Mechanical Properties and Structure of Abalone: Self-Assembled Ceramic Nanostructures

非技术描述：合成材料（金属、聚合物、陶瓷和复合材料）在过去的一个世纪里在研究实验室中开发出来，已经彻底改变了生活。然而，目前，设计和生产具有改进性能的合成材料的可能性正在用尽。因此，研究人员正将注意力转向大自然，试图更好地理解它，以模仿它的设计为目标。这一新兴的仿生学领域试图在模仿生物系统的基础上设计材料的特性。这项提议的研究针对的是鲍鱼壳，因为它是珍珠或珍珠母的重要来源。然而，它由95%的白垩组成，很脆弱。壳的复杂纳米结构和微观结构是这样的，添加5%的有机胶可以使其韧性比白垩高几个数量级。拟议研究的目标是在基础层面上理解为什么外壳如此坚固，并利用这些知识开发具有优越性能的新一代陶瓷复合材料。技术细节：将开展一个为期四年的项目，具有很强的表征和分析成分：开发新的微观和纳米力学测试方法，以建立作为瓷砖之间粘合剂的蛋白质层的粘弹性力学响应。这种方法需要使用原子力显微镜，纳米压痕和纳米划痕测试，小型化剪切测试（类似于PI使用的中观尺度测试），通过包含有机层粘弹性响应的新机制模拟机械响应；利用微拉曼光谱和傅里叶红外光谱对变形后有机层的变化进行了识别和量化，并确定了瓷砖以“圣诞树”模式生长并将其方向从一层传递到另一层的机制。基于这些观察，文石（CaCO3的正交相）的详细生长模型将被开发出来。最终目标是利用受生物学启发的技术来合成新材料。研究将在加州大学圣地亚哥分校、墨西哥国立自治大学和劳伦斯利弗莫尔国家实验室进行。来自圣地亚哥和墨西哥的研究生和本科生以及高中生将参与学习过程。为低收入家庭6 ~ 12年级学生提供大学预备强化教育的特许高中普鲁斯学校（Preuss School）也将参与其中。这些学生来自父母没有接受过大学教育的家庭。两名高中学生将在学年期间（每周4-6小时，根据普鲁斯学校的允许）和暑假期间（6周）全职工作。需要强调的是，这些实验没有伤害或杀死鲍鱼。本项目由国际科学与工程办公室和材料研究部共同资助。

NON-TECHNICAL DESCRIPTION: The synthetic materials (metals, polymers, ceramics, and composites) developed in research laboratories during the past century have revolutionized life. However, at present, the possibilities of designing and producing synthetic materials with improved performance are being exhausted. Therefore researchers are turning their attention to nature, trying to understand it better, with the goal of mimicking its designs. This emerging field of Biomimetics seeks to design properties into materials modeled after biological systems. The proposed study addresses the abalone shell that is highly prized as a source of nacre, or mother-of-pearl. Yet, is comprised of 95% chalk, which is weak and brittle. The complex nanostructure and microstructure of the shell are such that adding 5% of an organic glue leads to a toughness that is orders of magnitude higher than that of chalk. The goal of the proposed research is to understand, at the fundamental level, why the shell is so strong and to use this knowledge to develop a new generation of ceramic composites with superior properties. TECHNICAL DETAILS: A four-year program with strong characterization and analysis components will be carried out: development of new micro- and nano-mechanical testing methods to establish viscoelastic mechanical response of the protein layer(s) that act as an adhesive between tiles. This approach requires the use of atomic force microscopy, nanoindentation and nanoscratch tests, a miniaturized shear test (analogous to the meso scale test used by the PI), modeling mechanical responses through novel mechanisms incorporating viscoelastic response of organic layer; identification and quantification of the changes in the organic layers that occur after deformation using micro-Raman spectroscopy and FTIR, and identification of mechanisms by which tiles grow in "Christmas tree" pattern and transmit their orientation from level to level. Based on these observations, a detailed growth model for aragonite (the orthorhombic phase of CaCO3) will be developed. The ultimate goal is the use of biologically-inspired techniques to synthesize new materials. Research will be carried out at University of California San Diego, Universidad Nacional Autonoma de Mexico, and the Lawrence Livermore National Laboratory. Graduate and undergraduate students from San Diego and Mexico will be involved in the learning process, as well as high school students. The Preuss School, a charter high school that is designed as in intensive college preparatory educational program for low-income students in the grades 6-12, will be involved. These students come from families whose parents have not received college training. Two senior high school students will work during the school year (4-6 hrs/week, as allowed by The Preuss School) and full time during their summer breaks (6 weeks). It is emphasized that no abalone are harmed or killed for these experiments. This project is co-funded by the Office of International Science and Engineering and the Division of Materials Research.