Chemistry Reference
In-Depth Information
linear optical materials, and optical gating systems [1, 2]. They are also com-
monly used as ordering elements in high-strength polymers (i.e., main-chain
and side-chain LC polymers) [2, 15]. Non-functionalized thermotropic LCs
have also been explored for use as anisotropic solvents for chemical reac-
tions [16], and for delivery systems in the pharmaceutical industry [17].
Many examples of thermotropic LC systems with new or additional functional
properties also exist in the literature [18-22]. However, functional versions
of LLCs and demonstrated applications of LLC materials are much less de-
veloped. Only within the last two decades have examples of functional LLC
mesogens and functional materials based on LLC assemblies been realized.
The goal of this article is to provide an overview of the major research
areas and activities in the area of functional LLC materials over the last
10-20 years, and also describe some emerging new directions for this field of
materials research. In addition to limiting this review to LLC systems as de-
fined above, we will also restrict the scope of this review in several other ways
for focus. This review will also be restricted to LLC systems containing
small-
molecule or oligomeric
amphiphiles that self-assemble into ordered systems
in the presence of an added solvent. Ordered, phase-separated block copoly-
mer assemblies are similar in geometry and structure to LLC phases [23], but
they will not be included in this review as true LLC phases. This is because
block copolymers can self-organize in the absence of an added solvent, and
amphiphilic polymer systems have periodic features that are 1-2 orders of
magnitudelargerinsizethanthosefoundintypicalLLCphases.Recentre-
views on applications of functional amphiphilic block copolymer materials
are available [24, 25]. Additionally, this review will be focused solely on the
discussion of
functional
LLC materials. By the term “
functional
”, we mean
LLC-based systems (as defined structurally and compositionally above) in
which (1) the LLC mesogens themselves have
additional properties of poten-
tial utility
in addition to their intrinsic self-organization behavior; (2) the
mesogens
perform a specific function for generating useful materials
;and/or
(3) the collective material has a
demonstrated
application or useful function.
Whether such LLC materials are organic or hybrid, monomeric or polymer-
ized,orformedaroundwateroradifferentpolarsolvent,doesnotmatter.
This review is divided into sections according to the type of functional
properties or areas of application that have been identified or demonstrated
for LLC materials.
2
LLC-templated Materials and Composites
While LLCs have the intrinsic ability to self-organize in an added solvent,
an additional function frequently made use of is their ability to organize ex-
trinsic molecules, macromolecules, or materials into that LC structure. LLCs,
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