Paper Number
GG3 

Session
Out of Equilibrium Systems: Gels and Glasses

Title
Effect of attractive forces on slow dynamics in dense colloidal suspensions

Presentation Date and Time
October 21, 2019 (Monday) 10:40

Track / Room
Track 7 / Room 306C

Authors (Click on name to view author profile)

1. Schweizer, Kenneth S. (University of Illinois at Urbana-Champaign, Department of Materials Science and Engineering)
2. Ghosh, Ashesh (University of Illinois at Urbana-Champaign, Department of Chemistry)

Author and Affiliation Lines (in printed abstract book)
Kenneth S. Schweizer¹ and Ashesh Ghosh^2
1Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; ²Department of Chemistry, University of Illinois at Urbana-Champaign, Champaign, IL 61820

Speaker / Presenter 
Schweizer, Kenneth S.

Text of Abstract
How strong short-range attractive interactions can massively modify the dynamics and viscoelasticity of dense suspensions of spherical colloids remains a topic of enduring interest. Existing microscopic theories based on local cage scale physics typically assume dynamical constraints are fully quantified by equilibrium pair correlation functions. Despite some successes, these approaches qualitatively fail to explain a number of aspects of activated dynamics in dense attractive colloidal suspensions and supercooled thermal liquids. We construct a new microscopic theory for attractive colloidal suspensions formulated directly in terms of the real Newtonian forces within the framework of the Elastically Collective Nonlinear Langevin Equation (ECNLE) approach which treats activated relaxation as a coupled local-nonlocal event involving large amplitude cage hopping and a longer range facilitating elastic fluctuation. A rich interplay between physical bond breaking and cage escape processes is found. The theory appears to properly capture the key physics including a non-monotonic variation of the relaxation time and diffusion constant with attraction strength, the re-entrant repulsive glass to fluid to attractive glass transition behavior, and the crossover to dense-gel-like dynamics upon moderately lowering volume fraction. Moreover, the theoretical results for the variation of the bond-breaking and de-caging time scales with attraction strength and volume fraction are consistent with simulation. In contrast, even theories that go beyond the ideal mode coupling description which include activated hopping do not properly capture multiple dynamical phenomena if attractive forces are assumed to only modify local structure. An additional consequence of the new formulation is activated dynamics can be strongly dependent upon the functional form of the microscopic attractive forces (e.g., LJ versus exponential).