Effect of Solvents and Concentration on the Formation of a Self-Assembled Monolayer of Octadecylsiloxane on Silicon (001)

Abstract

We have explored the effects of solvent, adsorber concentration, and environment on the formation of high-coverage monolayers of alkylsiloxanes on silicon oxide surfaces from alkylsiloxane solutions. Specifically, we have varied the solvent polarity and the concentration of octadecyltrichlorosilane (OTS) used for the deposition process. We found that for a wide range of concentrations (25 µM to 2.5 mM) and normal laboratory air humidity (RH 45-85%) OTS dissolved in heptane causes the formation of a full-coverage self-assembled monolayer on hydrophilic silicon oxide. The resulting self-assembled layers were studied by atomic force microscopy, ellipsometry, and X-ray reflectometry. Deposition of OTS from dodecane solutions resulted in multilayered films. In contrast, the use of heptane as solvent (in which the solubility of water is at intermediate level between toluene and dodecane) caused the formation of high-quality monolayers. We found consistent and reproducible results for the effect of solvents (dodecane and heptane) and conditions on the formation of OTS layers on Si/SiO2 surfaces. The substrates, which are covered by a full monolayer, function as well-defined ultraflat hydrophobic surfaces for other experiments.

Effect of contact angle hysteresis on thermocapillary droplet actuation

“…The quality of the grafted monolayers depends strongly on the process environment, including the temperature, 34,35 total immersion time [36][37][38] solvent type, 38,39 silane concentration, 38 water content, 36,37 and roughness of the native oxide layer. 37 Given the number of variables controlling the coating quality, it is no surprise that the grafting process is extremely sensitive to environmental conditions.…”

Challenges and developments of self-assembled monolayers and polymer brushes as a green lubrication solution for tribological applications

“…32 Rozlosnik et al compared toluene with heptane and dodecane and found that multilayers were formed using dodecane. 53 However, it is thought that the multilayers were physisorbed and could be easily removed by a glove dipped in hexane. Heptane also produced a full coverage of OTS SAM similar to other solvents, however toluene was still regarded as the best.…”

“…Heptane also produced a full coverage of OTS SAM similar to other solvents, however toluene was still regarded as the best. 53 The reason for this is due to different solubility of water in these solvents, which can affect adsorption process of OTS on the hydrophilic silicon oxide surface.…”

“…144 OTS has shown the ability to form multilayers in poor solvent on both steel and silicon, however, it is reported that the layers were found to be extremely rough indicating a consistent multilayer has not been formed. 53,145 In addition, authors that have used MAC, 70,108,110 apply the mobile lubricant through spin coating possibly limiting applications in some areas.…”

Effects of Tailored Surface Chemistry on Desorption Electrospray Ionization Mass Spectrometry: a Surface-Analytical Study by XPS and AFM

“…However, despite extensive efforts, the silanization reaction could still be affected by irreproducibility in the macroscopic properties (i.e., wettability and contact angle hysteresis) of the deposited film, when experimental variables such as the nature of the substrate [19], temperature [20], concentration [21,22], solvent type [23], and water content [24,25] are not under strict control. By controlling these parameters, it can be possible to obtain a structure of alkylsilane monolayers with good reproducibility because agglomeration during the deposition is minimized [26,27].…”