Study of Crystal Morphology

Schematic diagram of a 1,4-polybutadiene crystal. The fold length is U and is approximately 3 butadiene units. The stem length corresponds to 15 monomer units. The crystal thickness is obtained from this value and the x-ray determined inclination angle of 114 (Schilling, F. C. Bovey, F. A. Tseng, S. Woodward, A. E. Macromolecules, 1983, 16, 808). 

By comparison of observed and theoretically calculated spectra it can be shown that these carbons are involved in gauche-trans conformational jumps of the C-D bond through a dihedral angle of 103% and from the correlation times as a function of temperature an activation energy of 5.8 kcal/mol is found. Several seemingly plausible motional models are excluded by these results, but the data agree with models proposed by Helfand (21,22) for motion about three bonds. 

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Additional information comes fixim a high-resolution transmission electron microscopy study of crystal morphology by Masse et al. [272]. From dark-field imaging crystallinity is estimated to be 50% in a film drawn to a ratio of 8-9. The aspect ratio of the crystallites is near 1.0 and their diameter is approximately 50 A. This value is considerably lower than the x-ray based value of 120 A, quoted above. The morphology is characterized as micellar , a network of oriented fibrils. 

Electron Microscopy can be used for resolution of smaller objects the practical limit of resolution being a few angstrom units. Electron Microscopy has been used in the study of the morphology of crystalline polymers. The usual techniques of replication, heavy-metal shadowing, and solvent etching are widely used. The direct observation of thin specimens, like polymer single crystals, is also possible and permits the observation of the electron-diffraction pattern of some specimen area, which is invaluable for... 

These effects have proved important in improving the methods available for resolution of enantiomers by crystallization (267). Furthermore, by studies of the morphological changes induced, one may determine the faces at which the impurities are dominantly attached (270,271). Then, in suitable systems, it is possible to determine the absolute configuration of a polar crystal if one knows that of the impurity (272), or to determine that of the impurity if one knows the structure of the centrosymmetric crystal with which it interacts (270). 

Utilized selective anisotropic solvent adsorption on specific crystal faces to favour the growth of morphologically polar crystals. Some additional reports of the study of crystal modification and nonlinear optical activity include those on anhydrous and hydrated sodium / -nitrophenolate (Brahadeeswaran et al. 1999), derivatives of 2-benzylideneindan-l,3-dione (Matsushima et al. 1992), straight-chain carbamyl compounds (Francis and Tiers 1992), benzophenone derivatives (Terao et al. 1990), a 1,3-dithiole derivative (Nakatsu et al. 1990), o -[(4 -methoxyphenyl)methylene]-4-nitro-benzene-acetonitrile (Oliver et al. 1990) and so-called lambda shaped molecules (Yamamoto et al. 1992). Hall et al. (1988) followed the thermal conversion of the centrosymmetric P2 /c) form of 2,3-dichloroquinazirin to the non-centrosymmetric Pc form by monitoring the development of an SHG signal. Consistent with the earlier observation, the centrosymmetric form was obtained under equilibrium conditions, while the non-centrosymmetric one could be obtained under more kinetic conditions. 

Clydesdale, G., Roberts, K. J. and Docherty, R. (1994fl). Computational studies of the morphology of molecular crystals through solid-state intermolecular force... 

Simulation can also be applied to longer length-scale phenomena. Examples include attempts to model the structural and mechanical properties of catalyst pellets, the mesopore structure of particle aggregates and phenomenological studies of crystallization. Here I mention just two examples, studies of crystallite morphology and quantitation of the effect of pore blockages on effective sorption capacities. 

Malkin, A.J. Kuznetsov, Y.G. Glantz, W. McPherson, A. Atomic force microscopy studies of surface morphology and growth kinetics in thaumatin crystallization. J. Phys. Chem. 1996, 100 (28), 11,736-11,743. 

To be of maximum benefit in studies of crystallization and morphology, monodisperse compounds with chains long enough to fold must be synthesized. Thus... 

Sauer, B.B. McLean, R.S. AFM and x-ray studies of crystal and ionic domain morphology in poly(ethylene-co-methacrylic acid) ionomers. Macromolecules 2000, 33, 7939. 

Interference microscopy as a tool of choice for investigating the role of crystal morphology in diffusion studies... 

Some of fhe Cryo-TEM and Cryo-HRTEM applications in polymer materials are (i) studies of crystal transformation, for example, the nucleation process and shape of crystals in lamellar crystals of polybutene-1 [74] (ii) studies of the morphology of several materials, such as polypeptides... 

Titania-supported vanadia catalysts have been widely used in the selective catalytic reduction (SCR) of nitric oxide by ammonia (1, 2). In an attempt to improve the catalytic performance, many researchers in recent years have used different preparation methods to examine the structure-activity relationship in this system. For example, Ozkan et al (3) used different temperature-programmed methods to obtain vanadia particles exposing different crystal planes to study the effect of crystal morphology. Nickl et al (4) deposited vanadia on titania by the vapor deposition of vanadyl alkoxide instead of the conventional impregnation technique. Other workers have focused on the synthesis of titania by alternative methods in attempts to increase the surface area or improve its porosity. Ciambelli et al (5) used laser-activated pyrolysis to produce non-porous titania powders in the anatase phase with high specific surface area and uniform particle size. Solar et al have stabilized titania by depositing it onto silica (6). In fact, the new SCR catalyst developed by W. R. Grace Co.-Conn., SYNOX , is based on a titania/silica support (7). 

Recent studies in supramolecular chemistry revealed that spontaneous separation of enantiomers is a phenomenon coinmonly observed in many phases, from the crystalline state to a dilute solution. Starting with early studies of the morphology of chiral crystals by optical microsco-... 

Electron-microscopy studies of the morphology of spherulites grown from the melt revealed that they were made up of stacks of lamellae of thicknesses quite similar to those of the lamellae crystallized from dilute solutions (Fischer 1957). Since the level of crystallinity of the spherulites was considerably less than 100%, it had to be concluded that the lamellae were separated by an amorphous component, often of similar thickness to the crystalline lamellae, producing characteristic X-ray-diffraction signatures of an amorphous component. 

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