Micro-regulation on the two-phase interface of heterogeneous braid-reinforced hollow fiber membrane via hydrophobic tail in surfactant: Molecular dynamics simulation and experimental analysis

Achieving strong interface interaction between the polymer and braid layers is crucial for sustaining the performance of heterogeneous braid-reinforced hollow fiber membranes (BR HFMs) and prolonging their service life. In this study, five types of Span-based surfactants with various hydrophobic tails were adopted for microregulation on the two-phase interface of the polymer-braid and separation layer in the membrane preparation via non-solvent induced phase separation (NIPS). Microscopic mechanisms of transmission processes on interface interaction and phase separation were studied using molecular dynamics simulation (MDS) and experimental analysis. The results showed that the nonpolar tail of Span-based surfactants exhibited different arrangements in two-phase interfacial environments. Specifically, they tended to move toward the solution-braid interface when contracting with the braid, whereas inclined to be immersed in the solution matrix during phase separation progress. The aggregation of hydrophobic tails at the interface contributed to reducing the surface tension of the solution and acquiring a more stable state of the solution-polyethylene terephthalate (PET) system, which enhanced the wettability of the solution on the braided filaments. Thereby, the interfacial compatibility between the casting solution and the BR material was improved. Moreover, Span 65 with a medium length of three hydrophobic branches induced more tightly packing on the solution-braid interface, diffusing and wetting the hydrophobic fiber surface easily, resulting in the strongest interface binding force. This study offered guidance for understanding the transmission processes of surfactants at the two-phase interface, as well as designing optimal additive structures to enhance the properties of heterogeneous BR HFMs.