title: Films, layers, and droplets: The effect of near-wall fluid structure on spreading dynamics.
abstract: We present a study of the spreading of liquid droplets on a solid substrate at very small scales. We focus on the regime where effective wetting energy (binding potential) and surface tension effects significantly influence steady and spreading droplets. In particular, we focus on strong packing and layering effects in the liquid near the substrate due to underlying density oscillations in the fluid caused by attractive substrate-liquid interactions. We show that such phenomena can be described by a thin-film (or long-wave or lubrication) model including an oscillatory Derjaguin (or disjoining or conjoining) pressure and explore the effects it has on steady droplet shapes and the spreading dynamics of droplets on both an adsorption (or precursor) layer and completely dry substrates. At the molecular scale, commonly used two-term binding potentials with a single preferred minimum controlling the adsorption layer height are inadequate to capture the rich behavior caused by the near-wall layered molecular packing. The adsorption layer is often submonolayer in thickness, i.e., the dynamics along the layer consists of single-particle hopping, leading to a diffusive dynamics, rather than the collective hydrodynamic motion implicit in standard thin-film models. We therefore modify the model in such a way that for thicker films the standard hydrodynamic theory is realized, but for very thin layers a diffusion equation is recovered.
authors.affiliation: Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, United Kingdom.
authors.forename: Hanyu
authors.initials: H
authors.lastname: Yin
authors.affiliation: Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, United Kingdom.
authors.forename: David N
authors.initials: DN
authors.lastname: Sibley
authors.affiliation: Institut für Theoretische Physik, Westfälische Wilhelms-Universität Münster, Wilhelm Klemm Str. 9, 48149 Münster, Germany.|Center of Nonlinear Science (CeNoS), Westfälische Wilhelms-Universität Münster, Corrensstr. 2, 48149 Münster, Germany.|Center for Multiscale Theory and Computation (CMTC), Westfälische Wilhelms-Universität, Corrensstr. 40, 48149 Münster, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Thiele
authors.affiliation: Department of Mathematical Sciences, Loughborough University, Loughborough LE11 3TU, United Kingdom.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Archer