Paper Number
GG20
Session
Rheology of Gels, Glasses and Jammed Systems
Title
Yielding of capillary suspensions using simultaneous confocal imaging and rheological measurements
Presentation Date and Time
October 11, 2022 (Tuesday) 10:30
Track / Room
Track 3 / Sheraton 5
Authors
- Allard, Jens (KU leuven)
- Koos, Erin (KU Leuven)
Author and Affiliation Lines
Jens Allard and Erin Koos
KU Leuven, Leuven, Belgium
Speaker / Presenter
Allard, Jens
Keywords
experimental methods; colloids; gels; microscopy; suspensions
Text of Abstract
Capillary suspensions are three phase mixtures of solid particles and two immiscible liquids, one liquid being present only in a few volume percent. Similar to wet granular media, the minority phase forms liquid bridges between the particles to create a sample spanning network, leading to an increase in bulk viscosity and/or the creation of a yield stress. Using a rheometer mounted to a confocal microscope, we are able to directly investigate rheological transitions such as the yielding of a capillary suspension network. Under oscillatory shear, the overall yielding mechanism starts with low amplitude vibrations, followed by local scale rearrangements around the G'' peak, and finally macroscopic yielding and the formation of a shear band near the geometry plate at the flow point. The particle clusters exhibit rigid body movement and the applied deformation leads to very local bridge rupture and reformation events. The properties of the particle surface, such as roughness, and of the liquid bridges, such as relative volume and contact angle, can be directly linked to key rheological transitions like the critical strain and the crossover point. Furthermore, we show that applying a small normal force during the sample loading step of a capillary suspension on the rheometer can significantly affect the measured viscoelastic properties due to an increased effective solid concentration by pushing out some bulk liquid.