Fig. 1: Spontaneously formed metal–elastomer nanophase and microscale 3D structure.

a Schematic illustration of the Au–PDMS nanophase self-forming via vaporized Au deposition on a PDMS substrate. By varying the crosslinking ratio of PDMS and the deposition thickness of metals, we controlled kinetics over three relevant dynamic processes: (1) migration of excess crosslinker, (2) condensation of metal atoms into interlinked Au nanostructures, and (3) growth of nanostructures and formation of the nanophase. Subsequently, spontaneous structural evolution followed to form microscale 3D structures owing to the stress inside. b Surface morphology change of Au–PDMS nanophases with various mixing ratio and deposition thickness of the metal. Scale bars denote 150 μm. c Photo images showing the corresponding colors of the samples for each condition. Three different of nanostructures were observed: “particles”, “3D nanophases”, and “continuous films.” Scale bars denote 1 cm. d Photographs showing spontaneous structural evolution over a period of 6 h after Au deposition. The length of the PDMS and metal rectangles are 10 mm and 5 mm, respectively. The colors of the samples changed according to 3D structure evolution. e An optical microscopy image of as-deposited sample (scale bar is 150 µm). f An optical microscopy image of 3D structure-formed (after 6 h) sample (scale bar is 150 µm). g Tilted SEM image of gyrified wrinkles (scale bar is 5 µm). h A cross-sectional SEM image of the gyrified structure. White arrows indicate folds due to structural expansion (scale bar is 1 µm). i An estimated local gyrification index (GI) of the human brain as an example akin to gyrified 3D structures of Au-PDMS nanophases. GI map of the brain adapted with permission from ref. ⁵¹. (CC BY 4.0).