Ionic actuators have attracted attention due to their remarkably large strain under low-voltage stimulation. Because actuation performance is mainly dominated by the electrochemical and electromechanical processes of the electrode layer, the electrode material and structure are crucial. Here, we report a graphitic carbon nitride nanosheet electrode-based ionic actuator that displays high electrochemical activity and electromechanical conversion abilities, including large specific capacitance (259.4 F g−1) with ionic liquid as the electrolyte, fast actuation response (0.5±0.03% in 300 ms), large electromechanical strain (0.93±0.03%) and high actuation stability (100,000 cycles) under 3 V. The key to the high performance lies in the hierarchical pore structure with dominant size <2 nm, optimal pyridinic nitrogen active sites (6.78%) and effective conductivity (382 S m−1) of the electrode. Our study represents an important step towards artificial muscle technology in which heteroatom modulation in electrodes plays an important role in promoting electrochemical actuation performance.

The human somatosensory network relies on ionic currents to sense, transmit, and process tactile information. We investigate hydrogels that similarly transduce pressure into ionic currents, forming a piezoionic skin. As in rapid- and slow-adapting mechanoreceptors, piezoionic currents can vary widely in duration, from milliseconds to hundreds of seconds. These currents are shown to elicit direct neuromodulation and muscle excitation, suggesting a path toward bionic sensory interfaces. The signal magnitude and duration depend on cationic and anionic mobility differences. Patterned hydrogel films with gradients of fixed charge provide voltage offsets akin to cell potentials. The combined effects enable the creation of self-powered and ultrasoft piezoionic mechanoreceptors that generate a charge density four to six orders of magnitude higher than those of triboelectric and piezoelectric devices.

The formation of associative networks in semidilute aqueous solutions of hydrophobically modified alginate (HM-alginate) is dependent on intermolecular hydrophobic interactions. Addition of beta-cyclodextrin (beta-CD) monomers to the system provides decoupling of these associations via inclusion complex formation with the polymer hydrophobic tails. This results in a dramatic decrease in the viscoelastic response of the system and a more extended local structure of the polymer chains, as shown by small-angle neutron scattering (SANS) measurements. The zero-shear viscosity decreases about an order of magnitude when the beta-CD concentration is increased from 0 to 12 mm. The lifetime of the associative network decreases strongly with increasing levels of beta-CD addition. These findings clearly demonstrate that the hydrophobic association effect is efficiently reduced as the amount of beta-CD is increased. In the framework of drug delivery, this effect may be useful to improve the release of therapeutic molecules that can be entrapped in the polymer matrix.

The synthesis and characterization of flexible solid polymer electrolytes (SPEs) based on interpenetrating polymer networks (IPNs) are discussed. IPNs were prepared from nitrile butadiene rubber (NBR) and poly(ethylene oxide) (PEO) using a two-step process. The NBR network was obtained by dicumyl peroxide cross-linking at high temperature and pressure. A free radical copolymerization of poly(ethylene glycol) methacrylate and dimethacrylate led to the formation of the PEO network within the NBR network. Polymerization kinetics were followed by dynamic mechanical analysis (DMA) for the NBR network and by Fourier transform spectroscopy in the near-and mid-infrared for the PEO network. IPN mechanical properties, examined using DMA and tensile strength tests, reveal an IPN elongation with a breaking point of 110%. IPN conductivities reach 7.4 Â 10 À7 S cm À1 at 30 °C when doped with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Moreover, IPNs exhibit an ionic conductivity as high as 0.7 Â 10 À3 S cm À1 at 30 °C when swollen in N-ethylmethylimidazolium bis(trifluoromethanesulfonyl)imide ionic liquid (EMITFSI).