The effect of humidity on the stability of octadecyltrichlorosilane for the self-assembled monolayer coating applications

The coating processes involving octadecyltrichlorosilane (OTS) self-assembled monolayers are known to be highly irreproducible due to the bulk hydrolysis reaction with the release of Cl, forming aggregates of siloxane (Si–O–Si) bonded networks. Factors known to affect deposition include temperature, solvent and most importantly water content of the coating solvents. Bulk silanization reaction of octadecyltrichlorosilane in cyclohexane was investigated at varying relative humidities. In situ FTIR transmission was used to determine OTS converting from silane to silanol along with water content and ion chromatography analysis from the release of Cl gas as a function of extended period of times. Silane to silanol conversion did not occur at less than 18% relative humidity over an 11 days test whereas all silanes converted to silanols after 2 days at a relative humidity of 83%. Based on these results, one may conclude that there is a finite lifetime for silane molecules during coating before converting into silanols.