Use of the upside-down method to prepare porous polymer films with tunable surface pore sizes.

Porous polyurethane films with well-ordered pores were prepared using polystyrene microspheres as a template, and the surface pore sizes were tuned using a new upside-down (USD) method. After polystyrene microspheres were self-assembled on a substrate and the voids between microspheres were infiltrated with a polyurethane prepolymer solution, the samples were placed upside down to allow the prepolymer solution to flow back before it was solidified. The surface pore sizes of the porous films were tuned by changing the time in which the samples were placed upside down. Using microspheres of the same size, we prepared porous polyurethane films with surface pore sizes ranging from 32 to 87% of the templating microsphere size.