Oriented lamellae

Figure 15 Morphological map of linear polyethylene fractions. Plot of molecular weight against crystallization temperature. The types of supermolecular structures are represented by symbols. Patterns a, b and c represent spherulitic structures with deteriorating order from a to c. Patterns g and d represent rods or sheet-like structures whose breadth is comparable to their length g or display a different aspect ratio d. Pattern h represents randomly oriented lamellae. Neither h nor g patterns have azimuthal dependence of the scattering. Reproduced with permission from Ref. [223]. Copyright 1981 American Chemical Society. (See Ref. [223] for full details.) Note the pattern a is actually located as o in the figure this was an error on the original.

If the structural entities are lamellae, Eq. (8.80) describes an ensemble of perfectly oriented but uncorrelated layers. Inversion of the Lorentz correction yields the scattering curve of the isotropic material I (5) = I (s) / (2ns2). On the other hand, a scattering pattern of highly oriented lamellae or cylinders is readily converted into the ID scattering intensity /, (53) by ID projection onto the fiber direction (p. 136, Eq. (8.56)). The model for the ID intensity, Eq. (8.80), has three parameters Ap, dc, and <7C. For the nonlinear regression it is important to transform to a parameter set with little parameter-parameter correlation Ap, dc, and oc/dc. When applied to raw scattering data, additionally the deviation of the real from the ideal two-phase system must be considered in an extended model function (cf. p. 124). 

The viscoelastic effects on the morphology and dynamics of microphase separation of diblock copolymers was simulated by Huo et al. [ 126] based on Tanaka s viscoelastic model [127] in the presence and absence of additional thermal noise. Their results indicate that for

bulk modulus of both blocks, the area fraction of the A-rich phase remains constant during the microphase separation process. For each block randomly oriented lamellae are preferred. 

Figure 18a,b displays SFM images of SV films that have been prepared from chloroform and from toluene solutions, respectively. The mixed pattern of featureless areas and round-shaped stripes in Fig. 18a can be identified as in-plane lamella and perpendicular-oriented lamellae, respectively. The microstructure prepared from toluene solutions (Fig. 18b) is attributed to P2VP micelles surrounded by the PS shell. The micelle morphology is a result of the SV self-assembly in a selective solvent [119], We have made use of this morphological difference to study the microstructure response to solvent uptake by block copolymer films. 

Deformed crystals. If a semi-crystalline polymer is deformed while undergoing crystallization, oriented lamellae form instead of spherulites. 

Semicrystalline polymers may crystallize from solution, as well as from the melt, in the form of chain folded lamellar crystals. The high spatial resolution of ATM enables one to assess lamellar thicknesses from images of these lamellar crystals in edge-on and flat-on orientation. As discussed in this section, images of flat-on oriented lamellae are particularly suitable for a quantitative determination of lamellar thicknesses. 

Under the condition of fibre symmetry signals in the pattern vertical to the tensile direction report highly oriented lamellae or lamellar fragments in tensile direction. This final pattern remains mainly constant also during further heating to about 160 °C (below the melting point) under load as well as unloaded. 

Other types of crystalline physical structures can be observed if crystallization occurs under stress (for example, under shear stress during processing). In this case, a continuous series of crystallization nucleation centers is formed by the induction of order along the lines of flow. A row structure of oriented lamellae is consequently produced. These row structures are related to the shish-kebab structures shown in Figure 5-27. 

Figure 3.1 shows schematic diagram representing lamellar crystal. The lamellar crystals (assemblies of folded chains) of different length can be either adjacent to each other or separated from each other by amorphous regions. Amorphous regions are also present between lengthwise oriented lamellae. Lamellae are connected by chains called tie molecules. 

The melt-spun poly(3-hydroxybutyrate) fibers contained boron nitride as nucleating agent. These fibers had longitudinally oriented lamellae rather than spheruhtic stmc-tures. Fibers contained domains of highly oriented molecules between crystallites. ... 

Figure 13.4 shows the difference in the SAXS pattern between crystallization rmder the quiescent conditions and the crystallization when shear is present. Under the quiescent conditions there is no anisotropy in the scattering pattern, but shear causes formation of orientation peak in the flow direction. This orientation leads to formation of oriented lamellae. The SAXS overall crystallinities of PCL are considerably higher than the DSC crystalhni-ties, most likely due to the contribution in SAXS of ctystalhne-amorphous transition layers. ... 

In block copolymers with lamellar morphology, mechanical properties and deformation structures vary with the orientation of the lamellae with respect to the direction of applied load. When the material is loaded in a perpendicular direction to the lamellar orientation, lamellae are folded in a fish-bone-like arrangement (57). Such a lamellar folding in a solution cast film of an SBS triblock copolymer is shown in Figure 20 (58). 

The subject is probably best advanced for polymers in contact with glass fibres and certain platy particles such as sheet silicates. As well as acting as nucleants, this type of material can alter the type of crystal structure present. Thus, it is now well established that glass-fibre surfaces can lead to trans-crystallinity. This is the growth of radially oriented lamellae extending for a few hundred micrometres from the fibre surface. This topic has been discussed in detail by Thomason [88]. Transcrystallinity is also discussed in Chapter 8 of this work. 

Crystals of ivory nut D-mannan have been grown on microfibrils from Valonia sp. cellulose. These crystals were in the form of perpendicularly orientated lamellae with widths of ca. 10 A as revealed by electron microscopy. The structure has been designated a shish-kebab type structure. Precipitation of the D-mannan on beaten softwood pulp fragments also gave shish-kebab type structures, indicating that the cellulosic fibre cell wall is a good substrate for orientated crystallization of D-mannan. 

In contrast to amorphous polymers, the structural details of semicrystalline polymers can also be visualized using diffraction phenomena (X-ray scattering or electron diffraction in electron microscopes). Depending on the processing, several other special semicrystalline morphologies are possible, such as shish kebab structures, oriented lamellae, microfibers, or spiral lamellae for details see Chapter 2 in Part 11. 

In particular, epitaxial effects can appear at the interfaces. Figure 4.9 shows an HDPE/rubber blend with oriented lamellae perpendicular to the boundaries of the rubber particles. However, such an arrangement of oriented lamellae also appears under shear forces (such as in an extruder). 

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