Lamellar core

The thickness of PBS lamellar crystals depend on the crystallization temperature (Gan et al. 2001). The thickness of the crystalline lamellar core increases steadily and that of the amorphous layer decreases with increase of the crystallization temperature. But the total degree of crystallinity varies little with temperature. 

Polymer brushes are frequently discussed in literature. They are composed of a lamellar core and free chains forming a brush. If such material is included in composition and it diflfiises into its surface layers, it may form properties related to the properties of brush chains and this could be one option of material design having high reactivity towards some adhesive, or with non-reactive, antiblocking surface. It is also possible that such material may interact with other materials in the formulation and modify their properties. 

Micellar structure has been a subject of much discussion [104]. Early proposals for spherical [159] and lamellar [160] micelles may both have merit. A schematic of a spherical micelle and a unilamellar vesicle is shown in Fig. Xni-11. In addition to the most common spherical micelles, scattering and microscopy experiments have shown the existence of rodlike [161, 162], disklike [163], threadlike [132] and even quadmple-helix [164] structures. Lattice models (see Fig. XIII-12) by Leermakers and Scheutjens have confirmed and characterized the properties of spherical and membrane like micelles [165]. Similar analyses exist for micelles formed by diblock copolymers in a selective solvent [166]. Other shapes proposed include ellipsoidal [167] and a sphere-to-cylinder transition [168]. Fluorescence depolarization and NMR studies both point to a rather fluid micellar core consistent with the disorder implied by Fig. Xm-12. 

Composites need not be made of fibres. Plywood is a lamellar composite, giving a material with uniform properties in the plane of the sheet (unlike the wood from which it is made). Sheets of GFRP or of CFRP are laminated together, for the same reason. And sandwich panels - composites made of stiff skins with a low-density core - achieve special properties by combining, in a sheet, the best features of two very different components. 

Similarly, in studies of lamellar interfaces the calculations using the central-force potentials predict correctly the order of energies for different interfaces but their ratios cannot be determined since the energy of the ordered twin is unphysically low, similarly as that of the SISF. Notwithstcinding, the situation is more complex in the case of interfaces. It has been demonstrated that the atomic structure of an ordered twin with APB type displacement is not predicted correctly in the framework of central-forces and that it is the formation of strong Ti-Ti covalent bonds across the interface which dominates the structure. This character of bonding in TiAl is likely to be even more important in more complex interfaces and it cannot be excluded that it affects directly dislocation cores. 

In conclusion, it can be suggested that the lamellar spacing of miktoarm-star copolymers is controlled by two parameters (i) the molecular weight of the corresponding AB diblock, which also controls the segregation strength, and (ii) the functionality of the central core. 

Fig. 43 Plot of normalized lamellar long periods, Dn/Rg,m of (PS) -arm-(PI)M miktoarm-star copolymers (n = 1, 2, 4 and 16) divided by corresponding diblocks of same series, Di/Rg,u against respective star functionality, n. Normalization factor PgiM represents unperturbed radius of gyration of diblock consisting of one PS block, one PI block and average number of bonds linking these two arms through core. From [121]. Copyright 2003 American Chemical Society...

At concentrations above their aqueous solubility, the so-called c.m.c., low-molar-mass biosurfactants form micelles in the aqueous phase. Micelles are spherical or lamellar aggregates with a hydrophobic core and a hydrophilic outer surface. They are capable of solubilising nonpolar chemicals in their hydrophobic interior, and can thereby mobilise separate phase (liquid, solid or sorbed) hydrophobic organic compounds. The characteristics for the efficiency of (bio)surfactants are the extent of the reduction of the surface or interfacial tension, the c.m.c. as a measure of the concentration needed to bring about this reduction, and the molar solubilisation ratio MSR, which is the number of moles of a chemical solubilised per mole of surfactant in the form of micelles [96]. 

In general, if the chains are oriented by external forces, the melting temperature is increased [28]. Further, it has been known for a long time that complex, row-nucleated structures occur if polymer solutions or melts are crystallized in the presence of flow [29,30]. These so-called shish-kebabs (sketched in Fig. 1.6), consist of a central fiber core, shish, surrounded by lamellar crystalline structures, kebabs, periodically attached along the shish. 

The fiberlike crystalline structures (shish) are highly stable to the point that they can be superheated [31]. Therefore, it is believed that the core of the shish is formed by crystallization of completely stretched polymer chains. The kebabs are believed to be folded-chain lamellar structures. The direction of growth of the kebabs is normal to the shish. The chain ahgnment in the kebabs is believed to be parallel to the shish. Similar structures are obtained by crystalhzation in polymer melt films exposed to orientational deformation [32,33]. These two-dimensional shish-kebabs also consist of a central fiber, shish, and periodically attached linear kebabs, with growth direction normal to the shish. 

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