Paper Number
SC20 

Session
Suspensions & Colloids

Title
Colloidal elasticity arises from packing of locally glassy clusters

Presentation Date and Time
October 16, 2018 (Tuesday) 1:55

Track / Room
Track 1 / Galleria I

Authors (Click on name to view author profile)

1. Swan, James (Massachusetts Institute of Technology)
2. Varga, Zsigmond (MIT)
3. Furst, Eric M. (University of Delaware, Dept. of Chemical and Biomolecular Engineering)
4. Solomon, Michael J. (University of Michigan, Chemical Engineering)
5. Hsiao, Lilian C. (North Carolina State University, Department of Chemical and Biomolecular Engineeirng)
6. Whitaker, Kathryn (Dow Chemical Company)

Author and Affiliation Lines (in printed abstract book)
James Swan¹, Zsigmond Varga¹, Eric M. Furst², Michael J. Solomon³, Lilian C. Hsiao⁴, and Kathryn Whitaker^5
1Massachusetts Institute of Technology, Cambridge, MA 02139; ²Dept. of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716; ³Chemical Engineering, University of Michigan, Ann Arbor, MI 48105; ⁴Department of Chemical and Biomolecular Engineeirng, North Carolina State University, Raleigh, NC 27606; ⁵Dow Chemical Company, Midland, MI

Speaker / Presenter 
Swan, James

Text of Abstract
Colloidal gels formed by arrested phase separation are widely found in agriculture, biotechnology, and advanced manufacturing; yet, the emergence of elasticity and the nature of the arrested state in these abundant materials remains unclear. Here, integrated experimental, computational, and graph theoretic approaches are used to understand the arrested state and the micro-structural origins of the elastic response via a model colloidal gel enabling combined measurements of the rheology, structure, and particle interactions as well as large-scale dynamic simulations. The experiments and simulations agree quantitatively in both the elastic modulus of the gel and the micro-structural correlation length as a function of strength of inter-particle attraction. To determine the micro-structural source of elasticity, the $l$-balanced graph partition is used to divide the simulated gels into minimally inter-connected clusters that act as rigid, load bearing units. We find that the number density of cluster-cluster connections grows with increasing inter-particle attraction, and explains quantitatively the emergence of elasticity in the network through the classic Cauchy-Born theory for elasticity. The graph decomposition provides further insight into the structure of the clusters -- they are amorphous -- and with increasing inter-particle attraction, the concentration of colloids internal to the clusters decreases. This internal cluster concentration maps onto the known attractive glass line of sticky colloids at low inter-particle attraction strengths and extends this glass line to higher strengths and lower particle volume fractions. The load bearing clusters in these thermodynamically unstable suspensions are arrested by a glass line, and the elasticity of the gel is the result of just a few weak contacts between these locally arrested, glassy clusters.