Paper Number
SG4 

Session
Self-assembled Systems, Gels and Liquid Crystals

Title
The rheology and microstructure of aging thermoreversible colloidal gels & attractive driven glasses

Presentation Date and Time
February 13, 2017 (Monday) 11:15

Track / Room
Track 3 / White Ibis

Authors (Click on name to view author profile)

1. Gordon, Melissa B. (University of Delaware, Chemical and Biomolecular Engineering)
2. Kloxin, Christopher J. (Univ. Delaware)
3. Wagner, Norman J. (University of Delaware, Chemical & Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Melissa B. Gordon, Christopher J. Kloxin, and Norman J. Wagner
Chemical & Biomolecular Engineering, University of Delaware, Newark, DE 19716

Speaker / Presenter 
Wagner, Norman J.

Text of Abstract
The properties of colloidal gels and glasses are known to change with age, but the particle-level mechanisms by which aging occurs is are fully understood, which limits our ability to predict macroscopic behavior in these systems. Homogeneous colloidal gels and glasses are disordered systems that are trapped in a dynamically arrested, non-equilibrium state. It is generally accepted that the aging of colloidal gels is governed by their potential energy landscape, where thermodynamic equilibrium is the global minimum; however, many systems cannot reach true equilibrium on an experimental timescale. Instead, the arrested material explores local potential energy minima resulting in aging behavior. Due to their fundamental significance and industrial applicability, we investigate the microstructural basis of aging in a model adhesive hard sphere (AHS) system, consisting of silica nanoparticles grafted with an octadecyl brush dispersed in tetradecane. In this work, we quantitatively relate rheological aging to structural aging by simultaneously measuring the bulk properties and gel microstructure using rheometry and small angle neutron scattering (Rheo-SANS), respectively. Specifically, we develop a quantitative and predictive relationship between the macroscopic properties and the underlying microstructure (i.e., the effective strength of attraction) of an aging colloidal gel and attractive driven glass, and study it as a function of the thermal and shear history. Analysis suggests local particle rearrangements as the mechanism of aging, which strongly supports aging as a trajectory in the free energy landscape dominated by local particle relaxations. The analyses and conclusions of this study may be 1) industrially relevant to products that age on commercial timescales, such as paints and pharmaceuticals, 2) applicable to other dynamically arrested systems, such as metallic glasses, and 3) used in the design of new materials.