Photogated humidity-driven motility

Abstract

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.

A monolithic hydro/organo macro copolymer actuator synthesized via interfacial copolymerization

“…The shape transformations of biological organisms [1][2][3][4][5][6] have been the inspiration for many products in the field of artificial muscles, [7][8][9][10][11][12][13] soft robotics, [14][15][16][17][18][19] sensors 20 and complex shape engineering. 21,22 For example, the leaves of the Venus flytrap snap together to capture insects by virtue of the synergy between the hydroelastic instability and asymmetric expansion of the inner and outer surfaces at the cellular level.…”

A solar actuator based on hydrogen-bonded azopolymers for electricity generation

“…Most of the currently known light-driven LCEs have been constructed by introducing azobenzenes into polymer networks. [1][2][3]5,[11][12][13][14][15][16][17][18][19][21][22][23][24][25] The trans-to-cis isomerization under UV light and cis-to-trans isomerization with visible light makes the azobenzene group a robust, durable, and fatigueless photoswitchable unit that is now ubiquitous in photoactive materials. [26][27][28] trans-Azobenzene is a liquid crystal mesogen, which stabilizes liquid crystal phases, while the cis-azobenzene is not a liquid crystal mesogen and usually destabilizes the liquid crystal phases.…”

“…Previous work has shown that the shape of AG-based actuators is the primary factor that determines their bending performance. 20,22 To investigate these effects, the response to sunlight of F-Azo@AG lms with different shapes were studied. F-Azo@AG lms were cut into strips with a xed length and different widths (length, 7 mm; width, 1, 3, or 5 mm) and clamped using a support (Fig.…”

“…Articial photoactuators are based on a variety of photoactive materials including gels, 6-8 crystals, 9,10 and liquid crystal elastomers (LCEs). 3,5,[11][12][13][14][15][16][17] Exposure of photoactuators to light can induce bending, 3,9 contraction, 5 rotation, 15,18 oscillation, 19 twisting, 17,20 and other motions 21,22 that are essential to applications in microuidic devices, 12 motors, 18 and electrical generators.…”

“…AG was used as the matrix based on previous results showing that when combined with photoswitchable molecules such as 1,4-bis(para-hydroxystyryl)benzene or azobenzene derivatives, AG is a mechanically compliant matrix that can be efficiently actuated. 20,22 The hydrogen bonding network of AG provides both moderate mechanical strength and soness required for photoactuation. Furthermore, the F-Azo@AG lm was coupled to a polyvinylidene diuoride (PVDF) lm that acts as a piezoelectric transducer (Fig.…”