Supramolecular microgels for Pickering emulsion stabilization in the limited coalescence regime: The key role of...

Oil-in-water Pickering emulsions can be stabilized by poly-N-Isopropylacrylamide microgels that adsorb, spread and entangle at the droplets surface. Several studies have tuned the microgels size and deformability to understand the relation between microgel structural parameters, their packing and conformation at the droplet surface and the resulting properties of emulsions. However, both the expected key role of the microgel structure and the mechanism that stops droplets coalescence in the particle-poor regime have never been deciphered. Here, we investigate an unprecedented range of structures, from "ultra" core-shell to more homogeneous ones. First, thanks to Langmuir trough experiments, the free spreading of the microgels at a model interface is proven to be independent of the structure. Second, by contrast, the surface coverage in emulsions Γ_emulsion, defined as the microgel mass per unit interfacial area, decreases for more core-shell structures. These structures thus stabilize smaller droplets than more homogeneous microgels. Comparing the surface coverage in emulsions to free spreading, it is deduced that the microgel compression at the droplet interface is lower for more core-shell microgels, likely due to their higher ability to make entanglements between adjacent microgels at the interface. Such entanglements counterbalance the overall stresses exerted on the droplets and limit coalescence at lower interfacial compression. Demonstrating the key role played by microgel microstructure in the Limited Coalescence process opens rich perspectives for better controlling emulsion properties.