Development of pendant drop mechanical analysis as a technique for determining the stress–relaxation and water‐permeation properties of interfacially polymerized barrier layers

Interfacial polymerization (IP) involves the formation of solid polymeric films at the interface between aqueous and immiscible organic solutions via an interfacial polycondensation reaction between complementary monomeric reactants present in the two solutions. IP films are very thin (<0.25 μm) and form effective barrier layers in interfacially polymerized thin‐film composite membranes. Considerable difficulties are encountered in applying conventional characterization techniques to such unsupported IP thin films. This article describes the development of a novel technique, pendant drop mechanical analysis (PDMA), which can be used to study the mechanical and transport behavior of unsupported IP films. Experiments were conducted on films formed in a PDMA apparatus via the IP polymerization of m‐phenylene diamine and trimesoyl chloride (TMC). Stress–relaxation data obtained via PDMA were fitted with the Williams–Watts equation, and the results indicated a statistically significant dependence of the model parameters on the TMC concentration. Permeation experiments also demonstrated a statistically significant dependence of the membrane constant on the TMC concentration. The results provide unique insights regarding the relationship between structure and performance in unsupported IP films and suggest that network formation is enhanced in a concentration range of 0.1–0.3 wt % TMC. Although refinements are required, PDMA appears to be a promising technique for identifying optimum IP reaction conditions and assessing corresponding mechanical and transport characteristics.