Fig. 2: Structure, mechanism, and actuation performance of the LCN/SF bilayers.

a Schematic illustration of material composition and actuation principle in the photothermal radiation state i) and high humidity state ii). b Photothermal actuation mechanism of the LCN layer. Light irradiation induces reversible switching between the splayed and disordered molecular configurations. c Humidity-triggered actuation mechanism of the SF layer. The flat bilayer film shows hygroscopic expansion when the RH increases to a level below 65% and reverts to its original flat state upon returning to 30% RH. However, when RH exceeds 65%, it shows transient bending due to the disruption of hydrogen bonds by water molecules, and subsequently bends toward the SF layer side upon removal of the high humidity. d Digital photos of the bilayer actuator under different light intensities. θ represents the bending angle. Scale bar: 5 mm. e Digital photos of the bilayer actuator under different RH (below 65%). κ represents the bending curvature. Scale bar: 5 mm. f Digital photos of three critical states during and after exposure to 85% RH: the peak transient state, equilibrium state, and final fixed state. Scale bar: 5 mm. g Dependence of bending angle on the light illumination time under different intensities. h Time-dependent variation in bending curvature during cyclic switching between 30% and 65% RH. i Evolution of bending curvature during the increase of humidity from 30% to 85% RH, holding at 85% RH, and subsequently returning to 30% RH