Lamellar orientation

GROWTH AS COMPOSITE. EACH ORIGINAL LAMELLAR ORIENTATION IS MAINTAINED... 

Spontaneous aggregation of lipids — double chain amphiphiles — in aqueous medium (smectic phase). Hydrophobic core of long alkyl chains (lamellar orientation) is covered by hydrophilic headgroups (see Figs. 2, 15). 

In any layer-like arrangement of stiff crystalline and soft amorphous regions a strong influence of lamellar orientation with respect to the principal stress direction is observed. The most compliant arrangement is shown in... 

The preferred orientation of the matrix parallel to the fiber bundles appears to be affected by processing pressure during pyrolysis (400-500°C), becoming more random as impregnation pressures are increased. Even transverse lamellar orientations can result (Figure lb). Because pitch mesophase coalescence has been inhibited by the pressure, grains of matrix may be transversely oriented to the filaments. 

Fig. 11 Lamellar orientation in the ultrathin films a many interfaces are created if the edge-on orientation is adapted h is the film thickness b few interfaces are created in the flat-on orientation...

The particle morphology of the talc materials from the various vendors was investigated with scanning electron microscopy. All the talc materials were found to be flaky and plate-like in appearance as shown in Figures 6-8. When viewed at 3000x, the lamellar orientation of the plates is evident, as well as the presence of smaller crystals growing on the surface. 

Note that t8 in Eq. (207) is measured in units of the total observation time (which was typically chosen as [325] tobs = 5000 MCS/monomer), so ts is normalized between zero and unity. For T > Tmst, we expect ft < >g(t)dt = J other hand, for T < Tmst when a lamellar orientation is essentially frozen-in over the time interval tobs,... 

Each stack of parallel lamellae yields a bundle of parallel microfibrils (Figure 2) that differ a little in average draw ratio from the adjacent bundle (fibril) as a consequence of slightly different micronecking conditions caused by the local variation in lamellar orientation and orientation of the microneck-... 

At the initial stage of extrusion, the parallel lamellae rotated or tilted to form inclined lamellar stacks and the perpendicular lamellae tended to increase in number. The perpendicular lamellae increased up to around EDR 4.6 in the second stage where the inclined lamellae started to transform steadily into fibrils. This perpendicular lamellar orientation characteristic for extrusion drawing is likely caused by the compressive force applied for extrusion. Such an effect of the compressive force has bran more clearly observed in our previous study of crystalline-state extrusion of polyethylene single crystal powder (21). 

Another possible link between the two schools may be established by observations of the X-ray photographs published by several workers (Refs. 22, 34, 37, 48, 59-62) which show indications, at least, of a loss of crystallinity with plastic strain. Jajima and Seto measured the change in lamellar orientation and c-axis orientation on redrawing oriented HDPE. They commented that the WAXS scattering from specimens experiencing a further tensile strain in the draw direction became too difluse to measure... 

Keywords solid-state extrusion, roll-drawing, orientation, crystallinity, mechanical properties, a-relaxation, solid-state deformation, compression ratio, morphology, tie molecules, lamellar orientation, laminate theory, fibrillar structure, rolling. 

To correlate the macroscopic properties and the structural changes occurring dtuing deformation the orientation functions evaluated from Eqs. (20 a—c) have been plotted in dependence of strain in Fig. 14. Onc and Asada have discussed in detail the expected changes of infrared dichroism and orientation functions due to the different molecular processes of lamellar orientation and chain unfolding. 

Polymeric spherulites have been known (14, 15) to grow with a radially directed and non-crystallographically branched lamellar orientation. The molecules are generally perpendicular to the lamellar... 

In addition, there is a high density of short-range defects in these regions. The strong curvature and sharp jumps in lamellar orientation reveal a high density of line and wall defects. The formation of these regions is probably due to defect interactions and defect pinning, as discussed in Section III.D. 

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