Deposition mechanism of microscopic impacting droplets on flexible porous substrates

Abstract

Flexible and breathable porous pressure sensors are gaining attention due to their potential in wearable devices for human motion monitoring. The controllable deposition and transport of droplets on porous surfaces are critical for achieving high - conductivity printing in flexible and wearable sensors, as well as in electronic applications. Due to the intricate microstructure of porous layers, accurately dynamically tracking alterations in droplet morphology and the detailed characterization of multiphase-coupled transport present significant challenges. To address these issues, this study employs a microscopic multiphase-coupled transport dynamics model based on the volume-of-fluid smoothing correction and the Kistler dynamic contact angle model (VOFS-KCA). The aim is to investigate the evolution of droplet transport on both the external surface and internal pore spaces of porous media. Furthermore, it reveals the correlation between the structural characteristics of porous media and the mass transfer process in multiphase flow. Results show that the wettability of porous surfaces is a pivotal factor in droplet clusters' dispersion and mobility. The effect of porosity on droplet penetration is nonlinear. Appropriate porosity is conducive to droplet penetration on the porous surface, while excessive porosity leads to lateral diffusion in the cavity. A smaller fiber diameter leads to an approximately circular and uniform distribution of droplets on the porous surface and reduces permeability, which is conducive to maintaining the linewidth of the printed circuit and improving the conductivity. This study systematically explores how surface wettability, porosity, and fiber structure affect droplet dispersion and infiltration, providing new insights into the design of high-performance porous systems. This work lays the foundation for the high-precision manufacturing of flexible sensors with porous surfaces, with applications in energy storage, filtration, and biomedical systems.