Fresh water is integral to health, food security and economic prosperity. An increasing reliance of communities on water desalination means that we need to better understand water transport and contaminant rejection in these systems.<br/>Commercial desalination membranes exhibit relatively rough surfaces on their active polyamide layer. Recently, a novel preparation via molecular-layer-by-layer spin coating of alternating monomer solutions has been presented by Christopher Stafford, that allows manufacturing thin polymer layers on very flat substrates. We prepare ultrathin (&lt;5 nm thickness) layers of cross-linked aromatic polyamide on wafers topped either with a native oxide layer of with Au or Pt coatings. We present high-resolution X-ray photoelectron spectroscopy of these layers, showing that their functional groups resemble those on commercial desalination membranes. The presence of these groups indicates the suitability of these films as model systems for desalination applications. We can provide qualitative assignments of the different chemical species and quantitative analysis of relative signal intensities. We quantify beam damage that occurs when investigating ultrathin polymer films with synchrotron-based X-ray light.<br/>Using ambient-pressure XPS, we probe the solid/liquid interface in situ with high chemical resolution. We present the interaction of water with the functional groups at the interface and in the film. Ambient pressure XPS can make the protonation of the amide groups directly visible. This study forms the basis of further investigations of the film structure, the diffusion of water, and the exclusion mechanism for water contaminants.

Reactivity at the solid/liquid interface of a desalination model system

2019 Spring National Meeting

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