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Yielding dynamics in capillary suspensions: the importance of local and semi-local structures

Event Type
Mechanical Science & Engineering
3100 Sidney Lu Mechanical Engineering Building
Jun 15, 2023   4:00 pm  
Professor Erin Koos, Department of Chemical Engineering, KU Leuven, Belgium
Amy Rumsey
Originating Calendar
MechSE Seminars


Ternary liquid-liquid-solid systems exhibit a wide variety of different morphologies depending on the ratio of the three components [1]. With small amounts of secondary fluid, the characteristic mechanical strength of such capillary suspensions arises due to the capillary force inducing a percolating network of particles bridged by small individual droplets of secondary fluid. These properties can be tuned by adjusting the individual processing route as well as through the choice of the three components. 

These suspensions can exhibit a wide range of rheological behaviors that are closely linked to the material properties on many length scales, ranging from direct particle contacts [2,3], aggregate flexibility [4], to network structure [5]. Using a rheometer mounted to a confocal microscope, we are able to directly investigate the yielding of a capillary suspension networks and observe the transition between reversible reorganizations of floppy contacts prior to yielding and bridge stretching and breaking leading to irreversible network changes above the yield points. These changes are also compared to MD computational model for the capillary suspension network where particle contacts can be either unbonded (freely able to rotate) or bonded (restricted rotation).

About the Speaker

Erin Koos, born in Oregon (USA), is a professor at KU Leuven in Belgium where she is the head of the Soft Matter, Rheology and Technology (SMaRT) division. She received her B.S. from Harvey Mudd College (Claremont, CA) and Ph.D. from the California Institute of Technology (Pasadena, CA). She was a postdoctoral researcher and group leader at the Karlsruhe Institute of Technology (Germany).  Her research interests include investigating solid-liquid-liquid systems including capillary suspensions. Using rheo-optical methods such as confocal microscopy, changes in microstructure and rheological response including network structure evaluation can be linked to an applied shear. Her research also concentrates on several applications for complex fluids including stress development in film drying and formulations for crack-free films, processing and stability of printed electronic pastes, and porous ceramics.

Host: Professor Randy Ewoldt 

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