Figure 5. Stimuli responses from different wrinkle structures with distinct size scales.

Optical microscope images of 2G structure observed (a) before and (b) after the RH response measurement. (c) a schematic illustration of the humidity response of the 2G structure. The humidity response can be categorized into three regimes; (i) wrinkle regime (response of wrinkles); (ii) complex regime (responses of both wrinkles and microcracks); (iii) self-healing regime (response of microcracks). With increasing RH modulation cycles, the humidity response changes from (i) through (ii) to (iii). Optical microscope images of 1G structure (d) before and (e) after the RH response measurement. The 1G structure (f) can be eliminated at higher relative humidity, to give an almost flat surface (g), and it recovers its original morphology at lower humidity, as shown in (d) and (e).