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.
Surfactant crystals can stabilize liquid foams. The crystals are adsorbed at bubble surfaces, slowing down coarsening and coalescence. Excess crystals in the liquid channels between bubbles arrest ...drainage, leading to ultrastable foams. The melting of crystals upon raising the temperature allows thermoresponsive foams to be designed. In the case of oil foams, the stabilization by crystals received substantial renewed interest in the last 5 years due to their potential applications, particularly in the food industry. For aqueous foams, several reports exist on foams stabilized by crystals. However, these two kinds of liquid foams possess similarities in terms of stabilization mechanisms and the design of surfactant crystal systems. This field will certainly grow in the coming years, and it will contribute to the engineering of new soft materials not only for food but also for cosmetics, pharmaceuticals, and biomedical applications.
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•Water marbles coated with a thin layer of silicone oil containing superhydrophobic particles are reported.•The composite marbles remained stable on solid and liquid supports.•The ...composite marbles remained stable when placed on a vibrating water bath.•The composite marbles withstand coalescence on collision with each other.•Bouncing of composite marbles with solid substrates was explored.
Liquid marbles are non-stick droplets coated with colloidal usually hydrophobic particles. We suggest that “composite” liquid marbles, i.e. bi-liquid droplets, may be prepared with water droplets coated by a thin silicone oil layer containing hydrophobic, colloidal particles.
The process enabling manufacturing water marbles coated with silicone oil containing fumed fluorosilica particles is reported. The marbles remained stable when placed on solid and liquid supports. Bouncing and coalescence of the composite marbles was explored.
Non-coalescence prolonged (ca. 20 min) jumping of composite marbles above a vibrating water bath was observed. Composite marbles withstand coalescence better than colloidal particle-stabilized liquid marbles. The effective surface tension of the composite marbles is markedly lower than that of water marbles coated with fumed fluorosilica particles. The coefficient of restitution of the composite marbles bouncing on a hydrophobic solid substrate is lower than that established for water marbles. This observation is related to the viscous dissipation occurring within the silicone layer making up the composite marbles.
Superparamagnetic Fe3O4 nanoparticles prepared by a classical coprecipitation method were used as the stabilizer to prepare magnetic Pickering emulsions, and the effects of particle concentration, ...oil/water volume ratio, and oil polarity on the type, stability, composition, and morphology of these functional emulsions were investigated. The three-phase contact angle (θow) of the Fe3O4 nanoparticles at the oil−water interface was evaluated using the Washburn method, and the results showed that for nonpolar and weakly polar oils of dodecane and silicone, θow is close to 90°, whereas for strongly polar oils of butyl butyrate and 1-decanol, θow is far below 90°. Inherently hydrophilic Fe3O4 nanoparticles can be used to prepare stable dodecane−water and silicone−water emulsions, but they cannot stabilize butyl butyrate−water and decanol−water mixtures with macroscopic phase separation occurring, which is in good agreement with the contact angle data. Emulsions are of the oil-in-water type for both dodecane and silicone oil, and the average droplet size increases with an increase in the oil volume fraction. For stable emulsions, not all of the particles are adsorbed to drop interfaces; the fraction adsorbed decreases with an increase in the initial oil volume fraction. Changes in the particle concentration have no obvious influence on the stability of these emulsions, even though the droplet size decreases with concentration.
Large‐sized carbon spheres with controllable interior architecture are highly desired, but there is no method to synthesize these materials. Here, we develop a novel method to synthesize ...interior‐structured mesoporous carbon microspheres (MCMs), based on the surfactant assembly within water droplet‐confined spaces. Our approach is shown to access a library of unprecedented MCMs such as hollow MCMs, multi‐chambered MCMs, bijel‐structured MCMs, multi‐cored MCMs, “solid” MCMs, and honeycombed MCMs. These novel structures, unattainable for the conventional bulk synthesis even at the same conditions, suggest an intriguing effect arising from the droplet‐confined spaces. This synthesis method and the hitherto unfound impact of the droplet‐confined spaces on the microstructural evolution open up new horizons in exploring novel materials for innovative applications.
Confinement is powerful: Surfactant assembly within Pickering droplet‐confined spaces makes a difference in the fabrication of inorganic microspheres. A library of mesoporous carbon microspheres (MCMs) including hollow, multi‐cored, multi‐chambered, bijel‐structured, honeycombed and “solid” MCMs has been synthesized.
