Paper Number
GG44 

Session
Rheology of Gels, Glasses and Jammed Systems

Title
Memory in aging colloidal gels with time-varying attraction

Presentation Date and Time
October 12, 2022 (Wednesday) 2:30

Track / Room
Track 3 / Sheraton 5

Authors (Click on name to view author profile)

1. Leheny, Robert (Johns Hopkins University)
2. Chen, Yihao (Johns Hopkins University)
3. Zhang, Qingteng (Argonne National Laboratory, Advanced Photon Source)
4. Ramakrishnan, Subramanian (FAMU-FSU College of Engineering)

Author and Affiliation Lines (in printed abstract book)
Robert Leheny¹, Yihao Chen¹, Qingteng Zhang² and Subramanian Ramakrishnan^3
1Johns Hopkins University, Baltimore, MD 21218; ²Advanced Photon Source, Argonne National Laboratory, Lemont, IL; ³FAMU-FSU College of Engineering, Tallahassee, FL 32310

Speaker / Presenter 
Leheny, Robert

Keywords
colloids; gels

Text of Abstract
We report a combined rheology, x-ray photon correlation spectroscopy (XPCS), and modeling study on gel formation and aging of suspensions of nanocolloidal spheres with volume fractions of 0.20 and 0.43 and with a short-range attraction whose strength is tuned by changes in temperature. Following a quench from high temperature, where the colloids behave essentially as hard spheres, to a temperature below the gel point, the suspensions form gels that undergo aging characterized by a steadily increasing elastic shear modulus and slowing, increasingly constrained microscopic dynamics. The aging proceeds at a faster rate for stronger attraction strength. When the attraction strength is suddenly lowered during aging, the gel properties evolve non-monotonically, in a manner resembling the Kovacs effect in glasses, in which the modulus decreases and the microscopic dynamics become less constrained for a period before more conventional aging behavior resumes. Eventually, the properties of the gel following the decrease in attraction strength converge to those of a gel that has undergone aging at the lower attraction strength throughout. The time scale of this convergence increases as a power law with the age at which the attraction strength is decreased and decreases exponentially with the magnitude of the change in attraction. A model for gel aging in which particles attach and detach from the gel at rates that depend on their contact number qualitatively reproduces these trends following a decrease in attraction strength. The model reveals that the non-monotonic behavior following the decrease results from the dispersion in the rates at which the populations of particles with different contact number adjust to the new attraction strength.