Nanocharacterization of Lyotropic Liquid Crystalline Systems - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 110

will focus on the use of electron microscopic and scattering techniques in
characterizing LLC dispersions.

4.3.1 Small-Angle X-ray Scattering in Dispersed LLC Systems

Synchrotron SAXS is particularly useful in the study of LLC dispersions since
the high-intensity X rays that are produced overcome many of the diffi culties
in collecting scattering data from these intrinsically dilute (i.e., low scattering)
samples.
SAXS can be employed to study bilayer thickness and interlamellar
spacings in dispersed lamellar LLCs (Balgavy et al., 2001), as well as phase
transitions resulting from lipid exchange/solubilization processes (Shen
et al., 2010) and interactions with drugs (Schutze and Muller-Goymann,
1998) or biomolecules such as DNA (deoxyribonucleic acid) (Koynova et al.,
2006 ).
SAXS has also been extensively applied to studying phase behavior and
transitions in nonlamellar LLC dispersions (Siekmann et al., 2002). In particu-
lar, the method has evolved as an important tool for the investigation of
cubosomes (Andersson et al., 1995; Boyd et al., 2007) and hexasomes (Almgren,
2003; Salonen et al., 2008).
For instance, Yaghmur and co-workers (2005) have shown that the addition
of tetradecane (TC) to monolinolinein-dispersed LLCs results in a phase
progression from bicontinuous cubic Pn3m (cubosomes) to inverted hexago-
nal H 2 (hexosomes) to discontinuous micellar cubic Fd3m (micellar cubo-
somes) particles (Yaghmur et al., 2005). A new form of particle denoted
emulsifi ed microemulsion (EME) was also identifi ed in this system. (See Fig.
4.10.) Mixtures of different members of this family of dispersions (which the
authors denote as isasomes) were found to equilibrate with each other by
material transfer (Moitzi et al., 2007).

4.3.2 Electron Microscopy Techniques for Dispersed LLC Systems

4.3.2.1 Cryogenic Transmission Electron Microscopy (Cryo-TEM)
Cryo-TEM has been used to probe the shape, defects, and morphology of
dispersed LLC particles. Studies of vesicle solubilization and amphiphile
exchange phenomena in lamellar LLC particles have also been undertaken
(Heerklotz, 2008; Silvander et al., 1996). Cryo-TEM images and SAXS data
are highly complementary. Indeed, much as in SAXS, fast Fourier transform
(FFT) analysis of cryo-TEM images can be used to determine the internal
crystallographic properties of dispersed LLC particles (Barauskas et al., 2005;
Gustafsson et al., 1996, 1997). Gustafsson et al. (1996, 1997) were the fi rst to
characterize cubosome morphology by cryo-TEM. They found faceted parti-
cles and internal peridocities consistent with SAXS d - spacing measurements.
Many other dispersed LLC particle morphologies have since been studied as
shown in Figure 4.11 .