Emulsification of lyotropic lamellar phases: new formulation routes for stabilized water-in-water emulsions

Stabilizing water-in-water emulsions remains a key challenge in soft matter science, with growing relevance for applications such as microencapsulation in food technology, bioseparation, and the construction of synthetic cells. Building on recent advances in interfacial self-assembly of fatty acid bilayers, we present here a robust and tunable strategy for stabilizing polyethylene glycol/dextran aqueous two-phase system emulsions using lyotropic lamellar phases doped with phase-separating polymers. We show that these lamellar phases spontaneously adsorb at the droplet interface, forming a stabilizing interfacial coating. By comparing multiple formulation routes, including lamellar phase pre-assembly with or without excess solvent and the previously used "one-pot" method, we demonstrate that all approaches yield equivalent droplet stabilization. Systematic variation of the lamellar phase concentration reveals a critical threshold necessary for emulsion stability. Beyond this threshold, excess lamellar material is dispersed into the continuous phase. A simple geometric model supports the hypothesis that this critical concentration corresponds to the amount required to fully coat the droplet interfaces. This strategy offers a straightforward yet precise formulation route that leverages the self-assembly and dilution behavior of lamellar phases, opening new avenues for designing fully aqueous emulsions stabilized without solid particles or synthetic surfactants.