Fatty acids (FAs) are carboxylic acids with a long aliphatic chain, either saturated or unsaturated. FA vesicles are colloidal suspensions of closed lipid bilayers, which are composed of fatty acids and their ionized species (soap). They are observed in a small region within the fatty acid-soap-water ternary phase diagram above the chain melting temperature (Tm) of the corresponding fatty acid-soap mixture. They always contain two types of amphiphiles, the nonionized neutral form and the ionized form (the negatively charged soap). The ratio of nonionized neutral form and the ionized form is critical for the vesicle stability. Moreover, FA vesicles are formed not only by unsaturated fatty acids such as oleic acid and linoleic acid, but also by saturated fatty acids such as octanoic acid and decanoic acid. Learn more: fatty acid micelle