| abstract |
A method of treating a membrane (16) comprises the steps of providing a membrane (16) with a structure of node (22) and fibrils (24). Surfaces of the nodes (22) and fibrils (24) define a plurality of pores (26) extending through the membrane (16). The membrane (16) is made from an expanded polytetrafluoroethylene material. A water-based dispersion of oleophobic fluoropolymer solids in a water-soluble solvent is provided. The dispersion has surface tension and relative contact angle properties such that the diluted dispersion is incapable of wetting the polytetrafluoroethylene material of the membrane (16). The dispersion is diluted with a liquid wetting agent so the diluted dispersion can wet the membrane (16). Surfaces of the nodes (22) and fibrils (24) are coated with the solids in the diluted dispersion. The wetting agent material and other fugitive material are removed. Solids in the diluted dispersion are thermally coalesced on surfaces of the nodes (22) and fibrils (24) without completely blocking the pores (26) in the membrane (16). |