II. Development History

The Iteration from Fluorine-containing Modification to Fluorine-free Superhydrophobic Technology

2.1 Ages of Fluorinated Compounds: The "Double-Edged Sword" of Early Hydrophobic Modification

In the early development of PES membranes, fluorine-containing compounds like PFAS were pivotal for hydrophobic modification. By introducing fluoropolymers, researchers achieved ultra-low surface energy on membrane surfaces, enabling hydrophobic or even superhydrophobic properties (as shown in Fig 3). Such modified membranes excelled in oil-water separation and gas filtration .^[2]

However, the downsides of PFAS became evident over time. Its extreme chemical stability led to persistent environmental accumulation, with studies revealing bioaccumulation through food chains, disrupting immune and endocrine systems in humans and animals. In response, global regulations emerged: the EU’s REACH restricted PFAS use/production, while the US EPA set product content limits. ^[4][5] These policies spurred researchers to develop fluorine-free alternatives, driving innovation in sustainable PES membrane technology.

2.2 Fluorine-free Transformation: Hydrophobic Reconstruction of Hydrophilic PES

PES molecular chain contains polar sulfone groups, endowing it with hydrophilicity, which is advantageous in hemodialysis and biomedical cell/protein separation. Yet in scenarios requiring hydrophobicity , modification is needed. Two key technologies: non - solvent induced phase separation (NIPS) constructs a porous structure by regulating solvent - non - solvent exchange to control pore size [6]. Surface coating uses fluorine - free polymers . PVP reduces fluoride dependence (as shown in Fig4), enhances membrane mechanical strength and lifespan [6]. After surface coating, the PES membrane’s water contact angle reaches ≈150°, achieving hydrophobicity while maintaining chemical stability and biocompatibility.

Long Literature Review

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