Sheet-like morphology

The X-ray diffraction lines corresponding to Mg(OH)2 were distinctive. The basal line (001) was very broad, the prism line (110) was very sharp and the other lines hkl) were intermediate in breadth. This was interpreted as implying that Mg(OH)a crystallites adopt an exaggerated sheet-like morphology in this system (Urwongse Sorrell, 1980b). The (001) line... 

The reduction of permeability arises from the longer diffusive path that the penetrants must travel in the presence of the filler (layered silicate in the present case). A sheet-like morphology is particularly efficient as it maximizes the path length. The tortuosity factor (f or T depending on the symbology) is defined as the ratio of the actual distance (d ) that a penetrant must travel to the shortest distance (d) that it would have traveled in the absence of the layered silicate and is expressed in terms of the length (L), width (W)/ and volume fraction of the sheets ((j)). 

Many types of polymers self-organize into lamellar (sheet-like) morphologies. This includes, among others, semicrystalline polymers, symmetric linear AB diblock copolymers, and smectic main-chain liquid crystalline polymers. The characteristic cf the lamellar morphology is that there is a variation of the electron density in the direction normal to the lamellae. The spatial period of the variation can be large, of the order lO-lOOnm, so the scattering occurs principally at small scattering vectors. 

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.

The microstructuie of films of the ferrocene dendrimers electrochemically deposited on platinum wire working electrodes was examined by scanning electron microscopy (SEM). The SEM micrograph in Figure 7 corresponding to a film of the octanuclear dendrimer 2 shows a sheet-like compact morphology and exhibits small agglutinations and some porosity. 

Whatever the precursor, the formation of an intermediate solid phase was always observed. It can be inferred from X-ray diffraction (Fig. 9.2.7) and infrared spectroscopy that this intermediate phase shows a lamellar, incompletely ordered structure (turbostratic structure) built up with parallel and equidistant sheets like those involved in the lamellar structure of the well-crystallized hydroxides Ni(OH)2 or Co(OH)2, these sheets are disoriented with intercalation of polyol molecules and partial substitution of hydroxide ions by alkoxy ions (29). The dissolution of this solid phase, which acts as a reservoir for the M(I1) solvated species, controls the concentration of these species and then plays a significant role in the control of the nucleation of the metal particles and therefore of their final morphological characteristics. For instance, starting from cobalt or nickel hydroxide as precursor in ethylene glycol, the reaction proceeds according to the following scheme (8) ... 

The three clays used in this study have different morphologies. The montmorilIonite and kaolinite are typical sheet or plate-like clays, whereas the attapulgite exhibits a needle-like morphology ( ). 

Prominent exceptions are studies on the liquid crystal phase formation and self-assembly of two-dimensional disc- or sheet-like nanomaterials such as the organization of nanodiscs or nanoplatelets into nematic, smectic, or columnar morphologies [263-270] (see Fig. 2 for an example of the self-assembly of nanoclay in aqueous suspensions) or the synthesis of CuCl nanoplatelets from ionic liquid crystal precursors as described by Taubert and co-workers [271-273]. 

In general, it has been argued that tubular morphology is an expression of the chirality of the monomeric species, though there are a number of examples of non-chiral surfactants (such as the dimorpholinophospho-amidate 5) that have been shown to self-assemble into such structures.78,79 In some contradictory reports it is even argued that chirality is a requirement and that cylinders are in fact sheet-like structures that are curled.69... 

Ozkan et al. [47] studied the morphological aspects of unsupported vanadia catalysts. Two types of vanadia were prepared. The preparation procedures described above resulted in thick particles (V20s(a)) and thin, sheet-like particles (decomposition of ammonium metavanadate V20s(d)). V20s(a) contains relatively more... 

Geometrical constraints can also be applied on rectangular sheets. Indeed, thin sheets compressed at one edge to follow a periodic sinusoidal profile and free at the other, i.e. a curtain-like morphology (Fig. 8.3), develop a self-similar hierarchy of folds [6, 7]. We will now demonstrate a universal method based on a scaling approach to find the morphology of constrained thin sheets. 

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