Non-Laplacian air-gap electrostatics for high-field oil-water nanoemulsion separation.

Oil-water separation is critical for energy and manufacturing industries, including crude refining and oil recycling, yet remains challenging for nanoscale emulsions where gravity-based methods are ineffective. Conventional demulsification techniques using immersed electrodes are limited by low electric field strengths to avoid shorting, requiring toxic demulsifiers and water-intensive desalting. Here, we propose a non-Laplacian electrocoalescence strategy using space-charge emitter electrodes with an air gap, enabling corona-based charge injection to achieve electric fields up to 8 kilovolts per centimeter and an eightfold enhancement over conventional methods. The enhanced electrostatic field enables a 64-fold increase in dipole-dipole attraction forces, leading to accelerated droplet coalescence and separation across water fractions ranging from 2 to 20%, without chemical demulsifiers. Furthermore, we demonstrate a scalable, flow-through space-charge emitter system capable of continuous demulsification of nanoscale emulsions. This approach provides a sustainable, chemical-free solution to address critical environmental and economic challenges in oil-water separation processes.