Solvent-Induced Triradial Pattern Formation on Solid-Supported Viscoelastic Thin Films and Gels

Solvent-driven surface instabilities in soft materials offer a powerful route to generate spontaneous patterns without external templating; yet the mechanisms governing their emergence, evolution, and long-term modulation remain elusive. Here, we uncover the time-dependent formation of quasi-periodic triradial patterns on the surface of thin, soft silicone-based viscous films undergoing hexane extraction and drying. Using dual-wavelength reflection interference contrast microscopy, we observe a reproducible morphological progression: from shallow circular domains at short extraction times to a well-defined array of triradial, three-armed patterns at longer durations, driven by the buildup of internal stress, surface-to-bulk modulus gradients, and network densification. Systematic studies across silicone elastomers and gels reveal that while the triradial patterning is broadly conserved, its geometry is tunable by factors such as cross-link density and solvent retention. These results establish a general mechanism of solvent-mediated pattern formation in soft silicone-based viscous films and offer a potential route for designing dynamic and programmable surface architectures through controlled solvent processing.