Sponge phases characterization

The structures of the phases L4, La, and L3 were characterized by means of several techniques and confirmed by freeze-fracture electron microscopy [47,79,86-88]. Typical electron micrographs showing the organization of the bilayers in phases L3 and L4 are shown in Fig. 5. These clearly show the continuity of the bi layer in the sponge phases and the existence... 

Surfactant micelles and bilayers are the building blocks of most self-assembly structures. One can divide the phase structures into two main groups [1) (1) those that are built of limited or discrete self-assemblies, which may be characterized roughly as spherical, prolate or cylindrical. (2) Infinite or unlimited self-assemblies whereby the aggregates are connected over macroscopic distances in one, two or three dimensions. The hexagonal phase (see below) is an example of onedimensional continuity, the lamellar phase of two-dimensional continuity, whereas the bicontinuous cubic phase and the sponge phase (see later) are examples of three-dimensional continuity. Figure 3.8 illustrates these two types schematically. 

Recourse to characterization of tertiary and finer sub-classification is generally unnecessary. Indeed, despite this complex frame, in the majority of the situations, drug release field deals with polymeric membranes made up of a continuous phase (usually a liquid phase) trapped in a swollen solid phase (polymeric netwoik) [4]. This stmctme can be seen as a coherent system, having mechanical characteristics in between those of solids and liquids [5]. The presence of cross-links between polymeric chains hinders polymer dissolution in the liquid phase that can only swell the network. This stmctme is roughly similm to that of sponge filled by a liquid phase. Nevertheless, this is a particulm sponge as, in... 

Xy is the intrinsic surface stress tensor that determines the excess pressure exerted on the solid under the curved surface [137]. We used the isotropic approximation (X . = (x8y, where x is the scalar coefficient. Due to the lack of experimental measurements of the x value for EuTiOs, we select an experimentally reasonable value based on the data for surface tension coefficients measured in ferroelectric ABO3 perovskites. The values reported for other ABOs-type perovskites vary in the range 3-30 N/m 36.6 N/m for PbTiOs [142] (or even 50N/m [143]), 2.6-10 N/m for PbTiOs and BaTiOs nanowires [144], and 9.4 N/m for Pb(Zr,Ti)03 [145]. Here we use averaged (x value 10 N/m, which is close to that extracted recently from Pb(Zr,Ti)03 sponges tetragonality temperature dependence. For comparison, we characterize the effect of (x = 30 N/m (higher end of the reported values) on the multiferroic phase transition. 

Sponge mesophases are characterized by flow birefringence (giving anisotropic optical textures), yet they are isotropic at rest. They are typically viscous, though less so than bicontinuous cubic mesophases. Their mesostructures are closely related to the bicontinuous cubics. They often form at high (water) dilution, usually in regions of the phase diagram intermediate to lamellar and bicontinuous cubic mesophases. 

Figure 6.1 shows a schematic representation of the pseudo three-component phase diagram of a typical (surfactant/cosurfactant)-oil-water system. Depending on formulas, fine oil droplets dispersed in the continuous aqueous phase [O/W (or direct) microemulsion] or water droplets in the continuous oily phase [W/O (or inverse) microemulsion] are obtained. Furthermore, the intermediate region between the OAV microemulsion phase and the W/O microemulsion phase is characterized by a bicontinuous microstructure in which the aqueous and oily microdomains are interconnected with each other [13, 14]. The presence of such a middle phase in the colloidal system was verified by literature data [15]. It was shown that the oil-water interfacial layer in the bicontinuous microstructure has a zero mean curvature (i.e., it is flat on the average), and this sponge-like microstructure is completely disor-... 

Neodysiherbaine 24 is a potent epileptogenic amino acid isolated from the marine sponge, Dysidea herbacea. Dysi-herbaine induces characteristic epilepsy-like seizures in mice and has been characterized to be the most potent epileptogenic excitatory amino acid yet identified. Its potent activity and unusual structure have attracted the interest of synthetic chemists, and this has resulted in the successful synthesis exploiting an asymmetric phase-transfer... 

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