Polybenzoxazole Nanofiber-Reinforced Moisture-Responsive Soft Actuators

Abstract

Hydromorphic biological systems, such as morning glory flowers, pinecones, and awns, have inspired researchers to design moisture-sensitive soft actuators capable of directly converting the change of moisture into motion or mechanical work. Here, we report a moisture-sensitive poly(p-phenylene benzobisoxazole) nanofiber (PBONF)-reinforced carbon nanotube/poly(vinyl alcohol) (CNT/PVA) bilayer soft actuator with fine performance on conductivity and mechanical properties. The embedded PBONFs not only assist CNTs to form a continuous, conductive film, but also enhance the mechanical performance of the actuators. The PBONF-reinforced CNT/PVA bilayer actuators can unsymmetrically adsorb and desorb water, resulting in a reversible deformation. More importantly, the actuators show a pronounced increase of conductivity due to the deformation induced by the moisture change, which allows the integration of a moisture-sensitive actuator and a humidity sensor. Upon changing the environmental humidity, the actuators can respond by the deformation for shielding and report the humidity change in a visual manner, which has been demonstrated by a tweezer and a curtain. Such nanofiber-reinforced bilayer actuators with the sensing capability should hold considerable promise for the applications such as soft robots, sensors, intelligent switches, integrated devices, and material storage.

Functional Fibers and Fabrics for Soft Robotics, Wearables, and Human–Robot Interface

“…[173,174] A stimulus-responsive fiber is a simple passive self-control system, which senses the change of environment and makes a mechanical response. [175,176] Besides, sensors endow the soft actuator with proprioception [177,178] and perception, [179][180][181][182] which are very importance for controlling and interactions between human-robots. Liu et al fabricated a sheath-core conducting fiber with the core of elastomer and the sheath of carbon nanotube, it acted as both a capacitive strain sensor and an electrical torsional actuator.…”

Unravelling humidity-gated, temperature responsive bilayer actuators

“…This constraint is oftentimes circumvented by examining actuation under isothermal or constant humidity conditions. 31,32 The simultaneous interaction of both temperature and humidity on adaptive structures has been less explored, even though a better understanding of interconnected stimuli may lead to programmed environmentally adaptive materials. 33,34 Recent publications addressing the interplay of (photo)thermal and humidity reveal that a constant, high humidity is crucial in facilitating thermal response of the fabricated materials.…”

Flexible Actuators for Soft Robotics

“…Various ionic actuators based on the aforementioned mechanism have emerged, greatly promoting the development of soft robotics on humans . In contrast, inspired by hydromorphic organisms, humidity actuators are attractive as flexible actuators for the capabilities of responding to a change in ambient moisture and converting to motion or mechanical work with a superior sustainability and low‐power consumption . Synthetic polymers and biological materials have been used to achieve similar hygroscopic actuations, which can be used for soft robotic locomotion on humans .…”