Combined Infrared Thermography, X-ray Radiography, and Computed Tomography for Ink Drying Studies

This work describes the comparison of drying behavior of ink deposited on two substrates used commonly in polymer electrolyte fuel cells (PEFCs): microporous layer (MPL) and Nafion. For the same drying conditions and ink composition, ink deposited onto the MPL dried faster and also formed cracks faster. During drying, ink deposited on the MPL had more cracks and smaller intercrack spacing compared to ink deposited on Nafion. Smaller intercrack spacing for ink on the MPL substrate is explained by the higher critical stress predicted by the model. A novel combination of infrared (IR) thermography, X-ray radiography, and computed tomography (CT) is used to characterize ink drying behavior. X-ray radiography with fast temporal resolution showed the existence of skin on the top of drying film that formed due to slow convective ink transport within the film and fast evaporative drying. From X-ray CT, detailed three-dimensional data was obtained on crack morphology within the drying film and was correlated to temperature profiles obtained with IR-thermography. The formation of a Y-crack in the film deposited on the MPL was correlated to the defect within the MPL substrate. The combination of three techniques is a unique probe to capture the temporal, thermal, and morphological evolution of drying ink.