Superhydrophilic PVDF membrane surface constructed with layer-by-layer assembly for oil/water separation

N-acryloyl glycinamide-based copolymer was synthesized via free‑radical polymerization. • Superhydrophilic/underwater superoleophobic PVDF membranes were fabricated via a layer‑by‑layer assembly. • Self-assembly membranes show high separation efficiency for various emulsions. • Anti-oil-fouling ability of self-assembly membrane was improved significantly. • Self-assembly membrane performance remains stable under adverse conditions. The efficient treatment of oil-contaminated water remains a persistent global challenge. Although polymer membranes with superwetting characteristics have seen rapid development, most existing materials face issues such as complex fabrication processes and an inability to separate different types of emulsions. In this study, a hydrophilic copolymer, P(NAGA‑co‑HEA), containing 2-hydroxyethyl acrylate (HEA) and N-acryloyl glycinamide (NAGA) units, was synthesized via free‑radical polymerization. Driven by hydrogen bonding between tannic acid (TA) and the copolymer, the superhydrophilic PVDF membrane was fabricated through a layer‑by‑layer (LBL) assembly strategy. The outcomes indicate that the membrane pore aperture decreases progressively with increasing coating degree due to pore blockage of deposited layers. The membrane surface exhibits a rough spherical micro‑/nanostructure, imparting superhydrophilicity, underwater superoleophobicity and anti‑oil adhesion properties. The pure water flux increases and then decreases with increasing coating coverage, while the separation efficiency for various oil-in-water emulsions reaches a maximum rejection ratio of 99.7%. A higher coating coverage also endows the separation membrane with enhanced antifouling properties, as demonstrated by its flux recovery ratio of 94.6% after three permeation cycles. The calculated membrane fouling index further reveals that as the coating coverage increases, the proportion of irreversible fouling in total fouling decreases, indicating that the introduction of the self-assembled coating significantly reduces irreversible oil fouling during the permeation process. Even after treatment with strong acid and high‑concentration saline solutions, the membrane retains stable surface wettability and separation efficiency. This work presents a promising surface‑modification approach for developing high‑performance membranes for oily wastewater remediation. Download: Download high-res image (256KB) Download: Download full-size image