Publisher DOI: 10.1103/PhysRevMaterials.6.116002
Title: 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
Language: English
Authors: Brinker, Manuel  
Thelen, Marc  
May, Manfred 
Rings, Dagmar 
Krekeler, Tobias 
Lakner, Pirmin 
Keller, Thomas F. 
Bertram, Florian 
Huber, Norbert  
Huber, Patrick  
Issue Date: Nov-2022
Source: Physical Review Materials 6 (11): 116002 (2022-11)
Abstract (english): 
Macroscopic strain experiments have revealed that silicon crystals traversed by parallel, channel-like nanopores functionalized with the artificial muscle polymer polypyrrole (PPy) exhibit large and reversible electrochemomechanical actuation in aqueous electrolytes. On a macroscopic scale these actuation properties are well understood. However, on the microscopical level this system still bears open questions, as to how the electrochemical expansion and contraction of PPy acts on to np-Si pore walls and how the collective motorics of the pore array emerges from the single-nanopore behavior. Here we present synchrotron-based, in operando x-ray diffraction on the evolving electrostrains in epilayers of this material grown on bulk silicon. An analysis of these experiments with micromechanical finite-element simulations, that are based on a full three-dimensional reconstruction of the nanoporous medium by transmission electron microscopy (TEM) tomography, shows that the in-plane mechanical response is dominantly isotropic despite the anisotropic elasticity of the single-crystalline host matrix. However, the structural anisotropy originating from the parallel alignment of the nanopores led to significant differences between the in- and out-of-plane electromechanical response. This response is not describable by a simple two-dimensional arrangement of parallel cylindrical channels. Rather, the simulations highlight that the dendritic shape of the silicon pore walls, including pore connections between the main channels, causes complex, highly inhomogeneous stress-strain fields in the crystalline host. Time-dependent x-ray scattering experiments 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, the very pore-scale processes causing the macroscopic electroactuation. From a more general perspective, our study demonstrates that the combination of TEM tomography-based micromechanical modeling with high-resolution x-ray scattering experiments provides a powerful approach for in operando analysis of nanoporous composites from the single nanopore up to the porous-medium scale.
ISSN: 2475-9953
Journal: Physical review materials 
Institute: Material- und Röntgenphysik M-2 
Betriebseinheit Elektronenmikroskopie M-26 
Werkstoffphysik und -technologie M-22 
Document Type: Article
Project: SFB 986: Teilprojekt B07 - Polymere in grenzflächenbestimmten Geometrien: Struktur, Dynamik und Funktion an planaren und in porösen Hybridsystemen 
SFB 986: Teilprojekt B04 - Mikromechanisches Materialverhalten hierarchischer Werkstoffe 
SFB 986: Zentralprojekt Z02 - Untersuchung multiskalig strukturierter Materialsysteme mit Synchrotron- und Neutronenstrahlung 
SFB 986: Zentralprojekt Z03 - Elektronenmikroskopie an multiskaligen Materialsystemen 
Energy harvesting via wetting/drying cycles with nanoporous electrodes 
Thermoelektrische Hybridmaterialien basierend auf porösem Silizium: der Zusammenhang zwischen makroskopischen Transportphänomenen und mikroskopischer Struktur und elementaren Anregungen 
Is supplemented by: 10.15480/336.4675
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