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

将合成材料科学与借鉴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，正如大自然操纵机械薄弱的工程材料（如碳酸钙）产生具有优异断裂韧性和独特形态的硬骨骼材料的能力所说明的那样。这些复合材料的一个关键特征，也是其优越的机械性能的基本特征，是它们的结构涉及到矿物主体内有机分子的强嵌入。在这里，有机物不仅可以存在于像珍珠质这样的晶体单位之间，也可以存在于单晶中，比如在海胆棘中。事实上，单晶生物矿物通常会阻塞大分子的几个重量百分比，这也许令人惊讶，因为结晶传统上被认为是纯化固体的一种方法。我们将研究这种生物源策略的应用-在单晶中封装“包合材料”-以创建新型复合材料。尽管基于这种方法合成复合材料的潜力是巨大的，但我们缺乏基本的理解意味着这一领域的进展仍然主要基于反复试验。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，我们将对以下方面有一个全面的了解：1)“包合材料”在晶格内被遮挡的机制；2)单晶复合材料的内部微纳米结构；以及3)最终形成的结构如何决定最终形成的复合材料的力学性能。我们的研究策略是基于对广泛的“包合”材料的系统研究-从分子到微观聚合物颗粒，从柔性到刚性框架。我们将设计和合成具有适当化学结构的定制分子、颗粒和凝胶，以促进嵌入，并在此过程中首次真正统一理解添加剂如何在晶体中被遮挡。预计这种方法还将产生聚合物颗粒和凝胶的新合成。了解生物矿物形成的策略，以及它们的设计如何导致优越的性能，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联合研究资助涉及美国和英国的世界领先研究小组之间的国际合作，他们通过密切合作，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。我们的最终目标是第一次真正统一地理解添加剂——从分子到聚合物，到颗粒，到柔顺和最终坚硬的框架——如何被纳入单晶中，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。这种综合方法将为合成复合晶体提供一种通用的方法，有助于我们对灵感来源的生物系统的理解，并最终为合成下一代材料（如人工骨和坚韧的合成牙釉质）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.