Light Stimuli-Responsive Superhydrophobic Films for Electric Switches and Water-Droplet Manipulation.

Fabrication of superhydrophobic films with large and sensitive deformed actuations driven by light stimuli for the emerging application fields such as biomimetic devices, artificial muscles, soft robotics, electric switches, and water-droplet manipulation remains challenging. Herein, a facile strategy is proposed to fabricate a light stimuli-responsive superhydrophobic film (LSSF) by integrating a bottom carbon nanotube/poly(vinylidene fluoride) (CNT/PVDF) layer, a middle chitosan (CS) layer, and a top superhydrophobic fumed silica-chitosan (SiO2/CS) layer modified with 1H,1H,2H,2H-heptafluorodecyltrimethoxysilane (FAS). Under near-infrared (NIR) light irradiation, the LSSF quickly bent toward the CS layer with a large bending angle (>200°), high sensitivity (∼7 °C change), and great repeatability (>1000 cycles), which was attributed to the significant difference in the coefficient of thermal expansion (CTE) between CS and PVDF and the water desorption-induced volume shrinking in the CS layer. Furthermore, the LSSF also exhibited superhydrophobicity with a high water contact angle of 165° and a low water sliding angle of 2.8°. Importantly, owing to the high light absorption of CNTs, the LSSF-based biomimetic flower was able to not only bloom under NIR light exposure but also normally work when applying sunlight irradiation. Thanks to the electric conductivity and excellent water repellency, the LSSF was capable of being designed as an electric switch to remotely turn on/off the circuit even under a watery environment, and the LSSF was further successfully applied in water-droplet manipulation. The findings conceivably provided a new strategy to fabricate light stimuli-responsive superhydrophobic films for versatile applications.

Bioinspired Superhydrophobic Thermochromic Films with Robust Healability.

Thermochromic films with intriguing functionalities have great potential in soft actuators, heat storage devices, and interactive interface sensors. Inspired by the unique features of bird feathers (such as Nicobar pigeon, Anna hummingbird, mandarin duck, etc.), a superhydrophobic thermochromic film (STF) with robust healability is proposed for the first time through sandwiching an electric heater between a top thermochromic layer and a bottom poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) substrate. The STF exhibits fast and reversible color conversions of blue-pink-yellow under a low input power and has a superhydrophobic property with a contact angle of 155°. Furthermore, owing to the strong dynamic dipole-dipole interactions between the polar CF3 groups of flexible PVDF-HFP chains, the STF possesses a robust healing capability of structure and conductivity. By means of the temperature difference generated by the objects contacting (finger, iron, and water) as a stimulus, the STFs achieve tactile imaging and writing record with advantages of transient display, automatic erasure, and excellent reusability. Additionally, the STF-based anti-counterfeiting security labels with superhydrophobicity and three-state color switching simultaneously realize facile distinguishment and difficult forgery. The findings conceivably stand out as a new methodology to fabricate functional thermochromic materials for innovative applications.