Lamellar organization, effect crystallization

Fig. 7. Schematic diagram showing the effect of cooling rate on the lamellar organization of TAG and the t,. T is the initial temperature and is the isothermal crystallization temperature.

The dimeric A(LS)2 structure was found remarkably effective even in the case where the unit A is a ionic moiety, such as viologen in 54 [78], or a strongly self-associating group, such as the NAf -disubstituted 3,4,9,10-perylenetetracarboxylic diimide core in 55 [79]. It was foimd that 54 forms a stable gel only in 1-butanol at low concentration (below 1 wt/vol %) of which the CD spectnun displayed the features typical of a chiral, clockwise aggregation of the gelator molecules. X-ray diffraction patterns of the xero-gel of 54 were similar to those of the neat crystal obtained from ethanol. They indicated the formation of a lamellar organization with an interlayer distance of 4.96 nm. The molecules 54 were proposed to exist in an extended conformation in the gel state and to be tilted relative to the normal of the... 

Orientation affeets the permeability of polyethylene by changing its degree of crystallinity, lamellar organization, and molecular constraints. Strain-induced crystallization may increase the degree of crystallinity, while noncrystalline regions become better paeked as a function of orientation [47,48], both of which reduce the free volume of the system and hence reduce its permeability. Not withstanding, the effects of orientation are complex, and contradictory results have been reported [49]. 

Amphiphilic molecules such as lipids have an extremely low solubility in water and tend to self-associate and form lyotropic liquid crystals [1] if their monomer concentration in aqueous surroundings exceeds a critical value (the critical monomer concentration, (CMC), [2]). This self-organization is due to the hydrophobic effect [2], It leads to the formation of micro- and mesoscopic structures, among them micellar, hexagonal, lamellar and cubic phases [3] and the respective transitions between them. ... 

Dibenzylidene sorbitol exists in the form of fibrils and usually acts as an effective nucleating agent to facilitate crystallization of poly-(olefin)s during manufacturing (12). In particular, when the dibenzylidene sorbitol concentration reaches a critical value, the fibrils will self-organize into a three-dimensional network when there is a decrease of temperature, but before crystallization takes place. The network of the fibrils may facilitate the subsequent process of nu-cleation and crystallization growth. An oriented deformation of the dibenzylidene sorbitol network could act as a template for anisotropic crystallization of PP, which then results in a high lamellar orientation level. 

In addition to their lyotropic properties, Hpids can also behave as thermotropic liquid crystals in a similar fashion to the rod-like liquid crystal molecules described in Chapter 2. In aqueous solution, the primary organization of the lipid phase is lyotropic however, the internal structural organization of the bilayer will vary as a function of temperature. In thinking about these thermotropic Hpid phases, it is helpful to consider the lipid to be in the lamellar phase, then to vary the temperature of this phase and look at the effects of temperature on molecular ordering within the bilayer. Lyotropic organization itself is also dependent on temperature, but more weakly so. For the following discussion, assume that the Hpids are organized in a lamellar phase composed of stacked Hpid bilayers. 

---