Monitoring the process of interfacial polymerization for fabrication of polyamide reverse osmosis membrane via molecular simulation based on π-π interaction between surfactant and monomer

Accurate regulation of the interfacial polymerization (IP) process is prerequisite for preparation of thin film composite reverse osmosis (RO) membranes with ideal polyamide (PA) layers, and surfactant assembly-regulated IP (SARIP) is proved to be an effective approach. However, mechanism in molecular level for modulation of IP based on surfactants is still inadequate. Here, sodium dodecylbenzene sulphonate (SDBS) and sodium dodecyl sulfate (SDS) have been chosen as surfactants to make comparison of the IP process based on π-π interaction between surfactant and monomer via molecular simulation. As illustrated by Molecular Dynamics (MD) simulations, surfactants enlarge the width of the miscible zone, increase the diffusion rate together with the relative concentration of MPD in the miscible zone, as well as regulate the position of IP reaction towards the aqueous phase. Compared to SDS, SDBS makes the diffusion of MPD in good order, thus avoiding the severe variation in structure and morphology on PA layer. As calculated by DFT, higher interaction energy between the phenyl group of MPD and SDBS based on the π-π interaction is achieved, leading to uniform distribution of MPD close to the phenyl group of SDBS instead of escaping violently into miscible zone. Thus, strong consistency between the position of IP reaction and the height of the phenyl group in SDBS is emerged, which further explains the intrinsic reason for the variation of the IP position and the modulation of the PA microstructure. The mechanism for IP regulation based on SARIP at molecular level is finally proposed via molecular simulation, providing new idea for the preparation of high-performance RO membranes. [Display omitted] •SDS and SDBS surfactants in aqueous phase increase the transport rate of the monomer.•SDS and SDBS surfactants increase the width of the miscible zone validated by molecular simulation.•MPD diffusion is modulated by the π-π interaction between SDBS and MPD.•SDBS adjusts the position of IP reaction in miscible zone towards aqueous phase.•The diffusion mechanism of surfactant modulation of MPD is proposed by DFT.