Hierarchically Organized Systems Based on Liquid Crystalline Phases - Self-Assembled Supramolecular Architectures: Lyotropic Liquid Crystals - page 155

6.1 Introduction — Basic Lyotropics to Hierarchical Structures 158

6.2 ISAsomes: Formation and Characterization 162

6.3 ISAsomes Stabilized by Nanoparticles: Pickering Emulsions 164

6.4 Transfer Kinetics of Hydrophobic Molecules in Mixed - ISAsome

Systems

170

6.5 ISAsomes Embedded in Thermoreversible Polymeric Gels and Films 176

6.6 Water - in - Oil Nanostructured Emulsions with Liquid Crystalline

Oil Phases

180

6.7 Summary 184

References 186

6.1 INTRODUCTION—BASIC LYOTROPICS TO
HIERARCHICAL STRUCTURES

Amphiphilic molecules, such as lipids, surfactants, and block copolymers, show
fascinating polymorphism when mixed with water or other solvents (Hyde
et al., 1997; Seddon, 1990). These polymorphs range from simple micelles to
complex, yet well - ordered, one - , two - , and three - dimensional assemblies (Fig.
6.1). The lamellar phase is quite common, as it forms an indispensable struc-
tural constituent of biological membranes; the latter also consists of other
amphiphiles including membrane proteins and fatty acids. Biological lipids
self-assemble into some additional shapes, such as tubules, liposomes, and
convoluted membranes, which form an integral part of the human body.
The type 1 of fundamental assembly that forms depends on the molecular
shape of the amphiphile, as shown in Figure 6.1. Molecules with larger head
groups form type 1 (normal) micelles, which are typically observed for
surfactants/detergents that contain a single hydrophobic chain; molecules of
cylindrical shape with one or two chains form type 0, which is the most
common assembly found in nature in the form of biological membranes. Lipids
or block copolymers with more hydrophobic character usually form type 2
(inverse) micelles, which are the major focus of the present work. Lipid meso-
phases can also form, or interchange, with external triggers such as tempera-
ture and/or pressure (Kulkarni, 2011; Kulkarni et al., 2011b; Salentinig et al.,
2010; Seddon et al., 2006; Yaghmur et al., 2010). The molecular shape and, in
turn, the mean curvature 2 of a phase is then altered. For example, chain splay
increases with rising temperature (Shearman et al., 2010), and this increases

1 Sign convention of the curvature adopted by different authors may vary, but the current work
adopts the convention as: positive curvature toward the chain region (type 1), whereas curvature
toward the water region as negative (type 2).

2 Mean curvature: A mean of two principle curvatures, c 1 and c 2 .