DPD simulation on the formation of polyamide thin-film membrane via interfacial polymerization and experimental verification

The rapid and complex dynamics of interfacial polymerization (IP) have long hindered real-time monitoring, limiting fundamental insights into the synthesis–structure–performance relationship of polyamide thin-film composite (PA TFC) membranes. In this work, the IP process, where aqueous and organic monomers react to form a thin PA membrane layer, was successfully simulated using the Dissipative Particle Dynamics (DPD) method at a large scale, with the hexane-trimesoyl chloride/water-piperazine (hexane-TMC/water-PIP) system serving as a representative model. Coarse-grained models and interaction parameters for all molecular species were first developed, and a DPD-based protocol for simulating the IP reaction was subsequently established, enabling a systematic investigation of membrane formation at the mesoscale level. By adopting the concentrations employed in experimental studies, the simulation results showed that, in the early stage of IP, high-molecular-weight polymer chains form rapidly; as steric hindrance accumulates, shorter chains are increasingly generated, stabilizing the PA molecular weight. Then, the effect of monomer concentration on membrane formation dynamics and the resulting PA layer morphology was systematically investigated. The results showed that simultaneous increases in both monomer phases promote the formation of shorter PA chain segments, leading to increased membrane thickness and reduced pore size. In contrast, increasing the concentration of a single monomer phase favors the formation of longer PA chains, resulting in negligible changes in membrane thickness while slightly reducing pore size. Finally, a support-free IP process was employed to prepare PA membranes, and the corresponding membrane structures and thickness evolution were measured to validate the simulation results. This work aims to provide a large-scale, DPD-based model capable of simulating the IP process in different practical systems to form TFC membranes, thereby enabling a deeper understanding of membrane formation kinetics.