Preparation of microsieves with a hierarchical structure via float-casting, using raspberry particles

This article describes the preparation of hierarchical microsieves via float-casting using raspberry particles. The raspberry particles consist of a larger spherical particle (the core) and smaller particles (satellites) that are attached on the surface of the core and were connected to the core via a surface reaction of isocyanate and amino groups. The raspberry particles were spread onto a water surface as a monolayer and a mixture of polymethylmethacrylate (PMMA) and toluene was poured over this monolayer. After evaporating the solvent, a composite membrane composed of a continuous polymer film with particles protruding out of at least one of its interfaces is obtained. The raspberry particles were etched away, and the membrane thus converted into a hierarchical microsieve comprising larger and smaller pores caused by the core and satellite particles, respectively. The most promising raspberry particles for this purpose consisted of glass beads of 75 μm diameter as core and Stober-particles of 316 nm respectively 275 nm diameter. The resulting microsieves were suitable for filtration and permeance tests. The permeance at low Reynold numbers (liquid flow velocity through the pores) is in accordance with established values for microsieves. The membranes were able to retain particles exceeding the pore size.