Non-dewetting porous membranes

A method of making a microporous membrane composite, comprising:

• a) coating a microporous membrane with a fluorocarbon liquid composition comprising a fluorocarbon liquid medium containing a fluorinated ionomer dissolved or dispersed therein to thereby form a coated microporous membrane composite, the fluorinated ionomer having iodine and/or bromine atoms at a terminal position, at least 90% by weight of the fluorinated ionomer consisting in particles of size lower than 200 nm, wherein the fluorinated ionomer comprises units from copolymerization of:
• i) tetrafluoroethylene;
• ii) fluorinated monomer units containing ethylenic groups and functional groups chosen from —SO2F, —COOR, —COF or combinations of these, wherein R is a C1 to C20 alkyl radical or a C6 to C20 aryl radical;
• iii) monomeric units deriving from a bis-olefin, chosen from formulae (OF-1), (OF-2), or (OF-3) where:
• wherein j is an integer between 2 and 10, and R1, R2, R3, R4, individually equal or different from each other, are H, F or C1 to C5 alkyl or (per)fluoroalkyl group;
• wherein each of A, equal or different from each other and at each occurrence, is independently F, Cl, or H;
• each of B, equal or different from each other and at each occurrence, is independently F, Cl, H or ORB, wherein RB is a branched or straight chain alkyl radical which can be partially, substantially or completely fluorinated or chlorinated;
• E is a divalent group having 2 to 10 carbon atom, optionally fluorinated, which may be inserted with ether linkages;
• wherein E, A and B have the same meaning as above defined;
• R5, R6, R7, independently equal or different from each other, are H, F or C1-5 alkyl or (per)fluoroalkyl group;
• and
• iv) a compound having the formula Rf(I)x(Br)y, wherein where Rf is a fluoroalkyl or (per)fluoroalkyl or a (per)fluorochloroalkyl group having from 1 to 8 carbon atoms, and wherein x and y are integers from 0 to 2, with 1≤x+y≤2;
• wherein the fluorocarbon liquid medium comprises a mixture of perfluoropolyethers, said perfluoropolyethers having the general formula F3C—O—[CF2—CF(CF3)—O]n—[CF2—O]m—CF3 wherein m and n are integers, being n>0 and m≥0, said perfluoropolyethers having molecular weight between 300 atomic mass units (amu) and 600 amu, said mixtures having prevailing average boiling points between 55° C. and 135° C. and an average ratio between the indexes m and n (m/n) below 0.05;
• wherein the fluorinated ionomer has an equivalent weight of between 380 g/eq and 620 g/eq, and
• b) crosslinking the coated microporous membrane by heating the coated microporous membrane to form a coated, crosslinked microporous membrane composite;
• wherein the fluorinated ionomer coating is between about 25 weight percent and about 30 weight percent of the microporous membrane composite,
• wherein the microporous membrane composite has a permeability of 876 l/atm*hr*m2 to 2852 l/atm*hr*m2 at 22.5° C. measured on 47 millimeter diameter microporous membrane composite samples, and
• wherein the microporous membrane has a rated pore size of 0.2 microns or less.