Molecular phenomena in dynamic wetting: superspreading and precursors

  • Molekulare Benetzungsphänomene: Superspreading und Präkursoren

Isele-Holder, Rolf Erwin; Ismail, Ahmed E. (Thesis advisor); Horsch, Martin T. (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2015)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2015


Wetting is a multiscale process that can be controlled simultaneously by complex flow patterns on the macroscale and contact line phenomena at the Ångstrom scale. While resolving the latter scale is often circumvented by usage of boundary conditions, there are molecular wetting phenomena in which this approach is infeasible. The focus of this study is to use molecular dynamics simulations to examine two of these phenomena: superspreading, the ultra-rapid wetting of aqueous solutions facilitated by trisiloxane surfactants, and molecular precursors, the development of films of molecular thickness that precede droplets. Molecular simulation resolves the atomistic scale and provides information that is inaccessible from experiment. A challenge in the context of wetting, however, is that dispersion interactions are typically considered short-ranged in molecular simulations, whereas they have long-ranged effects in wetting. To capture these interactions in wetting simulations, the particle-particle particle-mesh algorithm, a long-range solver that is well-established for Coulomb interactions, is extended to dispersion. It is shown that the correct use of this algorithm leads to accurate and efficient simulations.Despite intensive studies on superspreading in the last 20 years, the underlying molecular mechanisms of the process are not understood. That the process is sensitive to various parameters in experiment, and also that previous attempts to model this phenomenon using molecular dynamics simulations failed, motivated the development of a force field dedicated to superspreading. Application in large-scale spreading simulations provides a smooth contact line transition at superspreading conditions. It is shown that this observation offers plausible explanations for experimental findings and a coherent description of the superspreading mechanism.While the dynamics and mass transport mechanisms of molecular precursors are well understood, conditions that lead to precursor formation or different types of precursors are subject to debate. Large-scale spreading simulations, new analysis methods, and excessive free energy computations shed light on these issues and resolve the conflict about the role of the spreading coefficient for precursor formation.


  • Aachen Institute for Advanced Study in Computational Engineering Science [080003]
  • Department of Computer Science [120000]
  • Chair and Institute of Technical Thermodynamics [412110]