From Understanding Mechanical Behavior to Curvature Prediction of Humidity‐Triggered Bilayer Actuators

Abstract

Nature will always be an endless source of bioinspiration for man‐made smart materials and multifunctional devices. Impressively, even cutoff leaves from resurrection plants can autonomously and reproducibly change their shape upon humidity changes, which goes along with total recovery of their mechanical properties after being completely dried. In this work, simple bilayers are presented as autonomously moving, humidity‐triggered bending actuators. The bilayers—showing reproducible bending behavior with reversible kinematics and multiway behavior—are studied in terms of their mechanical behavior upon humidity changes. The active layer consists of a highly conducting polymer film based on poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) with poly(dimethylsiloxane) (PDMS) as passive layer. The response to humidity is explored with dynamic mechanical thermal analysis and quartz crystal microbalance measurements. Introduction of a composite beam model allows to predict the curvature of the actuators with input from the rheological measurements. It is clearly demonstrated that volumetric strain and Young's modulus, both heavily influenced by the water uptake, dominate the bending behavior and therefore the curvature of the actuators. This loop of rheological characterization coupled with an analytical model allows to predict curvatures of in principle any complex geometry and material combination for moving parts in soft robotics.

High Energy and Power Density Peptidoglycan Muscles through Super‐Viscous Nanoconfined Water

“…Recent demonstrations and theoretical predictions showed that such WR actuation could be extremely powerful and efficient, [7][8][9] inspiring the growing studies and development of WR structures for actuators and artificial muscles. [10][11][12][13][14][15][16][17] Notable WR examples include a titanium oxide film [18] and a twisted carbon nanotube yarn, [19] which exhibit WR energy densities of ≈1250 and 1800 kJ m −3 (2.17 kJ kg −1 ), respectively. Microrobots equipped with WR actuators of 𝜋-stacked carbon nitride films [8] and polyethylene oxide nanofibers [20] have been demonstrated to exhibit autonomous locomotion powered by fluctuations in ambient RH.…”

“…Recent demonstrations and theoretical predictions showed that such WR actuation could be extremely powerful and efficient, [ 7 , 8 , 9 ] inspiring the growing studies and development of WR structures for actuators and artificial muscles. [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ]…”

Pressure‐Perceptive Actuators for Tactile Soft Robots and Visual Logic Devices

“…Another kind of actuating and sensing system is based on actuating materials with sensing/perception functions, [ 6 , 7 , 8 ] which can respond to external stimuli such as light, [ 9 , 10 ] electricity, [ 11 , 12 ] temperature, [ 13 , 14 ] and humidity. [ 15 , 16 ] However, these actuating and sensing systems lack the response to mechanical stimuli, which limits their application in bionic systems and human–computer interactions.…”

Dual‐responsive and bidirectional bending actuators based on a graphene oxide composite for bionic soft robotics

“…The traditional bilayer actuator can only be driven by a single stimulus, such as light, [6][7][8] electricity, [9][10][11] humidity. [12][13][14] For example, Weng and coworkers proposed an electrothermal actuator based on graphite/polyaniline paper-like composites. The electrothermal actuator exhibited a large bending motion (bending curvature >1 cm À1 ) with an ultralow driving voltage of 2.5 V. 15 Hu and coworkers reported untethered soft light-driven actuators based on covalently-bridged black phosphorus-carbon nanotubes (CNT) heterostructure with self-oscillation and phototactic locomotion under light irradiation.…”