Functionalization of Electrospun Membranes with Polyelectrolytes for Separation of Oil‐In‐Water Emulsions

Membrane fouling in microfiltration of oil-in-water emulsions is influenced by electrostatic interaction between the membrane and surfactant-stabilized emulsions. A method to alter the electrostatic properties of electrospun fiber membranes using layer-by-layer (LbL) polyelectrolyte assembly is developed to improve fouling resistance. Plasma pretreatment and successive depositions of polycations and polyanions from solutions are shown to alter the surface charge of electrospun polyamide membranes, while maintaining their interconnected pore structure and high porosity. The LbL composite membranes were challenged by two types of emulsions, stabilized by anionic and cationic surfactants, respectively, in dead-end and cross-flow filtrations. When separating emulsions stabilized by anionic surfactants, the permeate flux of the plasma-treated and polyanion-coated membranes increased approximate to 3.2-fold and approximate to 2.5-fold, respectively, compared to that of the as-electrospun membranes, after 4 h of cross-flow filtration. When separating emulsions stabilized by cationic surfactants, the permeate flux of the polycation-coated membrane similarly increased approximate to 3.3-fold. Electrostatic repulsion strength is proposed as a metric to quantify this behavior. This work demonstrates the versatility of functionalizing electrospun microfiltration membranes using LbL assembly for the separation of oil-in-water emulsions, and suggests a strategy for membrane design to resist fouling based on tuning of the electrostatic interactions.