Interfacial Polymerization Kinetics for Reverse Osmosis Membranes

Reaction kinetics for interfacially polymerized reverse osmosis (RO) membranes are difficult to obtain and seldom reported due to the rapid (~seconds) formation of a thin film. In this work, film formation is studied using an interferometric based technique. Light is passed through a semireflective microfluidic device, to obtain fringes of equal chromatic order (FECO fringes). The wavelengths of FECO fringes are tracked as a function of time to obtain changes of refractive index, which correspond to changes in solute concentrations. Hence, monomer depletion in each phase is tracked throughout the reaction, with data acquisition at rates up to tenths of a second. Directly visualizing the depletion zone near the interface allows for measuring the reagent flux and ultimately properties of the reaction itself. We report the first measurement of concentration profiles as the reaction proceeds, as well as reaction rate.