Dip-Coating of a Nanometer-Thick Fluorinated Imidazolium Ionic Liquid: Layer Structure, Formation Mechanism and Wetting Behavior
Year: 2026
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide In this work, the film formation mechanisms and wetting behavior have been investigated for a nanometer-thick highly fluorinated imidazolium-based ionic liquid (HFILOH) deposited on silica substrate via dip-coating. Through systematic variation of solution concentration and dwell time, it is found that the nanometer-thick HFILOH forms a dual-layer structure consisting of a self-limiting bonded layer and a concentration-dependent mobile layer. Kinetic modeling reveals that the formation of the bonded layer follows reversible pseudo-first-order adsorption kinetics, with the equilibrium bonded thickness remaining constant at ∼0.8 nm across all concentrations, while characteristic time constants decrease from ∼2080 s to ∼ 314 s with increasing concentration. The mobile layer thickness exhibits excellent linear correlation with concentration ( R 2 = 0.99), consistent with Landau–Levich hydrodynamic theory for dilute solutions. These results demonstrate that HFILOH film formation in dip-coating is governed by the dual mechanisms of site-limited adsorption and viscous flow entrainment. Contact angle measurements reveal hydrophilic-oleophobic wetting behavior, with hexadecane contact angles remaining consistently high (∼70–75°) while water contact angles increase modestly from ∼ 30° to ∼ 40° with dwell time, indicating time-dependent molecular reorganization and preferential orientation of fluorinated chains at the HFILOH-air interface. This interpretation of a fluorine-rich outer surface is in good agreement with angle-resolved X-ray photoelectron spectroscopy and dynamic contact angle measurements previously reported for nanometer-thick HFILOH coatings on silica, which directly show fluorinated segments enriched at the film–air interface and stable hydrophilic–oleophobic wetting. Together, these findings provide mechanistic insight into the structure–property relationships controlling ionic liquid nanofilm functionality and establish HFILOH as a promising candidate for applications like antifogging, self-cleaning, and oil–water separation.
Source: Langmuir
Authors: Abdulmalik Dahiru, Lei Li
Institution: University of Pittsburgh
Language: English
Subfield: Catalysis
Field: Chemical Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $4,500
OpenAlex ID: W7151539796