Thursday, September 28, 20173:00pm - 4:00pm

The Mechanics of the Surfactant-Driven Fracture of Particle Rafts and the Influence of Surface Tension

Abstract

When a densely packed monolayer of hydrophobic particles is placed on a fluid surface, the particles interact through capillary bridges, leading to the formation of a particle raft or ``praft". Densely packed monolayers exhibit a two-dimensional elastic response, and they are capable of supporting both tension and compression. The introduction of a controlled amount of surfactant generates a surface tension gradient, producing Marangoni forces and causing the surfactant to spread, fracturing the monolayer. These systems are of interest to materials scientists and engineers because they provide an idealized setting for investigating the interplay between fluid flow and fracture. Previous studies of the surfactant-induced fracture of prafts have examined the role of viscosity and the initial packing fraction on the temporal and spatial evolution of the fractures. This seminar will describe a new continuum-based model and simulations that account for the interplay between the pressure exerted by a spreading surfactant and the elastic response of the praft, including the fracture toughness. While our results indicate that the stochastic aspects of the packing are important to the fracture process, we find that regimes of fracture are largely governed by differences in surface tension. Finally, we support our findings with newly designed experiments that validate the model and confirm the trends inferred from the simulations.

Biography

John Dolbow is a Professor of Civil and Environmental Engineering at Duke University, where he directs the Duke Computational Mechanics Laboratory. He has been a faculty member at Duke University since 1999, and his research concerns the development of numerical methods for evolving interface problems. He has received various awards for his research, including Young Investigator awards from both the USACM and the IACM. He is the Editor-In-Chief of the journal Finite Elements in Analysis and Design. He currently serves as the Vice President for the USACM, as well as on the DOE's Advanced Scientific Computing Advisory Committee.