Dattelbaum Andrew M, Amweg Meri L, Ruiz Julia D, Ecke Laurel E, Shreve Andrew P, Parikh Atul N
Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Phys Chem B. 2005 Aug 4;109(30):14551-6. doi: 10.1021/jp051401+.
The evolution of photochemical surfactant removal and silica condensation from organically templated thin film silica nanocomposites with mesoscopic ordering has been probed using a combined application of Fourier transform infrared (FT-IR) spectroscopy and single wavelength ellipsometry. Thin films of silica nanocomposites were prepared by a previously reported evaporation-induced self-assembly process. Specifically, oxidized silicon and gold substrates were withdrawn at 25 mm/min from a subcritical micelle concentration solution containing an ethylene oxide surfactant as a structure-directing agent and tetraethyl orthosilicate as a silica precursor. Real-time grazing incidence difference FT-IR spectra of the nanocomposite films on gold taken during exposure to short-wavelength ultraviolet light (184-257 nm) show that surfactant removal and silica condensation occur gradually and concomitantly. Surfactant removal and silica reconstructions were found to be nearly complete after 90 min of exposure. Further, a transient feature was observed in the FT-IR spectra around 1713 cm(-1) during the UV exposure process and was assigned to a carbonyl (C=O) stretching mode absorption, reflecting the transient formation of a partially oxidized surfactant intermediate. From these data we propose a stepwise model for surfactant removal from the nanocomposite films. Ellipsometrically determined index of refraction values collected as a function of UV exposure are also shown to support such a stepwise mechanism of surfactant removal from the ordered nanocomposite silica thin film mesophases studied here.
利用傅里叶变换红外（FT-IR）光谱和单波长椭偏仪的联合应用，研究了具有介观有序性的有机模板化薄膜二氧化硅纳米复合材料中光化学表面活性剂去除和二氧化硅缩合的演变过程。二氧化硅纳米复合材料薄膜是通过先前报道的蒸发诱导自组装过程制备的。具体而言，将氧化硅和金基底以25毫米/分钟的速度从含有环氧乙烷表面活性剂作为结构导向剂和正硅酸乙酯作为二氧化硅前驱体的亚临界胶束浓度溶液中取出。在短波长紫外光（184 - 257纳米）照射期间对金上的纳米复合薄膜进行实时掠入射差分FT-IR光谱分析，结果表明表面活性剂去除和二氧化硅缩合是逐渐且同时发生的。发现照射90分钟后表面活性剂去除和二氧化硅重构几乎完成。此外，在紫外照射过程中，FT-IR光谱在1713厘米⁻¹附近观察到一个瞬态特征，该特征归因于羰基（C=O）伸缩模式吸收，反映了部分氧化的表面活性剂中间体的瞬态形成。根据这些数据，我们提出了纳米复合薄膜中表面活性剂去除的逐步模型。作为紫外照射函数收集的椭偏测量确定的折射率值也表明支持此处研究的从有序纳米复合二氧化硅薄膜中间相中去除表面活性剂的这种逐步机制。
