Beyond Superwetting Surfaces: Dual-Scale Hyperporous Membrane with Rational Wettability for “Nonfouling” Emulsion Separation via Coalescence Demulsification

Membrane fouling is the obstacle that limits the practical application of membranes in efficient oil/water separation. The main reason for membrane fouling is the deposition of the dispersed phase (e.g., oil) on the membrane surface based on the sieving effect. The key challenge for solving the fouling problem is to achieve fouling removal via rationally considering hydrodynamics and interfacial science. Herein, a poly(vinylidene fluoride) membrane with a dual-scale hyperporous structure and rational wettability is designed to achieve a continuous "nonfouling" separation for oil/water emulsions via membrane demulsification. The membrane is fabricated via dual-phase separation (vapor and nonsolvent) and modified by in situ polymerization of poly(hydroxyethyl methylacrylate) (contact angle 59 ± 1°). The membrane shows stable permeability (1078 ± 50 Lm-2h-1bar-1) and high separation efficiency (>99.0%) in 2 h of continuous cross-flow without physicochemical washing compared to superwetting membranes. The permeation is composed of two distinct immiscible liquid phases via coalescence demulsification. The surface shearing and pore throat collision coalescence demulsification mechanism is proposed, and rational interface wettability facilitates the foulant/membrane interaction for "nonfouling" separation. Beyond superwetting surfaces, a new strategy for achieving "nonfouling" emulsion separation by designing membranes with a dual-scale hyperporous structure and rational wettability is provided.