Session: Analytical Division Poster:

Determining thin film properties, such as water content, is important to a variety of applications, including fuel cell efficiency, lipid bilayer characterization, and polymer analysis. Generally, current methods to measure thin film water content involve multiple instrumental techniques to measure thin film wet mass and dry mass separately, or costly neutron reflectivity facilities. By measuring the water content of a well-characterized polyelectrolyte film using a quartz-crystal microbalance with dissipation monitoring (QCM-D) paired with a deuterium oxide exchange (D₂O), the viability and limitations of this simple, single-instrument technique were examined. The method involved a two-step experiment to measure water content in situ. First, multilayer films of alternating poly(sodium 4-styrenesulfonate, PSS) and poly(allylamine hydrochloride, PAH) were self-assembled from solution onto the QCM-D sensor substrate. After measuring the hydrated film thickness of the self-assembled film by QCM-D, a D₂O solvent exchange was performed to quantify the exchangeable water within the polyelectrolyte film. Generally, the measured water contents of this work were in good agreement with literature studies that used coupled techniques, especially for films with hydrated thicknesses greater than 20 nm. These results highlight the utility of this single-instrument method to measure thin film solvent content.

Cadet Nestor Levin

USAF Academy

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