贝壳珍珠层的研究现状

贝壳中的珍珠层是由占壳重95%的CaCO3晶体和占壳重仅5%的有机体构成的一种优异的天然纳米复合材料.对珍珠层的研究现状和最新进展进行了评述.重点介绍了珍珠层形成机制中的隔室说、矿物桥说、模板说和多模板二步成因假说等4种学说,及裂纹的偏转、纤维的拔出、有机质的桥连、矿物桥机制和凹凸镶嵌结构等5种增韧机理,简述了珍珠层的组成和微结构,指出了珍珠层研究中有待解决的问题.     

三角帆蚌珍珠质层结构和珍珠质涂层的研究

利用扫描电镜和光学显微镜对三角帆蚌贝壳和珍珠的珍珠质层微观结构进行了分析研究, 发现贝壳的珍珠质层中存在异常的结构带, 主要有柱状珍珠质带, 针状晶体带以及棱柱状晶体带. 其中柱状珍珠质带中, 单片文石板片的厚度超过1μm, 是正常珍珠质中文石板片厚度的两倍. 而对正常珍珠的珍珠质层的大量观察却未发现类似的异常结构. 分析认为这可能是因为贝壳珍珠质的矿化微环境与珍珠的珍珠质矿化微环境不同导致的. 并利用圆柱形珍珠囊在钛金属牙种植体表面制备的珍珠质涂层具有沿整个圆周面均匀生长的特点.     

贝壳珍珠层生物矿化及其对仿生材料的启示

贝壳珍珠层作为一种典型的生物矿化材料而备受关注. 本文综述了贝壳珍珠层结构及其文石晶体的结晶学取向, 概述了贝壳珍珠层成因的生物矿化机理. 同时介绍了贝壳珍珠层特殊的组装方式在仿生材料方面近年来的研究进展, 认为选择合适的有机物,使其自组装成各种超分子结构作为无机物沉积的模板, 是仿生合成的关键.     

鲍鱼壳珍珠层无机文石片的层状微结构研究

贝壳珍珠层是软体动物壳的最内层,经过若干世纪的自然进化,贝壳珍珠层形成了优良的微结构,并使贝壳具有了相当高的强度、刚度及断裂韧性.本文利用扫描电镜(SEM)观察了鲍鱼贝壳珍珠层的主要微结构特征,发现其是由层状的无机文石片和有机胶原蛋白质组成的生物陶瓷复合材料.根据发现的贝壳珍珠层层状微结构特征,建立贝壳珍珠层三维有限元模型,并用此模型分析了珍珠层的拉伸屈服极限与无机文石片拉伸屈服极限及其厚度的关系,研究表明珍珠层的屈服极限随无机文石片屈服极限的增加和无机文石片厚度的减小而增加.     

淡水珍珠的生物矿化机理研究进展

碳酸钙广泛存在于生物矿物中, 是地球上最普遍的生物矿物之一。贝壳和珍珠的主要组成部分为碳酸钙无机相。我国淡水养殖珍珠多数品质优异, 具有良好的珍珠光泽。该种珍珠以文石晶型碳酸钙为无机相, 称为文石珍珠。近年来, 在我国淡水养殖珍珠中发现了球文石的存在, 球文石的出现是导致珍珠失去光泽、降低质量的主要原因。本文对比阐述了淡水文石珍珠和球文石珍珠的微观结构与性能, 总结了与珍珠层有关的体外模拟碳酸钙生物矿化的实验结果, 提出了珍珠层生物矿化机理未来的研究方向。     

淡水养殖珍珠中文石板片厚度的变化及其微结构分析

通过场发射扫描电镜(FE-SEM),对白、粉和紫3种颜色的淡水养殖珍珠的珍珠层微结构进行了较系统研究。结果表明,在白色、粉色及紫色3种色系的珍珠中,在沿珍珠的半径方向上,珍珠层板片的厚度是变化的,且离珍珠核心距离越远,文石板片的厚度逐渐变薄;在同一直径不同颜色的珍珠中,接近珍珠外表面区域内珍珠层文石板片的厚度及珍珠外表面"梯田式"结构形貌也存在明显的差异,且珍珠表面"梯田式"结构越致密,其近珍珠表面的文石板片的厚度就越薄。     

三角帆蚌贝壳不同壳层与其珍珠中文石微结构及热处理研究

采用傅里叶变换红外光谱(FTIR)、高分辨透射电镜(HR-TEM)、场发射扫描电镜(FE-SEM)、X射线粉晶衍射(XRD)及热重差热分析(TG-DTA)对三角帆蚌的珍珠层、棱柱层、韧带与其培育的珍珠中生物成因文石的微结构及热处理行为进行较系统地对比研究,并进一步讨论引起不同壳层中文石红外频移及热处理行为差异的原因。结果表明:基于XRD粉晶衍射结论,三角帆蚌中不同壳层与珍珠中无机相均为生物成因文石;不同壳层中文石的热处理行为表现出相异性,粒径大小与不同壳层中有机质的含量应是导致上述贝壳不同壳层与珍珠中文石热处理行为差异的直接原因。     

