Lamellar organizations

Fig. 5.12 Model for the lamellar organization in semicrystalline PE-PVCH diblocks crystallized from the ordered melt (Hamley et al. 1996b). The PE chains are folded with stems parallel to the lamellar interface. The convention for labelling of the axis system with respect to the shear direction is also indicated.

Lamellae obtained by direct crystallization from the melt into stable crystalline modifications at temperatures of 60-80 °C have thicknesses which differ only marginally from those of the fully mesomorphic samples. Such a finding, if confirmed, is highly relevant because it suggests that the lamellar organization depends only to a very limited extent on the particular crystal form while, to a first approximation, the pre-existing arrangement in the undercooled melt appears to play a key role. 

Figure 4.15 The structure of (a) complex [Gd(13)(N03)3 /2CH3CN /2H20 and (b) the head-to-tail stacking [29]. (Reprinted with permission from E. Terazzi, et al., Molecular control of macroscopic cubic, columnar, and lamellar organizations in luminescent lanthanide-containing thermotropic hquid crystals, Journal of the American Chemical Society, 127, no. 3, 888-903, 2005. 2005 American Chemical Society.)...

There may be biological sensitivities to the conformational presentation and sizing of the lipid formulation. For example the ability of antibodies to distinguish between lamellar organizing lipids and hexagonal-phase lipids are known and may form the basis for certain types of autoimmune dysfunction. Biological factors such as reticuloendothelial cell recognition of particles provide further impetus for control of the particle size and stability. 

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.

Nikundiwe AM, Bjaalie JG, Brodal P (1994) Lamellar organization of pontocerebellar neuronal populations. A multi-tracer and 3-D computer reconstruction study in the cat. Eur. J. Neurosci, 6, 173-186. 

Deniau JM, Chevalier G (1992) The lamellar organization of the rat substantia nigra pars reticulata distribution of projection neurons. Neuroscience, 46, 361-377. 

Copolymers with poly(butylacrylate) coil present lamellar organization. PPV lamellae have been observed with a wide range of coil fraction. Furthermore the distance between lamellae, increases when the coil volume fraction increases (Figure 4). 

The obtained copolymers exhibit a short range lamellar organization, with formation of PTV pellets with a width corresponding to a double layer of PTV. 

The crystalline lamellar organization of PP was clearly observed in the PP dominant matrix of the undrawn TPV. The TEM images of the drawn TPV sample indicated that the dispersed EPDM domains (dark portion in the image) are highly elongated along the extension direction, and the drawn process promotes a rather heterogeneous deformation in the matrix (Fig. 8.15). It should be noted here that the PP dominant matrix and the dispersed EPDM domains were completely bonded, and the interfacial separation between the matrix and the EPDM domains was not observed in the drawn TPV samples. 

Figure 12 Cryo-transmission electron micrographs of vitrified thin films of lamellar phase (brine 0.5 M-SDS 9%-pentanol 7%). Dark lines correspond to the contrast produced by the surfactant membranes. Micrographs a-c display a lamellar order with a variable characteristic distance, which is interpreted as the sign of strong fluctuations of the membranes. Micrograph d displays a disorganized structure that could be due to a modification of the labile lamellar organization by shear or during specimen preparation. Bar = 100 nm. (From Ref. 136.)...

This type of material often has quite high solid-mesophase temperatures and is insoluble in most organic solvents. These types of polymers are usually nematic, reasonably thermally stable and have Tg temperatures above 0°C. de Gennes has predicted that for type polymers smectic phases should be obtained if the flexible segments are of equal length allowing lamellar organization. 

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... 

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