Applied Surface Chemistry, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Goteborg, Sweden.
Langmuir. 2010 Feb 2;26(3):1983-90. doi: 10.1021/la902144h.
The interaction between silica and poly(ethylene oxide) (PEO) in water may appear trivial and it is generally stated that hydrogen bonding is responsible for the attraction. However, a literature search shows that there is not a consensus with respect to the mechanism behind the attractive interaction. Several papers claim that only hydrogen bonding is not sufficient to explain the binding. The silica-PEO interaction is interesting from an academic perspective and it is also exploited in the preparation of mesoporous silica, a material of considerable current interest. This study concerns the very early stage of synthesis of mesoporous silica under mild acidic conditions, pH 2-5, and the aim is to shed light on the interaction between silica and the PEO-containing structure directing agent. The synthesis comprises two steps. An organic silica source, tetraethylorthosilicate (TEOS), is first hydrolyzed and Pluronic P123, a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer, is subsequently added at different time periods following the hydrolysis of TEOS. It is shown that the interaction between the silica and the Pluronic is dependent both on the temperature and on the time between onset of TEOS hydrolysis and addition of the copolymer. The results show that the interaction is mainly driven by entropy. The effect of the synthesis temperature and of the time between hydrolysis and addition of the copolymer on the final material is also studied. The material with the highest degree of mesoorder was obtained when the reaction was performed at 20 degrees C and the copolymer was added 40 h after the start of TEOS hydrolysis. It is claimed that the reason for the good ordering of the silica is that whereas particle formation under these conditions is fast, the rate of silica condensation is relatively low.
二氧化硅与聚环氧乙烷（PEO）在水中的相互作用可能看起来微不足道，一般认为氢键是吸引力的原因。然而，文献检索表明，对于这种吸引力相互作用的机制并没有达成共识。有几篇论文声称，仅仅氢键不足以解释结合。从学术角度来看，二氧化硅-PEO 相互作用很有趣，它也被用于介孔二氧化硅的制备，介孔二氧化硅是目前非常感兴趣的一种材料。本研究涉及在温和酸性条件（pH 2-5）下合成介孔二氧化硅的早期阶段，目的是阐明二氧化硅与含 PEO 的结构导向剂之间的相互作用。该合成包括两个步骤。首先水解四乙氧基硅烷（TEOS），然后在 TEOS 水解后的不同时间加入聚环氧乙烷-聚环氧丙烷-聚环氧乙烷（PEO-PPO-PEO）嵌段共聚物 Pluronic P123。结果表明，二氧化硅与 Pluronic 的相互作用既取决于温度，也取决于 TEOS 水解开始后加入共聚物的时间。结果表明，相互作用主要由熵驱动。还研究了合成温度以及水解和共聚物加入之间的时间对最终材料的影响。当反应在 20°C 下进行且共聚物在 TEOS 水解开始后 40 小时加入时，获得了具有最高介孔有序度的材料。据称，二氧化硅有序度好的原因是在这些条件下，颗粒形成速度快，而二氧化硅缩合的速度相对较低。
