Mesophases defects

The mesophase defect textures exhibited by 47 were typical of those normally found for a chiral nematic phase, except they were only revealed upon annealing, which is probably a function of the viscosity of the material. Thus the sample was annealed just below the clearing point. After 24 h, large areas of the preparation evolved to show fingerprint defects and the Grandjean plane... 

These authors have used the technique of lamellar decoration [76] which enables detailed assessment of cheu-acteristic mesophase defects and texture on a much finer scale than previously possible with conventional electron-microscopy preparations. The defects and texture existing in the polymer melt state are first retained by thermal quenching of the polymer fluid to room temperature. The glassy LCP film is then annealed above its glass transition, but below the melting point. Crystalline lamellae grow perpendicular to the local chain axis and effectively decorate the molecular director... 

We will then examine other flexible polymer crystallization instances which may be interpreted, at least qualitatively, in terms of the bundle model. We will concentrate on crystallization occurring through metastable mesophases which develop by quenching polymers like isotactic polypropylene, syndiotactic polypropylene etc. In principle also hexagonal crystallization of highly defective polymers, and order developing in some microphase-separated copolymer systems could be discussed in a similar perspective but these two areas will be treated in future work. A comparison between the bundle approach and pertinent results of selected molecular simulation approaches follows. 

Hexagonal mesophases can be recognized by their typical fan-shape texture (Fig. 7a). Lamellar mesophases typically show oily streaks with inserted maltese crosses (Fig. 7b). The latter are due to defects, called confocal domains, that arise from a concentric rearrangement of plane layers. In some lamellar mesophases these defects prevail. Hence no oily streaks occur but maltese crosses are the dominant texture (Fig. 7c). 

Mesophase with a three-dimensional spatial distribution of helical director axes leading to frustrated structures with defects arranged on a lattice with cubic symmetry and lattice constants of the order of the wavelength of visible light. 

Defect-stabilised mesophase created when a smectic A mesophase is subjected to a twist or bend distortion. 

The case is quite different for copolymers 5-5. Here, the transformation from a nematic mesophase to a smectic one is a result of gradual decrease in flexibility of the main chain. As seen from Fig. 22a, b, the plots of Tcl and AHC, on composition have a minimum. This could be the consequence of a more defective packing of side groups due to incorporation within the backbone of units of different chemical nature. A sharp rise in AHC, indicating transformation to a smectic mesophase type, begins only at... 

T extures of lyotropic mesophases have been the object of numerous observations by optical (1,2,3) and electronic (4, 5, 6,7) microscopy. Except for the pioneering work of Lehmann (1) and Friedel (2) who intended to identify the various kinds of defects which constitute the textures, the purpose of these observations was to recognize the different existing phases—lamellar, hexagonal (or in the soaps language neat phase, median phase, etc.)—in correlation with x-ray data. 

T. Rades and C. C. Muller-Goymann, Electron and light microscopical investigation of defect structures in mesophases of pharmaceutical substances, Colloid Polym. Sci., 275 (1997) 1169-1178. 

Hubbard PL, McGrath KM, Callaghan PT (2005) A study of anisotropic water self-diffusion and defects in the lamellar mesophase. Langmuir 21(10) 4340-4346... 

Henon, S. Meunier, J. Phase transitions in Gibbs films star texture defects in tilted mesophases, J. Chem. Phys. 1993, 98, 9148. 

Thus, these mesostructures are predominantly lamellar, and identified as conventional (parabolic) lamellar phases, although they may in fact be hyperbolic. Indeed, unless v/al is exactly unity, a planar interface (lamellar mesophase) incurs a bending energy cost hyperbolic sponge monolayers or bilayers or mesh monolayer mesophases are favoured if v/al differs from unity. It is likely then that many "lamellar"" phases in fact adopt a hyperbolic geometry. Careful neutron-scattering studies of a lamellar phase have revealed the presence of a large number of hyperbolic "defects" (pores within the bilayers) in one case [16]. (An example of this mis-identification of hyperbolic phases in block copolymers is discussed in section 4.10.)... 

Long-wavelength deformations/fluctuations in block copolymers are important for several reasons. First, they are responsible for the mechanical properties of a block copolymer mesophase. Second, they determine the degree of long-range order and the effects of defects in the ordered phases. Finally, they are responsible for certain novel long-wavelength instabilities. 

The A1 bearing phase, when heated up to 750°C prior to direct cooling (sample A), showed a surface area of up to 1093 mVg (Table 1) and a substantial pore volume of 0.95 cmVg [4], suggesting a better structuration of the mesophase upon a more complete healing of internal or surface defects. XPS data proved undoubtedly that the Ca ions in sample A were on the exchange positions of the Al-bearing silica walls [4]. 

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