Chemistry Reference
In-Depth Information
other new direction for LLC phases that might generate new avenues for
medical therapies, is the use of cationic amphiphiles or lipids to complex
with DNA to form surfactant-DNA complexes that exhibit LLC phases [158].
LandH
II
-type phases have been observed in such systems. It is believed that
understanding the aggregation and LLC phase formation of these cationic
surfactant-DNA complexes may lead to the development of better gene deliv-
ery therapies.
6
LLC Materials for Membrane Separations
Membrane separations are of rapidly growing importance as world energy
demands are projected to continually increase and more stringent guidelines
are placed on the cleanup of waste streams [159]. Membranes potentially
offer many less energy intensive alternatives to traditional separation tech-
nologies [159]. Proper design considerations are needed to engineer high-
performance membranes that selectively segregate specific components from
mixtures based on affinity, shape, size, charge or other chemical and physical
properties [159]. However, a great deal of research is still needed in order for
membranes to be economically viable and displace older technologies [159].
Traditional membranes are either porous or dense materials. Porous mem-
branes operate via size discrimination and dense membranes by the solution-
diffusion mechanism [160]. Porous membranes can be highly ordered
materials such as zeolites [161] or materials such as polymers, processed to
create specific types of voids within their structure. Dense membranes are
typically rubbery or glassy polymers that lack voids and pinholes. Each class
of material lends itself to different applications yet has its own limitations.
Zeolites are capable of molecular sieving of gases and other small molecules,
but are difficult to process into uniform films of large surface area [161].
Porouspolymerscanbeusedinapplicationssuchasaqueousnanofiltration
(NF), but the processes that produce them result in the lack of a uniform
structure within the film [162]. These materials are thus unable to perform
precise molecular sieving [162]. Dense polymers are easily processed and
can be used for a variety of applications, such as reverse osmosis (RO) for
water desalination [163], gas separations [164], and barrier films [165], but
the solution-diffusion mechanism dictates that all solutes will penetrate the
membrane, making complete molecular sieving virtually impossible [160].
The need to overcome the disadvantages of each class of membrane
drives research for novel, composite materials that combine the advanta-
geous properties of each class [159]. LLCs have potential to offer desirable
hybrids of these two types of materials, as they allow for the incorpora-
tion of a porous, ordered nanostructure within an otherwise dense film.
LLC membranes capable of performing several different applications, such as
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