Regulating droplet dynamic wetting behaviors using surfactant additives on high-temperature surfaces

Impacting the behavior of surfactant droplets impinging upon a heated surface is an intriguing research topic, and is important in spraying cooling processes. Surfactant additives significantly increase nucleate boiling heat transfer by promoting vapor bubble nucleation and foaming. However, it is still not exactly clear how surfactants influence the droplet dynamic behaviors at the heated interfaces, nor is the relationship between the droplet dynamic behaviors and heat transfer performance. Here, three familiar surfactant molecules, i.e., anionic surfactant molecule sodium dodecyl sulfate (SDS), cationic surfactant molecule hexadecylcetyltrimethylammonium bromide (CTAB), and nonionic surfactant molecule poly(ethylene glycol) 1000 (PEG-1000), are chosen to investigate the dynamic behaviors of the water droplets with surfactant additives on the heated smooth surface with different chemical components. At low temperatures, surfactant-enhanced spreading of droplets on the hydrophilic and hydrophobic surfaces is achieved due to the surfactant adsorption. At high temperature, bubble jet and bubble explosion processes on the hydrophilic surfaces can generate plenty of bubbles, the bubbles flee away the heated surface and the heat transfer efficiency greatly is improved. SDS and CTAB significantly reduce the Leidenfrost point (LFP) on the hydrophilic and hydrophobic surfaces. PEG-1000 increases the LFP, which is little affected by variation of concentration.