Interfacial displacement of nanoparticles by surfactant molecules in emulsions

Vashisth, Charu; Whitby, Catherine P.; Fornasiero, Daniel; Ralston, John

doi:10.1016/j.jcis.2010.05.089

Cited by 92 publications

(71 citation statements)

References 42 publications

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“…Particle wettability (quantified by three-phase contact angles) as well as nature of surfactant (O/W vs. W/O stabilizing) have been shown to affect the competition as well. [168][169][170] Hence, it is expected that such competition plays a crucial role in the phase inversion process.…”

Section: Phase Inversion Of Particle-stabilized Emulsionsmentioning

confidence: 99%

Recent Developments in Phase Inversion Emulsification

Kumar

Cheng

et al. 2015

Ind. Eng. Chem. Res.

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Emulsions are multiphasic fluid systems in which liquid droplets are dispersed in another immiscible liquid. The main components of an emulsion are the two liquid phases, typically oil and water, and the emulsifier, which stabilizes the interface between the two liquid phases. Emulsifiers can be a variety of molecules, such as polymers, amphiphilic surfactants, and proteins, and they can also be colloidal particles. Emulsion phase inversion is the process of interconversion between two types of simple emulsions: water-in-oil and oil-in-water emulsions. Phase inversion can be induced by shifting the emulsifier affinity from one phase to the other, which is called transitional phase inversion. It can also be triggered by a change in the water-to-oil ratio of the emulsion, which leads to a process known as catastrophic phase inversion. With recent advances in the stabilization of emulsions using colloidal particles and stimuli-responsive surfactants, numerous novel emulsion systems that undergo emulsion phase inversion by means of various mechanisms have been developed. In this review, we highlight the most recent developments in the field of emulsion phase inversion, focusing on transitional phase inversion, inversion of particle-stabilized emulsions, and flowand shear-induced phase inversion. We also discuss and compare state-of-the-art analytical methods that have been used to detect and understand the emulsion phase inversion process. Our coverage spans from the early concepts of Bancroft's rule through the concept of semiquantitative hydrophilic−lipophilic balance to the more recent theoretical models used to predict and control phase inversion phenomena. We conclude this review by presenting an outlook on the future directions and outstanding problems that warrant future investigations to fully understand the mechanism of emulsion phase inversion at the single-droplet level.

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Section: Phase Inversion Of Particle-stabilized Emulsionsmentioning

confidence: 99%

Recent Developments in Phase Inversion Emulsification

Kumar

Cheng

et al. 2015

Ind. Eng. Chem. Res.

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“…26,27 At a high concentration of surfactant, particles were even replaced by surfactant molecules. 28 In our experiments, the surfactant concentration is high (1 wt%). In order to confirm the adsorption of NPs, we measured the static interfacial tension (g) of water (containing 1 wt% SDS)/toluene interface by pendant drop method.…”

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confidence: 94%

Magnetic nanoparticles-induced anisotropic shrinkage of polymer emulsion droplets

2011

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We here report magnetic nanoparticles (NPs)-induced buckling instability and anisotropic shrinkage behavior of polymer emulsion droplets. The oil-in-water emulsion is stabilized by the surfactant, and NPs are dispersed into the oil phase. The surface ligands (oleic acid and oleylamine) number of the NPs is an important factor to affect the shrinkage process. When a part of the ligands of the NPs is removed, the NPs show good interface attachment at the oilwater interface even with the presence of a large amount of surfactant. The increase of the interfacial viscoelasticity resulting from the attachment of NPs induced the occurrence of a buckling process. The mechanism is explored and the effect of the concentration of polystyrene and NPs is investigated in detail. The results could be helpful to understand and solve problems related with coating techniques and elastic instabilities in nature.The drying or shrinkage of colloidal suspensions has attracted noticeable attention for fundamental and practical reasons.1-3 Liquid droplets even only containing tiny colloidal particles show different and more complicated rheological behaviour. For example, the shell buckling phenomena was observed when a latex suspension drop was drying on the superhydrophobic planar substrate, or when a free liquid drop was shrinking on a hot plate with a temperature above 150 C (Leidenfrost effect). 4,5 Normally, when a colloid suspension droplet is shrinking, the evaporation of the solvent results in the rise of colloidal particle concentration and the reduction of the interparticle distance accordingly with the receding of the liquid/gas interface. 2,5,6 If the solvent loss is fast enough, these particles do not have enough time to diffuse to the bulk phase to homogenize the whole liquid drop, and they will be jammed at the interface.2 This process can transform the interface layer from a viscous liquid state to a glass-like solid state. The further loss of solvent decreases the pressure of the inner phase. Under the external pressure, the elasticity of the shell results in an inversion of curvature. However, the onset of buckling is dependent on particle interaction.5 Before the occurrence of buckling, the liquid droplet behavior is dominated by its viscosity, thus the shrinkage process is isotropic.7 However, the buckling of the shell results in an anisotropic shrinkage.Similar buckling phenomena have been intensively studied in the shrinkage of the interface of Pickering emulsion. Generally, simple liquid drops have isotropic interface shrinkage in a continuous bulk phase with the solvent evaporation.8 However, colloidal particles are considered to irreversibly attach to an oil-water interface by a selfdriving of minimum energy. This attaching behavior could affect the interface properties.9-11 The corresponding reduction of the interfacial energy is expressed as E ¼ pr 2 g ow (1 + cos q) 2 , where r is particle radius, g ow is the tension of the oil-water interface, and q is the contact angle measured through the water phase.9 Tho...

