Minimal Surfaces in Porous Materials: X-Ray Image-Based Measurement of the Contact Angle and Curvature in Gas Diffusion Layers to Design Optimal Performance of Fuel Cells

We inject water at a low flow rate through gas diffusion layers containing different percentages of polytetrafluoroethylene (PTFE) coating: 5, 20, 40, and 60%. use high-resolution three-dimensional X-ray imaging to identify the arrangement fibers, water, air in pore space. also quantify contact angle meniscus curvature once has spanned layer, ceased, reached position equilibrium. The average pressure breakthrough increase with amount coating, although we see wide range angles values both above below 90°, indicating mixed-wet state. that menisci form minimal surfaces (interfaces zero curvature) consistent pinned gas-water-solid contacts. Scanning electron microscopy images fibers show coated have rough surface. Between 93 100% contacts identified were found on rough, hydrophobic, or boundary between uncoated (hydrophilic) (hydrophobic) regions; hypothesize these are pinned. one exception is 60% PTFE which shows distinctly hydrophobic properties negative capillary (the higher than air). presence suggests pressures equal, allowing readily without build-up. From topological principles, Gaussian implies fluid phases well connected. implication results explored for design porous materials where simultaneous two occurs over saturation range.