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 of the particle. Particle properties such as hydrophobicity, shape, and size, as well as the electrolyte concentration of the continuous phase and the volume ratio of the two phases 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, making the emulsion more stable. If oil and water are mixed and small oil droplets are formed and dispersed throughout the water (oil-in-water emulsion), 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. Pickering emulsions were named after S.U. Typically, the emulsions are either water-in-oil or oil-in-water emulsions, but other more complex systems such as water-in-water, oil-in-oil, water-in-oil-in-water, and oil-in-water-in-oil also do exist. A Ramsden emulsion, sometimes named Pickering emulsion, is an emulsion that is stabilized by solid particles (for example colloidal silica) which adsorb onto the interface between the water and oil phases.
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