Advanced membrane separation is a highly efficient technology for cutting energy consumption in the traditional chemical separation process. Further performance improvements demand greater knowledge of the current membrane system at the microscopic scale. However, the complexity and heterogeneity often present in commercialized membranes confound the link between the morphology and performance observed. This difficulty is particularly prominent in the study of thin film composite membranes with polyamide made by interfacial polymerization, the dominant materials platform used globally for reverse osmosis and nanofiltration. To clear the existing ambiguity, the molecular layer-by-layer assembly method (mLbL) has been developed to prepare thin films with nanoscale control. We report on the mLbL fabrication and characterization of novel polyamide networks. The thin film is fabricated by the alternating dispense of two monomers that rapidly react with each other. The thickness of thin films, ranging from sub-10 nm to tens of nanometers, is precisely controlled by the cycle number and a linear thickness growth rate is confirmed by spectroscopic ellipsometry. The orientation and molecular spacing of films are investigated by the grazing-incidence X-ray scattering. The network density is determined from the functionalities inside the thin film measured by infrared reflection-absorption spectroscopy. These high-fidelity characterizations based on the well-defined organic networks can contribute to the illustration of performance observed in the further application and the knowledge is translatable to other separation membrane platforms.

Nanoscale structure control and high-fidelity characterization of molecular layer-by-layer assembled thin film

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