Growth of molecular crystals

In the last few years significant progress has been made toward transforming the growth of molecular crystals from an art to a science. The... 

To understand how additives can influence crystal growth, an understanding of the fundamental processes of crystal growth and nucleation is required. Hence, this chapter briefly covers some aspects of crystallization, and then discusses how the growth of molecular crystals can be controlled and modified by additive molecules. Finally, some discussion on the most recent developments in crystal growth science highlights possible future directions for... 

Zone-casting, originally developed for the oriented growth of molecular crystals, has been used to achieve large-scale alignment of nanoscale domains in microphase-separated BCPs. Kowalewski... 

CARTER ET AL. Growth of Molecular Crystals on Molecular Interfaces 187... 

R. Docherty, K. J. Roberts. Modeling the morphology of molecular crystals Applications to anthracene, biphenyl and B-succinic acid. J Cryst Growth 55 159, 1988. 

Paraffin crystalline waxes Apart from asphaltenes, a number of differing molecular weight paraffinic waxes are also present. These progressively crystallize at lowering temperatures (their respective pour points). These waxes increase friction and resistance to flow, so that the viscosity of the fuel is raised. This type of problem is controlled by the use of pour-point depressants (viscosity improvers), which limit the growth of the crystals at their nucleation sites within the fuel. They also have a dispersing effect. 

The other process is the transformation of an organic precursor into a continuous thin ceramic fiber. In the spinning process, polycarbosilane, a high molecular weight polymer containing Si and C, is obtained by thermal decomposition and polymerization of polydimethylsilane. The fiber thus produced consists of a mixture of P-SiC, carbon crystallite and SiO. The presence of carbon crystallite suppresses the growth of SiC crystals. Yajima and coworkers (Yajima et al., 1976, 1978, 1979) were the first to produce fine (10-30 pm in diameter), continuous and flexible fibers, which are commercialized with the trade name of Nicalon (Nippon Carbon Co.). 

Polymorphic structures of molecular crystals are different phases of a particular molecular entity. To understand the formation of those phases and relationships between them we make use of the classic tools of the Phase Rule, and of thermodynamics and kinetics. In this chapter we will review the thermodynamics in the context of its relevance to polymorphism and explore a number of areas in which it has proved useful in understanding the relationship between polymorphs and polymorphic behaviour. This will be followed by a summary of the role of kinetic factors in detecting the growth of polymorphic forms. We will then provide some guidelines for presenting and comparing the structural aspects of different polymorphic structures, with particular emphasis on those that are dominated by hydrogen bonds. 

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