Self-Standing High-Performance Transparent Actuator Based on Poly(dimethylsiloxane)/TEMPO-Oxidized Cellulose Nanofibers/Ionic Liquid Gel

Bio-Inspired Hydrogel-Elastomer Actuator with Bidirectional Bending and Dynamic Structural Color

In nature, some creatures can change their body shapes and surface colors simultaneously to respond to the external environments, which greatly inspired researchers in the development of color-tunable soft actuators. In this work, we present a facile method to prepare a smart hydrogel actuator that can bend bidirectionally and change color simultaneously, just like an octopus. The actuator is fabricated by elastomer/hydrogel bilayer and the hydrogel layer was decorated with thermoresponsive microgels as the photonic crystal blocks. Compared with the previously reported poly(N-isopropylacrylamide) hydrogel-based bilayer hydrogel actuators, which are generally limited to one-directional deformation, the elastomer/hydrogel bilayer actuator prepared in our work exhibits unique bidirectional bending behavior in accordance with the change of structural color. The bending degrees can be changed from -360° to 270° in response to solution temperatures ranging from 20 °C to 60 °C. At the same time, the surface color changes from red to green, and then to blue, covering the full visible light spectrum. The bending direction and degree of the hydrogel actuator can easily be adjusted by tuning the layer thickness ratio of the elastomer/hydrogel or the composition of the hydrogel. The color-tunable hydrogel-elastomer actuator reported in this work can achieve both programmable deformations and color-changing highly resembling the natural actuating behaviors of creatures.

Cellulose-Based Ionic Conductor: An Emerging Material toward Sustainable Devices

Ionic conductors (ICs) find widespread applications across different fields, such as smart electronic, ionotronic, sensor, biomedical, and energy harvesting/storage devices, and largely determine the function and performance of these devices. In the pursuit of developing ICs required for better performing and sustainable devices, cellulose appears as an attractive and promising building block due to its high abundance, renewability, striking mechanical strength, and other functional features. In this review, we provide a comprehensive summary regarding ICs fabricated from cellulose and cellulose-derived materials in terms of fundamental structural features of cellulose, the materials design and fabrication techniques for engineering, main properties and characterization, and diverse applications. Next, the potential of cellulose-based ICs to relieve the increasing concern about electronic waste within the frame of circularity and environmental sustainability and the future directions to be explored for advancing this field are discussed. Overall, we hope this review can provide a comprehensive summary and unique perspectives on the design and application of advanced cellulose-based ICs and thereby encourage the utilization of cellulosic materials toward sustainable devices.

Electroactive Soft Actuators Based on Columnar Ionic Liquid Crystal/Polymer Composite Membrane Electrolytes Forming 3D Continuous Ionic Channels

Here, we report low-voltage-driven fast-response nanostructured columnar ionic liquid crystal/polymer composite actuators that form three-dimensional continuous ion channels. A three-component self-assembly of a zwitterionic rod-like molecule (49.5 wt %), an ionic liquid (27.5 wt %), and poly(vinyl alcohol) (23.0 wt %) provided a free-standing stretchable membrane electrolyte. The dissociated ions can move through a continuous 3D ionophilic matrix surrounding the hydrophobic columns formed by the hexagonally organized rod-mesogens. Three-layer actuators composed of the electrolyte film sandwiched between two conductive polymer film electrodes of doped polythiophene exhibited a bending motion with 0.32% strain and moved 2 mm within 220 ms under 1 V at 0.1 Hz in 70% relative humidity due to the formation of electric double layers at the soft solid electrolyte/electrode interfaces. The bending strain of the columnar nanostructured actuator is comparable to those of polymer iongel actuators and block polymer actuators containing 25-80 wt % of ionic liquids. It is noteworthy that a small number of ions organized into the 3D nanochannels can generate the large bending deformation, which can contribute to reduce the risk of leakage of ions and the production cost. In addition, we have demonstrated a low-voltage-driven deformable mirror actuator that is expected to be applied to optical devices.

Ion Transport in the EMITFSI/PVDF System at Different Temperatures: A Molecular Dynamics Simulation

We used all-atom molecular dynamics simulations to study the ion transport in the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/poly(vinylidene fluoride) (EMITFSI/PVDF) system with 40.05 wt % EMITFSI at different temperatures. The glass-transition temperature (T g = 204 K) of this system shows a good agreement with the experimental value (200 K). With the increase of temperature, the peaks of the pair correlation function show an increasing trend. Interestingly, the coordination numbers of ion pairs and the degree of independent ion motion are mainly affected by the binding energy between ion pairs as the temperature increases. In addition, the ion transport properties with increasing temperature can be studied by the ion-pair relaxation times, ion-pair lifetimes, and diffusion coefficients. The simulation results illustrate that the ion transport is intensified. Especially, the cations can always diffuse faster than the anions. The power law shows that mobilities of anions and cations are seen to exhibit a "superionic" behavior. With the increase of temperature, transference numbers of anions decrease first and then increase and transference numbers of cations show the opposite changes; ionic conductivity increases gradually; and viscosity decreases gradually, indicating that the diffusion resistance of ions decreases. In general, after adding PVDF into the EMITFSI system, the glass-transition temperature and viscosity increase, the ionic conductivity and degree of independent ion motion decrease, and diffusion coefficients of cations decrease faster than those of the anions.