Effect of hydrophilic chain length on the impact and wetting behavior of nonionic surfactants regulating droplets on hydrophobic surfaces

Regulation of the droplet impact and wetting behavior of hydrophobic surfaces is a difficult problem to solve. The addition of surfactants is commonly used to improve droplet retention by modifying interfacial properties. The effect of the surfactant structure on the regulation of droplet rebound and wetting behavior needs further research. In this study, the physicochemical properties and regulation of droplet behavior for nonionic surfactants with different hydrophilic chain lengths were investigated. The results indicate that with an increasing hydrophilic chain (Epoxyethane (EO) numbers) length, Isodecyl polyoxyethylene ether (XL) surfactant solutions could better regulate the droplet impact behavior on hydrophobic surfaces and better suppress droplet rebound. This mainly attributed to a faster diffusion of surfactant molecules to newly formed interfaces, thus leading to better wetting reversal and deposition of substrates. Additionally, it was found that with the reduction of the hydrophilic chain length, XL surfactant solutions could better regulate droplet wetting, mainly attributed to its critical micelle concentration and surface tension, creating greater Marangoni forces during spreading and leading to faster spreading rates and larger spreading areas. The results from this study promote understanding of the mechanism for regulation of impact behavior and surfactant solution wetting on hydrophobic surfaces by regulating the EO chain length. This provides an effective strategy in regulating droplet deposition on hydrophobic surfaces and provides the basic data or guidance for the use of nonionic surfactants as tank-mixing adjuvants in unmanned aerial vehicle plant protection.