Autonomous Interfacial Assembly of Polymer Nanofilms via Surfactant-Regulated Marangoni Instability

Interfacial polymerization (IP) provides a versatile platform for fabricating defect-free functional nanofilms for various applications, including molecular separation, energy, electronics, and biomedical materials. Unfortunately, coupled with complex natural instability phenomena, the IP mechanism and key parameters underlying the structural evolution of nanofilms, especially in the presence of surfactants as an interface regulator, remain puzzling. Here, we interfacially assembled polymer nanofilm membranes at the free water-oil interface in the presence of differently charged surfactants and comprehensively characterized their structure and properties. Combined with computational simulations, an in situ visualization of interfacial film formation discovered the critical role of Marangoni instability induced by the surfactants via various mechanisms in structurally regulating the nanofilms. Despite their different instability-triggering mechanisms, the delicate control of the surfactants enabled the fabrication of defect-free, ultra-permselective nanofilm membranes. Our study identifies critical IP parameters that allow us to rationally design nanofilms, coatings, and membranes for target applications.