辛基三乙氧基硅烷/十八烷基三氯硅烷均相混合自组装单分子膜的表征及其形成机制

使用接触角、原子力显微镜(AFM)、静电力显微镜(EFM)和傅里叶变换红外(FTIR)光谱对辛基三乙氧基硅烷(C8TES)/十八烷基三氯硅烷(OTS)均相混合自组装单分子膜(SAM)及其形成过程中样品表面的润湿性、表面形貌、表面电势和膜内分子的有序度进行了表征,对采用分步法利用C8TES分子空间位阻制备C8TES/OTS均相混合SAM的反应机制进行了研究.结果表明,C8TES/OTS均相混合SAM表面接触角为105°,样品表面平整、光滑;对样品表面电势进行分析后发现,混合SAM表面电势分布均匀,电势频率分布为典型的正态分布;在均相混合SAM的形成过程中,样品表面电势的分布始终十分均匀,电势频率分布均为典型的正态分布;C8TES/OTS均相混合SAM是一种具有上下两层分子排列密度不同的膜结构的单分子膜,其内部结构至少在500 nm×500 nm到20μm×20μm尺度上是高度均匀一致的,膜内没有明显的特征结构,具有典型的均相混合SAM特征.

Characterization of a Homogeneously Mixed Octyltriethoxyilane/Octadecyltrichlorosilane Self-Assembled Monolayer and Analysis of Its Formation Mechanism

The wettability, surface topography, surface potential, and degree of order of a homogeneously mixed octyltriethoxysilane (C8TES)/octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) were characterized by means of contact angle analysis, atomic force microscopy (AFM), electrostatic force microscopy (EFM), and Fourier transform infrared (FTIR) spectroscopy. The formation mechanism of the SAM was studied as the monolayer was constructed using a stepwise approach, taking advantage of the steric hindrance of C8TES. The SAM was found to have a contact angle of 105° and the formation process of the mixed SAM was obviously different from the SAM formation mechanisms of both pure C8TES and OTS. The AFM and EFM characterizations indicated that the mixed SAM had a smooth surface and a homogeneous surface potential distribution with a typical, normal surface potential frequency distribution. The internal structure was highly homogeneous over regions ranging from 500 nm×500 nm to 20 μm×20 μm in size. The FTIR analysis indicated that the mixed SAM had a double-layer film structure, and that the molecular densities were different in the two layers, with the layer closer to the substrate being denser. This work shows that steric hindrance effects can be used to allow the stepwise formation of homogeneously mixed SAMs, and that this method is especially applicable to the construction of the homogeneously mixed SAMs composed of two types of molecules having different head groups.