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In-Depth Information
Fig. 22
Model for light gas separations in H
II
-phase LLC polymer membranes. Repro-
duced with permission from [167].
©
2007 by Elsevier
the localized polarity in the H
II
nanochannels served to increase solubility
of CO
2
in the material by
35%. Such interactions were not as prevalent
in the isotropic analogue. This is because the polar headgroups are rear-
ranged and hidden inside of closed micelles, which were much less accessible
to CO
2
.Asaresult,H
II
membranes could achieve enhanced CO
2
/N
2
and
CO
2
/CH
4
ideal separation factors than disordered membranes of the same
composition. Other separations relevant to industry not involving CO
2
,such
as O
2
/N
2
, are largely unaffected by the presence of nanostructure. These first-
generation LLC membranes fall close to the “upper bound” of the Robeson
Plot for CO
2
/N
2
separation. Thus, further research into LLCs as materials for
gas separations appears warranted.
∼
6.3
Selective Vapor Barrier Materials
Among its many uses, cross-linked butyl rubber (BR) is widely used as a pro-
tective garment against harmful chemical vapors. However, as it is largely
impermeable to all vapors, those wearing BR suits often experience discom-
fort, as their perspiration cannot escape. In a major step to overcome this
issue, selectively “breathable” composites can be made by copolymerizing
LLC monomers with BR. Initial work focused on incorporating the H
II
phase
formed by the aforementioned LLC monomer into BR [169]. The addition
of H
II
domains into BR was found to increase the water vapor transport
through the composite by over four orders of magnitude compared to pure
cross-linked BR. In contrast, the permeability of a chemical warfare simu-
lant, chloroethyl ethyl sulfide (CEES), increased only by a factor of 75%. Pure
cross-linked BR was observed to have a water/CEES molar transport selec-
tivity of 0.25, while the composite material exhibited a selectivity of 23. The
inclusion of hydrophilic, nanostructured water channels through the polymer
allowed water vapor to readily pass through the material and resulted in an
drastic improvement in selectivity between pure BR and the composite.
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