Paper Number
SC21
Session
Suspensions & Colloids
Title
Dynamics and flow instabilities in sheared colloidal rod gels
Presentation Date and Time
October 16, 2018 (Tuesday) 2:20
Track / Room
Track 1 / Galleria I
Authors
- Das, Mohan (IESL-FORTH, University of Crete, Department of Material Science and Technology)
- Petekidis, George (FORTH, IESL)
Author and Affiliation Lines
Mohan Das and George Petekidis
IESL, FORTH, Heraklion, Greece
Speaker / Presenter
Das, Mohan
Text of Abstract
Gelation is the process where attractive particle interaction leads to changes in dynamical and rheological behavior of colloidal suspensions. At sufficiently high particle concentrations the suspension behavior changes from liquid-like to solid-like and the particles are trapped in a non-ergodic state. Colloidal rod gels share many similarities with their spherical counterparts, albeit notable differences exist in the suspension microstructure, phase behavior (e.g. liquid crystallinity), single particle dynamics and flow behavior owing to their high aspect ratio. Here we present the study of dynamics and mechanical properties of attractive colloidal rod suspensions. Silica rods (L = 4.5 µm, L/D = 10) suspended in 65 wt% CsCl solution is used as a model system to understand colloidal rod gel behavior at microscopic scale. We used a stress controlled rheometer in conjunction with bright-field and confocal microscopy to observe changes in suspension microstructure at different length scales during linear and nonlinear rheological measurements. Furthermore, we carried out 3D particle tracking to follow single rod dynamics under equilibrium and non-equilibrium conditions. Step-rate measurements show irreversible formation of macroscopic vorticity aligned dense particle clusters that show “log-rolling” behavior. We probe the relation between this phenomenon and confinement by varying the gap in rheometer geometry. We propose a phase diagram based on particle volume fraction and Peclet number to identify the log rolling regime. Finally, experimental results are compared with results obtained from computer simulations*, taking into account both Hydrodynamic interactions and confinement effects. *Work in collaboration with Z. Varga and J. Swan, Department of Chemical Engineering, MIT, USA.