Method for providing textured, porous polymeric films
Textured and porous organic polymeric films can be obtained by subjecting organic polymeric films that are swellable in carbon dioxide, to supercritical carbon dioxide while such films are under an atmospheric pressure of at least 73 bar and an applied physical force of at least 0.05 Newtons. The textured and porous organic polymeric films have surface wrinkles having an average peak to valley height of at least 1 μm and up to and including 3,000 μm, and a porosity of at least 10%.
1. A method for providing a textured and porous polymeric film, comprising the steps of, in order:
A) providing an organic polymeric film having first and second opposing surfaces and a dry thickness of less than 1 mm, and that is composed of a material that is swellable with supercritical carbon dioxide;
B) applying a physical force to at least a partial surface area of both the first and second opposing surfaces of the organic polymeric film of at least 0.05 Newtons;
C) subjecting the organic polymeric film to supercritical carbon dioxide under a pressure of at least 73 bar and a temperature of at least 31° C. for a time sufficient to swell the organic polymeric film with the supercritical carbon dioxide;
D) removing the supercritical carbon dioxide; and
E) after D) has begun or has been completed, removing the physical force from the at least partial surface area of both the first and second opposing surfaces,
to provide a textured and porous organic polymeric film having:
a) textured first and second opposing surfaces in the at least partial surface area, having wrinkles having an average peak to valley height of at least 1 μm and up to and including 3,000 μm, and
b) a porosity of at least 10% provided by pores between the first and second opposing surfaces, the porosity being based on the total final volume of the textured and porous organic polymeric film.
2. The method of claim 1 , wherein the textured and porous organic polymeric film is cooled to a temperature that is less than the temperature used in C).
3. The method of claim 1 , wherein the organic polymeric film is disposed on a substrate that is not swellable by supercritical carbon dioxide under the conditions of C).
4. The method of claim 1 , wherein the organic polymeric film is composed of one or more amorphous or semi-crystalline polymers.
5. The method of claim 1 , wherein the organic polymeric film is composed of poly(vinylidene fluoride) or a copolymer derived in part from vinylidene fluoride, an acrylate homopolymer or copolymer, a polycarbonate, a polyurethane, or a blend of two or more of such polymers.
6. The method of claim 1 , wherein the organic polymeric film is a composite composed of one or more organic polymers and an inorganic or organic filler material.
7. The method of claim 1 , wherein the textured and porous organic polymeric film comprises both open pores and closed pores.
8. The method of claim 1 , wherein the textured and porous organic polymeric film comprises predominantly closed pores.
9. The method of claim 1 , wherein the organic polymeric film comprises a single organic polymeric layer.
10. The method of claim 1 , wherein the organic polymeric film comprises a laminate of two or more organic polymeric films of different composition.
11. The method of claim 1 , wherein the textured first and second opposing surfaces in the at least partial surface area have wrinkles having an average peak to valley height of at least 25 μm and up to and including 1500 μm.