Chemistry Reference
In-Depth Information
4.1
INTRODUCTION
Lyotropic liquid crystalline (LLC) phases result from the self-assembly
of amphiphilic molecules such as lipids and surfactants in water. Classical
examples of LLCs are the lamellar, hexagonal, and cubic phases, as shown in
Figure 4.1. LLCs often possess long-range orientational order (in the range of
nanometers to millimeters), resulting in unique hydrophobic-hydrophilic
“nanoenvironments,” which has led to their development in a number of tech-
nological areas such as personal care products and pharmaceutics (Spicer,
2005a). Concomitant with this has been the need for detailed analysis of LLC
properties, including their thermodynamic equilibrium and metastable phase
behavior, and nanostructure. This latter need has in turn driven the develop-
ment of new techniques for LLC nanocharacterization.
In this chapter, we review the current techniques that are employed for
LLC nanocharacterization. Section 4.2 discusses characterization of “bulk”
LLC nanostructure, while Section 4.3 deals with dispersed (i.e., colloidal) LLCs.
Section 4.4, meanwhile, explores recent developments in the characterization
of LLC interfacial properties. The aim is to give an overview of key techniques
for researchers joining this exciting subfi eld of “ soft - matter nanotechnology ” .
4.2 BULK LYOTROPIC LIQUID CRYSTALS:
NANOCHARACTERIZATION AND PHASE BEHAVIOR
The key determinant of LLC equilibrium nanostructure is the thermodynamic
phase behavior of the amphiphile-water system. Since phase behavior is also
Increasing water content in system
lamellar (L)
Normal
micelle
normal
hexagonal (H
I
)
inverted
hexagonal (H
II
)
Reverse
micelle
normal
discontinuous
cubic (I
I
)
normal
bicontinuous
cubic (Q
I
)
inverted
bicontinuous
cubic (Q
II
)
inverted
discontinuous
cubic (I
II
)
Figure 4.1
Representations of different lyotropic liquid crystal phases (Gin et al.,
2008 ).
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