Preparation Of The Mixed Octyltriethoxysilane And Octadecyltrichlorosilane Self-Assembled Monolayers

Self-Assembled Monolayer (SAM) and its technology is a very important branch in the area of the modern nano-science and engineering. This paper studied the preparation technology of the mixed self-assembled monolayers (mixed SAMs) composed of octyltriethoxysilane (C8TES) and octadecyltrichlorosilane (OTS). Both the coadsorption method and the stepwise method were employed to construct the C8TES/OTS mixed SAMs. Our experimental results showed that, it was difficult to prepare mixed C8TES/OTS SAMs by means of the coadsorption method, since the difference of the reactive activities between the C8TES and OTS molecules could not be balanced through the tailoring of the concentration ratios of two components in the coadsorption solutions. However, by taking advantage of the steric restriction offered by the three ethoxyl groups on the heads of the C8TES molecules, as well as the difference of the chemical activities between the OTS and C8TES molecules, it was possible to construct both the homogeneously and phase-separated mixed C8TES/OTS SAMs by means of the stepwise method. We also explored the structure characteristics inside the C8TES SAM by the AFM scanning experiments, in which AFM cantilever tips with different spring constants were used, as well as the theoretical analysis of the molecular steric during the formation process of C8TES SAM. The research indicated that, the structure inside the pure C8TES SAM was indeed loose and unassembled completely, the molecule density inside the SAM was very low, which would result in an ultra-low surface contact angle, only 20～21°, on the C8TES SAM surface.