The First Organosiloxane Thin Films Derived from SiCl3-Terminated Dendrons. Thickness-Dependent Nano- and Mesoscopic Structures of the Films Deposited on Mica by Spin-Coating

Abstract

This article describes a new type of organosiloxane thin films derived from SiCl3-terminated carbosilane dendrons of the second, third, and fourth generations, containing 9, 27, and 81 SiCl3 terminal groups. The films were deposited on mica surfaces by spin-coating from solutions of the dendrons with a series of concentrations. The resulting submonolayer to multilayer films were investigated with atomic force microscopy (AFM). AFM studies showed that the morphology of the films was highly dependent upon the generation of the dendrons and the film thickness. Mesoscopic ring, disk, or hole structures were observed. These structures were composed of nanoparticles with sizes corresponding to one dendron molecule or the cluster of a few laterally bound molecules. At submonolayer coverage, the molecules tended to flatten and spread out on mica surfaces. Significantly, this study showed that molecularly flat monolayers could be obtained with the dendrons containing up to 81 SiCl3 terminal groups. Prior to curing, the dendron films could be shaved by an AFM tip, while the films became robust after curing at elevated temperatures, indicating the formation of a strong siloxane network among the dendron molecules. Direct AFM observations indicated that the ring structures were formed from isolated droplets during the evaporation of the liquid thin films. The mechanisms for the formation of the observed film morphology are discussed, based on the structure and properties of the dendrons and the effect of the evaporation process.