Visualization of Film Formation by Interfacial Polymerization

Interfacial polymerization (IP) is widely used in the synthesis of thin film composite membranes. However, there are few reports on the observation of film formation by interfacial polymerization. In the present work, a visualized technology was developed for studying film formation by interfacial polymerization. The visualization used an optical contact angle measuring device (OCA) to visualize the film surface morphology. By the observation of the film surface morphologies facing organic phase and water phase, it was found that convexities were on the film surface adjacent to the organic phase, whereas concavities were on the film surface adjacent to the water phase. This clearly showed that the film grows toward the organic phase. The effects of various synthesis conditions (such as organic solvent, reaction time, reactants concentration, etc.) on film morphology were further studied. Particle image velocimetry (PIV) was employed to investigate the flow field in the vicinity of the water-oil interface. The results showed that convexities on the film surface were attributed to interfacial instability arising from the variations of interfacial tension with interfacial concentration near the water-oil interface. These convexities ultimately gave rise to the rough film surface. Based on the results of OCA and PIV, the film growth mechanism was proposed. This paper also indicated that OCA and PIV are very useful tools for in situ studying the fundamentals of IP film formation process.