Growth anisotropy

In this category, the shapes that cannot be explained by the selective binding model tend to maximize the surface area of the most stable 111 crystal face. In most cases this simply involves a reverse of the growth anisotropy that is observed with the selective binding model. In the case of nanoprisms (and nanoplates), flat 111 faces are favoured but there is clearly another factor at work giving rise to the typical flat morphology of these nanostructures. 

This preparation is unusual as one would expect PVP to selectively bind to less stable crystal faces of single crystals of silver, such as the 100 face, to generate nanocubes. Indeed, in this reaction silver nanocubes are the initial product as expected, but by continuing the reaction, after nanocubes have already formed, further growth leads to cuboctahedra, truncated octahedra and then finally to octahedra, see Figure 11.36. It is quite uncertain why the growth anisotropy switches in this manner. 

Schiessl K, Kausika S, Southam P, Bush M, Sablowski R. JAGGED controls growth anisotropy between cell size and cell cycle during plant organogenesis. Curr Biol 2012 22(19) 1739 6. 

Baskin T.I., Meekes H.T.H.M., Liang B.M., and Sharp R.E. 1999. Regulation of growth anisotropy in well-watered and water-stressed maize roots. II. Role of cortical microtubules and cellulose microfibrils. Plant Physiol 119 681-692. 

Experimental estimation of growth rate anisotropy. Crystal growth anisotropy is a complex phenomenon which depends on many experimental conditions. However, from a practical point of view it is very important to employ this factor in crystal production techniques since it may help to control the crystal morphology and to explain better the crystal growth phenomena. 

The phenomena described in this chapter centered on interfacial disorder, sometimes liquid like disorder, of both a thermodynamic and dynamic origin, and the redistribution of both the disordered material and impurities at solid-liquid interfaces. Because of the change in the surface structure created by both surface roughening and surface melting, they have a profound influence on the local attachment kinetics, and ultimately on pattern formation in ice crystals. We have a clear picture of several issues, namely (i) that roughening is a crucial aspect of growth anisotropy, and (ii) that inter-facially melted water at subfreezing interfaces is mobile and responds in a thermodynamically consistent and predictable manner. Less clear however are a number of other issues as discussed below. 

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