Interfacial synergistic modulation via surfactant-electric field interactions for enhanced spray atomization

Hypothesis: Spray technology is important for many industrial and environmental processes, but precise control over droplet atomization and charging remains challenging. We propose an interfacial engineering strategy that couples surfactant adsorption—anionic sodium dodecylbenzenesulfonate (SDBS), cationic hexadecyltrimethylammonium bromide (CTAB), and nonionic polyoxyethylene (80) sorbitan monooleate (TW80)—with an externally applied electric field to jointly tune atomization and droplet charge. We hypothesize that surfactant-induced surface-tension reduction together with electric-field-driven charge separation will act synergistically to enhance atomization efficiency, and that mixed surfactant formulations will outperform single-component systems via cooperative micellization and modified interfacial charge distribution. Experiments: A custom electrostatic spray platform was built to quantify droplet-size distribution and charge-to-mass ratio. The setup combines a pressure-swirl nozzle with an annular inductive electrode (0–30 kV), a Phase Doppler Particle Analyzer (PDPA) for droplet-size measurement, and a Faraday cage coupled to a microammeter for charge measurement. We systematically varied surfactant type (SDBS, CTAB, TW80), concentration (including each surfactant's critical micelle concentration, CMC), and electrode voltage, and compared single-surfactant and composite (SDBS + TW80) formulations. Key solution properties (surface tension, viscosity) were measured at 25 °C and each condition was repeated three times. Findings: This study reveals the synergistic effect between “surfactant type” and “external electric field” during spray. The applied electric field consistently reduced Sauter mean diameter (SMD) and enhanced droplet chargeability, with selective responses: SDBS showed strong field sensitivity near its CMC (SMD further decreasing), and TW80 produced the largest reduction in SMD (up to ∼30 % at its CMC). Besides, the nonionic-anionic (SDBS–TW80) composite system generated a synergistic effect surpassing single components—it integrated both advantages, yielding smaller SMD (≈100 μm, ∼10 % lower than SDBS alone at 16 kV). These findings provide a novel approach for active design of spray interfacial properties, offering practical guidance for precision spraying in precision agriculture, coating processes, and particulate mitigation.