Janus membranes via atomic layer deposition
A Janus membrane exhibiting sides with different properties and methods of fabricating such a Janus membrane. The membrane comprises a polymer material lacking polar functional groups. One side of the membrane is masked during atomic layer deposition (ALD). ALD is utilized to deposit a conformal coating on an exposed side of the membrane.
1. A method of fabricating a Janus membrane comprising:
positioning a membrane in a housing in an Atomic Layer Deposition (ALD) reactor, the membrane having a first side and a second side and comprising a material, the membrane positioned within the housing with the entire second side disposed on and physically masked from precursor exposure by a portion of the housing and the first side exposed to a reaction chamber of the ALD reactor, wherein the membrane lacks polar functional groups; and
depositing an oxide coating on the first side of the membrane and within a network of pores within the membrane by performing at least 150 cycles of atomic layer deposition, wherein a cycle of the at least 150 cycles comprises the steps of:
exposing a first ALD precursor flux comprising a first ALD precursor at a first deposition temperature, a first vapor pressure, and for a first exposure time;
absorbing the first ALD precursor to the first side of the membrane and within a portion of the network of pores;
a purge step, after absorbing the first ALD precursor, comprising a pulse of inert gas for purge time of between 10 seconds and 60 seconds;
after the purge step, exposing a second ALD precursor flux comprising water at a second deposition temperature, a second vapor pressure, and for a second exposure time;
reacting the absorbed first ALD precursor with the second ALD precursor; and
forming a coating on the first side and the portion of the network of pores;
wherein flow of the first ALD precursor in the network of pores is governed by Knudsen diffusion; and
wherein the deposition of the oxide coating forms a uniform thickness on the first side and a thickness gradient of oxide coating within the network of pores and further wherein the second side is free of the oxide coating.
2. The method of claim 1 , wherein the membrane is polypropylene.
3. The method of claim 1 , wherein the first ALD precursor is an organometallic precursor.
4. The method of claim 1 , wherein the network of pores is tortuous.
5. The method of claim 1 , wherein the second ALD precursor is water.
6. The method of claim 1 , wherein the housing comprises a fixture and a masking plate, the fixture engageable with the masking plate and the membrane retained within the housing.
7. The method of claim 1 , wherein the first deposition temperature is between 60° C. and 110° C.
8. The method of claim 1 , wherein the first vapor pressure is up to 1 Torr.
9. A method of fabricating a membrane comprising:
positioning a membrane lacking polar functional groups in a housing in an Atomic Layer deposition (ALD) reactor, the membrane having a first side and a second side, so that the second side of the membrane is disposed on and physically masked from precursor exposure by a portion of the housing; and
depositing an oxide on the first side of the membrane and within a network of pores within the membrane by atomic layer deposition by the steps of:
performing an ALD cycle of:
exposing a first ALD precursor flux comprising a first ALD precursor at a first deposition temperature, a first vapor pressure, and for a first exposure time;
absorbing the first ALD precursor to the first side of the membrane and within a portion of the network of pores;
exposing a second ALD precursor flux comprising a second ALD precursor at a second deposition temperature, a second vapor pressure, and for a second exposure time;
reacting the absorbed first ALD precursor with the second ALD precursor; and
forming a plurality of oxide seeds on the first side and the portion of the network of pores,
wherein the ALD cycle is repeated 100 to 300 times; and
wherein the oxide within the network of pores has a monotonically decreasing thickness gradient with increasing pore depth.
10. The method of claim 9 , wherein the membrane is polypropylene.
11. The method of claim 9 , wherein the coating is an oxide and wherein the first ALD precursor is an organometallic precursor.
12. The method of claim 9 , wherein the network of pores is tortuous.
13. The method of claim 9 , wherein the second ALD precursor is water.
14. The method of claim 9 , wherein exposing the second precursor flux occurs immediately after exposing the first precursor flux without an intervening purge step.