Pickering emulsion

Operational mode 6 led to nearly the same results compared to mode 1, but ran more stable due to the lower viscosity of the mixing stream (no sticking of the mixing stream) and the pure disperse phase in the high-pressure stream (no phase separation within the inlet). 

AH three operational modes may be applied and do not significanfly differ in the resulting particle-stabilized droplet sizes. Operational mode 6 ran most stable, especially at low homogenizing pressures. Because no premix has to be produced, it seems to be an attractive possibility for future applications. 

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The most widely studied deformable systems are emulsions. These can come in many forms, with oil in water (O/W) and water in oil (W/O) the most commonly encountered. However, there are multiple emulsions where oil or water droplets become trapped inside another drop such that they are W/O/W or O/W/O. Silicone oils can become incompatible at certain molecular weights and with different chemical substitutions and this can lead to oil in oil emulsions O/O. At high concentrations, typical of some pharmaceutical creams, cosmetics and foodstuffs the droplets are in contact and deform. Volume fractions in excess of 0.90 can be achieved. The drops are separated by thin surfactant films. Selfbodied systems are multicomponent systems in which the dispersion is a mixture of droplets and precipitated organic species such as a long chain alcohol. The solids can form part of the stabilising layer - these are called Pickering emulsions. 

Binks BP, Lumsdon SO. Pickering emulsions stabilized by monodisperse latex particles effects of particle size. Langmuir 2001 17 4540-4547. 

An example of the importance of the wettability of fine particles is provided by what are called Pickering emulsions, that is, emulsions stabilized by a fdm of fine particles. The particles can be quite close-packed and the stabilizing fdm between droplets can be quite rigid, providing a strong mechanical barrier to coalescence. See Section 5.4.1. 

The most stable Pickering emulsions occur when the contact angle is close to 90°, so that the particles will collect at the interface. Combining Young s equation with... 

Microcapsules whose shells consist of coagulated or fused colloid particles. Where a liquid is encapsulated within a liquid these bear some relation to Pickering emulsion. An example is given in Ref. [300],... 

Binks, B. P. Clint, J. H. Solid Wettability from Surface Energy Components Relevance to Pickering Emulsions. Langmuir 2002, 18,1270-1273. 

These considerations come into play in oil recovery schemes applied to reservoirs of mixed wettability or where the rock is predominantly oilwetting. Another example is the case of the so-called Pickering emulsions. 

No attempt has been made to include every term that may be encountered in dealing with petroleum emulsions. Some basic knowledge of underlying fields such as physical chemistry and chemical engineering is assumed. Many named emulsions and phenomena (such as Pickering emulsions) have been included, but named equations and constants have generally not been included. 

Pickering Emulsion An emulsion stabilized by fine particles. The particles form a close-packed structure at the oil-water interface, with significant mechanical strength, which provides a barrier to coalescence. 

Lan, Q. etal., Synthesis of bilaycr oleic acid-coated FeLjO4 nanoparticles and their apphcation in pH-responsive Pickering emulsions, I. Colloid Interf. Sci., 310, 260, 2007. 

More than a century ago, Pickering [2] and Ramsden [3] investigated paraffin-water emulsions contains solid particles such as iron oxide, silicon dioxide, barium sulfate, and kaolin and discovered that these micron-sized colloids generate a resistant film at the interface between the two immiscible phases, inhibiting the coalescence of the emulsion drops. These so-called Pickering emulsions are formed by the self-assembly of colloidal particles at fluid-fluid interfaces in two-phase liquid systems (Fig. 1). 

Giermanska-Kahn J et al (2002) A new method to prepare monodisperse Pickering emulsions. Langmuir 18(7) 2515-2518... 

These considerations come into play in petroleum emulsions. The so-called Pickering emulsions are emulsions stabilized by a film of fine... 

