Patent ID: 7588796

Claim:
A method of making a composite membrane with ion exchange properties, said method comprising the steps of: providing a porous base membrane comprising a plurality of pores and made from a first material; dissolving a coating material in a fluid comprising a densifed gas, the coating material selected from the group consisting of fluorinated vinyl-based copolymers having sulfonyl functionality, fluorinated acrylic-based copolyrners having at least one of hydroxyl groups, acid groups, sulfonyl groups, and sulfonic acid groups, and fluorinated styrenic-based copolymers having at least one of hydroxyl groups, acid groups, sulfonyl groups, and sulfonic acid groups; exposing the porous base membrane to the coating material dissolved in the densifed gas; depositing a uniform coating of the coating material onto surfaces defining the pores in the porous base membrane by changing conditions of the fluid to below a solubility limit of the coating material in the fluid; and applying an ion exchange material to the coated porous membrane so that the ion exchange material is in contact with substantially all of the coated surfaces of the porous base membrane, the ion exchange material substantially incompatible with the first material of the porous base membrane, the coating material substantially compatible with the first material and the ion exchange material.