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Investigation of the viscoelastic and transport properties of interfacially polymerized barrier layers using pendant drop mechanical analysis



Pendant drop mechanical analysis (PDMA) enables the mechanical and transport characterization of unsupported interfacially polymerized (IP) thin films. PDMA was used to study the viscoelastic and permeation behavior of films formed by the interfacial polymerization of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). The viscoelastic properties were obtained by stress-relaxation experiments wherein IP films on the surface of aqueous MPD drops were deformed and the decrease in the internal pressure resulting from stress relaxation was monitored with time. The stress-relaxation behavior was interpreted using the fractional exponential relaxation model. The two model parameters, τ and β, are related to the degrees of crosslinking and branching, respectively. Water transport was generated by an osmotic gradient across the IP films, and permeation data were obtained by monitoring the increase in the drop size with time. Whereas the network structure was relatively insensitive to MPD concentration, the TMC concentration had a significant effect on the degrees of crosslinking and branching; τ evidenced a maximum at 0.1 wt % TMC concentration and β decreased monotonically with TMC concentration. The effect of organic-phase reactant functionality was studied by incorporating isophthaloyl chloride (difunctional) with TMC. For TMC fractions > 25 wt %, the network structure was relatively insensitive to TMC fraction in the isophthaloyl chloride–TMC mixture. The transport experiments enabled the determination of a membrane constant A. The transport results generally corroborated the trends observed in the stress-relaxation experiments, thus demonstrating the close association between the network structure and transport behavior. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 558–568, 2004