Abstract Nanoparticles (NPs, diameter range of 1-100 nm) can have size-dependent physical and electronic properties that are useful in a variety of applications. Arranging them into hollow shells introduces the additional functionalities of encapsulation, storage, and controlled release that the constituent NPs do not have.This chapter examines recent developments in the synthesis routes and properties of hollow spheres formed out of NPs. Synthesis approaches reviewed here are recent developments in the electrostatics-based tandem assembly and interfacial stabilization routes to the formation of NP-shelled structures. Distinct from the well-established layer-by-layer (LBL) synthesis approach, the former route leads to NP/polymer composite hollow spheres that are potentially useful in medical therapy, catalysis, and encapsulation applications. The latter route is based on interfacial activity and stabilization by NPs with amphiphilic properties, to generate materials like colloidosomes, Pickering emulsions, and foams. The varied types of NP shells can have unique materials properties that are not found in the NP building blocks, or in polymer-based, surfactant-based, or LBL-assembled capsules. 

He YJ, Yu XY (2007) Preparation of silica nanoparticle-armored polyaniline microspheres in a Pickering emulsion. Mater Lett 61(10) 2071-2074... 

Zhang K, Wu W, Meng H, Guo K, Chen J-F. Pickering emulsion polymerization Preparation of polystyrene/nano-SiOj composite microspheres with core-shell structure. Powder Technology. 2009 190(3) 393-400. 

Chevalier Y, Bolzinger M-A. Emulsions stabilized with solid nanoparticles Pickering emulsions. Colloids and Surfaces A. Physicochemical and Engineering Aspects. 2013 439(0) 23-34. 

Tsuji S, Kawaguchi H. Thermosensitive Pickering emulsion stabilized by poly (N-isopropylacrylamide)-carrying particles. Langmuir. 2008 24(7) 3300-3305. 

Frelichowska J, Bolzinger M-A, Pelletier J, Valour J-P, Chevalier Y. Topical delivery of lipophilic drugs from o/w Pickering emulsions. International Journal of Pharmaceutics. 2009 371(l-2) 56-63. 

In the past, many groups have tried to encapsulate clay platelets inside latex particles. This encapsulation poses some extra challenges because of the tendency of the clay platelets to form stacks and card-house structures. Most of the attempts resulted in the so-called armored latex particles, i.e. clay platelets in the surface of the latex. Recently, natural and synthetic clays were successfully encapsulated. The anisotropy of the clay resulted in non-spherical latex particles (Figs. 5 and 6), either peanut-shaped [63] or flat [64]. Clay platelets also turned out to be good stabilizing agents for inverse Pickering emulsion polymerizations [65]. 

Emulsion Polymerization Solids-Stabilized, or Pickering, Emulsion Polymerization. 42... 

The use of either styrene or butyl methacrylate as monomer led to stable latexes that were not covered by silica particles. Bon and coworkers proposed a mechanism for the solids-stabilized, or Pickering, emulsion polymerization that effectively combines coagulative nucleation with heterocoagulafion throughout the polymerization process. The growing latex particles become unstable and collide irreversibly with the nanoparticles that are dispersed in the water phase. The key to successful polymerization is that this collision process is fast with respect to the timescales of particle nucleation and growth. 

Fig. 14 TEM images of (a) PMMA latex rumored with sdica nanopaiticles obtained by Pickering emulsion polymerization. Multilayered nrmocomposite polymer colloids with (b) a hairy outer-layer of poly(acrylonitrile) and (c) a soft shell of poly(n-butyl acrylate). Scale bars 100 nm. Figure and legend are taken from [117]...

Ma and Dai [121] reported the synthesis of polystyrene latexes armored with silica nanoparticles (10-15nm in diameter, PA-ST silica sol, Nissan Chemicals) via solids-stabilized emulsion polymerization. They used VA-086, 2,2 -azobis [2-methyl-lV-(2-hydroxyethyl)propionamide], as nonionic initiator. Whereas we found that Pickering emulsion polymerization of styrene using Ludox TM-40 and a low flux of radicals generated from potassium persulfate did not result in an armored latex, the hydroxyethyl groups probably enhance the wettability of the surface of the latex particles to promote silica adhesion. This was confirmed by a... 

Chen T, Colver PJ, Bon SAF (2007) Organic-inoigtinic hybrid hollow spheres prepared from Ti02-stabilized Pickering emulsion polymerization. Adv Mater 19(17) 2286-2289... 

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