The preparation of porous spherical microstructures has attracted a large interest over the past decades for their potential in catalysis, separation, controlled release… Recently, solid-stabilised emulsions have been used as templates for the preparation of such materials where the particle monolayer adsorbed at the original interface forms the capsule wall. It has been shown previously that these structures are mechanically robust and that their porosity can be controlled by varying the particle size and the extent of fusing/cross-linking between the particles. However, these procedures often involve challenging processes in order to lock the particle monolayer in place.

In this work we present a simple one-pot procedure for the synthesis of microcapsules whose shell consists of an inner porous polymeric film onto/within which an outer layer of colloidal nanoparticles is embedded. Our method is based on a simple, inexpensive and rapid procedure consisting of two steps:

• We first prepare an oil-in-water emulsion stabilised only by colloidal particles, the dispersed phase of which contains a high molecular weight polymer in a mixture of a volatile good solvent and a high-boiling poor solvent.

• Subsequently, we precipitate the polymer at the oil-water interface. The polymer forms a film on the inner surface of the emulsion droplets and entraps the colloidal particles adsorbed at the oil-water interface.

We demonstrate the versatility of this method by presenting the structures we obtained with a range of colloidal particles used as emulsifiers. Furthermore, we show how the porosity and size of the obtained structures can be varied by controlling the evaporation rate of the solvent and discuss the incorporation of inorganic nanoparticles to the capsule membrane.