Materials World Network: Composite Single Crystals - From Structural Evolution to Mechanical Characterization

将合成材料科学与源于自然的设计理念相结合，是开发新材料的一条很有前途的途径。骨骼、牙齿和贝壳等生物矿物为这种方法提供了理想的灵感，大自然能够操纵碳酸钙等机械强度较弱的工程材料，生产出具有优异断裂韧性和独特形态的坚硬骨骼材料。这些复合材料的一个关键特征是它们的结构涉及到矿物主体中有机分子的强烈插层，这也是它们优异机械性能的一个基本特征。在这里，有机物不仅可以位于晶体单元之间，就像珍珠岩这样的材料一样，而且还可以位于单晶体中，例如在海胆刺中发现的单晶中。事实上，单晶生物矿物通常会遮挡高达几个重量%的大分子，考虑到结晶传统上被认为是一种提纯固体的方法，这可能令人惊讶。我们将研究这一生物起源策略的应用--在单晶中包裹“包裹体材料”--以创造新的复合材料。尽管基于这种方法合成复合材料的潜力是巨大的，但由于我们缺乏基本的理解，这一领域的进展在很大程度上仍然是基于反复试验。在这个项目中，我们组建了一个独特的国际研究团队来填补这一空白，通过这样做，我们将全面了解1)“包裹体材料”被阻挡在晶格中的机制；2)所产生的单晶复合材料的内部微纳米结构；以及3)所产生的结构如何最终决定所产生的复合材料的机械性能。我们的研究策略是基于对广泛的“包裹体”材料的系统研究--从分子到微观聚合物颗粒，从顺应性到刚性框架。我们将设计和合成具有适当化学结构的定制分子、粒子和凝胶来促进插层，并在这样做的过程中建立第一个真正统一的理解，即添加剂是如何封闭在晶体中的。生物矿物的形成策略及其设计如何产生优异的性能显然是一个复杂的多学科问题，包括晶体生长、材料表征、聚合物化学和机械性能分析等领域。这项NSF-EPSRC联合研究拨款涉及设在美国和英国的世界领先研究小组联盟之间的国际合作，这些研究小组通过密切合作，寻求将每个团队的多学科专业知识结合起来，以解决这一复杂的科学问题，从而使新型生物材料的合理设计成为可能。我们的最终目标是首次对如何在单晶中加入添加剂-从分子、聚合物、颗粒、到顺应性和最终刚性框架-建立真正统一的理解，并确定如何将这一策略应用于具有特定机械性能的新材料的设计。这种综合的方法将为合成复合晶体提供一种通用的方法，有助于我们了解灵感来自的生物系统，并最终为合成人工骨和坚韧的合成牙釉质等下一代材料提供基础。

The combination of synthetic materials science with design concepts adapted from Nature is a promising route to the development of new materials. Biominerals such as bones, teeth and seashells provide an ideal inspiration for this approach, as illustrated by Nature's ability to manipulate mechanically weak engineering materials such as calcium carbonate to produce hard skeletal materials that exhibit excellent fracture toughness and unique morphologies. One key feature of these composite materials, which is an essential feature of their superior mechanical properties, is their structures involve strong intercalation of organic molecules within the mineral host. Here organics can not only be located between crystalline units as for materials such as nacre, but also within single crystals, as found for example in sea urchin spines. Indeed, single crystal biominerals often occlude up to several weight per cent of macromolecules, which is perhaps surprising given that crystallization is traditionally considered to be a method for purifying solids. We will investigate the application of this biogenic strategy - the encapsulation of "inclusion materials" within single crystals - to create novel composite materials. Although the potential for synthesizing composite materials based on this approach is enormous, our lack of fundamental understanding means that progress in this field remains largely based on trial-and-error experiments. In this project, we have assembled an international team of researchers uniquely positioned to fill this gap, and by doing so we will develop a comprehensive understanding of 1) the mechanisms by which "inclusion materials" are occluded within a crystal lattice; 2) the internal micro- and nano-structure of the resulting single crystal composites; and 3) how the resulting structures ultimately dictate the mechanical properties of the resulting composite material. Our research strategy is based on a systematic study of the incorporation of a broad range of "inclusion" materials - ranging from molecules to microscopic polymer particles, and from compliant to stiff frameworks. We will design and synthesise bespoke molecules, particles and gels with appropriate chemical structures to promote intercalation, and in doing so develop the first truly unified understanding of how additives are occluded within crystals. It is also expected that novel syntheses of polymeric particles and gels will also result from this approach.Understanding the strategies by which biominerals form, and how their design leads to superior properties is clearly a complex, multidisciplinary problem, encompassing fields such as crystal growth, materials characterisation, polymer chemistry, and analysis of mechanical properties. This joint NSF-EPSRC research grant involves an international collaboration between a consortium of world-leading research groups based in the USA and the UK, who by working closely together seek to combine the multidisciplinary expertise of each team to address this complex scientific problem and hence enable the rational design of novel biomaterials. Our ultimate goal is to create for the first time a truly unified understanding of how additives - ranging from molecular, to polymeric, to particulate, to compliant and ultimately stiff frameworks - can be incorporated within single crystals, and to determine how this strategy can be applied to the design of new materials with specific mechanical properties. This integrated approach will provide a general methodology for synthesizing composite crystals, contribute to our understanding of the biological systems from which the inspiration came, and will ultimately provide the basis for synthesizing next-generation materials such as artificial bone and tough synthetic dental enamel.