(98v) Molecular Dynamics Simulations of Superspreaders

Superspreading is the greatly enhanced spreading of aqueous droplets on hydrophobic surfaces due to the addition of trisiloxane surfactants, the so-called superspreaders. Because of the relatively small number of known superspreaders, and because of the wide range of industrial applications of superspreading—including coatings, cosmetics, paints, and textiles—numerous theoretical, experimental, and computational studies  have been undertaken to uncover the secrets behind this process. However, the driving mechanisms of superspreading are still barely understood, largely because the relevant processes at the molecular scale cannot be resolved in experiments. The behavior of trisiloxane surfactants at the water-air and water-substrate interfaces and in solution, especially at the leading edge of the spreading droplet, is currently still subject to speculation.

We use advanced molecular dynamics simulations and optimized force fields to address open questions regarding the physical behavior of trisiloxane surfactants. We perform simulations of trisiloxane surfactants at the water-air interface as well as at the interfaces of hydrophobic substrate materials in contact with water. Moreover, we perform simulations of droplet spreading for aqueous solutions of trisiloxane surfactants and droplets of pure trisiloxane surfactants on various hydrophobic substrates to explore the mechanisms of superspreading and terraced wetting. In addition, we perform reference simulations with surfactants that do not lead to superspreading to gain additional insight into the relevant mechanisms of this fascinating phenomenon.