Molecular layer-by-layer (mLbL) polyamide films are model polyamide films relevant to desalination membranes, which depend on a polyamide active layer to achieve high salt rejections. The key difference between mLbL polyamide films and the interfacial polymerized (IP) polyamide films traditionally found in desalination membranes, is the ability to grow the mLbL films one monomer layer at a time. This layer-by-layer growth allows for more control over the film’s material properties, such as film thickness, and was constructed by sequentially depositing trimesoyl chloride and m-phenylene diamine monomers via spin coating until the desired film thickness was achieved. The different functional groups of the two monomers promote bonding only at specific interaction points and allows the polymer to grow roughly 0.2-0.3 nm per spin. To gain additional insight on the relationship between the structure and the properties of the mLbL polyamide films, the mechanical properties and swelling behavior were characterized for films of varying thickness and compared to those of conventional IP polyamide films. The mechanical properties of the films were determined using the wrinkling-cracking technique, where thin films placed on a PDMS substrate and systematically strained. This technique allowed the plane-strain modulus of elasticity, fracture strength, and the onset fracture strain to be determined experimentally. Changes in film thickness upon varying humidity were also studied using ellipsometry. These results provide insight on the polyamide network structure and, when combined with the mechanical property data, expand our understanding of the structure-property relationship in polyamide films. By investigating polyamide films, important knowledge on how to positively impact the separating abilities of this film can be tested and obtained.

Mechanical properties and swelling behavior of molecular layer-by-layer polyamide films

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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