Size Limit on the Formation of Periodic Mesoporous Organosilicas (PMOs)

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• 作者：Vivian Rebbin ; Andr茅 Rothkirch ; Noboru Ohta ; Takaaki Hikima ; S茅rgio S. Funari
• 刊名：Langmuir
• 出版年：2014
• 出版时间：February 25, 2014
• 年：2014
• 卷：30
• 期：7
• 页码：1900-1905
• 全文大小：252K
• 年卷期：v.30,no.7(February 25, 2014)
• ISSN：1520-5827

文摘

The decrease of the lattice size of periodic mesoporous organosilicas (PMOs) is one important goal in obtaining a microporous material for storage or adsorption of small molecules. To determine the influence of different synthesis parameters in the lattice size, here we performed in situ small-angle X-ray diffraction studies and show that a variation of the surfactant鈥檚 headgroup size is not directly followed by the lattice parameter of the resulting structure. We show that in the surfactant series of penta-, hexa-, hepta-, octa-, nona-, and decaethylene glycol monododecyl ether (C₁₂(EO)_n, n = 5, 6, 7, 8, 9, 10) the lattice size decreases between n = 5 and n = 8 and then increases, while the ordering of the materials is always cubic (space group Fd3m). This size effect is due to the ethylene oxide (EO) chain conformation that changes as the number of EO groups increases. Short ethylene oxide chains tend to have a so-called 鈥渮igzag鈥?conformation while an increase of the chain length leads to a 鈥淢盲ander鈥?(coiling) conformation. Although this phenomenon is most commonly observed for chains consisting of more than 10 ethylene oxide units, we found a minimum PMO lattice size for 8 EO units and intermediate values for 6 and 7 EO units. The increase of the lattice parameter for more than 9 EO units is attributed to the increasing number of 鈥淢盲ander鈥?configurated EO units.