Fri June 1st 2018
11:00 – 12:00
Seminar "Painting with Numbers”; Spraying and Air-Assisted Atomization of Complex Fluids
Gareth McKinley


The extensional rheological properties of dilute polymer solutions play a dominant role in many industrially-important free-surface processes such as air-blast atomization. This high deformation rate process is important in the dispensing of diverse materials such as paints, fertilizer sprays and delivery of airborne drugs. Similar hydrodynamic conditions also govern physiological processes such as sneezing and airborne disease transmission. In this talk I will explore the physics behind atomization of complex fluids using model polymer solutions, several industrial paint formulations as well as human mucin. Although the viscosity and surface tension of the polymeric fluids are close to those of the underlying Newtonian solvent, both the mean droplet size and the droplet size distribution change considerably. To understand why non-Newtonian fluids differ so dramatically, one must recognize that the hydrodynamics of capillary breakup and atomization are governed by an independent material function – the extensional viscosity. To probe the response of dilute polymeric solutions at realistic timescales and deformation rates we develop a new instrument, the Rayleigh Ohnesorge Jet Elongational Rheometer (ROJER). Analyzing the evolution in the jet diameter before break-up enables meaningful measurement of fluid relaxation times down to values as small as 50 µs, and these values can be directly correlated with differences in spray size distributions. High-speed flow visualization images show that this behavior arises from the non-linear dynamics close to the break-up point which are dominated by an elasto-capillary force balance within the thinning ligaments that sets the magnitude of the extensional viscosity in a complex non-Newtonian fluid. This balance between elasticity and capillarity on small length scales also leads to a very broad and universal droplet size distribution that can be described by a single parameter Gamma distribution.

Gareth H. McKinley is the School of Engineering Professor of Teaching Innovation within the Department of Mechanical Engineering at MIT. He received his BA and M.Eng. degrees from the University of Cambridge and his Ph.D (1991) from the Chemical Engineering department at MIT. He taught in the Division of Engineering and Applied Sciences at Harvard from 1991-1997 and was an NSF Presidential Faculty Fellow from 1995-1997. He won the Annual Award of the British Society of Rheology in 1995 and the Frenkiel Award from the APS Division of Fluid Dynamics in 2001. He served as Executive Editor of the Journal of Non-Newtonian Fluid Mechanics from 1999 to 2009 and as Associate Editor of Journal of Fluid Mechanics from 2007-2009. He most recently served as the Associate Dept. Head for Research of the Mechanical Engineering Department at MIT from 2008-2013. He is also a co-founder of of Cambridge Polymer Group. His research interests include extensional rheology of complex fluids, non-Newtonian fluid dynamics, microrheology & microfluidics, field-responsive fluids, super-hydrophobicity, wetting of nanostructured surfaces and the development of nanocomposite materials. He is the author of over 275 technical publications and was one of the winners of the 2007 Publication Award of the Society of Rheology. He is a Fellow of the American Physical Society and President of the US National Committee of Theoretical and Applied Mechanics (USNC/TAM). He was the recipient of the 2013 Bingham Medal of the Society of Rheology and served as President of the Society from 2015-2017. Most recently he won the 2014 Gold Medal of the British Society of Rheology.
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The 10th Complex Motion in Fluids 2020
Max Planck Gesellschaft
Centre for Scientific Computing