穹顶状珍珠层板片的形成机理

发布时间：2018-03-04 06:15

本文选题：珍珠层　切入点：穹顶状板片　出处：《广西大学》2017年博士论文　论文类型：学位论文

【摘要】：珍珠层是天然的有机-无机复合材料,具有优越的结构和杰出的力学性能。然而,它仅需利用环境中常见的Ca2+和C032-在常温常压下即可在生物体中合成。因此,珍珠层是一种环保材料,长久以来成为了生物矿化领域以及仿生合成材料领域的经典研究对象。目前,关于珍珠层的研究积累了很多知识,但仍有很多问题存在争议,如珍珠层的基本结构单元-文石板片的形貌、排列、内部结构等。此外,几乎所有的相关知识均基于研究成熟的平板状板片而来,而忽略了板片的形貌和生长阶段,这导致了珍珠层研究的不足。在本工作中,我们以翡翠贻贝珍珠层板片为主要研究对象,尤其是具有独特形貌的穹顶状板片。我们采用场发射SEM、HRTEM、XRD、DSC以及FTIR等对穹顶状板片的形成机理进行研究,包括板片的三维形貌与排列、内部结构、成核与生长、结晶学关系与界面结构、以及形成环境等,获得以下结论:(1)穹顶状板片和平板状板片在翡翠贻贝中共存,前者是后者吸收外力发生形变后的产物;(2)板片呈梯度变化排列,包括厚度梯度和曲率梯度。自珍珠层底部到顶部,板片厚度由0.84±0.08 μm变为0.24±0.01 μm,曲率由0.77±0.12 μm-1变为0 μm-1,即板片厚度和曲率之间是逐渐过渡的,没有明显的界限。基于观察,我们推测厚度梯度是由于贝壳中心和贝壳边缘的生长速率不同引起的,而曲率梯度是由于板片受到来自闭壳肌关闭贝壳和套膜回收表壳层时的压应力梯度引起的;(3)平板状板片和成熟的穹顶板片为单晶,未成熟穹顶状板片为无序文石纳米颗粒的集合体。其中,早期未成熟穹顶状板片由粒径为18-41 nm但只有部分结晶的椭圆形胶体纳米颗粒组成,晚期未成熟穹顶状板片由粒径为20-150 nm且完全结晶的胶体纳米颗粒组成。我们推测单个成熟穹顶状板片是由ACC纳米颗粒定向粘结形成的;(4)新生的板片均成核于底层板片的环表面上,呈自限生长模式生长。板片的水平生长速率不均匀,与成核时间成反比。我们推测板片的成核与水平生长速率是受到晶格不匹配诱导的应力所控制的;(5)穹顶状板片的结晶学定向一致,其层间膜由直径为30-50 nm的椭球形结晶蛋白质构成。层间膜通过厚度为10-20 nm的超晶格区域与板片相连接,继而继承并传递底层板片的结晶学定向,使得所用板片结晶学定向一致;(6)穹顶状板片和平板状均为天然的高能文石并伴随着v2带红外频移,其中穹顶状板片和平板状板片v2带频移分别高达8cm-1和12cm-1,这可能是由于板片的纳米粒径效应、低结晶度以及晶格畸变引起的。与平板状板片相比,穹顶状板片的能量相对较低,这是由于穹顶状板片是平板状板片通过形变实现应力松弛降低能量后的产物;(7)腹侧和后端表壳层存在结构差异性。其中,腹侧表壳层内层最薄,中层最厚,中层由直径为43-106 nm的非晶质纳米球体组成,而后端表壳层中各结构层厚度自外而内递增,中层由直径约为178nm的纤维组成。腹侧表壳层中层的纳米球体由少量蛋白质和含Ca,Mg以及CO32-的非晶质磷酸盐组成,这不仅能给珍珠层的形成提供原材料,还能稳定环境的pH,促进珍珠层的矿化;(8)乳状突起层由具有呈抛物面形状(底部平均直径d=2.5 μm,平均高度h=4.6 μm)的蛋白质突起组成,它们嵌入到棱柱层中形成独特的互锁界面,有效防止表壳层和棱柱层之间的滑动,并替代表壳层充当了贝壳的初始矿化基底,相比于表壳层能够给生物矿化提供约4倍大的表面积,有助于初始矿化的进行。基于观察,我们推测乳状突起是由于贝壳关闭时表壳层受到压应力引起的。本工作中,我们重构了穹顶状板片的三维形貌并建立板片的梯度排列模型,并提出了 ACC定向粘结的非传统结晶理论。此外,我们还首次在双壳纲贝壳中直接观察到了穹顶状板片的界面结构,发现结晶的层间膜通过超晶格区域与板片相连接,继承并传递底层板片的结晶学定向。这些研究结果将进一步揭示珍珠层的形成机理,有助于类珍珠层材料的合成。
[Abstract]:Nacre is organic inorganic composite material of natural, has the superior structure and mechanical properties of outstanding. However, it only uses Ca2+ and C032- common environment can be synthesized in the body under normal temperature and pressure. Therefore, the pearl layer is a kind of environmental protection material, has long been the field of biomineralization and biomimetic fields the classic synthetic materials research object. At present, the research on pearl layer accumulated a lot of knowledge, but there is still controversy many problems, such as the basic structural unit of nacre aragonite sheets - morphology, arrangement, internal structure and so on. In addition, the related knowledge of almost all the flat plate based on the mature research come, while ignoring the morphology and growth stage of the plate, which led to a shortage of nacre research. In this work, we take the pearl mussel plates as the main research object, especially with unique morphology The dome shaped plate. We use the field emission SEM, HRTEM, XRD, DSC and FTIR on the dome shaped plate forming mechanism of the internal structure of three-dimensional shape and arrangement, including plate, nucleation and growth, the relationship between crystallography and interface structure, and the formation of the environment, the following conclusions are obtained: (1) dome shaped plate and a flat plate coexist in the mussel, the former is the product of absorption force after deformation; (2) plate gradient arrangement, including thickness gradient and curvature gradient. From the bottom to the top of the nacreous layer, the thickness of the plate from 0.84 + 0.08 m to 0.24 0.01 + m, 0.77 + 0.12 M-1 by curvature is 0 M-1, which is between plate thickness and curvature gradually, no obvious boundaries. Based on the observation, we speculate that the thickness gradient is due to the growth rate of shell and shell edge center caused by different, while the curvature is due to gradient The plate from closed shell and adductor muscle film recovery case layer when the compressive