Paper Number
GS9 

Session
Gels and Self-Assembled Systems

Title
Microstructure, rheology and heterogeneity in colloidal gels

Presentation Date and Time
October 10, 2017 (Tuesday) 2:45

Track / Room
Track 5 / Crestone B

Authors (Click on name to view author profile)

1. Jamali, Safa (Northeastern University, Mechanical Engineering)
2. McKinley, Gareth H. (Massachusetts Institute of Technology, Department of Mechanical Engineering)
3. Armstrong, Robert C. (Massachusetts Institute of Technology, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Safa Jamali¹, Gareth H. McKinley², and Robert C. Armstrong^3
1Mechanical Engineering, Northeastern University, Cambridge, MA; ²Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139; ³Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA

Speaker / Presenter 
Jamali, Safa

Text of Abstract
A wide range of complex and structured fluids including colloidal gels can be identified as Thixotropic ElastoViscoPlastic (TEVP) materials. TEVPs, show a rich and complex set of rheological responses to imposed deformations in different regimes: before yielding, the network formed by individual particles remains intact and resists large deformations and the material acts as a viscoelastic solid. Above the yielding point, the material starts to flow and undergoes plastic deformation and microstructural rearrangement over a wide range of length scales. Plastic flow results in a viscous-like response; however, due to constant formation and breakage of interparticle bonds that form the network, thixotropic behavior begins to emerge. These time/rate dependent responses lead to other secondary effects including micro-phase separation, vorticity-aligned structure formation, etc. We employ a mesoscale numerical simulation method that captures attractive colloids at a sufficiently coarse-grained level that we can reproduce characteristic rheological features of a TEVP fluid under flow, and identify the sequence of microstructural changes that give rise to these macroscopic features. In order to correlate the microstructural changes of a TEVP fluid to its rheological response, we define a fabric tensor, Z, formed by an ensemble average of the spatial configuration of particle-particle bonds. In this work we will show that the fabric tensor provides a quantitative microstructural measure of the system and correlates to the macroscopic stress response in a TEVP fluid in both steady and transient states. The evolution in the components of Z with strain provides quantitative insight on the flow instabilities and secondary structures that develop in the sheared microstructure.