Interfaces between water and apolar media (gases, liquids, or solids) have a high cost in free energy. Therefore they tend to recombine to reduce the total interfacial area: in water, oil drops coalesce and air bubbles recombine following collision. The metastability of emulsions, foams, and polymer dispersions is achieved through adsorption of amphiphilic molecules (ionic or non-ionic), macromolecules, or particles, which block the recombination. The mechanisms of this stabilization are well understood.Yet very fine emulsions made of pure oil droplets in pure water have also been found to be metastable in the absence of any added stabilizers.
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