Crystalline lamellar phases

The morphologies of various copolymers composed of polyethylene oxide), PEO, and poly (1,2-butylene oxide), PBut, were recently reviewed by Ryan et al. [61]. The corresponding phase diagrams of PEO-fr-PBut, PBut-fo-PEO-fo-PBut and PEO-fo-PBut-fo-PEO melts are depicted in Fig. 11. In all phase diagrams the semi-crystalline lamellar phase was not attained because of the copolymers low melting points. 

Analogous gel matrices of liquid crystalline lamellar phases can also be formed with nonionie mesogens, such as the combination of cetyl/stearyl alcohol and ethoxy-lated fatty alcohol, provided that the hydrophilic and lipophilic properties of the surfactant molecules are more or less balanced to favor the formation of lamellar structures. 

Fig. 5.25 Phase diagrams for PS-PEO diblocks in diethyl phthalate (Ciervais and Gallot 1973a), a selective solvent for PS. SEO-3 M = 34.7kgmol 59% PEO.This sample forms a non-crystalline lamellar phase (lam) and a lamellar crystalline phase (crystal). SEO-9 Ma - 75 kg mol-1, 70.5% PEO. This sample forms a non-crystalline hexagonal-packed cylinder phase (hex) and a crystal phase.

In the SC lipids form two crystalline lamellar phases.27 The mixture of both phases produces the optimal barrier to water loss from SC. The balance between the liquid crystalline and the solid crystal phases is determined by the degree of fatty acid unsaturation, the amount of water, and probably by other yet undiscovered factors. A pure liquid crystal system, produced by an all-unsaturated fatty acid mixture, allows a rapid water loss through the bilayers with a moderate barrier action. The solid system produced with an all-saturated fatty acid mixture causes an extreme water loss due to breaks in the solid crystal phase.6,23 Studies with mixtures prepared with isolated ceramides revealed that cholesterol and ceramides are very important for the formation of the lamellar phases, and the presence of ceramide 1 is crucial for the formation of the long-periodicity phase.27 The occurrence of dry skin associated with cold, dry weather for example, may result from an extensive, elevated level of skin lipids in the solid state. Therefore, a material that maintains a higher proportion of lipid in the liquid crystalline state may be an effective moisturizer.6... 

The Liquid Crystalline Lamellar Phase and Its Relevance to Real Food Systems... 

Shear-Induced Mesostructural Changes and Rheology of the Liquid Crystalline Lamellar Phase... 

The elasticity of multilamellar vesicles can be discussed in reference to that of emulsion droplets. The crystalline lamellar phase constituting the vesicles is characterized by two elastic moduli, one accounting for the compression of the smectic layers, B, and the second for the bending of the layers, K [80]. The combination has the dimension of a surface tension and plays the role of an effective surface tension when the lamellae undergo small deformations [80]. This result is valid for multilamellar vesicles of arbitrary shapes [81, 82]. Like for emulsion droplets, the quantity a/S is the energy scale that determines the cost of small deformations. 

A Unique Liquid-Crystalline Lamellar Phase Comprised of Mineral... 

Figure 1.89 Structure of dipalmitoyl L-a-phosphatidylcholine (DPPC) to illustrate the main molecular parameters and structural features that dictate the formation of crystalline lamellar phases of macromolecular lipid assemblies. Schematic representation of a phospholipid molecule is also show (inset).

J.-C.P. Gabriel, F. Camerel, B.J. Lematre, H. Desvaux, P. Davidson, P. Betail, Swollen liquid-crystalline lamellar phase based on extended solid-like sheets. Nature 413, 504-508 (2001)... 

SmBcr Da, X T(0) Crystalline lamellar phase with upright molecules and hexagonal lattice. True three-dimensional positional order. Soft crystal with small shear elastic modulus... 

Under irradiation at high doses (up to 10 MGy) the crystalline, lamellar phase also degrades. This causes a loss in crystallinity and strength [89]. 

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