Abstract:  Several applications of interest in coating flows, the spreading of pesticides, and in microfluidics involve the Marangoni-driven spreading of fluids using surfactants, or being affected by contaminants. This talk will describe the spreading of a surfactant-laden droplet showing a striking and intriguing fingering instability. The modeling, and subsequent identification of the underlying physical mechanisms for the instability, will be discussed in detail. The spreading behaviour of the droplet changes as one increases the surfactant concentration past the critical micelle concentration and the coupled modeling of surfactant aggregation with the fluid motion is required. The presence of surfactant micelles and absorption of surfactant to the substrate are observed to lead to strongly enhanced spreading rates and the model gives a possible explanation for the observed "superspreading" effect that is seen in some experiments. This is joint work with: G. Karapetsas, O. Matar, B. Edmonstone and M. Warner

Bio:  Richard Craster is Professor of Applied Mathematics at Imperial College. He has research interests across a broad spectrum of fluid mechanics and elasticity (fracture mechanics, diffraction theory, wave phenomena, applied complex analysis, Newtonian thin-layer theories, viscoplasticity, guided elastic waves, surfactant driven flows, instability theory, pattern formation) and is involved in their applications in engineering and physics. He also has interests in asymptotic theories for differential equations (WKBJ methods, Fuchsian equations) and in the development of techniques to solve free boundary problems and conformal mapping theory. Richard Craster's personal webpage can be found at http://www.ma.ic.ac.uk/~rvcras/

Host: Rouslan Krechetnikov, ME