Open the Pores: Particles with Fully Accessible Hierarchical Pore Networks by Controlling Phase Separation in Confinement.

Hierarchical porous materials combine large surface area with efficient mass transport, in particular when macropores directly connect mesopores. Polymerization-induced spinodal decomposition of poly(ethylene glycol) and tetraethyl orthosilicate can produce such macro-mesoporous material in bulk. However, the confinement of this spinodal decomposition process to emulsion droplets typically produces porous particles with a dense silica shell that blocks pore accessibility. Here, we address this issue by controlling the interfacial energies of the two phases undergoing spinodal decomposition within the emulsion droplet. We use surfactant mixtures to induce neutral wetting to prevent shell formation and generate particles with fully open, accessible and interconnected pore systems. Lattice Boltzmann simulations corroborate the experimental findings and underline that neutral wetting conditions with a contact angle to the continuous phase of ∼90° for both phases are essential to form open surface pores. Our work provides a simple strategy for producing hierarchical porous particles with controlled surface and bulk porosity between ∼200 and ∼6000 nm, expanding their potential for applications in catalysis, separation technologies, and adsorption.