A novel method to tune surface wettability rapidly and reversibly has been developed by ion exchange of the counterions at the surface of a multilayer film assembled via electrostatic interaction.rnThe design and fabrication of smart surfaces with dynamically controllable properties has become a challenging task in materials science. Wettability is one of the important surface properties because it is crucial in many practical applications, such as adhesion, coating, microfluidics and superhydro-phobic surfaces. Surface wettability can be changed in an accurate manner by external stimuli, and the classical method is mainly concentrated on triggering the conformational or chemical changes on solid surfaces upon environmental variations, such as electrochemical potential, pH, solvent, irradiation or ionic strength. A potentially more versatile route to modulation of surface properties has emerged recently, which showed that the wettability of charged thin films can be tuned by choosing the proper counterions. Choi and co-workers reported that the wettability of monolayers self-assembled on gold substrate with imidazolium ions at the tail ends depended on the nature of the counterion, where the water contact angle increased from 25° to 65° when the Br~-counterion was replaced with bis(trifluoromethane) sulfoni-mide anion (TFSI).
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