Paper Number
GG23
Session
Arrested Systems: Gels and Glasses
Title
New insights into the rheological aging of a model thermoreversible colloidal gel with short-range interactions
Presentation Date and Time
October 12, 2021 (Tuesday) 2:45
Track / Room
Track 6 / Ballroom 1
Authors
- Suman, Khushboo (University of Delaware, Department of Chemical and Biomolecular Engineering)
- Wagner, Norman J. (University of Delaware, Chemical & Biomolecular Engineering)
Author and Affiliation Lines
Khushboo Suman and Norman J. Wagner
Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE 19716
Speaker / Presenter
Wagner, Norman J.
Keywords
experimental methods; colloids; gels
Text of Abstract
In this work, we investigate the aging behavior in a well-studied model system of adhesive hard spheres (AHS) quenched above and below the spinodal. The AHS system is comprised of octadecyl-coated Ludox TM-50 silica nanoparticles. On cooling, the AHS particles suspended in tetradecane exhibit a thermoreversible gel transition from a fluid-like (sol) state to a soft-solid state. The decrease in the temperature drives the crystallization of the surface brush layer, which results in the development of short-range attraction between the particles in contact. While the literature suggests evidence of shear-reversible aging and overaging behavior for gels quenched only slightly below the gel temperature, Rheo-SANS studies (Min Kim et al., Journal of Rheology, 2014, 58(5)) on this system suggest that deeper quenches may lead to gel densification under shear. We investigated the effects of deeper quenching on this system in our work. The aging behavior in the model AHS system is monitored by small amplitude oscillatory shear rheology measurements conducted while rapidly quenching from 40°C to a temperature below the critical gel temperature. Interestingly, for deeper quenches, a unique and new phenomenon is reported – namely after an initial rise in the modulus, a sudden and reproducible drop in the modulus at a time period of 300 – 600 s is observed, followed by a plateau in the modulus value. After this drop of nearly an order of magnitude in modulus, the AHS gel remains in the softened state over the experimental timescale. Our rheological characterization at different volume fractions shows intriguing effects of the extent of quenching to different states relative to the underlying phase behavior on aging behavior of colloidal gels. Through this research, we aim to establish a relationship between the mechanical aging and various quench protocols in these gels.