Crystallization: The Future is Controllable

结晶是包括药品和特种产品在内的固体材料制备和生产中最重要的过程之一；70%以上的固体都是以固体形式加工和利用的。尽管有这一突出之处，但可以说，结晶领域是潜在目标与已实现目标之间差距最大的领域。生物矿物，如骨骼、贝壳和牙齿，表现出比合成矿物优越得多的性能，但由于我们不受环境温度和压力的限制，应该有可能改进自然的设计策略。迫切需要在这一领域进行实质性改进，以生产尺寸、形状和结构定义明确的晶体，这是新兴纳米技术所必需的。只有通过更好地控制包括结晶在内的两个过程：成核和生长，才能实现改进。成核描述了结晶的初始阶段，由此形成了结晶相的第一个稳定的核，而晶体生长考虑了这些稳定的核的生长到更大的维度。这项提议的目的有两个。首先，对模型系统进行基础研究，以显示如何在每个阶段和长度尺度上控制结晶；其次，将这些新进展应用到更复杂的系统中，以提供理想的结果。其中包括生产定义明确的大小和形状的晶体，以及生产改进的骨骼仿制品。我们打算展示如何控制结晶可以导致材料的性能得到极大的改善，最终将与生物矿物相媲美。这项工作将涉及库珀博士最近的关键发现的开发。特别是，库珀博士率先使用可调成核系统来提供对成核率的前所未有的控制。这些结果是通过使用乳状液实现的，乳状液是油滴在水中的混合物，或水滴在油中的混合物。通常，将油和水混合在一起后，两者会迅速分离，形成水面上的一层油。然而，如果你加入被称为表面活性剂的添加剂，小油滴就可以稳定下来，形成乳状液，就像牛奶一样。我们在乳液中使用了特殊的表面活性剂，可促进成核，但仅在有限的温度范围内，因此我们可以有效地打开和关闭结晶。这意味着我们可以更好地控制晶体的大小和形状，以及晶体形成的速度。我们的系统也可以用来提供异常效果。例如，众所周知，结晶可以在冷却溶液时发生。这可以通过将尽可能多的糖溶解在热水中，然后让水冷却来很容易地证明。然而，使用我们的系统，我们可以在加热和冷却时实现结晶。在晶体生长领域，我们使用乳剂创造了不寻常的晶体形态，包括多孔晶体和形状复杂的类似羽毛和编织布的晶体。这种形状错综复杂的晶体通常只在生物矿物中看到，比如海胆产生的骨骼。这些效果是通过使用附着在生长中的晶体上的油滴来实现的。如果晶体完全围绕着油滴生长，就可以产生多孔性晶体。如果晶体生长只在液滴的两侧进行，那么形状复杂的晶体就会形成，所以许多晶体分支是从主晶体生长出来的。从简单的体系中产生如此复杂的形貌的能力表明了晶体生长调控的有效性。通过液滴粘合实现可调成核和生长抑制的整体组合，将有助于提供改进的结晶控制，以获得优异的结晶材料。

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.