Garcia-Bennett Alfonso E, Brohede Ulrika, Hodgkins Robert P, Hedin Niklas, Strømme Maria
Nanotechnology and Functional Materials, Department of Engineering Sciences, The Angström Laboratory, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden.
Langmuir. 2007 Sep 11;23(19):9875-81. doi: 10.1021/la700899s. Epub 2007 Aug 16.
The purpose of this work is to study the kinetics of self-assembly in the formation mechanism of anionic templated mesoporous solids (AMS-n) during the first few seconds of the synthesis as well as to demonstrate the use of alternating ion current (AIC) conductivity measurements to follow the self-assembly in complex hybrid systems. The formation of different AMS-n caged-type mesostructures through the delayed addition of the silica source is demonstrated and explained in terms of the interaction between the co-structure-directing agent (CSDA) and the oppositely charged surfactant headgroup regions. Our findings, supported by transmission electron microscopy, 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, dynamic light scattering (DLS) measurements, and powder X-ray diffraction suggest that the interaction of the CSDA with the surfactant headgroup occurs within seconds after its addition to the synthesis gel leading to interaction between the polymerizing CSDAs and the oppositely charged micelle and to an increase in the micelle-CSDA aggregate size. Both DLS and AIC measurements agree that this process occurs within the first 1000 s after addition of the CSDA to the synthesis gel at room temperature. In addition to the mechanistic study it was found that the intermediate materials are comprised of a three-layer entity. Time-dependent 29Si MAS NMR studies reveal that an organo-silica layer forms around the micelles prior to a condensed outer inorganic shell of silica.
这项工作的目的是研究阴离子模板介孔固体（AMS-n）形成机制中自组装的动力学，研究合成最初几秒内的情况，并证明使用交变离子电流（AIC）电导率测量来跟踪复杂混合体系中的自组装过程。通过延迟添加硅源来形成不同的AMS-n笼型介观结构，并根据共结构导向剂（CSDA）与带相反电荷的表面活性剂头基区域之间的相互作用进行了说明。我们的研究结果得到了透射电子显微镜、29Si魔角旋转核磁共振（MAS NMR）光谱、动态光散射（DLS）测量和粉末X射线衍射的支持，表明CSDA与表面活性剂头基的相互作用在其添加到合成凝胶后的几秒钟内发生，导致聚合的CSDA与带相反电荷的胶束之间相互作用，并使胶束-CSDA聚集体尺寸增加。DLS和AIC测量均表明，在室温下将CSDA添加到合成凝胶后的最初1000秒内会发生此过程。除了机理研究外，还发现中间材料由三层实体组成。随时间变化的29Si MAS NMR研究表明，在二氧化硅的凝聚外层无机壳形成之前，胶束周围会形成一层有机硅层。
