Two liquids can form different types of emulsions. Examples of emulsions include vinaigrettes, homogenized milk, liquid biomolecular condensates, and some cutting fluids for metal working. In an emulsion, one liquid (the dispersed phase) is dispersed in the other (the continuous phase). Although the terms colloid and emulsion are sometimes used interchangeably, emulsion should be used when both phases, dispersed and continuous, are liquids. Emulsions are part of a more general class of two-phase systems of matter called colloids. The surfactant (outline around particles) positions itself on the interfaces between Phase II and Phase I, stabilizing the emulsionĪn emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation.The unstable emulsion progressively separates.An emulsion of Phase II dispersed in Phase I.Two immiscible liquids, not yet emulsified.Recently, it was shown that also dispersions consisting of phase-separated aqueous polymer solutions can be stabilised using Pickering stabilisation. Recently, using latex particles for Pickering stabilization and then fusing these particles to form a permeable shell, a new form of particle, called a colloidosome, has been developed for encapsulation. The casein replaces the milkfat globule membrane, which is damaged during homogenisation.
Casein (protein) units are adsorbed at the surface of milk fat globules and act as a surfactant. Homogenised milk is an example of a Pickering-stabilized emulsion. This is evident when observing emulsion stabilization using polyelectrolytes. Generally, the phase that preferentially wets the particle will be the continuous phase in the emulsion system.Īdditionally, it has been demonstrated that the stability of the Pickering emulsions can be improved by the use of amphiphilic "Janus particles", due to the higher adsorption energy of the particles at the liquid-liquid interface. When the contact angle is approximately 90°, the energy required to stabilize the system is at its minimum. Where r is the particle radius, is the interfacial tension, and is the contact angle. contact angle of approximately 90°) are better stabilizers because they are partially wettable by both liquids and therefore bind better to the surface of the droplets. Particles that are partially hydrophobic (i.e. If the contact angle of the particle to the interface is low, the particle will be mostly wetted by the droplet and therefore will not be likely to prevent coalescence of the droplets. The particle’s contact angle to the surface of the droplet is a characteristic of the hydrophobicity. Properties such as hydrophobicity, shape, and size of the particle can have an effect on the stability of the emulsion. However, if solid particles are added to the mixture, they will bind to the surface of the interface and prevent the droplets from coalescing, thus causing the emulsion to be more stable. If oil and water are mixed and small oil droplets are formed and dispersed throughout the water, eventually the droplets will coalesce to decrease the amount of energy in the system. Pickering, who described the phenomenon in 1907, although the effect was first recognized by Walter Ramsden in 1903. This type of emulsion was named after S.U. A Pickering emulsion is an emulsion that is stabilized by solid particles (for example colloidal silica) which adsorb onto the interface between the two phases.
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