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| Home > Publications database > How nanoporous silicon-polypyrrole hybrids flex their muscles in aqueous electrolytes: In operando high-resolution x-ray diffraction and electron tomography-based micromechanical computer simulations |
| Home > Publications database > How nanoporous silicon-polypyrrole hybrids flex their muscles in aqueous electrolytes: In operando high-resolution x-ray diffraction and electron tomography-based micromechanical computer simulations |
| Journal Article | PUBDB-2022-07589 |
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2022
APS
College Park, MD
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Please use a persistent id in citations: doi:10.1103/PhysRevMaterials.6.116002 doi:10.3204/PUBDB-2022-07589
Abstract: Macroscopic strain experiments have revealed that silicon crystals traversed by parallel, channel-likenanopores functionalized with the artificial muscle polymer polypyrrole (PPy) exhibit large and reversibleelectrochemomechanical actuation in aqueous electrolytes. On a macroscopic scale these actuation propertiesare well understood. However, on the microscopical level this system still bears open questions, as to how theelectrochemical expansion and contraction of PPy acts on to np-Si pore walls and how the collective motorics ofthe pore array emerges from the single-nanopore behavior. Here we present synchrotron-based, in operando x-raydiffraction on the evolving electrostrains in epilayers of this material grown on bulk silicon. An analysis of theseexperiments with micromechanical finite-element simulations, that are based on a full three-dimensional reconstructionof the nanoporous medium by transmission electron microscopy (TEM) tomography, shows that thein-plane mechanical response is dominantly isotropic despite the anisotropic elasticity of the single-crystallinehost matrix. However, the structural anisotropy originating from the parallel alignment of the nanopores led tosignificant differences between the in- and out-of-plane electromechanical response. This response is not describableby a simple two-dimensional arrangement of parallel cylindrical channels. Rather, the simulations highlightthat the dendritic shape of the silicon pore walls, including pore connections between the main channels, causescomplex, highly inhomogeneous stress-strain fields in the crystalline host. Time-dependent x-ray scatteringexperiments on the dynamics of the actuator properties hint towards the importance of diffusion limitations,plastic deformation, and creep in the nanoconfined polymer upon (counter)ion adsorption and desorption, thevery pore-scale processes causing the macroscopic electroactuation. From a more general perspective, our studydemonstrates that the combination of TEM tomography-based micromechanical modeling with high-resolutionx-ray scattering experiments provides a powerful approach for in operando analysis of nanoporous compositesfrom the single nanopore up to the porous-medium scale.
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