Aggregation structure and surface properties of 18-nonadecenyltrichlorosilane monolayer and multilayer films prepared by the Langmuir method

The 18-nonadecyltrichlorosilane (NTS) monolayer with a vinyl end group was prepared by the Langmuir method. The monolayer with a hydrophilic carboxylated surface was subsequently obtained by oxidation of the vinyl end group. For the multilayer preparation, the NTS monolayer was immobilized onto the hydrophilic carboxylated NTS (NTS_COOH) monolayer. The NTS multilayer film was obtained by repetitions of depositions and oxidations. Aggregation structure of the NTS multilayer film was evaluated on the basis of X-ray reflectivity (XR), Brewster angle infrared (IR) spectroscopic measurements, electron diffraction (ED) and atomic force microscopic (AFM) observations. It was revealed that the NTS multilayer film with a well-ordered structure could be prepared by the Langmuir method. The local height control was performed by utilizing the phase-separated mixed monolayer being composed of the NTS and [2-(perfluorooctyl)ethyl]trichlorosilane (FOETS) molecule. The (NTS/FOETS) mixed monolayer showed phase-separated structure like sea-island, whose domain and matrix phases were composed of crystalline NTS and amorphous FOETS molecules, respectively. The (NTSCooH/FOETS) mixed monolayer with the hydrophilic domain and the hydrophobic matrix was obtained by selective oxidization of the NTS phase in the (NTS/FOETS) mixed monolayer. Furthermore, the local height control on the NTS_COOH phase of the (NTS_COOH/_FOETS) mixed monolayer was performed by chemisorption of NTS from the solution. The height increase in the NTS_COOH phase was confirmed by AFM and lateral force microscopy (LFM).