Enabling Soft Molds for Manufacturing Polymeric Surface Structures with Overhangs

This study establishes design principles that enable soft polymer molds to reliably replicate microstructured surfaces containing re-entrant and doubly re-entrant overhangs—geometries that normally interlock and fail during demolding. The authors develop a physics-based stability model by balancing elastic recovery energy of overhanging ‘cantilever’ features against adhesion energy (self-adhesion) that drives microscale collapse. The model predicts critical aspect-ratio thresholds as a function of elastic modulus and geometry for several overhang types (rectangular beam, circular-hole cantilever, ring-shell cantilever). The framework is experimentally validated using PDMS daughter molds with tuned moduli (via base:curing-agent ratio) and SEM inspection, showing that stiffer PDMS formulations maintain hierarchical overhang integrity while softer formulations collapse. Using stable molds, the team successfully molded thermosetting polymers (PDMS, SU-8, polyurethane) to produce high-fidelity doubly re-entrant micropillar arrays over large areas. Functional liquid repellency tests (water and IPA) confirmed defect-free replication, demonstrating a scalable route to manufacturing complex biomimetic omniphobic surfaces.