| Summary: | 碩士 === 國立臺灣大學 === 化學工程學研究所 === 85 ===
Self-assembled monolayers (SAMs) have many potential applications in a wide variety of fields and their durability makes an appealing alternative to Langmuir-Blodgett (LB) monolayers. The mechanism for monolayer formation is not yet well understood and there are discrepancies in the literature. For instance, Schwartz et al.(1992) showed that the growth pattern of the formation of octadecyltrichloro-silane (OTS) SAM on mica is nucleating isolated, self-similar domains according to their Atomic Force Microscopy (AFM) measurements. On the other hand, Xiao et al.(1995) found that incomplete monolayers form clusters without nucleation.
In this work, adsorption of OTS on steam-treated mica surfaces in hexadecane (HD) solution has been studied by AFM at different temperatures. Our measurements indicated the amount and distribution of adsorbed OTS was strong temperature dependent. OTS formed self-similar islands via nucleation at 20 ℃. A uniform distribution of many small domains without nucleation was seen at 35℃. Besides, the rate of reaction at 35℃ was faster than that of 20℃. A comparsion between the silanation process in HD with different water content showed the rate of reaction was faster in higher water content. It also suggested OTS was hydrolyzed not only on the substrate but also in the bulk phase. The rate of reaction was also faster in higher humidity and silane molecules formed large clusters on top of the monolayer. In addition, the coverage of the large clusters increased with silanization time. The height of the cluster was uniform (~ 6 nm) and the distribution was homogeneous. The kinetics of the silanation process under different reaction condition have been studied.
In the case of methyloctadecyidichlorosilane (MODS) incomplete monolayer with low coverage and inhomogeneous distribution formed without nucleation. The rate of reaction was slow.
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