Once the double emulsions were produced, we observed, in some cases, the release of the internal W1 aqueous droplet in the W2 continuous phase, leaving a 'simple' empty O/W droplet. Although PEG itself can stabilize the inner W/O droplet , some can release with time. This was confirmed by observing an emulsion after resting 2 days since increasing amounts of empty octanol droplets were observed (not shown). The stability of the inner droplet was further markedly increased adding common emulsifiers (span 85, pluronic L61 or PGPR) together with PEG in 1-octanol. Glycerol was also added to the water phase to stabilize the emulsion. As an aside, transparent double-emulsions were obtained as the reflective index of the mixture of the water-glycerol mixture can be adjusted to match the one of octanol (not shown).