Improving the wettability of structural steels by employing ionic liquids

Abstract

Surface wetting behavior is tied to different surface phenomena such as lubrication and corrosion resistance of steel surfaces. In this study, the surface wetting behavior of room-temperature ionic liquids (RTILs) treated steel surfaces is investigated. To this end, polished steel surfaces are individually surface-treated using seven imidazolium-based RTILs with varying alkyl chain lengths ([CnMIM], n = 2, 4, 6) and anion groups ([PF6], [NTf2], [Br], [BF4], [AlCl4]) for two different exposure durations (0.5 h and 4 h). The wetting behavior of RTIL-treated steel surfaces is quantified in terms of contact angles and surface energies corresponding to polar (water) and non-polar (diiodomethane) probing liquids. The RTIL surface treatment is observed to improve the surface wetting behavior of steel surfaces for both polar and non-polar probing liquids. The average initial water contact angle of steel surfaces decreased by 24−87% after RTIL surface treatment. Similarly, the average initial non-polar liquid contact angles of RTIL-treated steel surfaces decreased by 25−66% when compared to the untreated steel surface. The water contact angle decreased with an increase in the time elapsed after droplet impingement on the surface, whereas, for the non-polar liquid, the contact angle remained relatively unchanged during the elapsed duration adopted herein. The average surface free energy of RTIL-treated steel specimens increased by 49%−100%, which rendered the RTIL-treated steel surfaces more wettable. The increase in the RTIL treatment time only nominally improved the wetting of steel surfaces for both polar and non-polar probing liquids. The results reported herein can be used to prepare the surfaces of inaccessible structural steel components and bridge bearings for efficient water cleaning and lubrication.