Backside deposition without an electrostatic sprayer: Molecular insights into the role of a surfactant additive

Backside deposition on solid surfaces is crucial for many industrial and agricultural applications. However, the most effective method, electrostatic spraying usually requires specialized and expensive equipment for applying high voltages (several thousand volts) to the liquid, thereby increasing the cost and risk of implementation significantly. A method that overcomes this limitation via surfactant additive is highly desirable without an electrostatic sprayer while the molecular mechanism of charging droplets has rarely been studied and is still elusive. Herein, we demonstrate that sodium dodecyl benzene sulfonate (SDBS) assists abaxial deposition superiorly compared to the use of an electrostatic sprayer. SDBS has larger dipole moment and polarity, smaller HOMO–LUMO gap and higher conductivity than other surfactants like sodium dodecyl sulfate and sodium dodecyl sulfonate. These physicochemical properties induce the highly polarized and orderly arranged water molecules at the air–liquid interface and ensure the highest probability of negative charge of spraying droplets, and thus, the best abaxial deposition to a positively charged substrate. This work provides molecules insights for enhancing the charging ability of spraying droplets via surfactant additives and can be applied in spraying, coating, disinfecting and dusting areas.