Molecular and Mesoscopic Structures of Transparent Block Copolymer-Silica Monoliths
Molecular and Mesoscopic Structures of Transparent Block Copolymer-Silica Monoliths
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DOI：
10.1021/ma9817323
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发表时间：
1999-06
期刊：
影响因子：
5.5
通讯作者：
N. Melosh;P. M. Lipic;F. Bates;F. Wudl;G. Stucky;G. Fredrickson;B. Chmelka
中科院分区：
文献类型：
--
作者：
N. Melosh;P. M. Lipic;F. Bates;F. Wudl;G. Stucky;G. Fredrickson;B. Chmelka
采用两亲性三嵌段聚环氧乙烷-聚环氧丙烷-聚环氧乙烷（PEO-PPO-PEO）共聚物制备了介观有序、透明的二氧化硅表面活性剂单体。嵌段共聚物作为一种结构导向剂，因为水相二氧化硅阳离子在自组装体系的亲水区域内分配，并优先与PEO嵌段结合。随后在强酸性条件下（pH 1）聚合二氧化硅前驱体产生密集交联的二氧化硅网络，该网络可以由嵌段共聚物物种在介观上组织成具有特征有序长度尺度为bbb10 nm的复合材料。当这伴随着水溶剂的缓慢蒸发时，这种复合介观结构可以形成透明且无裂纹的整体（例如，直径2.5厘米，厚3毫米）。利用29 Si{1 H}和13 C{1 H}二维固体异核相关核磁共振技术和1 H核磁共振弛豫测量，原位研究了PEO和PPO共聚物嵌段在二氧化硅基体中的分布和动力学。用x射线衍射和透射电镜测定了细观结构的有序度。微相分离的程度和由此产生的大块样品的介观结构被发现强烈依赖于嵌段共聚物的浓度，浓度越高，有序度越高。
Mesoscopically ordered, transparent silica-surfactant monoliths have been prepared using amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) copolymer species to organize polymerizing silica networks. The block copolymer acts as a structure- directing agent, as the aqueous silica cations partition within the hydrophilic regions of the self-assembled system and associate preferentially with the PEO blocks. Subsequent polymerization of the silica precursor species under strongly acidic conditions (pH 1) produces a densely cross-linked silica network that may be mesoscopically organized by the block copolymer species into composites with characteristic ordering length scales of >10 nm. When this is accompanied by slow evaporation of the aqueous solvent, such composite mesostructures can be formed into transparent and crack-free monoliths (e.g., 2.5 cm diameter 3 mm thick). Distributions and dynamics of the PEO and PPO copolymer blocks within the silica matrix were investigated in situ using 29 Si{ 1 H} and 13 C{ 1 H} two-dimensional solid-state heteronuclear correlation NMR techniques and 1 H NMR relaxation measurements. Mesostructural ordering was determined by X-ray diffraction and transmission electron microscopy. The degree of microphase separation and the resulting mesostructure of bulk samples were found to depend strongly upon the concentration of block copolymer, with higher concentrations producing higher degrees of order.