Hygroinduced motion is a fundamental process of energy conversion that is essential for applications that require contactless actuation in response to the day–night rhythm of atmospheric humidity. Here we demonstrate that mechanical bistability caused by rapid and anisotropic adsorption and desorption of water vapour by a flexible dynamic element that harnesses the chemical potential across very small humidity gradients for perpetual motion can be effectively modulated with light. A mechanically robust material capable of rapid exchange of water with the surroundings is prepared that undergoes swift locomotion in effect to periodic shape reconfiguration with turnover frequency of <150 min−1. The element can lift objects ∼85 times heavier and can transport cargos ∼20 times heavier than itself. Having an azobenzene-containing conjugate as a photoactive dopant, this entirely humidity-driven self-actuation can be controlled remotely with ultraviolet light, thus setting a platform for next-generation smart biomimetic hybrids.

Cloud-seeding materials as a promising water-augmentation technology have drawn more attention recently. We designed and synthesized a type of core/shell NaCl/TiO (CSNT) particle with controlled particle size, which successfully adsorbed more water vapor (∼295 times at low relative humidity, 20% RH) than that of pure NaCl, deliquesced at a lower environmental RH of 62-66% than the hygroscopic point (h., 75% RH) of NaCl, and formed larger water droplets ∼6-10 times its original measured size area, whereas the pure NaCl still remained as a crystal at the same conditions. The enhanced performance was attributed to the synergistic effect of the hydrophilic TiO shell and hygroscopic NaCl core microstructure, which attracted a large amount of water vapor and turned it into a liquid faster. Moreover, the critical particle size of the CSNT particles (0.4-10 μm) as cloud-seeding materials was predicted via the classical Kelvin equation based on their surface hydrophilicity. Finally, the benefits of CSNT particles for cloud-seeding applications were determined visually through in situ observation under an environmental scanning electron microscope on the microscale and cloud chamber experiments on the macroscale, respectively. These excellent and consistent performances positively confirmed that CSNT particles could be promising cloud-seeding materials.

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A porous composite of 3-dimensional (3D) reduced graphene oxide (rGO) and silica dioxide nanoparticles (PrGO-SN) was synthesized via a single-step hydrothermal process, which can initiate facile ice nucleation and growth starting from temperature as high as −8 °C and 5–8% RH supersaturation and sustain rapid ice crystal growth. The excellent ice nucleation activity of the PrGO-SN composite demonstrates a novel means of ice nucleation relative to known materials, attributed to not only the lattice match between the ice and crystalline structure of the PrGO-SN composite but also higher specific surface area, larger water vapor adsorption capacity, better porosity, and more hydrophilic surface of the composite than rGO. Moreover, environmental scanning electron microscope (E-SEM) in situ observation confirmed detailed growth patterns of ice crystals on the composite, which were affected by the regions with different surface roughness. These findings enabled further understanding of the factors that affected the heterogeneous ice nucleation process and shed light on the design and fabrication of more efficient functional porous ice nucleation materials for many practical applications such as cloud seeding.