Paper Number
GG16 

Session
Arrested Systems: Gels and Glasses

Title
Intersection of percolation, phase separation and glassy behavior sets minimal conditions for gelation of colloidal systems

Presentation Date and Time
October 12, 2021 (Tuesday) 1:55

Track / Room
Track 6 / Ballroom 1

Authors (Click on name to view author profile)

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

Author and Affiliation Lines (in printed abstract book)
Brian K. Ryu¹, Scott Fenton², Tuan Nguyen², Poornima Padmanabhan³, Matthew E. Helgeson² and Roseanna N. Zia^1
1Department of Chemical Engineering, Stanford University, Stanford, CA 94305; ²Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA 93106; ³Department of Chemical Engineering, Rochester Institute of Technology, Rochester, NY

Speaker / Presenter 
Ryu, Brian K.

Keywords
colloids; gels; glasses

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 processing strategies for biphasic materials. Repeated annealing and quenching produces materials that combine the properties of individual phases, such as ductility, strength and memory. While such techniques have existed since antiquity, the use of sophisticated thermal processing of colloidal systems is in its infancy. The first step forward is establishing precise locations of arrested states on a phase diagram. Attempts to locate arrested states on equilibrium phase diagrams have met with some success, including identification of glass transition and gel lines which define regions of extremely slowed kinetics. Yet, a mechanistic understanding of how gelation occurs for a particular set of thermodynamic state variables applicable across multiple material classes lags behind. A key element missing in current models is the impact of kinetic rate processes during quenches that arrest phase transition. As a result, predictive connections between particle concentration, interparticle potential and final state are weak. Here we present a method for systematically determining the location of the gelation line on a colloidal phase diagram via modulated quenches in attraction strength using a novel combination of experiments and dynamic simulations. The method is applied to develop gelation lines for an experimental thermoresponsive nanoemulsion system as well as two computational model systems. We identify three distinct regimes on the gelation line, which emerge for all in vitro and in silico systems. We additionally present a detailed investigation of structural and rheological properties at each regime to describe the mechanism of gelation relative to percolation, phase transition, and glass transition. We find that an interplay of these three processes sets the conditions necessary for gelation of colloidal systems.