Generating porous polymer microspheres with cellular surface via a gas-diffusion confined scCO2 foaming technology to endow the super-hydrophobic coating with hierarchical roughness

Porous polymer microspheres have been applied in various fields due to their hierarchical morphology and extensive surface area. However, it is difficult to create porous microspheres, especially porous microspheres without solid skin layer, via conventional supercritical carbon dioxide (scCO2) foaming technology due to the fast diffusion of gas. In order to prevent gas diffusing from microspheres, a continuous polymethyl methacrylate (PMMA) phase is employed as a gas-diffusion confinement in this work. When pressure quenched, CO2 is retained in/on the polystyrene (PS) microspheres for the cell nucleation and development. Therefore, a porous PS microsphere is fabricated by a diffusion-confined scCO2 foaming technology for the first time. The prepared microsphere displays an open cellular surface and a closed cellular core. The cell structure of porous microspheres is tunable depending on the foaming parameters. This method with the advantages of simple, versatile and controllable provides a novel perspective for fabrication of porous polymer microspheres. Furthermore, a super-hydrophobic coating is constructed using polymer microspheres as fillers and beeswax as a hydrophobic agent. Compared to the arrays composed of solid microspheres, the arrays composed of porous polymer microspheres show a super-hydrophobicity, low water-adhesion, outstanding antifouling and self-cleaning property.