Epitaxial nucleation

Epitaxial nucleation, with nonchemical technology 340 Equilibrium phosphate concentration theory 472... 

McPherson, A. and Shlichta, P. (1988). Heterogeneous and epitaxial nucleation of protein crystals on mineral surfaces. Science 239, 385-387. 

Rodriguez-Hornedo, N., Lechuga-Ballesteros, D., and Wu, H.-J. (1992). Phase transition and hetero-geneous/epitaxial nucleation of hydrated and anhydrous theophylline cryiibtUs J. Pharm., 85 149-162. 

McPherson, A., and Shlichta, P. J. Facilitation of the growth of protein crystals by heterogeneous/epitaxial nucleation. J. Crystal Growth 85, 206-214 (1987). 

Fig. 4.1 (a) Temperature scan recorded on a PET film using a heatable AFM probe [1], (b) TM-AFM images captured during the crystallization of an elastomeric PP film. The arrows point at homo-epitaxial nucleation events the subsequent growth of lamellar crystals proceeds with different rates. While lamellar patches 1 and 3 grow steadily, patch 2 remains dormant for at least 500 s before growing slowly. Reprinted with permission from [2], Copyright 2003. American Chemical Society... 

Rodriguez-Hornedo N, Lechuga-Ballesteros D, and Wu HJ. Phase Transition and Heterogeneous/epitaxial Nucleation of Hydrated and Anhydrous Theophylline Crystals. IntJPharm 1992 85 149-162. 

The maximum in catalytic activity observed for the multiphase region of the phase diagram necessarily arises from interactions between the separate phases. The bismuth rich and cerium rich solid solutions can readily form coherent interfaces at the phase boundaries due to the structural similarities between the two phases which can permit epitaxial nucleation and growth. A good lattice match exists between the [010] faces of the compounds, this match is displayed in Figure 6. We have also shown that regions of an [010] face of a Ce doped bismuth molybdate crystal resembles cerium molybdate compos tionally. This means that the interface between the two compounds need not have sharp composition gradients. It is structurally possible for the Bi-rich phase to possess a metal stiochiometry at the surface that matches that of the Ce-rich phase. 

The crystallisation from strained melt as for instance in a blown film or in the jet during fibre spinning produces a row nucleated structure. " Linear nuclei are formed parallel to the strain direction. They contain more or less extended polymer chains. Secondary epitaxial nucleation on the surface of such linear row nuclei produces folded chain lamellae which are oriented perpendicular to the strain (Fig. 6). In such a case the sample exhibits a high uniaxial orientation of chain axes in the strain direction with random orientation of the a- and b-axes perpendicular to it. If the growing lamellae exhibit a helical twist the chain orientation in the strain direction is very soon replaced by the orientation of the axis of maximum growth rate (b-axis in the case of polyethylene) perpendicular to the strain direction and a more random orientation of the remaining two axes (a- and c-axes in the case of polyethylene) with a maximum in the strain direction. Such a row nucleated structure has parallel cylindrical spherulites (cylindrites) as its basic supercrystalline element. 

Boron nitride was fonnd to produce epitaxial nucleation in PP. ... 

The repeating intervals of the phenyl and thiophene units in the TPCO chain approximately match the ionic lattice constant along the < 1 10>kci direction, 0.44 nm. This lattice matching causes the epitaxial nucleation and the growth of the needle crystals to be promoted by the intermolecular interaction due to the partly planar jt-conjugating structure of the thiophene block and also to their moderate molecular diffusion on the surface. 

Some water-softening (conditioning) units which are sold for domestic use are advertized as no saltwater conditioners. These units are reported to remove CaCOs from hard water by using a catalyst, which by epitaxial nucleation, and the reduction of pressure by virtue of a change in water velocity, converts the Ca(HC03)2 into CaCOs and CO2. These units are very attractive and are advertised to work with detergents but are not intended for use with soap. This can be interpreted to mean that the calcium ions are not removed from the water system and that a precipitate will form from the calcium salt of the fatty acid from the soap (Eq. 15.14). 

Furthermore, kinetic results from both small-angle X-ray scattering and DSC indicate that the crystallization mechanism is altered due to the silicate from that of homogeneous nucleation for the pure polymer to heterogeneous and epitaxial nucleation with the increase of the inorganic material. 

Haubruge HG, Daussin R, Jonas AM, Legras R, Wittmann JC, Lotz B. Epitaxial nucleation of poly (ethylene terephthalate) by talc, Structure at the lattice and lamellar scales. Macromolecules 2003 36 4452 456. 

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