Lamellar packing

In addition, data obtained from infrared, thermal, and fluorescence spectroscopic studies of the outermost layer of skin, stratum corneum (SC), and its components imply enhancer-improved permeation of solutes through the SC is associated with alterations involving the hydrocarbon chains of the SC lipid components. Data obtained from electron microscopy and x-ray diffraction reveals that the disordering of the lamellar packing is also an important mechanism for increased permeation of drugs induced by penetration enhancers (for a recent review, see Ref. 206). 

Variation of v. The last mixed micelle case studied were mixtures in which the volume of the hydrophobic tails was varied by mixing monoalkyl and dialkyl cationic surfactants (DTAB/DDAB). The aggregate structures found as a function of composition are detailed in Table IV. TTiey range from lamellar packed liquid... 

Figure 1 Schematic presentation of the skin barrier (stratum corneum). The lipids are organized in crystalline lamellar packing. The repeat distances (d) of the two lamellar phases are 6 and 13 nm, respectively. 

Crystals of most polar lipids can swell in the presence of water. The corresponding phases, gel-phases, with lamellarly packed lipid, and water layers, are sometimes thermodynamically stable (Larsson, 1994, p. 41). Also, the hydrocarbon chain packing of gel-phases usually show some axial rotational disorder. The alkyl chain cross-sectional area is close to 20 A2 in a plane perpendicular... 

Figure 5.1 illustrates the calculated structure of the DCNDBQT molecule. The thiophene units as well as the alkyl chains are mostly aligned in the plane, which would allow good lamellar packing. 

Figure 13.13. Lamellar packing of poly(3-alkyllhiophenes), Reproduced from ref. 74 by kind permission of American Chemical...

Figure 3. Lamellar packing model for polypeptide containing rod-coil diblock copolymers (A) Model for polybuta-diene-b-PBLG diblock copolymer in which the PBLG chains fold in the lamellar layer and adopt hexagonal packing. This corresponds to a SmB mesophase [9]. (B) Model for amphiphilic polypeptide diblock copolymer. Note that the rods are tilted relative the lamella layer normal while maintaining hexagonal close packing with a constant domain D independent of tilt angle.

Small-angle x-ray scattering (SAXS) provides information on packing and lamellar thickness [5,33]. The scattering maxima of the SAXS intensity profile of nanocomposites were found to be less defined than that of pure PP, indicating that the lamellar packing of PP became less regular in the presence of CNTs. Furthermore, CNTs led to an increase of lamellar thickness. The lamellar thickness of PP increased from 14.3 to 17.5-18.7nm in the presence of PP-y-MWCNTs [33]. 

A more detailed interpretation of the internal structure of the PODMA domains is possible based on WAXS data for a semi-crystalhne block copolymer (Lam-20 nm) measured at room temperature using a Bruker D500 system (Fig. 12.8). Data for polystyrene and semi-crystalline PODMA homopolymers are shown for comparison. It is obvious that the scattering curve for the microphase-separated block copolymer can be interpreted as a superposition of contributions originating from both individual components. The first two peaks (1 32) at q 2.1 nm and q 4.3 nm indicate the nanophase separation and the lamellar packing of main and side chains in semi-crystalline... 

For instance, the two allotropic forms of carbon, such as diamond, and graphite, owing to their different space lattice structure exhibit different densities. Actually, diamond owing to its closely packed cubic structure has a specific gravity of 3.512 while the graphite with its loosely hexagonal lamellar packed structure has specific gravity 2.230. 

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