Emulsion templating: Unexpected morphology of monodisperse macroporous polymers

We synthesised monodisperse macroporous polymers via polymerisation of water-in-monomer droplet emulsions and obtained non-spherical pores with layered pore walls. We hypothesise that this morphology is caused by surfactant diffusion and phase separation during polymerisation.

We varied the surfactant mass fraction of the emulsions and polymerised the templates with a water-soluble initiator. From the resulting macroporous polymers we determined the shape of the pores and thickness of the layers via scanning election microscopy. The response of the monomer/surfactant mixture to polymerisation was studied by a ternary phase diagram that simulated polymerisation.

The emergence of non-spherical pores with layered pore walls is indeed caused by surfactant diffusion and phase separation. During polymerisation the surfactant molecules diffuse either to the water/monomer interface or deeper into the continuous monomer phase. The first process results in non-spherical pores, while the second process generates layered pore walls.