Introduction
Crystallography concerns both the internal and external form of a crystal [1]. Crystalline solids are an essential part of our modern technological environment, being important components of pharmaceuticals, foods, cosmetics, metals, ceramics and plastics. The process of crystallisation is used both for purification and as a separation process for the production of particular materials.
The customary way of forming crystals through suspension processes always relies on the usage of solvents in which solution phase is used as a media for homogenisation of the starting composition as well as enabling the molecular assembly processes. These solvents have been found to influence the crystallisation processes to the point of altering both the nucleation rate and the crystal morphologies and state of aggregation of the end product. Despite this, our knowledge and the understanding of the nature of the molecular assembly processes in supersaturated solutions, as well as the interaction of solvents with the crystal faces is severely lacking.
In the fine chemicals and pharmaceutical industries, where products are of high value, organic solvents are routinely used [2]. The ability of solvents to manipulate the structure and morphology of the crystals formed becomes invaluable. This becomes even more important when the drug or the dyestuffs are polymorphic in which case changing the solvent can result in a different polymorph crystallising more than one crystal structure. Modifying the polymorph can alter its physical behaviour. For example, in the case of a drug the rate of uptake in the body can increase making one polymorph more desirable over the other. Thus understanding the interactions between a solvent and solute as well as the fundamental theories lying behind the whole solution crystallisation can increase the performance of the final product as well as extending our ability to select solvents for crystallisation control.