Ion-specific effect on self-cleaning performances of polyelectrolyte-functionalized membranes and the underlying nanomechanical mechanism

Abstract In chemical and environmental engineering processes, polyelectrolyte surfaces have been widely used and exploited for their antifouling and self-cleaning properties. Ions widely exist in these processes; however, the influence of ions has been conventionally over-simplified. Herein, we have investigated the ion-specific effect on the wetting behaviors on polyelectrolyte surfaces as well as the self-cleaning performance of polyelectrolyte-functionalized membranes. The underlying nanomechanical mechanisms were characterized by direct force measurements between water droplets and various polyelectrolyte surfaces in oil (i.e., toluene). Interestingly, the aqueous anions can significantly modulate the surface interactions through aligning or disordering interfacial water molecules, which subsequently facilitate or inhibit the water wetting behaviors on polyelectrolyte surfaces, respectively. The ion-specific effect of different anions coincides with the well-known Hofmeister series. In contrast, cations show negligible effect. The polyelectrolyte-functionalized membranes show excellent antifouling and self-cleaning performances to oil in KAc and KCl solutions, but relatively poor performance in KSCN solution, agreeing well with the force measurements. This work provides new insights into the ion-specific interaction mechanism between water and polyelectrolyte surfaces, with useful implications for the efficient use of the antifouling and self-cleaning properties of polyelectrolyte-based materials in various chemical and environmental engineering applications (e.g., membrane filtration, oil/water separation).