Paper Number
SM39 

Session
Polymer Solutions and Melts

Title
Quantifying the linear and non-linear rheology of sprayable complex liquids

Presentation Date and Time
October 8, 2014 (Wednesday) 2:45

Track / Room
Track 3 / Commonwealth C

Authors (Click on name to view author profile)

1. Keshavarz, Bavand (Massachusetts Institute of Technology, Mechanical Engineering)
2. McKinley, Gareth H. (Massachusetts Institute of Technology, Department of Mechanical Engineering)
3. Houze, Eric C. (Axalta Coating Systems)
4. Moore, John R. (Axalta Coating Systems)
5. Koerner, Michael R. (Axalta Coating Systems)

Author and Affiliation Lines (in printed abstract book)
Bavand Keshavarz¹, Gareth H. McKinley¹, Eric C. Houze², John R. Moore², and Michael R. Koerner^2
1Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139-4307; ²Axalta Coating Systems, Wilmington, DE 19803

Speaker / Presenter 
Keshavarz, Bavand

Text of Abstract
Air-assisted atomization and spraying of complex liquids is a key process in many industrial applications as well as in physiological situations such as coughing and sneezing, but the effects of different rheological properties on these process are poorly understood. Rheological properties measured in linear deformations or steady simple shear flow correlate poorly with the observed results of atomization. In order to better understand these issues a selection of canonical latex-based fluids that are widely used in commercial paint spraying operations were characterized in both the linear and non-linear regions. These complex fluids tend to exhibit power-law like characteristics in both small amplitude oscillatory shear (SAOS) and stress relaxation tests. A Fractional Maxwell Model (FMM) augmented with an appropriate nonlinear damping function can quantitatively predict this response in both linear and nonlinear deformation regions. However despite this accurate description of these model sprayable materials, the steady shear measurements and small amplitude oscillatory data do not provide much insight into understanding the observed differences in the atomization results. We show that the nonlinear intra-cycle coefficients obtained from large amplitude oscillatory shear (LAOS) tests can help us to understand these nonlinear phenomena in a better and more meaningful way. This new framework can connect the rheological fingerprints of a material that are obtained from a relatively straightforward test such as LAOS to widely-used industrial terminologies such as “stringiness” and “sprayability” that heuristically describe a given fluid’s spraying performance.