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

Abstract

Oil‐in‐water emulsion droplets spontaneously adopt, below some temperature Td, 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 Td by >50 °C, implying formation of drastically different interfacial structures. Furthermore, “magic” alcohol chain lengths maximize Td. 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.

Non-Classical Euler Buckling and Brazier Instability in Cylindrical Liquid Droplets

“…The dramatic reduction of γ in the vicinity of T SE , enables the elastic energy of the interfacial crystal to dominate the shape of the liquid droplets, giving rise to droplet shape transformations. , Furthermore, on cooling to T < T SE , droplets’ interfaces transiently adopt a negative γ, which promotes further shape transformations with a dramatic increase in interfacial area. , While a different droplet self-shaping mechanism has been proposed in some early studies, , recent experimental evidence strongly supports the present scenario. ,,, In the negative-γ regime, many droplets adopt a cylindrical shape, with the length of the cylinder increasing as a function of time. This increase is accompanied by thinning of cylinder’s cross section, warranting droplet’s volume conservation.…”

“…The length of the cylindrical droplets at the buckling transition is equal to the diameter of the well, L = 70 μm. Interfacial crystal’s thickness is ,, t ≈ 2 nm. The radius of the thickest cylinders observed to buckle is r = 2.9 μm.…”