Interfacial polymerization (IP) plays a crucial role in the fabrication of high-performance polymer membranes. However, challenges such as rapid reaction rates, confined reaction zones, and unpredictable membrane morphologies have hindered their industrial application and optimization. Recent research has concentrated on the kinetics of IP by observing changes in concentration, temperature, and thickness at the reaction interface. Despite these efforts, few studies have considered the effect of varying flow rates during IP.

In this study, a coaxial microfluidic device was designed to investigate the membrane formation along an immiscible liquid-liquid interface in both dripping and jetting modes. The reaction takes place near the interface between hydrophilic anime (TEPA, dispersed pha...[ Read more ]

Interfacial polymerization (IP) plays a crucial role in the fabrication of high-performance polymer membranes. However, challenges such as rapid reaction rates, confined reaction zones, and unpredictable membrane morphologies have hindered their industrial application and optimization. Recent research has concentrated on the kinetics of IP by observing changes in concentration, temperature, and thickness at the reaction interface. Despite these efforts, few studies have considered the effect of varying flow rates during IP.

In this study, a coaxial microfluidic device was designed to investigate the membrane formation along an immiscible liquid-liquid interface in both dripping and jetting modes. The reaction takes place near the interface between hydrophilic anime (TEPA, dispersed phase) and isocyanate dissolved in paraffin oil (HMDI, continuous phase) without producing any biproducts. In-situ observation with an optical microscope revealed that the outer surface of the membrane became crumpled due to reaction instability triggered by a relatively high concentration of HMDI (15.0 wt%). SEM images of inner and outer surface morphologies indicated the partitioning of monomer TEPA into the oil phase, resulting in homogenous polymerization with two distinct stages. Furthermore, the flow of the continuous phase significantly inhibits the process of IP, and the membrane formation rate is of the order of 10⁻³ of the interfacial velocity. By defining three physical parameters, the experiments demonstrated that the interfacial velocity is inversely proportional to the membrane formation rate across various HMDI concentrations. To clarify the mechanism of IP kinetics, a reaction-diffusion-advection model was established to describe this inhibitory effect. From a Lagrangian perspective in fluid mechanics, we found that the nature of inhibiting is due to the continuous removal of oligomers by the flow, which interrupts the IP reaction. On the other hand, the Eulerian perspective suggested that a specific point exists in space where the reaction could overcome the advection, allowing the reaction to proceed. Numerical simulations of membrane formation were conducted using COMSOL Multiphysics. At a relatively low concentration (5.0 wt%), results showed that the membrane formation rate was around 0.15 µm/s, with thickness changes remaining under 1 µm, consistent with experimental observations.