Department of Materials Science and Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States.
Langmuir. 2017 May 30;33(21):5261-5268. doi: 10.1021/acs.langmuir.7b00759. Epub 2017 May 15.
Spectroscopic ellipsometry (SE) and quartz crystal microbalance (QCM) measurements are two critical characterization techniques routinely employed for hydration studies of polymer thin films. Water uptake by thin polymer films is an important area of study to investigate antifouling surfaces, to probe the swelling of thin water-containing ionomer films, and to conduct fundamental studies of polymer brush hydration and swelling. SiO-coated QCM crystals, employed as substrates in many of these hydration studies, show porosity in the thin electron-beam (e-beam) evaporated SiO layer. The water sorption into this porous SiO layer requires correction of the optical and mass characterization of the hydrated polymer due to changes in the SiO layer as it sorbs water. This correction is especially important when experiments on SiO-coated QCM crystals are compared to measurements on Si wafers with dense native SiO layers. Water adsorption filling void space during hydration in ∼200-260 nm thick SiO layers deposited on a QCM crystal resulted in increased refractive index of the layer during water uptake experiments. The increased refractive index led to artificially higher polymer swelling in the optical modeling of the hydration experiments. The SiO-coated QCM crystals showed between 6 and 8% void as measured by QCM and SE, accounting for 60%-85% of the measured polymer swelling in the low humidity regime (<20% RH) and 25%-40% of the polymer swelling in the high humidity regime (>70% RH) from optical modeling for 105 and 47 nm thick sulfonated polymer films. Correcting the refractive index of the SiO layer for its water content resulted in polymer swelling that successfully resembled swelling measured on a silicon wafer with nonporous native oxide.
光谱椭圆术（SE）和石英晶体微天平（QCM）测量是两种常用于聚合物薄膜水合研究的关键特性化技术。研究聚合物薄膜的水合作用对于研究防污表面、探测含有水的薄离聚物薄膜的溶胀以及进行聚合物刷水合和溶胀的基础研究是非常重要的。在许多这些水合研究中，SiO 涂层的 QCM 晶体被用作基底，在薄的电子束（e-beam）蒸发的 SiO 层中显示出多孔性。由于 SiO 层在吸水时发生变化，因此需要对水合聚合物的光学和质量特性进行修正，以修正多孔 SiO 层中水分的吸附。当将 SiO 涂层的 QCM 晶体上的实验与具有致密天然 SiO 层的 Si 晶片上的测量进行比较时，这种修正尤为重要。在 QCM 晶体上沉积的约 200-260nm 厚的 SiO 层的水合过程中，水吸附填充空隙空间，导致水吸收实验过程中该层的折射率增加。在水合实验的光学建模中，增加的折射率导致聚合物的人为溶胀更高。SiO 涂层的 QCM 晶体通过 QCM 和 SE 测量显示出 6%至 8%的空隙，占低湿度（<20%RH）下测量的聚合物溶胀的 60%-85%和高湿度（>70%RH）下的聚合物溶胀的 25%-40%，用于 105nm 和 47nm 厚的磺化聚合物膜的光学建模。对 SiO 层的折射率进行水分修正后，聚合物的溶胀成功地与非多孔天然氧化物硅晶片上的溶胀测量相匹配。
