Hierarchical and self-similar growth of self-assembled crystals.
Hierarchical and self-similar growth of self-assembled crystals.
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DOI：
10.1002/anie.200390126
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发表时间：
2003-01
影响因子：
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通讯作者：
Z. Tian;Jun Liu;J. Voigt;B. McKenzie;Huifang Xu
中科院分区：
文献类型：
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作者：
Z. Tian;Jun Liu;J. Voigt;B. McKenzie;Huifang Xu
贝壳 [1, 2] 和硅藻 [3] 等生物材料表现出丰富的形态和多尺度有序性。最近在合成的自组装中间相硅酸盐中报道了显着的类生物材料形貌。[4±8]这些不寻常形状的形成与曲率效应有关，与基本结构单元无关。[4, 5]通过将微图案化与表面活性剂自组装相结合，制备了分级介孔氧化物和图案化薄膜。[9±13]此外，从毫米大小的物体组装出有序图案和开放结构。[14±16]合成材料还使用预先存在的模板制备了包含生物图案的材料。[17±19]此外，在一些简单的晶体系统中研究了分形生长。[20±22]在此，我们报告了一种新颖的分层和自相似晶体生长过程，导致自发形成具有受控形态和从纳米到宏观尺度有序的大型物体。据我们所知，这是基于微观多面体单晶组装的自组装材料的真正分层和自相似晶体生长的第一份报告。 1992年首次报道了用硅酸和季铵表面活性剂自组装的周期性硅酸盐。[23, 24]此后，杂化硅烷和桥联有机倍半硅氧烷被用于制备介孔粉末[25±28]和薄膜。[29, 30]最近Inagaki和同事使用1, 2-bis制备了明确的杂化介孔晶体。 (三甲氧基甲硅烷基)乙烷 (BTME) 作为二氧化硅源，十六烷基三甲基氯化铵 (CTAC) 作为表面活性剂。 [31]在此，我们使用杂化有机硅烷 BTME 与 CTAC 通过异质成核和生长来创建一类新型支持的分层中间相晶体（即由晶体构件形成的大型中间相结构）。 [32]将 BTME 和 CTAC 在碱性水溶液中混合并在特氟隆容器中加热。将显微镜载玻片垂直放置在容器中，使晶体在表面成核和生长。30分钟内，在玻璃表面上形成界限分明且定向的中间相晶体。图 1a 显示了中间相晶体大型阵列的典型扫描电子显微镜 (SEM) 图像。这些晶体的形状和尺寸相当均匀（12 μm 宽）。低角 X 射线衍射 (XRD) 和透射电子显微镜 (TEM) 表明这些中间相晶体具有立方结构 (Pm3n, ao= 98 ä)，如文献报道。 [31]图1b显示了立方结构<001>区轴方晶格的TEM图像。正如稍后将讨论的，图1a中的晶体是由初级八面体晶体形成的次级八面体结构，并且以平行于基底的{111}面之一取向。我们进一步证明这些介晶可以在玻璃基板上的预制聚苯乙烯线上形成图案（图1c）。定向中间相晶体的形成对于实际应用具有重要意义，但迄今为止，关于如何制备均匀且定向的自组装晶体的报道还很少。相比之下，在相似条件下从溶液中沉淀出来的颗粒具有多种形态并且形状不明确（图 1d）。
Biomaterials, such as seashells [1, 2] and diatoms [3] display rich morphologies and multiple-scale ordering. Recently remarkable biomaterial-like morphologies were reported in synthetic, self-assembled mesophase silicates.[4±8] The formation of these unusual shapes is related to curvature effects and is independent of the basic structural units.[4, 5] Hierarchical mesoporous oxides and patterned films were prepared by combining micropatterning with surfactant self-assembly.[9±13] In addition, ordered patterns and open structures were assembled from millimeter-sized objects.[14±16] Synthetic materials containing biological patterns were also prepared using pre-existing templates.[17±19] Furthermore, fractal growth has been investigated in some simple crystalline systems.[20±22] Herein, we report a novel hierarchical and self-similar crystal-growth process leading to the spontaneous formation of large objects with controlled morphology and ordering from nano-to macro-scale. To our knowledge this is the first report of true hierarchical and self-similar crystal growth for self-assembled materials based on the assembly of microscopic polyhedral single crystals. Self-assembled periodic silicates were first reported in 1992 from silicic acid and quaternary ammonium surfactants.[23, 24] Since then hybrid silanes and bridged organic silsesquioxanes have been used to prepare mesoporous powders [25±28] and films.[29, 30] Recently Inagaki and co-workers prepared well-defined hybrid mesoporous crystals using 1, 2-bis (trimethoxysilyl) ethane (BTME) as a silica source and hexadecyltrimethylammonium chloride (CTAC) as a surfactant.[31] Herein, we use the hybrid organic silane BTME along with CTAC to create a new class of supported hierarchical mesophase crystals (that is, large mesophase structures formed from crystalline building blocks) through heterogeneous nucleation and growth.[32] BTME and CTAC were mixed in basic aqueous solutions and heated in a Teflon container. A microscope glass slide was placed vertically in the container to allow the crystals to nucleate and grow on the surface.Well-defined and oriented mesophase crystals were formed on the glass surface within 30minutes. Figure1a shows a typical scanning electron microscopy (SEM) image of large arrays of the mesophase crystals. These crystals are rather uniform in shape and size (12 μm wide). Low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate that these mesophase crystals have a cubic structure (Pm3n, ao= 98 ä) as reported in the literature.[31] Figure1b shows a TEM image of the< 001> zone axis square lattice of the cubic structure. As will be discussed later, the crystals in Figure 1a are secondary octahedral structures formed from primary octahedral crystals, and are oriented with one of the {111} planes parallel to the substrate. We further demonstrated that these mesocrystals can be patterned on preformed polystyrene lines on glass substrates (Figure 1c). The formation of oriented mesophase crystals is significant for practical applications, but to date there have been few reports on how to prepare uniform and oriented self-assembled crystals. In contrast, the particles that precipitated from the solutions under similar conditions have a wide range of morphologies and have poorly defined shapes (Figure 1 d).