(415a) Free Energy Surface Landscape of Interfacial Polymerization for Polyamide Membrane Formation

Conventional thin film composite polyamide membranes formed by interfacial polymerization (IP) has been widely used for water purification with nanofiltration (NF) and reverse osmosis (RO) applications. More recently, polyamide membranes have been developed for organic solvent resistant NF membranes. IP employs fast irreversible polymerization at the interface between the multifunctional monomers, m-phenylene diamine (mPD) in aqueous phase and trimesoyl chloride (TMC) in the organic phase yielding thick or thin films with low or high water permeance and good solute rejection. It is difficult to control the reaction leading a rough surface. Molecular layer-by-layer (mLBL) deposition has the potential to generate a kinetically controlled smooth membrane with desired pore structure and porosity. In order to better understand the reaction between mPD and TMC during IP, it is desirable to determine the reaction free energy and reaction rate as well as the effects of solvent, additives on the polymerization reactions. Here ab initio molecular dynamics (MD) simulations coupled with metadynamics (MTD) were performed to determine the free energy landscape for the IP reaction under different solvent conditions. Our results indicate that solvent plays a major role on the activation energy of the reaction and could potentially speed up or slow down the reaction for better control of the polyamide membrane structures.