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4.2.3
Scattering Techniques
Scattering techniques provide a powerful method for obtaining quantitative
information on size, shape, and nanostructure within LLC phases. Three kinds
of radiation are typically used in LLC scattering studies, light, X-ray, and
neutron studies. The principles of small-angle X-ray and neutron scattering are
broadly the same and have been discussed in a large number of articles.
(Glatter and Kratky, 1982; King et al., 1999). In this section, we focus on X-ray
and neutron scattering approaches to the characterization of LLC phase
behavior.
4.2.3.1 Small-Angle X-ray Scattering
Small - angle X - ray scattering
(SAXS) is the most recognized method used to study the nanostructural fea-
tures of lyotropic liquid crystals, both in their bulk and dispersed forms. (Pabst
et al., 2000; Rappolt et al., 2000). Cubic lyotropic liquid crystals were fi rst
recognized using X-ray scattering techniques by Luzzati and Husson in 1962
(Luzzati and Husson, 1962), and several structural models were proposed.
(Luzzati et al., 1968a,b). Around the same time, the temperature-composition
phase diagram of monoglycerides in water was published by Lutton (1965).
Since then, a great diversity of amphiphile systems have been studied using
SAXS, including simple and complex natural/synthetic surfactants, phospho-
lipids, glycolipids, synthetic and natural carbohydrate surfactants, dispersed
LLCs (see later), and many more (Bäverback et al., 2009; Briggs et al., 1996;
Mencke and Caffrey, 1991).
Figure 4.5 is a schematic diagram of a SAXS experiment. A collimated
beam of X-ray radiation of wavelength
1 Å ) is incident upon a
thin solution sample, typically millimetres or less in thickness.
The radiation passes through the sample (i.e., is transmitted), is absorbed,
or is scattered (elastically/inelastically). The intensity of scattering as a func-
tion of angle is measured relative to the incident beam using an X-ray detector,
such as a charge-coupled device (CCD) camera.
Non-sample-related scattering (background) is subtracted from data fi les,
and the scattered intensity is normalized relative to sample transmission.
λ
(typically
∼
Scattered
k'
Q = K-K'
k
2
θ
Incident
Transmitted
Sample
Figure 4.5
Wave vector geometry in a small-angle scattering measurement.
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