stress caused by the gradient; (3) flat plate and dome plate mature for single crystal, dome shaped plate as a collection of immature disordered aragonite nanoparticles. The early immature dome shaped plate by particle size 18-41 nm but elliptical nanoparticles only partially crystalline composition, late immature dome shaped plate by the diameter of colloidal nanoparticles of 20-150 nm and fully crystallized. We speculate that single mature dome shaped plate is formed by bonding the ACC nano particle orientation; (4) the new plate surface nuclear ring on the bottom plate, a self limited growth model. In the level of growth rate is not uniform, and the nucleation time. We speculate that the plate is inversely proportional to the nucleation and growth rate is affected by the level of lattice mismatch induced stress control; (5) the dome shaped plate with crystallography orientation, the interlayer film with diameter of ellipsoidal crystal protein of 30-50 nm. The structure of the interlayer film through the thickness of the superlattice region and the plate 10-20 is connected to the nm, and then inherit and pass the bottom plate of the crystallographic orientation, the sheet crystallography orientation consistent; (6) the dome shaped plate and the plate are natural and accompanied by high-energy aragonite V2 with infrared shift, the dome shaped plate and a flat plate V2 with frequency shift were as high as 8cm-1 and 12cm-1, which may be due to the size effect of nanoparticles plate, low crystallinity and due to lattice distortion. Compared with the flat plate, dome shaped plate energy is relatively low, this is because of the dome shaped plate is a flat plate through the realization of deformation stress relaxation after the reduction product of energy; (7) there are differences in the structure of the ventral side and rear case layer. Among them, the ventral table The inner shell of the thin, middle thick, middle diameter by amorphous nano spheres composed of 43-106 nm, and each layer of layer thickness in the case is from outside to inside diameter increases, the middle is composed of 178nm fibers. The ventral case layer nano sphere by a small amount of protein and Ca containing amorphous. Mg and CO32- phosphate composition, which can not only provide the raw material for the formation of pearl layer, but also stable environment pH, promote the nacre mineralization; (8) papillae layer is composed with a parabolic shape (at the bottom of the average diameter of d=2.5 m, the average height of h=4.6 ~ m) protein consisting of protrusions, embedding them into the interlocking interface forms a unique prismatic layer, effectively prevent sliding between case and prismatic layer, and acts as a representative for the shell basal initial mineralization of shells, compared to the case for biomineralization layer can provide about 4 times as large as the surface area, help For the initial mineralization. Based on observation, we speculate that the papillae is due to closed shell case layer by compressive stress caused. In this work, we reconstructed the three-dimensional shape of the dome shaped plate and a gradient plate arrangement model, and proposes the traditional crystallization theory ACC directional bonding. In addition, we also for the first time in bivalve shells were observed directly in the interface structure of dome shaped plate, found that the crystallization of the interlayer film is connected by a superlattice region and plate, inherit and transfer plate bottom crystallography orientation. These results will further reveal the formation mechanism of nacre, contribute to the synthesis of class pearl layer material.

【学位授予单位】：广西大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB33

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