Nanoscale silica capsules ordered on a substrate: oxidation of nanocellular thin films of poly(styrene-b-dimethylsiloxane).
Nanoscale silica capsules ordered on a substrate: oxidation of nanocellular thin films of poly(styrene-b-dimethylsiloxane).
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DOI：
10.1002/anie.200602274
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发表时间：
2006-09
影响因子：
--
通讯作者：
Lei Li;Hideaki Yokoyama
中科院分区：
文献类型：
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作者：
Lei Li;Hideaki Yokoyama
6338 2006 Wiley-VCH Verlag GmbH & Co. KGaA，魏因海姆Angew. Chem.Int.Ed.2006，45，6338-6341在102.6eV处。在用UV光/臭氧氧化10分钟后，该峰移动到104 eV，从而表明形成了氧化硅。[16]在蚀刻30分钟后，由于来自硅衬底的元素硅而出现在99 eV处的峰;这是膜厚度减小的指示。[16]因此，从分析中排除了由于元素硅引起的低于101 eV的信号。Si、C和O的原子分数绘制在图2b中。碳原子分数随氧化时间线性下降，在40 min时达到4.2%，这表明几乎完美的转化。O/Si比为2.4：1，接近二氧化硅的比例，表明PDMS纳米结构域已成功转化为有序的二氧化硅颗粒在substrate.We先前报道了一个成功的制造纳米细胞的嵌段共聚物薄膜的过程中，涉及超临界CO2（scCO 2）。[9-12]将具有亲CO2嵌段的嵌段共聚物的薄膜用CO2加压以将其定位在亲CO2纳米域中。在降低的温度下降低CO2压力后，亲CO2域中的CO2体积转化为空隙。在这项研究中，我们采用相同的方法与PS-PDMS嵌段共聚物，而不是氟化共聚物，在CO2-亲PDMS域制造纳米细胞。[13]将PS-PDMS薄膜置于20 MPa和60 ° C的高压容器中2小时;然后将温度等压降至0 ° C。随后，以0.5MPa每升的速率释放压力。整个过程与我们以前研究中用于氟化嵌段共聚物的过程相同。[9-12]将温度降低至08 ℃会冻结周围的PS基质（PS在20 MPa CO2中的Tg约为308 ℃）[17]并固定形态，同时大量CO2仍保留在PDMS域中。分析椭圆偏振法可以用来测量CO2过程之前和之后的膜的厚度和折射率，前提是纳米单元的尺寸比光的波长小得多，并且有效介质近似是有效的。scCO 2工艺后的厚度增量Δd为4.2 nm，初始厚度为43 nm。孔隙率为8.7%，假设膜尺寸在平面中由基底固定并且质量守恒。折射率从1.56降低到1.50，这对应于9%的孔隙率，根据Lorentz-Lorenz方程[Eq.（1）]。[18]在此，nf和ns是折射率。
6338 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2006, 45, 6338–6341 at 102.6 eV. This peak shifts to 104 eV after oxidation for 10 min with UV light/ozone, thereby indicating formation of silicon oxide.[16] After etching for 30 min, a peak at 99 eV due to elemental silicon from the silicon substrate appears; this is an indication of reduced film thickness.[16] The signal below 101 eV due to elemental silicon was therefore excluded from the analysis. The atomic fractions of Si, C, and O are plotted in Figure 2b. The atomic fraction of C decreases linearly with oxidation time and reaches 4.2% at 40 min, which indicates nearly perfect conversion. The O/Si ratio is 2.4: 1, which approximates to that of silicon dioxide and indicates that the PDMS nanodomains have been successfully converted into silica particles that are ordered on the substrate.We have previously reported a successful fabrication of nanocells in block-copolymer thin films by a process involving supercritical CO2 (scCO2).[9–12] A thin film of block copolymer with a CO2-philic block was pressurized with CO2 to localize it in the CO2-philic nanodomains. Upon reducing the CO2 pressure at reduced temperature, the volume of CO2 in the CO2-philic domains is converted into voids. In this study, we employ the same methodology with a PS-PDMS block copolymer instead of a fluorinated copolymer to fabricate nanocells in the CO2-philic PDMS domains.[13] A PS-PDMS thin film was placed in a high-pressure vessel at 20MPa and 608C for 2h; the temperature was then reduced isobarically to 08C. Subsequently, the pressure was released at a rate of 0.5 MPaminÀ1. The whole process is the same as that used for the fluorinated block copolymers in our previous study.[9–12] Reducing the temperature to 08C freezes the surrounding PS matrix (Tg of PS in 20 MPa of CO2 is approximately 308C)[17] and fixes the morphologies while a significant amount of CO2 still remains in the PDMS domains. Analytical ellipsometry can be used to measure the thicknesses and refractive indices of the films before and after the CO2 process, provided that the size of the nanocells is much smaller than the wavelength of light and the effective medium approximation is valid. The increment of thickness, Δd, after the scCO2 process is 4.2 nm from the initial thickness of 43 nm. The porosity is 8.7%, assuming that the film size is fixed in the plane by the substrate and the mass is conserved. The refractive index decreases from 1.56 to 1.50, which corresponds to 9% porosity, according to the Lorentz–Lorenz equation [Eq.(1)].[18] Herein, nf and ns are the refractive