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of the neutral solutes [119]. However, these H
II
-phase LLC membranes suf-
fered from markedly lower water flux than the commercially available NF
membrane [166]. The limitations on water throughput appear to be related to
the processing of the films, and not as a material shortcoming. Only a small
percentage of the aqueous channels were oriented normal to the membrane
surface and were accessible for filtration [166]. Nonetheless, this work repre-
sents a shift in the rationale of polymer membrane design.
Expanding upon the successes of aqueous NF with an LLC membrane,
promising preliminary results were obtained with the same H
II
networks
of the three-tailed LLC monomer (Fig. 21) in water desalination applica-
tions [119]. These systems were only capable of removing a small percentage
of metal ions from aqueous solution because the effective nanopore size
was significantly larger than the diameter of the hydrated small metal salt
ions [119]. As the hydrated ionic diameters of the metal ions increased (Rb
+
,
Na
+
,Mg
2+
,andNd
3+
), the amount rejected also increased. The H
II
mem-
branes were unable to compete with the current commercially available RO
membranes in either rejection or water flux. However, preliminary results
showed that these polymerized LLC membranes have superior hypochlorite
(ClO
-
) resistance properties when compared to polymers typically used in
RO [119]. ClO
-
degradation is a significant problem for current RO mem-
branes. Research in this field will proceed further. LLC systems with smaller
pores as well as those exhibiting more hydrophilic Q phases have been specu-
lated to be better candidates for RO applications than H
II
materials.
6.2
Gas Separations
The cross-linked H
II
phase of the triacrylate LLC monomer shown in Fig. 21
has also been studied as a gas separation membrane material [167, 168].
In the first report of the fabrication and use of large area, freestanding,
photo-cross-linked LLC film for gas separations [167], the transport prop-
erties of five light gases (CO
2
,N
2
,O
2
,CH
4
and H
2
) were determined in
both polymerized H
II
membranes and disordered films with the same chem-
ical composition. The presence of an H
II
-phase nanostructure was found to
have significant effects on CO
2
transport when compared to an isotropic
analogue. The periodic, aqueous nanochannels in the H
II
membrane im-
peded diffusion of all gases, and as such, higher fluxes for all gases were
observed in the disordered material. It was proposed that “non-interacting”
gases (N
2
,O
2
,CH
4
,andH
2
)mustcircumventtheopen,polarnanochan-
nels, as they are repelled from those regions. Thus, a longer path length
through the membrane must be taken (Fig. 22). The behavior of CO
2
in the
H
II
system is exceptionally different. CO
2
exhibited strong non-covalent in-
teractions with the ordered, ionic nanochannels present in the membrane,
and its diffusion was slowed more than the other four gases tested. However,
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