Triboelectric charge generation in porous elastomers

Recent studies have shown that introducing pores within dielectric elastomers enhances their triboelectric performance substantially. However, the physical mechanisms through which the porous morphology affect electrostatic induction and contact electrification remain underexplored. Here, we tune the porosity of polydimethylsiloxane dielectrics by varying the concentration of the foaming agent in a chemical foaming reaction, which leads to a fourfold increase in the open circuit voltage and short circuit current when the material undergoes compressions of various strains from 0-50% and contact pressures ranging from 2 kPa to 28 kPa. We find an optimal porosity of 52% at which the charge density generated per compressive cycle is at a maximum. This is because excess pore coalescence diminishes the available surface area for triboelectric charge generation as revealed by X-ray micro-computed tomography reconstructions. Surface roughness and internal porous features, confirmed through optical Keyence microscopy, are found to modulate the effective contact area available for contact electrification. Furthermore, pressure-voltage sensitivity measurements reveal distinct pressure sensitivity behavior in which two scaling regimes are observed for highly porous dielectrics. We hypothesize that this scaling behavior is likely due to the linear elastic deformation of microstructures on the surface, followed by the subsequent nonlinear compression of pores. Integration of such porous dielectrics into a smart shoe insole enables detection of diverse gait patterns with stable and reproducible signals, while a full-bridge rectifier test shows that the materials can be used for highly efficient ambient energy harvesting.

Keywords- Contact electrification, electrostatic induction, porosity, strain sensing, microstructures

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