Crystallization: The Future is Controllable

Crystallization is one of the most important processes for the preparation and production of solid materials, including pharmaceuticals and speciality products; over 70% of solids are processed and utilized in their solid forms. Despite this prominence, the crystallization area is arguably one in which the gap between potential and realised goals is widest. Biominerals, such as bones, shells and teeth, exhibit far superior properties than their synthetic counterparts, and yet it should be possible to improve on nature's design strategies since we are not constrained to processing at ambient temperatures and pressures. Substantial improvements in this area are urgently required for the production of crystals with well-defined size, shape and structure that are so necessary for emerging nanotechnologies. Improvements can only be realised through better control over the two processes comprising crystallization: nucleation and growth. Nucleation describes the initial stage of crystallization, whereby the first stable nuclei of the crystallizing phase are formed, whilst crystal growth considers the growth of these stable nuclei to larger dimensions. The aims of this proposal are two-fold. Firstly to perform fundamental studies on model systems to show how crystallization can be controlled at every stage and length scale, and secondly the implementation of these new advances into more complex systems to provide desirable outcomes. These include the production of crystals with well-defined size and shape, and the production of improved bone mimics. We intend to show how controlling crystallization can lead to the production of materials with vastly improved properties, which will ultimately rival those of biominerals.This work will involve the exploitation of key recent discoveries by Dr Cooper. In particular, Dr Cooper has pioneered the use of tunable nucleating systems to provide unprecedented control over nucleation rates. These results are accomplished by using emulsions, which are mixtures of oil droplets in water, or water droplets in oil. Normally, after mixing oil and water together, the two rapidly separate into a layer of oil on top of the water. However, if you add additives, known as surfactants, the small oil droplets can be stabilized and an emulsion is formed, like milk. We use special surfactants in our emulsions that promote nucleation, but only in a limited temperature regime, so that we can effectively switch crystallization on and off. This means we can obtain far greater control over the crystal size and shape, and the rate at which crystals are formed. Our systems can also be used to deliver anomalous effects. For instance, it is widely known that crystallization can occur on cooling a solution. This can be demonstrated readily by dissolving as much sugar as possible in hot water, and then letting the water cool. Using our systems, however, we can achieve crystallization on both heating and cooling.In the crystal growth field, we have used emulsions to create unusual crystal morphologies including porous crystals and crystals with intricate shapes resembling feathers and woven cloth. Such intricately-shaped crystals are normally only seen in biominerals, such as the skeletons produced by sea urchins. These effects are achieved by using oil droplets that adhere onto the growing crystal. If the crystal grows completely around the oil droplets, porous crystals can be produced. The intricately shaped crystals develop if crystal growth proceeds only on each side of the droplets, so that many crystal offshoots grow from the main crystal. The ability to produce such intricate morphologies from simple systems illustrates the effectiveness of crystal growth regulation. The holistic combination of tunable nucleation and growth inhibition via droplet adhesion will help provide the improved crystallization control necessary to achieve superior crystalline materials.