“Magic Numbers” in Self‐Faceting of Alcohol‐Doped Emulsion Droplets

Abstract Oil‐in‐water emulsion droplets spontaneously adopt, below some temperature T_d, counterintuitive faceted and complex non‐spherical shapes while remaining liquid. This transition is driven by a crystalline monolayer formed at the droplets' surface. Here, we show that ppm‐level doping of the droplet's bulk by long‐chain alcohols allows tuning T_dby >50 °C, implying formation of drastically different interfacial structures. Furthermore, “magic” alcohol chain lengths maximize T_d. This we show to arise from self‐assembly of mixed alcohol:alkane interfacial structures of stacked alkane layers, co‐crystallized with hydrogen‐bonded alcohol dimers. These structures are accounted for theoretically and resolved by direct cryogenic transmission electron microscopy (cryoTEM), confirming the proposed structures. The discovered tunability of key properties of commonly‐used emulsions by minute concentrations of specific bulk additives should benefit these emulsions' technological applicability.