Wetting And Spreading Behaviors Of Nanodroplets: The Interplay Among Substrate Hydrophobicity, Roughness, And Surfactants

Molecular dynamics simulations were employed here to explore the molecular mechanism for wetting and spreading behaviors of droplets on smooth and textured substrates in either the absence or presence of surfactants. In particular, we focus on the interplay among substrate hydrophobicity, roughness, and the addition of surfactants. Our simulation results indicate that substrate roughness exerts different effects on the contact angle of nanodroplets, depending on the substrate chemistry, while the presence of surfactants always changes the droplet contact angle via reducing both the vapor-liquid and liquid-solid interfacial tensions, which is independent of the substrate chemistry and roughness. In addition, our calculation results show that the addition of surfactants may lead to the wetting transition of nanodroplets on hydrophobic textured surfaces or induce the appearance of precursor film for droplet spreading on hydrophilic textured surfaces. On the spreading dynamics, we also discuss how the introduction of roughness changes the motion mode of the contact line and how the initial distribution of surfactants affects droplet spreading.