Parallel lamellae sheet

The success of the model for the loss anisotropy led Owen and Ward to use equivalent assumptions to calculate the modulus anisotropy. The loss anisotropy calculations assume simple shear between the lamellae only, which for parallel lamellae sheet would imply that inter-lamellar shear is not activated when the tensile stress is applied along the initial draw direction i.e. parallel to the lamellar plane normals). A very appreciable fall in tensile modulus was. however, observed in this case, although as e.xpected by comparison with the corresponding loss factor in... 

Fig. 17. Low density polyethylene. Schematic morphology of drawn, rolled and annealed sheets (i) b-c sheet (ii) parallel lamellae sheet (Hi) et-b sheet.

An increase in annealing temperature causes rotation of lamellae about the h-axis until the basal planes are perpendicular to the original draw direction (parallel lamellae sheet). Further annealing causes further rotation so that the c-axis becomes perpendicular to the plane of the sheet a-b sheet). 

Figure 8.12 Schematic structure diagrams of mechanical loss spectra and 10 s isochronal creep moduli (a), (d) and (g) for be sheet (b), (e) and (h) for parallel lamellae sheet (c), (f) and (i) for ab sheet. P, interlamellar shear process Q, c-shear process (note absence of c-shear process in (f)) R, small-angle X-ray diagram, beam along X... 

The cornified cell envelope is the outermost layer of a corneocyte, and mainly consists of tightly bundled keratin filaments aligned parallel to the main face of the corneocyte. The envelope consists of both protein and lipid components in that the lipid is attached covalently to the protein envelope. The envelope lies adjacent to the interior surface of the plasma membrane. " The corneocyte protein envelope appears to play an important role in the structural assembly of the intercellular lipid lamellae of the stratum corneum. The corneocyte possesses a chemically bound lipid envelope comprised of A-co-hydroxyceramides, which are ester linked to the numerous glutamate side chains provided possibly by both the ot-helical conformation and p-sheet conformation of involucrin in the envelope protein matrix. In the absence of A-oo-hydro-xyceramides, the stratum corneum intercellular lipid lamellae were abnormal and permeability barrier function was disrupted. 

The most compliant directions, and thus those in which tan is a maximum, occur when the maximum resolved shear stress is parallel with the lamellar planes. An inter-lamellar shear mechanism is suggested, the mechanical anisotropy of the j relaxation being determined by the configuration of the lamellae, and not by the molecular orientation within the lamellae, which differs between annealed, a-c and b-c sheets. Differences in the magnitudes of the relaxation peaks for different types of specimen will depend on the spread of deviations from the mean angle of the lamellae, and on the lamellae in the annealed sheet being arranged in cones around the stretch direction rather than in flat layers. 

Studies of possible deformation mechanisms in drawn, rolled and annealed sheets have been made by Owen and Ward, as an extension of the model of Davies et a. for specimens having transverse isotropy. Because of the anneal involved in the production process c/c shear is a less important deformation mechanism in this form of material. If the lamellae exist as platelets of very large extent compared with the thickness of inter-lamellar material this latter could undergo only simple shear, with the shear direction parallel with the surface of the lamellae but if the platelets are effectively of infinite extent only in one direction then inter-lamellar material could deform when the platelets are subjected to a normal stress. The inter-lamellar material then undergoes pure shear. (Some consequences of this model have been discussed in Chapter 4.)... 

Amphiphilic molecules undergo a geometry-dependent rearrangement when aqueous phase is added, in order to mask the hydrophobic moieties from the polar aqueous enviromnent [2,7]. If an amphiphilic molecule has a cylindrical geometry (i.e., the cross-sectional area of polar and nonpolar moieties are approximately equal), adjacent molecules align parallel to each other to form a monolayer, which in turn arranges symmetrically with another monolayer to form a bilayer sheet called the lamella or lamellar (cubic) phase. 

Before developing a general expression for block copolymer electrothermodynamics, a simple model will help in understanding the forces at work. Consider the material formed from alternating sheets of material illustrated in Fig. 20. In the first case the lamellae lie in the plane of the capacitor plates, and in the second, perpendicular to the plates. These two cases are referred to as parallel and perpendicular orientations, respectively. The electrostatic contribution to the thermodynamic potential is calculated next for these two cases. 

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