Characterization of Particle Transport and Deposition Due to Heterogeneous Dewetting on Low-Cost Inkjet-Printed Devices

Abstract

This work investigates the deposition patterns left by evaporating particle-laden droplets on heterogeneous surfaces with spatially varying wettability. Spatial differences in receding contact angles give rise to scalloped-shaped contact lines. During evaporation, the contact line recedes in one location and remains pinned in another. This nonuniform contact line recession results in particle self-assembly above areas where the contact line remains pinned but not where it recedes. This behavior is fairly robust across a variety of particle sizes, concentrations, and device geometries. We hypothesize that particle self-assembly in these cases is due to the competition between particle diffusion and evaporative-driven advective flow. Diffusion appears to be more pronounced in regions where the contact line recedes, while advection appears to be more pronounced near the pinned portion of the contact line. As such, particles appear to diffuse away from receding areas and toward pinned areas, where advection transports them to the contact line. The distribution of particle deposition above the pinned regions was influenced by the particle size and the concentration of particles in the droplet. Similar to homogeneous surfaces, deposition was more prevalent at the pinned portion of the contact line for smaller particles and lower concentrations and more uniformly distributed across the entire pinned region for larger particles and higher concentrations. A better understanding of this process may be beneficial in a wide variety of particle separation applications, such as printing, cell patterning, biosensing, and anti-icing.