Self-assembly of octadecyltrichlorosilane monolayers on mica

Abstract

A method is described to deposit a securely attached, self-assembled monolayer of octadecyltrichlorosilane (OTS) on the surface of freshly cleaved muscovite mica. Comparison of the infrared methylene spectra with those of closely packed Langmuir-Blodgett films implies that the surface coverage of the OTS films was a fraction 0.8–0.9 that of films formed by Langmuir-Blodgett (LB) methods. However, LB monolayers are less securely attached to the substrate. The contact angle of water on these self-assembled monolayers remained over 100° for over 24 h and it suffered no noticeable degradation after prolonged reflux in cyclohexane. The method to form an OTS monolayer on mica involves three steps; first, ion exchange of the native K+ ions of cleaved mica for H+ ions; second, control of the quantity of resulting water on the mica surface; third, adsorption and surface polymerization of octadecyltrichlorosilane (OTS) by self-assembly from dilute cyclohexane solution.

An AFM Study of the Effects of Silanization Temperature, Hydration, and Annealing on the Nucleation and Aggregation of Condensed OTS Domains on Mica

“…Similarly, the amount of water present in the reaction solution and at the solution-substrate interface also influences the packing and organization of the monolayer. Tripp and Hair have demonstrated that OTS monolayers do not form on completely dehydrated silica (26,27) and Carson and Granick report similar results for dehydrated mica (28). The self-assembly process requires a certain amount of water (either in the bulk solution or on the substrate surface) to hydrolyze the OTS molecules.…”

“…The HCl treatment is designed to produce surface hydroxyl groups on mica, similar to the steam treatment procedure (3,28). Pashley has demonstrated that mica surfaces exposed to slightly acidic solutions (pH ~ 6) undergo complete exchange of K + counterions for solution H + ions (37).…”

“…Parameters such as silanization temperature and hydration greatly influence monolayer self-assembly (26)(27)(28)(29)(30)(31). A solvent independent critical temperature of around 28°C for OTS monolayer formation on silica has been identified; above this temperature adsorbed OTS molecules are disordered and expanded and below which they are closely packed and ordered (29)(30)(31).…”

Characterization of Montmorillonite Surfaces After Modification by Organosilane

“…Various methods have been employed to increase the number of surface-OH groups on mica (which is nearly devoid of active surface sites), which act as anchoring points for additional surface-OH groups. For example, increased coverage by silanes on mica was attained by (1) pre-treatment with water and hydrochloric acid for octadecyltrichlorosilane (C18H37SIC13) coverage (Carson and Granick, 1990), (2) prehydrolysis of alkyltrialkoxysilanes followed by monolayer self-assembly (Kessel and Granick, 1991), (3) pretreatment with water vapor plasma (Parker et aL, 1989(Parker et aL, , 1990, and (4) a combination of (2) and (3) (Wood and Sharma, 1994). The objective of the acid pre-treatment is to remove octahedral cations, each of which leaves behind two additional Si-OH groups (RausellColom and Serratosa, 1987).…”

Nano- and microtribological characterization of silanes deposited on cobalt substrate

“…Fluoroalkylsilanes as a self-assembled monolayer (SAM) consist of three building groups: a head group that reacts with a substrate, a backbone molecular chain group, and a terminal group that interacts with the outer surface of the film [2,3]. Fluoroalkylsilanes are formed through hydrolysis reactions, to make bridging siloxane bonds that anchor to the surface and also crosslink to form stable interconnections with adjacent molecules [4][5][6][7][8][9][10]. In recent research, the modification of surface properties and functionality through changes in the terminal group has been studied [11][12][13].…”