Modulating surface interactions for regenerable separation of oil-in-water emulsions

Developing antifouling coatings is of both fundamental and practical significance, but challenging, for membrane separation of oil-in-water (O/W) emulsions with charged surfactants, which has been conventionally achieved through the short-range hydration interaction from hydrophilic membrane surfaces as a physical barrier. Herein, we report a mussel-inspired antifouling coating formed by carboxyl and quaternary ammonium moieties bearing adjustable surface charge property, employing tunable long-range electrostatic interaction to achieve adaptive antifouling performance in response to the varying electrical characteristic of emulsions. The surface force measurement results showed that modulating the surface electrical properties of the coatings through varying the solution pH could effectively alter their electrostatic interactions with emulsions from attraction to repulsion, in combination with hydrodynamic interactions, to enable emulsion repellence of the coatings. Such functional coatings were further applied on a PVDF membrane with an enhanced water permeability and reusability achieved to separate both the positively and negatively charged emulsions. By properly modulating the membrane surface charge, the modified membrane demonstrated its adaptive antifouling performance for efficient and universal water treatment. This work provides useful insights into the antifouling mechanisms of membranes to O/W emulsions, as well as developing functional materials with tunable surface interactions for various engineering applications. [Display omitted] •An intelligent membrane with tunable long-range surface interaction is developed.•The as-prepared membrane is efficient in separating oil-in-water emulsions.•The membrane shows adaptive antifouling performance to the charged emulsions.•The membrane can be regenerated by simple immersion in aqueous solution.•The antifouling mechanism is discussed via direct surface force measurement.