Platschek Barbara, Köhn Ralf, Döblinger Markus, Bein Thomas
Department of Chemistry and Biochemistry, University of Munich, Butenandtstrasse 5-13 (E), 81377 Munich, Germany.
Langmuir. 2008 May 6;24(9):5018-23. doi: 10.1021/la7010937. Epub 2008 Apr 10.
The formation and subsequent transformations of mesostructured silica within the confined tubular environment of anodic alumina membrane (AAM) channels [porous alumina membrane (PAM) channels] were investigated for the first time in situ with grazing incidence small-angle X-ray scattering (GISAXS) techniques, in combination with ex situ transmission electron microscopy (TEM) of the same samples. A better understanding of the mesostructure formation mechanism within the confined space of the AAM pores is a direct result of this study. Three different surfactants were used as the structure-directing agents in acid-catalyzed silica synthesis solutions. With ionic cetyltrimethylammonium bromide acting as the structure-directing agent, a columnar hexagonal structure with mesopores oriented parallel to the AAM channels was observed to form directly from the beginning of the synthesis. In samples synthesized with the nonionic surfactants Brij 56 and Pluronic P123, a circular hexagonal structure was found to form first; here, the mesopores are aligned around the circumference of the AAM channels. The circular structure subsequently transforms directly into a columnar hexagonal (P123 surfactant), or a mixture of columnar hexagonal and a new curved lamellar phase with lamellae oriented parallel to the walls of the AAM channels (Brij 56 surfactant). These transformations occur after complete solvent evaporation and therefore differ from a simple evaporation-induced phase formation. The existence of a previously postulated lamellar phase could be proven by GISAXS and TEM investigations.
首次采用掠入射小角X射线散射（GISAXS）技术并结合对相同样品的非原位透射电子显微镜（TEM），在阳极氧化铝膜（AAM）通道[多孔氧化铝膜（PAM）通道]的受限管状环境中原位研究了介孔二氧化硅的形成及其后续转变。更好地理解AAM孔受限空间内的介观结构形成机制是本研究的直接成果。在酸催化的二氧化硅合成溶液中，使用了三种不同的表面活性剂作为结构导向剂。以离子型十六烷基三甲基溴化铵作为结构导向剂时，观察到从合成开始就直接形成了柱状六方结构，其介孔与AAM通道平行排列。在用非离子表面活性剂Brij 56和Pluronic P123合成的样品中，首先发现形成了圆形六方结构；此处，介孔围绕AAM通道的圆周排列。圆形结构随后直接转变为柱状六方结构（P123表面活性剂），或转变为柱状六方结构与新的弯曲层状相的混合物，其中层状结构与AAM通道壁平行排列（Brij 56表面活性剂）。这些转变发生在溶剂完全蒸发之后，因此不同于简单的蒸发诱导相形成。通过GISAXS和TEM研究可以证明先前假设的层状相的存在。
