Block copolymer templated crazing for membrane separation
A porous composite ultrafiltration membrane including a block copolymer layer having (a) one or more soft block polymer(s) having an elongation at break of greater than about 50%, as measured by ASTM D638 and an elastic modulus of between 10 MPa to 3 GPa as measured by the ASTM D638 tensile test; and (b) one or more hard block polymer(s) having an elongation at break of less than about 65%, as measured by ASTM D638, and an elastic modulus of higher than 1 GPa as measured by the ASTM D638 tensile test, and a macroporous support layer having a pore size larger than a pore size of the block copolymer layer. Also described is a method for making the porous composite membrane.
1 . A porous composite ultrafiltration membrane comprising:
a block copolymer layer having a thickness of not more than about 500 nm, comprising
a) one or more soft block polymer(s) having an elongation at break of greater than about 50%, as measured by ASTM D638 and an elastic modulus of between 10 MPa to 3 GPa as measured by the ASTM D638 tensile test; and
b) one or more hard block polymer(s) having an elongation at break of less than about 65%, as measured by ASTM D638, and an elastic modulus of higher than 1 GPa as measured by the ASTM D638 tensile test; and
c) a macroporous support layer having a pore size larger than a pore size of the block copolymer layer, and
wherein tensile strain is applied to a composite membrane including elements a-c) to cause craze formation and form the porous composite ultrafiltration membrane.
2 . The composite membrane of claim 1 , wherein the one or more hard block polymer(s) comprises one or more blocks selected from the group consisting of a polystyrene block, a polymethacrylate block, a poly (methyl methacrylate) block, a polyvinylpyridine block, a polyvinylcyclohexane block, a polyimide block, a polyamide block, a polypropylene block, a poly (2,6-dimethyl-1,4-phenylene oxide) block, a polyolefin block, a poly (t-butyl vinyl ether) block, a poly (cyclohexyl methacrylate) block, a poly (cyclohexyl vinyl ether) block, poly (t-butyl vinyl ether) block, polyethylene block, and polyvinylidene fluoride block and combinations thereof.
3 . The composite membrane of claim 1 , wherein the block copolymer comprises a copolymer selected from the group consisting of polystyrene-block-polyethylene oxide, polystyrene-block-poly (4-vinylpyridine), polystyrene-block-poly (methyl methacrylate), and polystyrene-block-polylactide.
4 . The composite membrane of claim 1 , wherein the one or more soft block polymer(s) comprises a polyethylene (oxide) block.
5 . The composite membrane of claim 1 , wherein the one or more soft block polymer(s) is present in an amount of from about 5% by volume to less than 50% by volume, based on the total volume of the block copolymer.
6 . The composite membrane of claim 1 , wherein the one or more hard block polymer(s) is present in an amount of greater than 50% by volume to less than 95% by volume, based on the total volume of the block copolymer.
7 . The composite membrane of claim 1 , wherein the one or more soft block polymer(s) is covalently bonded to the one or more hard block polymer(s).
8 . The composite membrane of claim 1 , wherein the block copolymer layer has a thickness of greater than 50 nm to about 500 nm.
9 . The composite membrane of claim 1 , wherein the macroporous support comprises a polymer selected from the group consisting of polyethersulfone, polyphenylsulfone, polyacrylonitrile, polyester, polyether ether ketone, polyvinylidene fluoride, and polytetrafluoroethylene.
10 . The composite membrane of claim 1 , wherein pores of the block copolymer layer have a pore width of 1 nm to less than 40 nm.
11 . The composite membrane of claim 1 , wherein the one or more hard block polymer(s) has a number average molecular weight of from about 10,000 g/mol to about 500,000 g/mol, as measured by gel permeation chromatography.
12 . The composite membrane of claim 1 , wherein the one or more soft block polymer(s) has a number average molecular weight of from about 1,000 g/mol to about 75,000 g/mol, as measured by gel permeation chromatography.
13 . The composite membrane of claim 1 , wherein the block copolymer layer is devoid of random polymers.
14 . The composite membrane of claim 1 , wherein the macroporous support layer is saturated with water.
15 . The composite membrane of claim 1 , wherein the block copolymer layer comprises a poly(styrene) hard block and a poly(ethylene oxide) soft block.
16 . The porous composite ultrafiltration membrane of claim 1 , wherein the tensile strain stretches the composite membrane by at least 10%, based on an original dimension of the composite membrane.