Utilising spontaneous self-organization of particles to prepare asymmetric, hierarchical membranes comprising microsieve-like parts.

Mixtures of suitable small particles, large particles and an "oil", spontaneously form mixed layers on a water surface. In these layers the small particles adhere to the upper interface while the large particles adhere to the lower interface. Solidification of the "oil" by photopolymerization, followed by removal of the particles yields asymmetric, hierarchical membranes with microsieve-like parts.