Paper Number
PO52 

Session
Poster Session

Title
Microstructure, rheology and heterogeneity in colloidal gels

Presentation Date and Time
February 15, 2017 (Wednesday) 6:00

Track / Room
Poster Session / Foyer-Stairs/Windows

Authors (Click on name to view author profile)

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

Author and Affiliation Lines (in printed abstract book)
Safa Jamali, Gareth H. McKinley, and Robert C. Armstrong
Massachusetts Institute of Technology, Cambridge, MA 02139

Speaker / Presenter 
Jamali, Safa

Text of Abstract
A wide range of complex and structured fluids including colloidal gels can be identified as Thixotropic Elasto-Visco-Plastic (TEVP) materials. TEVPs, show a rich and complex set of rheological responses to imposed deformations in different regimes: below the yield stress, the microstructural network formed by individual particles remains intact and resists large deformations and the material acts as a viscoelastic solid. By increasing the applied stresses 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, shear banding, rigid plug development as well as shear-induced rejuvenation of the particle network. In this work we employ a mesoscale numerical simulation method that captures a canonical anisotropic and weakly attractive material microstructure at a sufficiently coarse-grained level that we can firstly reproduce characteristic rheological features of a TEVP fluid under flow, and secondly 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.