Wettabilities of Organosiloxane Thin Films Derived from SiCl3-Terminated Carbosilane Dendrons on Mica

Abstract

We prepared submonolayers, monolayers, and multilayers of organosiloxanes derived from the second to fourth generation (G2−G4) SiCl3-terminated carbosilane dendrons on mica by spin-casting. The surface properties of these films, such as wettabilities, surface tensions, works of adhesion with various liquids, pore size, and surface coverage, were investigated by means of contact-angle measurements. All G2−G4 films exhibit high hysteresis of ∼20°, probably due to molecular scale chemical heterogeneity and surface roughness. The surface tensions of the G2−G4 monolayers are similar: γS (total) = ∼29 mJ/m2, γSd (dispersive) = ∼24 mJ/m2, and γSp (polar) = ∼5 mJ/m2. However, only γSd (∼21 mJ/m2) contributes to the surface tensions of the multilayers, suggesting that the underlying polar mica substrate is significantly screened by the dendron multilayers. Works of adhesion (WSL) for water, glycerol, dimethylformamide, methylene iodide, squalane, and hexadecane on the films were measured. The multilayers exhibit a lower WSLd (dispersive) than the monolayers (difference of ∼3 mJ/m2), consistent with a decrease of γSd from monolayers to multilayers. Furthermore, both the average pore size and the surface coverage of the G2−G4 monolayers were estimated to be 0.31−1.1 nm2 and ∼77%, respectively.