current research on Pickering emulsions focuses primarily on how to tune the properties of colloidal particles to generate stable emulsions with less overall emphasis on methods to destabilize them. Lastly, an aqueous, two phase system is stabilized with 6 nm and 50 nm silica particles modified with 2-(methoxy(polyethyleneoxy)6-9propyl)trimethoxysilane (PEG-silane). Stabilization of the water/water interface results in emulsions that have relatively good stability to shear. Water-in-water emulsions do not contain any oil which is often considered a major limitation of Pickering emulsions for EOR, therefore these emulsions are potential candidates for enhanced oil recovery

It is well known that charged colloidal particles may form an effective two dimensional suspension at a fluidic interface. Research toward the understanding of the dynamics and collective behavior of these suspended particles is at the core of engineering Pickering emulsions, which have a broad range of practical applications. In the first half of this dissertation, we will explore the single phase particle monolayer. Although microscopic images and rheological measurements have been obtained in abundance, the underlying physics behind the collective behavior of such systems is yet to be fully understood. We started by examining the attractive and repulsive potentials in this system. In the case of charged colloidal particles at a fluidic interface, capillary attraction rises from the meniscus deformation, which is predominantly due to the mismatch of dielectric constants between the aqueous phase and the non-polar phase. On the other hand, aggregation is prevented by the long range Coulombic repulsion through the non-polar phase as proposed by Aveyard and coworkers. With the basic knowledge of interaction potentials present, Monte Carlo simulation and Brownian dynamics simulation were performed, assuming pair-wise interactions with all physical constants of a system consisting of latex particles trapped at a water-decane interface. Microscopic images of such a system were recorded concurrently, serving as an internal verification of the numerical simulation. Furthermore, the pair distribution function in the radial direction and the angular order parameter, were extracted from the equilibrium configuration of the Monte Carlo simulation as well as real-time microscopic images to investigate the phase transition behaviour. The primitive simulation results agreed with the experimental observation qualitatively, showing a two-dimensional phase transition from a disordered phase to an ordered solid phase as the surface coverage of the particles increases. In the second half of the dissertation, we focus on the coalescence experiments involving a Pickering droplet. Many experiments have been performed where two particle laden interfaces have been brought into close contact in a controlled manner and various observations, including particle "bridging", have been made in an attempt to understand the stabilization mechanism of interfacial particles in a Pickering emulsion. One of the most interesting observations is the tendency for the particles on one interface to "evacuate" and those on the other interface to "aggregate" during the close approach of the surfaces. In this work, we propose to understand the mechanism of particle evacuation- aggregation via a combined experimental and theoretical approach. First, we performed real-time experiments where two particle-laden water-decane interfaces were brought into contact. Many phenomena including particle evacuation-aggregationand bridging were observed. We then developed a Brownian dynamics simulation of the evacuation-aggregation including the important relevant interparticle interactions that we presumed were important in describing the phenomena. In order to do so, we had to answer three questions. First, what are the relevant aspects of the charged particle interaction within the same interface? Second, what is the charge interaction across the two approaching interfaces? Third, what are the flow effects, including the flow between the two interfaces during approach, on the particle motion and how can we model such a flow? Toward this goal, we have incorporated both reasonable electric inter-particle interactions from available literature studies and flow interactions via a porous media model that relates the particle velocity to the local surface coverage through the effective permeability of a porous media. Thus the flow effects are captured in a mean field sense. The BD simulations were able to capture the evacuation-aggregation qualitatively and, in most instances, quantitatively. In particular the diameter of the evacuated area decreases with increasing surface coverage in both simulations and experiments, and we will describe the physical mechanisms leading to this behavior by analyzing the particle force balance in the BD simulations.

Small solid particles adsorbed at liquid interfaces arise in many industrial products and process, such as anti-foam formulations, crude oil emulsions and flotation. They act in many ways like traditional surfactant molecules, but offer distinct advantages. However, the understanding of how these particles operate in such systems is minimal. This book brings together the diverse topics actively being investigated, with contributions from leading experts in the field. After an introduction to the basic concepts and principles, the book divides into two sections. The first deals with particles at planar liquid interfaces, with chapters of an experimental and theoretical nature. The second concentrates on the behaviour of particles at curved liquid interfaces, including particle-stabilized foams and emulsions and new materials derived from such systems. This collection will be of interest to academic researchers and graduate students in chemistry, physics, chemical engineering, pharmacy, food science and materials science.

A discussion of fundamental characteristics, theories and applications for liquid-liquid colloidal dispersions. It profiles experimental and traditional measurement techniques in a variety of emulsified systems, including rheology, nuclear magnetic resonance, dielectric spectroscopy, microcalorimetry, video enhanced microscopy, and conductivity.

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.

From the basics to the most recent developments- A concise review of suspensions, emulsions, and foams Updating and expanding their highly popular Colloidal Systems and Interfaces, Ian Morrison and Sydney Ross now provide authoritative coverage of the concepts and techniques applicable to suspensions, emulsions, and foams. Concisely yet thoroughly encompassing the significant developments of the past fourteen years, Colloidal Dispersions: Suspensions, Emulsions, and Foams describes a wide range of topics, including particles in liquids, interactions at interfaces, surfactants, and the technology of emulsions and foams. Industrial chemists and chemical engineers will discover among the book's insights recently developed computer-based methods that offer fast, precise measurements of particle concentration, size, and charge by acoustics, application of acid-base concepts to adsorption, the role of electric charges in nonpolar media, and the fundamentals of nanotechnology. This new edition includes: * Updated material and major advances in the field, including the development of new equipment * In-depth instruction on methods for producing emulsions and suspensions * Extensive industrial and practical applications of general principles * Expanded sections on particle sizing, nonpolar dispersions, and polymer stabilization

This text explains how properties of the system are affected by such factors as the crystallisation of the fat, the surface behaviour of the proteins, and presence of various small molecules and ions in the aqueous phase.

Bicontinuous interfacially jammed emulsion gels, now commonly termed 'bijels', are a class of soft materials, in which interpenetrating, continuous domains of two immiscible fluids are maintained in a rigid arrangement by a jammed layer of colloidal particles at their interface. Such gels have unusual material properties that promise exciting applications across diverse fields from energy materials and catalysis, to food science. This is the first book on the subject and provides the reader with a fundamental introduction. Edited by a recognised authority on bijels, the reader will learn about the bijel and its formation. Bringing together current understanding, this book aims to bring the potential application of bijels to diverse materials challenges closer to fruition. This is a must-have resource for anyone working in soft matter and applied fields.