Paper Number
GG30 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
Not too cold, not too crowded: Identifying minimal conditions for gelation and thermokinetic processing of colloidal solids

Presentation Date and Time
October 11, 2022 (Tuesday) 4:05

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

1. Fenton, Scott M. (University of California Santa Barbara, Chemical Engineering)
2. Padmanabhan, Poornima (Rochester Institute of Technology, Chemical Engineering)
3. Ryu, Brian K. (Stanford University, Chemical Engineering)
4. Nguyen, Tuan (University of California Santa Barbara, Chemical Engineering)
5. Zia, Roseanna N. (Stanford University, Chemical Engineering)
6. Helgeson, Matthew E. (University of California, Santa Barbara, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Scott M. Fenton¹, Poornima Padmanabhan², Brian K. Ryu³, Tuan Nguyen¹, Roseanna N. Zia³ and Matthew E. Helgeson^1
1Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106; ²Chemical Engineering, Rochester Institute of Technology, Rochester, NY 14623; ³Chemical Engineering, Stanford University, Stanford, CA 94305

Speaker / Presenter 
Fenton, Scott M.

Keywords
colloids; emulsions; gels; glasses; jammed systems

Text of Abstract
Thermodynamic phase instability provides a versatile toolkit for developing non-equilibrium structure in atomic and molecular mixtures, where the tendency for kinetic arrest underlies thermomechanical processing strategies for biphasic materials. Repeated annealing and quenching produce materials that combine the properties of individual phases, such as ductility, strength and memory. While such techniques have existed since antiquity for processing of materials like metals and ceramics, the use of sophisticated thermal processing of colloidal systems is in its infancy yet holds potential for engineering the properties of colloidal gels. Developing more complex thermal processing in these systems will require a better understanding of how to precisely establish locations of non-equilibrium states on a colloidal phase diagram and means for controlling time-temperature trajectories through them. Here, we present a new method for doing this that uses modulated quenches in attraction strength to determine the minimal conditions for gelation for model experimental and simulated colloidal systems. In all in vitro and in silico systems we identify three distinct regimes of gelation set by an interplay of percolation, phase instability and glassy arrest that encode the ability to form gels. The method also resolves the extension of the attractive glass transition into the region of phase instability, which has proven difficult for experiment. Using this information, we dissect the equilibrium phase boundary, gelation threshold, percolation line, and glass line into a complete colloidal phase diagram, and identify a “Goldilocks zone” in which thermal processing can be used to modulate ultimate gel structure and rheology. We leverage this new understanding and control of colloidal gelation to demonstrate how programmed thermokinetic quenches can be used to tune the arrested length scales of colloidal gels and thereby tune various mechanical properties such as gel stiffness and toughness.