Functional Lyotropic Liquid CrystalMaterials - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 179

Abstract Lyotropic liquid crystals (LLCs) are amphiphilic molecules that have the ability
to self-organize into highly ordered yet fluid, phase-segregated assemblies in the pres-
ence of an added polar liquid such as water. The resulting ordered assemblies, called
LLC phases, have specific nanometer-scale geometries with periodic hydrophilic and
hydrophobic features ranging in structure from bilayer lamellae to extended and inter-
connected channel systems. Because of their highly uniform, porous nanoscale structures,
LLC phases and LLC-based materials have been proposed for use in a number of materials
applications. However, only during the last two decades have LLC materials with func-
tional properties and demonstrated applications of LLC systems been realized. This work
provides an overview of functional LLC materials and the areas of application where they
have made an impact. As new functional properties and capabilities are realized in LLC
materials, it is almost certain that they will play more prevalent roles in nanoscience and
nanotechnology in the near future.

Keywords Functional · Lyotropic · Liquid crystal · Materials · Polymers · Self-assembly ·

Surfactant

1
Introduction

Liquid crystals (LCs) are molecules that have the ability to self-assemble into
organized mesophases with properties intermediate between those of crys-
talline solids and isotropic liquids [1, 2]. In LC phases, the molecules are
dynamic and collectively behave as a viscous liquid but retain on average
a degree of organization reminiscent of an ordered, crystalline solid. Conse-
quently, they can be considered ordered fluids, as a more accurate definition.
LCs can be subdivided into two general classes—thermotropic LCs and ly-
otropic LCs—depending on the environmental and molecular factors that
govern how they form ordered fluid phases.
By definition, thermotropic LCs are molecules that form ordered fluid
phases in which the degree of average order depends primarily on the tem-
perature of the material [1, 2]. Unlike conventional materials which undergo
a melting transition from a crystalline solid directly to an isotropic liquid, ther-
motropic LCs lose their order incrementally by adopting a number of ordered
yet progressively more fluid states with increasing temperature. In terms of
their molecular structure, thermotropic LCs are molecules with an anisotropic
shape (e.g., typically rod- or disk-shaped) containing a relatively rigid core and
a number of flexible peripheral alkyl tails. The rigid cores of these molecules
encourage ordered packing while the flexible tails tend to disorder the system
until a compromise is met to produce an ordered fluid state.
In contrast, lyotropic LCs ( LLCs ) are molecules that form ordered fluid
phases that are phase-separated mixtures in which the degree of order de-
pends on the proportion of LC mesogen relative to an added immiscible
solvent such as water [3, 4]. In addition to morphology dependence on sys-
tem composition, LLC phases are also sensitive to other external parameters