Nanoporous Polymeric Membranes for Hydrogen Separation
367
drying. This procedure may be quite simple when the removed film is mechanically
stable that can be used as a self-supported membrane, but it turns very difficult for the
thin film which needs mechanical stabilization. It is tedious when a block copolymer
thin film is transferred from a dense substrate to the porous material, and on a large
scale, it can hardly perform. So, to provide more stabilization, this film is transferred
onto the porous substrate (Basyooni et al. 2017; Beard et al. 2014; Kim et al. 2001;
Phillip et al. 2010; Sirelkhatim et al. 2015; Zhang et al. 2016).
In a block copolymer, mechanism of synthesis is independent, and it is formed by
joining two or more chemically distinct polymers which are bonded by a covalent
bond. Phase behavior of the block copolymer strongly depends on the selected composition, block copolymer structure, degree of polymerization, and the interaction
parameter between the fragment–fragment (van Zoelen and ten Brinke 2009). In a
block copolymer, shapes of the isolated domains are produced by the volume fraction of minority block (f). The regular shape and uniform spaced nanodomains occur
when minority blocks are segregated from the majority block (Segalman 2005).
An effort is done for gas permeability application by depositing the block copolymer nanotemplates on the highly porous track-etched membrane so that the upper
layer can help in improving selectivity and lower have high selectivity. Kamakshi
et al. (2017) have used porous PET membranes having different pore sizes (0.1–
0.2 μm) which are taken as mechanical support, and then a layer of the block copolymer (PS-b-P4VP) with the additive (HABA) is casted on this porous PET support.
After solvent annealing, the additive is removed from PET coated BC membranes
to recover porosity again. It was demonstrated that the gas permeability for both
gases changes drastically and shows a remarkable change after the coating of block
copolymer nanotemplates. Thus, the upper layer of block copolymer nanotemplates
influences the permeability and reduces the gas permeability of H 2 and CO 2 through
the composite membrane. The schematic diagram for such a composite membrane
is presented in Fig. 7.
Bonder et al. (2000) found an application of block copolymers in the exclusion of
CO 2 from mixtures with H 2 , and PEBA block has been identified to be responsible
for high selectivity. They also examined the permeability of H 2 , N 2 , and CO 2 in
block copolymers and CO 2 permeability is directly correlated with PE block composition. Permeability increases with increasing the amount of polyether. Selectivity
for CO 2 /H 2 was found 9.8 whereas for CO 2 /N 2 it was found 56. Kim et al. (2001)
have demonstrated the PE block of the block copolymer is responsible for the higher
permeability and perm-selectivity of polarizable gases. High permeability and high
selectivity achieved with PE BAX copolymer. Obtained results show the selectivity
for CO 2 /N 2 was 61 whereas SO 2 /N 2 was 500. Lindemann et al. (2014) prepared
conjugated microporous polymer membranes via layer by layer approach on sacrificial substrates and found with gas permeability measurements that these membranes
show high selectivity.
367
drying. This procedure may be quite simple when the removed film is mechanically
stable that can be used as a self-supported membrane, but it turns very difficult for the
thin film which needs mechanical stabilization. It is tedious when a block copolymer
thin film is transferred from a dense substrate to the porous material, and on a large
scale, it can hardly perform. So, to provide more stabilization, this film is transferred
onto the porous substrate (Basyooni et al. 2017; Beard et al. 2014; Kim et al. 2001;
Phillip et al. 2010; Sirelkhatim et al. 2015; Zhang et al. 2016).
In a block copolymer, mechanism of synthesis is independent, and it is formed by
joining two or more chemically distinct polymers which are bonded by a covalent
bond. Phase behavior of the block copolymer strongly depends on the selected composition, block copolymer structure, degree of polymerization, and the interaction
parameter between the fragment–fragment (van Zoelen and ten Brinke 2009). In a
block copolymer, shapes of the isolated domains are produced by the volume fraction of minority block (f). The regular shape and uniform spaced nanodomains occur
when minority blocks are segregated from the majority block (Segalman 2005).
An effort is done for gas permeability application by depositing the block copolymer nanotemplates on the highly porous track-etched membrane so that the upper
layer can help in improving selectivity and lower have high selectivity. Kamakshi
et al. (2017) have used porous PET membranes having different pore sizes (0.1–
0.2 μm) which are taken as mechanical support, and then a layer of the block copolymer (PS-b-P4VP) with the additive (HABA) is casted on this porous PET support.
After solvent annealing, the additive is removed from PET coated BC membranes
to recover porosity again. It was demonstrated that the gas permeability for both
gases changes drastically and shows a remarkable change after the coating of block
copolymer nanotemplates. Thus, the upper layer of block copolymer nanotemplates
influences the permeability and reduces the gas permeability of H 2 and CO 2 through
the composite membrane. The schematic diagram for such a composite membrane
is presented in Fig. 7.
Bonder et al. (2000) found an application of block copolymers in the exclusion of
CO 2 from mixtures with H 2 , and PEBA block has been identified to be responsible
for high selectivity. They also examined the permeability of H 2 , N 2 , and CO 2 in
block copolymers and CO 2 permeability is directly correlated with PE block composition. Permeability increases with increasing the amount of polyether. Selectivity
for CO 2 /H 2 was found 9.8 whereas for CO 2 /N 2 it was found 56. Kim et al. (2001)
have demonstrated the PE block of the block copolymer is responsible for the higher
permeability and perm-selectivity of polarizable gases. High permeability and high
selectivity achieved with PE BAX copolymer. Obtained results show the selectivity
for CO 2 /N 2 was 61 whereas SO 2 /N 2 was 500. Lindemann et al. (2014) prepared
conjugated microporous polymer membranes via layer by layer approach on sacrificial substrates and found with gas permeability measurements that these membranes
show high selectivity.