![]() īy adjusting the grafting rate, it is possible to obtain particles of varying wettability. The grafting of hydrocarbon chains, such as dimethyl silyl, reduces their affinity with the aqueous phase, the most hydrophobic ones containing 14% silanols. Pure, 100% of their groups are hydrophilic Si-OH silanols, so they are unable to stabilize the interface except with certain oils. This is the case, for example, with pyrogenic, hydrophilic silica particles. A grafting of molecules giving them their affinity with the water-oil interfaces is therefore carried out. If they are too hydrophilic or hydrophobic, they do not sufficiently stabilize the emulsion, the drops obtained are large (>100 μm) and unstable toward coalescence. In general, the particles used are hydrophobic (such as carbon black) or hydrophilic (such as silica). However, as in the case of surfactants, to allow them to be anchored at the interface, they must be partially wetted by each of the two phases. Their size must be adapted to the desired emulsion, because an emulsion with droplets of at least a few micrometers is obtained from particles of 1–100 nm and an emulsion with drops of the order of a millimeter with particles of about 100 nm. The most common are nano spherical silica particles. There are various nature and shape of the particles used, such as spherical, cubic, in the form of rods, silica, titanium, melamine-formaldehyde, polystyrene, clays, spores or bacteria. According to Scopus, 17 publications containing the terms “Pickering emulsion” in the title, keywords or abstract were published in 2005, 100 in 2011 and 220 in 2014. After many years, Pickering emulsions have been studied again since the 2000s and are of increasing interest to researchers. Pickering's work published in 1907 describes these phenomena more fully and shows that these particles, having a greater affinity with the aqueous phase than with the oily phase, are alternatives, often more advantageous than surfactants to obtain easily very stable O/W emulsions. Ramsden has shown that emulsions or bubbles can be permanently stabilized by means of fine solid or highly viscous particles placed at the interface of two liquids. Their anchoring at this interface is almost irreversible and the inhibition of coalescence is very effective. They exist in nature with, for example, fat crystals in butter or casein particles in milk. These solid particles adsorb at the interface between the two phases. Pickering emulsions are defined as the dispersion of one liquid into another, with which it is immiscible and stabilized by solid particles. ![]()
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