The shaping of metal–organic frameworks (MOFs), referring to the integration of small sub-millimeter MOF crystals into bulk samples of desired size and shape, is an important step in the practical ...use of this class of porous material in many applications. Herein, we demonstrate for the first time the fabrication of hierarchical 3D MOF monoliths in situ within an MOF particle-stabilized high internal phase emulsion (HIPE). In this approach, a subfamily MOF (ZIF-8) is selected as the sole Pickering emulsion stabilizer for an oil-in-water (O/W) HIPE. With 2-methylimidazole and zinc nitrate in the continuous phase, ZIF-8 is formed in the emulsion to “bond” the ZIF-8 particles fabricating a ZIF-8 monolith without the addition of a polymer or polymerization of monomers. Freeze-drying of the HIPE produces a 3D ZIF-8 monolith. The monolith is packed into a chromatography column to test its catalytic performance as a flow-through catalyst in the Knoevenagel reaction. The monolith catalyst exhibits very high catalytic efficiency. Almost all the reaction mixture transforms to product within 2 min. Besides, the 3D ZIF-8 monolith showed excellent performance as an oil absorbent in oil–water separation. It achieved an absorption equilibrium of oil in less than 5 s, much faster than traditional high oil absorption materials.
There is still a debate about the effectiveness of globular proteins of several nanometers in stabilizing oil-in-water high internal phase emulsions (HIPEs). In this work, we report that a strong ...internal structural integrity and high refolding ability is one requirement for globular proteins to perform as soft particles to stabilize HIPEs. Using bovine serum albumin (BSA) as the model protein, it is demonstrated that BSA glycated with galactose (Gal), possessing a much stronger structural integrity and higher refolding ability, exhibited much improved HIPE emulsification performance and subsequent Pickering stabilization than native BSA. The underlying mechanism for the improvement is largely associated with the formation of a core-shell nanostructure with a hydrophilic Gal shell surrounding the protein core in glycated BSA. The ultra-stable HIPEs (gels) were stabilized by glycated BSA at a protein concentration in the aqueous phase as low as 0.1 wt%, much lower than that reported in the literature. These HIPEs exhibited a self-supporting gel network, an extraordinary stability upon long-term storage or against drastic heating as well as good freeze-thaw reversibility. The findings are of importance for the facile fabrication of biocompatible Pickering HIPE formulations with promising applications in the food, cosmetics and pharmaceutical fields.
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•Glycation of bovine serum albumin (BSA) with galactose led to formation of a very compact internal structure.•Glycated BSA was demonstrated to perform as an outstanding Pickering nanostabilizer for HIPEs.•The HIPEs stabilized by glycated BSA exhibited excellent stability against heating and long-term storage.•HIPE gels could be facily formed at low protein concentrations.•Glycated BSA stabilized the HIPEs through acting as soft nanoparticles.
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Oil-in-dispersion emulsions can be stabilized by like charged particles and surfactant. Surfactant adsorbs at the oil–water interface to reduce the interfacial tension and endow the ...interface with charge, while particles remain dispersed in the aqueous phase to provide electrostatic repulsion between droplets and particles. Can weakly surface-active organic electrolytes adsorb at the oil–water interface and behave like surfactants in stabilizing oil-in-dispersion emulsions with like charged particles?
Symmetrical organic electrolytes, tetraalkylammonium bromides (R4NBr), with either no or very low interfacial activity endowing oil droplets with charge were combined with alumina nanoparticles to stabilize emulsions. The effect of R chain length (varying from methyl to butyl) on the type and stability of emulsions was investigated.
Mixtures of high concentrations of short chain R4NBr salts (R = methyl or ethyl) and alumina particles stabilise oil-in-water Pickering emulsions, whereas longer chain (R = propyl or butyl) analogues stabilize oil-in-dispersion emulsions assisted by alumina particles. Tetrapropylammonium and tetrabutylammonium cations adsorb at the oil–water interface reducing the interfacial tension and endowing the interface with charge. The stability of the oil-in-dispersion emulsions is dominated by the electrostatic repulsion between the droplets and between droplets and particles in the continuous aqueous phase.
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