Method for preparing free-standing polymer film with micropores

A method for preparing a free-standing polymer film with through pores, comprising:

• (a) forming a thin film of a water-soluble polymer on a substrate;
• (b) applying, on the water soluble polymer thin film, a hydrophobic polymer solution prepared by dissolving a hydrophobic polymer in a single pure solvent to form a non-porous thin film of a hydrophobic polymer on the water-soluble polymer thin film;
• (c) applying, on the hydrophobic polymer thin film, a mixed solvent that contains a solvent and a non-solvent,
• wherein the non-solvent is a C1-C3 alcohol and the content of the C1-C3 alcohol in the mixed solvent is 5 to 20 vol. %,
• and drying the resulting substrate at a relative humidity of 20 to 90%, thereby generating honeycomb-patterned through-pores in the non-porous thin film of the hydrophobic polymer;
• and
• (d) immersing the dried substrate in water to dissolve the water-soluble polymer thin film, thereby enabling the hydrophobic polymer thin film having a honeycomb-patterned through-pore structure to be peeled from the substrate.