Multi-Scale Simulation of Droplets on Solid Surfaces: Superhydrophobicity and Superspreading

ABSTRACT

Proposal Number: CBET- 07300987

Principal Investigator: Kristen A. Fichthorn

University/Institution: Pennsylvania State Univ.

Title: Multi-Scale Simulation of Droplets on Solid Surfaces:

Super-hydrophobicity and Super-spreading

This project consists of an investigation of the spreading of liquid drops on solid substrates using molecular-dynamics (MD) simulations and hybrid MD and continuum computations. These studies address three major challenges in understanding spreading and capillary flows: (1) Understanding mechanisms of surfactant-mediated spreading; (2) Elucidating mechanisms of Super-hydrophobicity on rough and patterned surfaces and; (3) Developing a simulation methodology that incorporates the vast temporal and spatial scales involved in spreading, ranging from molecular-level kinetic mechanisms operating at the contact line to macroscopic hydrodynamic mechanisms. The MD simulations will be beneficial in unlocking important molecular details, while the hybrid model will allow insight into the interplay between molecular and hydrodynamic mechanisms that drive spreading.

Intellectual Merit: Droplet spreading on solid surfaces plays an important role in numerous industrial applications, such as coating, painting, spraying, molding, fiber manufacturing, and Micro-fluidics, as well as in biological applications, such as surfactant replacement therapy. Most theoretical studies in this area have employed continuum models that lack microscopic details at the moving contact line. The MD simulations will furnish molecular-level details important for understanding surfactant-mediated spreading and super-hydrophobicity. These details are important in the choice or design of surfactant molecules and the effective creation of hydrophobic surfaces. The proposed research also addresses a clear challenge in this area: The development of a simulation methodology that incorporates the vast temporal and spatial scales, ranging from large-scale convection to molecular

details at the contact line. Development of a multi-scale simulation method will allow us to fully capture the intricate interplay between microscopic processes and macroscopic events in spreading and other surface involving moving three-phase contact lines.

Broader Impacts: In addition to graduate student and postdoctoral training and the involvement of undergraduate students in computational research, aspects of the proposed research will be incorporated into a graduate course on interfacial transport phenomena. Professors Borhan and Fichthorn will team-teach a graduate course on computational methods to introduce students to multi-scale modeling and the hybrid MD-continuum method. Finally, the PIs will advance the state of the art in multi-scale modeling and understanding of interfacial transport by organizing a symposium on wetting and capillary phenomena at the 6th International Conference on Interdisciplinary Transport Phenomena.