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“…The most common approaches to particle removal from fluid interfaces are based on the physicochemical modification of the fluid phases or the interface. Desorption has been obtained for instance by the addition of a surface-active agent (10,11). In addition, by tuning the strength of electrostatic repulsion between charged particles at an interface through pH and electrolyte concentration, the surface density of particles can be shifted to very low values up to complete removal (12,13).…”

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confidence: 99%

Ultrafast desorption of colloidal particles from fluid interfaces

Poulichet

Garbin

2015

Proc. Natl. Acad. Sci. U.S.A.

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The self-assembly of solid particles at fluid-fluid interfaces is widely exploited to stabilize emulsions and foams, and in materials synthesis. The self-assembly mechanism is very robust owing to the large capillary energy associated with particle adsorption, of the order of millions of times the thermal energy for micrometer-sized colloids. The microstructure of the interfacial colloid monolayer can also favor stability, for instance in the case of particle-stabilized bubbles, which can be indefinitely stable against dissolution due to jamming of the colloid monolayer. As a result, significant challenges arise when destabilization and particle removal are a requirement. Here we demonstrate ultrafast desorption of colloid monolayers from the interface of particle-stabilized bubbles. We drive the bubbles into periodic compression-expansion using ultrasound waves, causing significant deformation and microstructural changes in the particle monolayer. Using high-speed microscopy we uncover different particle expulsion scenarios depending on the mode of bubble deformation, including highly directional patterns of particle release during shape oscillations. Complete removal of colloid monolayers from bubbles is achieved in under a millisecond. Our method should find a broad range of applications, from nanoparticle recycling in sustainable processes to programmable particle delivery in lab-on-achip applications.self-assembly | colloidal interactions | Pickering | interfacial assemblies C olloidal particles can adsorb to fluid-fluid interfaces and confer outstanding stability to emulsions and foams (1, 2). The interfacial self-assembly of colloids has been used to create novel materials, for instance colloidosomes (3) and bijels (4). These applications rely on the large decrease in free energy accompanying particle adsorption, ΔE = −γ 0 πa 2 ð1 − cos θÞ 2 , which depends on the surface tension γ 0 , the particle size a, and the three-phase contact angle θ (5), and ranges from hundreds to millions of times the thermal energy for nanometer-to micrometer-sized particles. The microstructure that the colloidal particles form at the interface has also been shown to enhance stability. For instance, jamming of an interfacial colloid monolayer prevents coarsening in bicontinuous emulsions (4) and can arrest the dissolution of particle-stabilized bubbles (6). Particle removal from fluid-fluid interfaces is a significant challenge in emerging applications of functional nanoparticles in interfacial biocatalysis (7), gas storage (8), and biomass conversion (9), where the ability to recover and regenerate the nanoparticles at the end of the process is a key requirement. The most common approaches to particle removal from fluid interfaces are based on the physicochemical modification of the fluid phases or the interface. Desorption has been obtained for instance by the addition of a surface-active agent (10, 11). In addition, by tuning the strength of electrostatic repulsion between charged particles at an interface through pH and el...

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Interfacial displacement of nanoparticles by surfactant molecules in emulsions

Cited by 92 publications

References 42 publications

Recent Developments in Phase Inversion Emulsification

Recent Developments in Phase Inversion Emulsification

Magnetic nanoparticles-induced anisotropic shrinkage of polymer emulsion droplets

Ultrafast desorption of colloidal particles from fluid interfaces

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