multiple emulsions with an “ onion ” topology are useful vehicles for drug delivery , biochemical assays , and templating materials . they can be assembled by ternary liquid phase separation using microfluidics , but the control over their design is limited because the mechanism of their creation is unknown . here it is shown that phase separation occurs via self - similar cycles of mass transfer , spinodal decomposition or nucleation , and coalescence into multiple layers . mapping out the phase diagram demonstrates a linear relation between concentric layer diameters , whose slope depends on the initial ternary composition and the molecular weight of the surfactant . these general rules quantitatively predict the number of droplet layers . further , self - assembly routes for polymer capsules and liposomes are provided with techniques to assemble lipid - stabilized droplets with ordered internal structures .