以12-3-12/SDS混合系统为模板合成碳酸钙-环糊精复合材料

双子型表面活性剂12-3-12与阴离子表面活性剂SDS混合系统在不同配比下生成不同的自组织体(包括胶束、囊泡、液晶)。分别以这些自组织体为模板,利用碳酸化法合成了具有贝壳珍珠层"砖-泥"结构的碳酸钙-环糊精仿生复合材料。以X射线衍射、红外光谱、扫描电子显微镜测试表征产品组成与形貌,通过不同类型的自组织体模板与碳酸钙-环糊精复合材料形貌的对比研究,探讨模板与材料形貌的关系,为新型材料的设计合成提供了新的思路。     

淡水三角帆蚌贝壳珍珠质的同步辐射XRD研究

利用同步辐射XRD研究淡水三角帆蚌贝壳珍珠质的内应力和珍珠质中单个文石板片的微结构, 发现淡水三角帆蚌贝壳珍珠质中单个文石板片内存在晶内有机物, 且该晶内有机物导致珍珠质层中产生拉应力. 这一拉应力沿不同晶向呈现强烈的各向异性, 表明晶内有机物在文石板片内很可能以某一特定的方式排列. 同步辐射XRD图谱的线形分析进一步证实淡水三角帆蚌贝壳珍珠质中的晶内有机物吸附于文石板片的(002)晶面. 这些研究结果将促进珍珠质矿化及强韧化机制的研究, 为设计高性能无机-有机复合材料及培育珍珠提供科学的根据.     

贝壳珍珠层及其仿生应用

综述了贝壳珍珠层结构及其文石晶体的结晶学取向特征，并概述了珍珠层中参与调控生物矿化的有机基质的结构和功能方面的最新研究进展。从裂纹偏转、纤维拔出、有机基质桥连及矿物桥的作用等方面对珍珠层的高韧性机制进行了讨论。同时介绍了珍珠层的微结构特征及其特殊的组装方式在仿生材料制备方面的应用。     

Nanostructured artificial nacre

Finding a synthetic pathway to artificial analogs of nacre and bones represents a fundamental milestone in the development of composite materials. The ordered brick-and-mortar arrangement of organic and inorganic layers is believed to be the most essential strength- and toughness-determining structural feature of nacre. It has also been found that the ionic crosslinking of tightly folded macromolecules is equally important. Here, we demonstrate that both structural features can be reproduced by sequential deposition of polyelectrolytes and clays. This simple process results in a nanoscale version of nacre with alternating organic and inorganic layers. The macromolecular folding effect reveals itself in the unique saw-tooth pattern of differential stretching curves attributed to the gradual breakage of ionic crosslinks in polyelectrolyte chains. The tensile strength of the prepared multilayers approached that of nacre, whereas their ultimate Young modulus was similar to that of lamellar bones. Structural and functional resemblance makes clay- polyelectrolyte multilayers a close replica of natural biocomposites. Their nanoscale nature enables elucidation of molecular processes occurring under stress.     

The toughening mechanism of nacre and structural materials inspired by nacre

Abstract

The structure and the toughening mechanism of nacre have been the subject of intensive research over the last 30 years. This interest originates from nacre’s excellent combination of strength, stiffness and toughness, despite its high, for a biological material, volume fraction of inorganic phase, typically 95%. Owing to the improvement of nanoscale measurement and observation techniques, significant progress has been made during the last decade in understanding the mechanical properties of nacre. The structure, microscopic deformation behavior and toughening mechanism on the order of nanometers have been investigated, and the importance of hierarchical structure in nacre has been recognized. This research has led to the fabrication of multilayer composites and films inspired by nacre with a layer thickness below 1 μm. Some of these materials reproduce the inorganic/organic interaction and hierarchical structure beyond mere morphology mimicking. In the first part of this review, we focus on the hierarchical architecture, macroscopic and microscopic deformation and fracture behavior, as well as toughening mechanisms in nacre. Then we summarize recent progress in the fabrication of materials inspired by nacre taking into consideration its mechanical properties.     

Why is nacre so tough and strong?

In this paper we describe the details of simulations conducted on three-dimensional finite element models of nacre integrated with experiments. This work gives an overview of modeling mechanical behavior in nacre and quantitatively elucidates the specific role of many details of structure in nacre on the stress–strain response. We describe the role of each of the details of nanostructure on the mechanics and deformation behavior of nacre as well as identify the key mechanisms responsible for the unique mechanical behavior of nacre. Nanoscale asperities and mineral contacts have marginal role on mechanical response of nacre and platelet interlocks have a significant role on deformation in nacre. We describe the key strengthening and toughening mechanisms in nacre as:

• 1.Material properties of aragonite and organic matrix, especially the unique properties of the organic phase in the confined space between platelets.
• 2.Structure at micro scale: size, shape of platelets etc.
• 3.Interlocking of aragonite platelets: progressive failure of interlocks guides the fracture path.
• 4.Molecular interactions at the organic–inorganic interface.

