Method of fabricating semipermeable ultrathin polymer membranes
A semipermeable ultrathin polymer membrane comprises a substantially optically transparent polymer film having a surface area to thickness ratio of at least 1,000,000:1, and an array of precisely spatially ordered pores of a user-selected diameter defined therethrough. Such membranes can be fabricated by providing a mold having a patterned array of nanoholes femtosecond laser ablated in a surface thereof; applying a first polymer solution onto the mold surface so that the first polymer solution infiltrates the nanoholes; allowing the first polymer solution to dry and form a replica of the mold having a plurality of freestanding nanoneedles extending from a surface of the replica; removing the replica from the mold; coating the replica surface with a second polymer solution; drying the second polymer solution to form a porous polymer film; and dissolving the replica in a solvent to release the film from the replica as a semipermeable ultrathin polymer membrane.
1. A method of fabricating a semipermeable polymer membrane, consisting of:
providing a mold having a patterned array of nanoholes femtosecond laser ablated in a surface of the mold;
applying a first polymer solution onto the surface of the mold whereby the first polymer solution infiltrates the nanoholes;
drying the first polymer solution to form a negative replica of the mold, the replica having a first surface, a second surface opposite the first surface, and a plurality of freestanding nanoneedles extending a nanoneedle height from the first surface;
removing the replica from the mold;
coating the first surface of the replica with a second polymer solution, whereby the first surface of the replica is covered with a layer of the second polymer solution having a thickness less than the nanoneedle height such that the nanoneedles extend through the layer of the second polymer solution;
drying the second polymer solution to form a porous polymer film; and
dissolving the replica in a solvent to release the porous polymer film from the replica.
2. The method of claim 1 , wherein:
the porous polymer film has a thickness of less than one micron; and
the first surface of the replica is coated with a second polymer solution by spin-coating assisted deposition.