Biomimetic actuators with rapid response speed, high sensitivity, and selectivity to external stimulus have found potential applications in smart switches, artificial muscles, and soft robots. The nanoscale structures of actuators enhance the exposed area to stimulus as well as enable versatile control of the actuation behaviors. Freestanding, flexible, and porous water-driven actuators with poly­(vinyl alcohol-co-ethylene) (EVOH) nanofibers as the substrate and super hydrophilic nanoscale cellulose materials (cellulose nanofibers, cellulose nanocrystals, bacterial cellulose) as the active substance via uniform mixing or surface depositing were fabricated. The effects of the EVOH nanofiber substrate, the structures and concentrations of nanoscale cellulose materials, as well as the different environmental stimuli like humidity and temperature on the performance of actuators were studied. The water-driven actuation mechanism was proposed from the macroscopic and molecular aspects and the analysis of Gibbs free energy and mechanical energy. The actuator could bend to an angle of 180° and recovered less than 1 s for more than 100 circles without compromising properties when the environmental moisture changed. Furthermore, the multidimensional deformation behaviors of the water-stimulated actuators could also be well tuned by varying the orientations of the nanoscale materials. Additionally, the applications of the prepared actuator were demonstrated.

Fiber-shaped strain sensors with great flexibility and knittability have been tremendously concerned due to the wide applications in health manager devices, especially in human motion detection and physiological signal monitoring. Herein, a novel fiber-shaped strain sensor has been designed and prepared by interpenetrating Ag nanowires (NWs) into polyolefin elastomer nanofibrous yarn. The easy-to-obtain structure and simple roll-to-roll process make the continuous large-scale production of nanofibrous composite yarn possible. The continuous and alternating stretching and releasing reversibly change the contact probability between AgNWs in this interpenetrating network, leading to the variations of electrical resistance of the sensor. The gauge factors of strain sensors are calculated to be as high as 13920 and the minimum detection limit is only 0.065%. In addition, the strain sensor shows excellent durability during 4500 cycles with the strain of 10%. The response times of stretching and releasing strains are 10 and 15 ms, respectively. Furthermore, the strain sensor has been successfully applied in human motion detections both in single yarn and knitted fabrics. The result shows the practicability in applications of monitoring limbs movements, eye motion changes, artificial vocal cords, human pulse, and complex motions, which shows great potential in wearable sensors and electronic skin.

Despite much progress in solvent-sensitive actuators, most of the actuators are sensitive to water, ethanol, or acetone with low responsive speed and small curvature. Herein, a simple approach was introduced to fabricate a new solvent-sensitive bilayer actuator consisting of a poly(vinyl alcohol-co-ethylene) (EVOH) nanofibrous membrane and polystyrene (PS) microspheres. The actuator showed superfast and multistimulus responsive ability to organic vapors of toluene, chloroform, THF, and acetone. With solvents stimulation, the difference in swelling degree between the EVOH layer and PS microspheres layer contributed to the asymmetric expansions or contractions of two layers, therefore resulting in the mechanical deformation of the actuator. The flexible and porous EVOH nanofibrous membrane, as well as the spherical PS, could improve the response rate and deformation scale. This bilayer actuator could bend quickly into a multicoil with the curvature of 21.02 cm −1 within 0.15 s in response to toluene vapor, and the bending−unbending process could repeat more than 150 times when the deformation degree was controlled by cross-linking PS microspheres with divinylbenzene. This study will provide an important insight for the development of new solvent-sensitive devices and applications in volatile organic compounds detecting.

Two series of novel ternary copolyimides containing perylene and fluorene units in the backbone were synthesized by one‐step polycondensation of diamine (4,4′‐(9H‐fluoren‐9‐ylidene)bisphenylamine, FBPA) with perylene dianhydride (3,4,9,10‐perylenetetracarboxylic dianhydride, PTCDA) and a comonomer [4,4′‐(hexafluoroisopropylidene) diphthalic anhydride, 6FDA or 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride, BDTA]. The polymers were named as PFFx (PTCDA‐FBPA‐6FDA) and PFBx (PTCDA‐FBPA‐BTDA), respectively, and their chemical structures were identified by FT‐IR spectra and elemental analyses. Perylene contents in the copolyimides were determined through a quantitative UV‐vis spectroscopy method, which are in agreement with the values calculated from the added raw materials both for PFFx and PFBx. Gel permeation chromatography (GPC) measurement suggested that the weight average molecular weight (Mw) is in the range 2.1–5.09 × 104 and the molecular weight distribution (MWD) is 1.86–2.72 for PFFx, and those for PFBx are 2.64–4.73 × 104 and 2.44–2.92, respectively. Thermogravimetric analysis (TGA) measurements showed that the copolyimides are very thermally stable with a temperature of 10% weight loss (T10) in the range 546–563°C for PFFx, and 538–548°C for PFBx. The copolyimides also have good solubility in common organic solvents such as chloroform and tetrahydrofuran. These unique properties can be attributed to the existence of the bulky diphenylfluorene moieties in the polymer backbone. All the copolyimides can emit strong fluorescence both in solution and in films, which make them possibly be used as thermostable light‐emitting materials for organic light‐emitting diodes. Copyright © 2006 John Wiley & Sons, Ltd.

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