Hygrothermal degradation of (3-glycidoxypropyl)trimethoxysilane films studied by neutron and X-ray reflectivity and attenuated total reflection infrared spectroscopy
Hygrothermal degradation of (3-glycidoxypropyl)trimethoxysilane films studied by neutron and X-ray reflectivity and attenuated total reflection infrared spectroscopy
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DOI：
10.1021/la0474870
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发表时间：
2005-05-10
期刊：
影响因子：
3.9
通讯作者：
Majewski, J
中科院分区：
文献类型：
--
作者：
Yim, H;Kent, MS;Majewski, J
有机硅烷薄膜在促进附着力、耐久性和耐腐蚀性方面具有重要的技术价值。然而，众所周知，水可以降解有机硅烷薄膜，特别是在高温下。本文采用X射线和中子反射率(XR和NR)和衰减全反射红外光谱(ATR-IR)相结合的方法，研究了3-缩水甘油基三甲氧基硅烷(GPS)在80℃饱和D2O或H2O中暴露不同时间后薄膜内部的化学和结构变化。D2O和H2O都提供了与GPS的中子散射对比。测量了样品干燥后的中子散射长度密度(SLD)分布(质量密度和原子组成的函数)随时间的变化，并在室温下用H2O或D2O蒸汽膨胀。对于在测量前干燥的样品，水调节直到3.5天几乎没有变化，但在调节30天后观察到很大的变化。随着XR的出现，这种结构变化的调节时间范围缩小到4至10天。SLD分析表明，处理后的GPS膜的上半部分转变为一层厚的低密度层，但下半部分的结构变化不大。以前的硝基硝基甲烷溶胀GPS膜的NR研究表明，膜的中心部分的交联度比离衬底最近的区域低得多。目前的数据表明，中央部分也随着水的膨胀而膨胀得更大，水解率更快。红外光谱分析表明，其化学降解机理为硅氧烷键的降解。对于ATR-IR，GPS薄膜是通过浸渍涂覆的方法制备的，这导致了比旋涂样品更大和更可变的厚度。红外光谱显示，在处理的前3天，邻近硅醇的生成增加，随后是双硅醇的生成。因此，NR和XR检测到的结构变化大致与双硅醇产生的开始相吻合。最后，在80摄氏度下用D2O处理1个月的薄膜的反射率数据几乎没有变化。这表明，在D2O中，Si-O-Si的水解比在H2O中慢得多。
Thin films of organosilanes have great technological importance in the areas of adhesion promotion, durability, and corrosion resistance. However, it is well-known that water can degrade organosilane films, particularly at elevated temperatures. In this work, X-ray and neutron reflectivity (XR and NR) were combined with attenuated total reflection infrared (ATR-IR) spectroscopy to study the chemical and structural changes within thin films of (3-glycidoxypropyl)trimethoxysilane (GPS) after exposure for various periods of time to air saturated with either D2O or H2O at 80 degrees C. For NR and XR, ultrathin (similar to 100 angstrom) films were prepared by spin-coating. Both D2O and H2O provide neutron scattering contrast with GPS. Variations in the neutron scattering length density (SLD) profiles (a function of mass density and atomic composition) with conditioning time were measured after drying the samples out and also swelled with H2O or D2O vapor at room temperature. For samples that were dried out prior to measurement, little or no change was observed for H2O conditioning up to 3.5 days, but large changes were observed after 30 days of conditioning. The range of conditioning time for this structural change was narrowed to between 4 and 10 days with XR. The SLD profiles indicated that the top portion of the GPS film was transformed into a thick low-density layer after conditioning, but the bottom portion showed little structural change. A previous NR study of as-prepared GPS films involving swelling with deuterated nitrobenzene showed that the central portion of the film has much lower cross-link density than the region nearest the substrate. The present data show that the central portion also swells to a much greater extent with water and hydrolyzes more rapidly. The chemical degradation mechanism was identified by IR as hydrolysis of siloxane bonds. For ATR-IR, GPS films were prepared by dip-coating, which resulted in a greater and more variable thickness than for the spin-coated samples. The IR spectra revealed an increase in vicinal silanol generation over the first 3 days of conditioning followed by geminal silanol generation. Thus, the structural change detected by NR and XR roughly coincided with the onset of geminal silanol generation. Finally, little change in the reflectivity data was observed for films conditioned with D2O at 80 degrees C for 1 month. This indicates that hydrolysis of Si-O-Si is much slower with D2O than with H2O.