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.

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We demonstrate the application of implanted-ion β-detected NMR as a probe of ionic liquid molecular dynamics through the measurement of 8 Li spin-lattice relaxation (SLR) and resonance in 1-ethyl-3-methylimidazolium acetate. The motional narrowing of the resonance, and the local maxima in the SLR rate, 1/T1, imply a sensitivity to sub-nanosecond Li + solvation dynamics. From an analysis of 1/T1, we extract an activation energy EA = 74.8(15) meV and Vogel-Fulcher-Tammann constant TVFT = 165.8(9) K, in agreement with the dynamic viscosity of the bulk solvent. Near the melting point, the lineshape is broad and intense, and the form of the relaxation is non-exponential, reflective of our sensitivity to heterogeneous dynamics near the glass transition. The depth resolution of this technique may later provide a unique means of studying nanoscale phenomena in ionic liquids.arXiv:1907.03684v3 [cond-mat.soft]

Millimeter sized polymer crystallites grow rapidly when anthracene-containing siloxanes are photocrosslinked using UV light.