Acrylonitrile Butadiene Polystyrene–SiO₂ Composite Nanostructures for Self-Regulated Superhydrophobic Liquid Dosage Systems

Superhydrophobic coatings are widely studied for fluid regulation due to their water-repellent surface characteristics. However, there are not many reports on fluid behavior when it flows from a region of higher wettability to that of lower wettability. A fundamental understanding of such behavior would be very useful for regulating the fluid flow through a superhydrophobic channel. Therefore, this work focused on the fabrication of superhydrophobic nanostructured coatings inside fine cylindrical channels and the investigation of the fluid flow behavior through them. The superhydrophobic SiO2 coatings were obtained through an ultrasound-assisted one-step immersion technique. A self-stratified mechanically durable conformal superhydrophobic coating was obtained inside millimeter-sized fine 3D structures. A binder-free precursor solution has low viscosity and thereby enhances the penetration of the solvent into the polymer surface through ultrasonication. The self-stratification-based surface formation mechanism was explained using scanning electron microscopy images. The fluid behavior inside the superhydrophobic channels was experimentally investigated by analyzing the flow through the hollow cylindrical superhydrophobic channels. Experiments were conducted for different channel lengths (l) and radii (r), and mathematical formulations were developed to determine the maximum pressure (Pmax) that the superhydrophobic cylinders could hold when the fluid inside the channel was under static equilibrium. Finally, a self-regulated fluid delivery system was postulated based on the experimental and theoretical findings.