Dynamic Contact Angle Studies of Self-Assembled Thin Films from Fluorinated Alkyltrichlorosilanes

Abstract

Dynamic contact angle studies on self-assembled thin films from C 7 F 15 CH 2 OCH 2 CH 2 CH 2 SiCl 3 reveal a range of interesting behavior. Solution-based processing conditions have been identified that allow preparation of essentially monolayer films on quartz exhibiting water adv/rec contact angles of 119/104 ( 2°and extremely low contact angle hysteresis (hexadecane adv/rec ) 74/70°, heptane adv/rec ) 56/55°) with hydrocarbon liquids. This compound provides an example of a fluorinated trichlorosilane that is able to deliver lowhysteresis films by deposition at room temperature. Adsorption of silane oligomers, formed by hydrolysis and condensation reactions in solution, was also found to occur, slower than but competitive with monolayer formation. This process became more significant as dip coating times increased. Ellipsometric data on silicon wafers confirmed that film thicknesses increased with dip time, while AFM imaging showed that the oligomeric material was deposited in the form of particulates. The effects of this process on water dynamic contact angles are discussed. We also compare contact angles on these films with those on films prepared from C n F 2n+1 CH 2 CH 2 SiCl 3 (n ) 6, 8, 10) and draw some conclusions regarding structure-property effects in these systems. Finally, we propose a mechanism that can account qualitatively for the bulk of the results observed here. Its central feature is reaction of the fluorinated alkyltrichlorosilane with surface-adsorbed water to yield a self-assembled monolayer consisting of silanetriol molecules hydrogen-bonded to the substrate. Effects of high humidity aging on dynamic contact angles of these films suggest that they are at most only lightly cross-linked when prepared under conditions utilized here.

In vitro stability study of organosilane self-assemble monolayers and multilayers

“…Nihei et al reported that hydrophobic organosilane coatings are more effective in enhancing hydrolytic stability than hydrophilic organosilane coatings, while tested in vivo in the oral cavity for years [34]. Water was believed to be able to penetrate SAM and multilayer coatings, especially hydrophilic ones, through imperfections [35,36]. This process caused the surface to reconstruct, and even displaced the organosilane molecules on the surface.…”

Hydrophobic monolayer preparation by Langmuir–Blodgett and chemical adsorption techniques

“…A 10-μl drop of Milli-Q water was first dispensed onto the surface, and subsequently a fluid volume of 5 μl was withdrawn from the drop at a rate of 0.1 μl/s, and the drop profile was imaged. A high receding contact angle of 102.2 • was attained, confirming complete surface coverage of the chemically adsorbed film [22]. The Owens, Wendt, and Fowkes concept [23,24] is often used to calculate the free energy of smooth, homogeneous surfaces, via the following extension of the Young equation:…”

Superoleophobic Coatings with Ultralow Sliding Angles Based on Silicone Nanofilaments

“…The CA of water and hexadecane on the sample are 117.78 and 79.68, respectively; these values are among the highest for self-assembled fluoroalkylsilane films on flat substrates. [14] According to the Wenzel model, the introduction of surface roughness will make the surface more oleophilic if the CA of organic liquids is lower than 908. Indeed, the surface becomes superoleophobic after nanofilaments are introduced under proper conditions.…”