Nanodancing with Moisture: Humidity‐Sensitive Bilayer Actuator Derived from Cellulose Nanofibrils and Reduced Graphene Oxide

Abstract

Bilayer actuators, traditionally consisting of two laminated materials, are the most common types of soft or hybrid actuators. Herein, a nanomaterial‐based organic–inorganic humidity‐sensitive bilayer actuator composed of TEMPO‐oxidized cellulose nanofibrils (TCNF‐Na+) and reduced graphene oxide (rGO) sheets is presented. The hybrid actuator displays a large humidity‐driven locomotion with an atypical fast unbending. Cationic exchange of the anionically charged TCNF‐Na+ and control of the layer thickness is used to tune and dictate the locomotion and actuator's response to humidity variations. Assembly of a self‐oscillating electrical circuit, that includes a conductive rGO layer, displays autonomous on‐and‐off lighting in response to actuation‐driven alternating electrical heating.

Cellulose‐Based Soft Actuators

“…Multilayer cellulose-based actuators are more common in hydrogels and composites. [86,87] For instance, Wu and coworkers proposed a novel CNC nanocomposite film mimicking the shell of Chrysina resplendens. [85] The film comprising a uniaxially oriented PA-6 interlayer sandwiched between CNCs/PEGDA layers.…”

Cellulose‐Reinforced Programmable and Stretch‐Healable Actuators for Smart Packaging

“…[1] Inspired by these motile plants, actuators with such functionality are gradually integrated into our daily life. [2,3] A new generation of smart responsive actuators that are capable of converting various environmental energies such as light, [4] temperature, [5] electricity, [6,7] magnetism, [8] and humidity [9] into reversible and programmable shape transformation has been designed, which offer fascinating applications in sensors, [10,11] robotics, [12] wearable electronics, [13] artificial muscles, [14] and smart packaging. [15] Specifically, humidityresponsive actuators have received considerable research interest owing to the environmentally friendly mode of actuation, resembling the actuation of plant tissues and the ubiquity of water.…”

“…[19,20] Despite the great advances, the widespread applications of humidity-responsive actuators are generally limited by three disadvantages. Firstly, most of the reported humidityresponsive actuators suffer from insufficient tunability in the direction and speed of actuation, [10] which poses significant limitations for their use as smart devices. Secondly, the traditional molecular design of humidity-responsive actuators with non-covalently crosslinked networks usually leads to poor mechanical properties (particularly low strength and toughness) and the inability to dissipate energy during load-bearing working conditions.…”

Construction and Performance of a Nanocellulose–Graphene-Based Humidity Sensor with a Fast Response and Excellent Stability

“…For example, paper-based humidity sensors with the incorporation of carbon nanotubes (CNTs) or graphene have been proposed via spray-coating, dip-coating, and layer-by-layer (LBL) assembly. − The excellent water affinity of cellulose endowed the as-prepared sensor with significant sensing performances for humidity. However, the sensitivity of the paper-based sensors was limited (<0.5/% RH). ,,, Moreover, the stability could not satisfy the practical application owing to the incompatibility and weak affinity between the rigid conductive filler and flexible paper, which might cause cracking or stripping during the deformation process. To address these issues, oxidized carbon nanotubes and reduced graphene oxide (rGO) were used to coat the functionalized cellulose or nanocellulose films to improve the response performances.…”

“…However, the sensitivity of the paper-based sensors was limited (<0.5/% RH). 14,16,19,20 Moreover, the stability could not satisfy the practical application owing to the incompatibility and weak affinity between the rigid conductive filler and flexible paper, which might cause cracking or stripping during the deformation process. To address these issues, oxidized carbon nanotubes and reduced graphene oxide (rGO) were used to coat the functionalized cellulose or nanocellulose films to improve the response performances.…”