Design Rules for Capillary Force-Induced Clustering and Recovery of Monolithic Microbridges on Microapertured Polymer Membrane.

Microbridge structures have been widely used in microelectromechanical systems. When the devices with microbridges operate in diverse environments, including wet conditions, structural failures such as crumples, clustering, and collapse of micro/nanostructures occur due to the capillary force of liquid in this environment. It is necessary to establish comprehensive design criteria to address this. Herein, we investigate the structural stability of microbridges on microsized apertures in wet conditions. The multiscale structure is fabricated with microbridge width, spacing of 10 µm, and height of 6 µm while varying the supporting micro aperture size. The behavior of the microbridges is observed through an optical microscope during water dispensing on the bridges and evaporation. It is found that the microbridges remain stable on apertures of 100 µm in diameter, while clustering occurs on larger-sized apertures (300, 500 µm). Interestingly, in contrast to the 500 µm-sized aperture, the clustered microbridges on the 300 µm-sized aperture gradually recover to their original configuration after completely evaporating water. A simple theoretical model for capillary force-induced clustering and recovery is proposed to elucidate this phenomenon, which agrees with the experimental results. The microbridges constructed following the design rule can ensure robust and stable operation even in wet conditions. These findings contribute to advancing micro/nanoscale engineering and offer insights for developing innovative microdevices.

Multiscale Architectured Membranes, Electrodes, and Transport Layers for Next-Generation Polymer Electrolyte Membrane Fuel Cells.

Over the past few decades, considerable advances have been achieved in polymer electrolyte membrane fuel cells (PEMFCs) based on the development of material technology. Recently, an emerging multiscale architecturing technology covering nanometer, micrometer, and millimeter scales has been regarded as an alternative strategy to overcome the hindrance to achieving high-performance and reliable PEMFCs. This review summarizes the recent progress in the key components of PEMFCs based on a novel architecture strategy. In the first section, diverse architectural methods for patterning the membrane surface with random, single-scale, and multiscale structures as well as their efficacy for improving catalyst utilization, charge transport, and water management are discussed. In the subsequent section, the electrode structures designed with 1D and 3D multiscale structures to enable low Pt usage, improve oxygen transport, and achieve high electrode durability are elucidated. Finally, recent advances in the architectured transport layer for improving mass transportation including pore gradient, perforation, and patterned wettability for gas diffusion layer and 3D structured/engineered flow fields are described.

Fabrication and design of mechanically stable and free-standing polymeric membrane with two-level apertures.

Herein, we report the fabrication process and the investigation of mechanically stable, flexible and free-standing polymeric membranes with two-level apertures. By using overlapped oxygen inhibition layers (OILs) with variation in diameters of the micro-sized supporting layer, we successfully fabricated the mechanically stable and free-standing polymeric membrane with micro/nano two-level apertures. The nano aperture membrane was stably sustained on the micro aperture membrane with a diameter of 50 µm and 100 µm, but was torn off in the case of 300 µm and 500 µm sized supporting layers. To analyze the results, we propose a simple model to set the criteria of the geometrical features which are mechanically stable during the demolding process. It is worth noting that an appropriate material modulus, length, and thickness of the membrane are required for designing and achieving the robust free-standing hierarchical polymeric membrane.