Abstract: A method of making a porous polymeric material by heating a mixture comprising polyvinylidene fluoride and a solvent system initially comprising a first component that is a latent solvent for polyvinylidene fluoride and a second component that is a non-solvent for polyvinylidene fluoride wherein, at elevated temperature, polyvinylidene fluoride dissolves in the solvent system to provide an optically clear solution. The solution is then rapidly cooled so that non-equilibrium liquid-liquid phase separation takes place to form a continuous polymer rich phase and a continuous polymer lean phase with the two phases being intermingled in the form of bicontinuous matrix of large interfacial area, and cooling is continued until the polymer rich phase solidifies. The polymer lean phase is removed from the solid polymeric material.

Abstract: Pores that are smaller than or larger than a predetermined range of pore sizes in a porous membrane barrier are blocked with a controlled porosity blocking agent. The pores are first filled with a liquid so as to remove any air therein and then subjected to a transmembrane gas blow at a pressure which will clear the larger pores of the liquid. The larger gas filled pores or the smaller liquid filled pores are then blocked by a blocking agent using a polymer-forming chemical reaction, a precipitate-forming chemical reaction or the physical deposition of solids.