     

Crystal orientations in nacreous layers of organic–inorganic biocomposites

Abalone shell comprises a bio-composite material, combining the properties of inorganic calcite intergrown with organic nacre. This paper reports about the microstructure of this composite. By examining the Kikuchi patterns obtained for nacre (Haliotis discus hannai) using transmission electron microscopy, we have shown that the tiles within nacre have specific orientations. The stereographic projection spheres for the tiles of nacre can be divided into two main types, namely a right oriented region and a left oriented region with respect to the c axis as a reference plane (001). The cluster character of nacre can be explained in terms of the growth mechanism of the ‘Christmas tree’ pattern. The orientation of the c-axis in the nacreous layer is elucidated for the first time. We demonstrate the use of the soluble protein obtained from the tiles of nacre in in vitro calcium carbonate crystallization.     

贝壳珍珠母增韧机理研究进展

基于国内外对贝壳材料微结构研究的实验照片与力学性能的研究成果,描述了贝壳珍珠母独特的微观结构,包括无机层与有机基质层"砖-泥"式交错层叠结构、文石层波纹表面和文石表面纳米凸起与矿物桥结构等,同时也揭示了贝壳珍珠母微结构对其韧性的增强机理。对国内力学家近年来提出的微观结构"缺陷不敏感"增韧理论进行了理论阐述。     

Modeling microarchitecture and mechanical behavior of nacre using 3D finite element techniques Part I Elastic properties

Three dimensional finite element models of nacre were constructed based on reported microstructural studies on the 'brick and mortar' micro-architecture of nacre. 3D eight noded isoparametric brick elements were used to design the microarchitecture of nacre. Tensile tests were simulated using this model. The tests were conducted at low stresses of 2 MPa which occur well within the elastic regime of nacre and thus effects related to locus and extent of damage were ignored. Our simulations show that using the reported values of elastic moduli of organic (0.005 GPa) and aragonitic platelets (205 GPa), the displacements observed in nacre are extremely large and correspond to a very low modulus of 0.011 GPa. The reported elastic modulus of nacre is of the order of 50 GPa. The reason for this inconsistency may arise from two possibilities. Firstly, the organic layer due to its multilayered structure is possibly composed of distinct layers of different elastic moduli. The continuously changing elastic modulus within the organic layer may approach modulus of aragonite near the organic-inorganic interface. Simulations using variable elastic moduli for the organic phase suggest that an elastic modulus of 15 GPa is consistent with the observed elastic behavior of nacre. Another explanation for the observed higher elastic modulus may arise from localized platelet-platelet contact. Since the observed modulus of nacre lies within the above two extremes (i.e. 15 GPa and 205 GPa) it is suggested that a combination of the two possibilities, i.e. a higher modulus of the organic phase near the organic-inorganic interface and localized platelet-platelet contact can result in the observed elastic properties of nacre.     

功能无机材料在海水淡化技术中的应用与开发

由于水资源紧缺问题日益突出，海水淡化技术的研究与开发将越来越显得紧迫。海水淡化研究的根本是如何降低成本，而其中关键问题是材料的选择。本文旨在对功能无机材料应用于海水淡化技术这一新的研究方向作一详细的分析与展望。其中着重分析无机分离膜在反渗透海水淡化技术中的应用，包括无机分离膜的特点和制备方法，无机反渗透膜替代有机反渗透膜和无机超滤膜应用于海水预处理等；并讨论了无机材料中硅酸盐矿物（粘土和沸石矿物等     

Biomimetic Pathways for Nanostructured Poly(KAMPS)/aragonite Composites that Mimic Seashell Nacre

Complex microstructures of biominerals such as seashell nacre, bone, and teeth are awe‐inspiring. Nature has devised schemes to combine hard inorganic platelets of aragonite (CaCO₃) and an organic matrix that produce tough biocomposites. The ability of the organic‐inorganic components to “slide” internally leads to the toughening of the materials, though a recreation of this system at the nanoscale has yet to be shown. Here, we implement a poly(KAMPS)‐based assembly, which is carried out entirely from dilute aqueous solutions of the materials to create a “brick and mortar”‐type aragonite structure that mimics the platelet sliding and exhibits toughening. The negatively charged poly(KAMPS) chains are attracted to the positively charged divalent cations, by which addition of NaHCO₃ to an aqueous mixture of Ca²⁺‐poly(KAMPS), results in the growth of aragonite nanorods with a width of 120 nm. The reversible nature of the physical gel formation of poly(KAMPS) in solution results in adhesion of the nanorods into a microscale structure. The new nacre‐like carbonate composite, has a modulus (44 GPa) and hardness (2.8 GPa) on a similar order as to that of nacre and other bio‐composites, exhibits limited creep, and demonstrates a mechanism with nanoscale deformation.