Paper Number
GG21
Session
Rheology of Gels, Glasses and Jammed Systems
Title
Influence of surface topography on the yielding of thermo-reversible colloidal gels
Presentation Date and Time
October 11, 2022 (Tuesday) 10:50
Track / Room
Track 3 / Sheraton 5
Authors
- Müller, Florence J. (ETH Zurich, Materials)
- Isa, Lucio (ETH Zurich, Materials)
- Vermant, Jan (ETH Zürich, Materials)
Author and Affiliation Lines
Florence J. Müller, Lucio Isa and Jan Vermant
Materials, ETH Zürich, Zürich, Switzerland
Speaker / Presenter
Müller, Florence J.
Keywords
colloids; gels
Text of Abstract
Colloidal gels derive part of their technological interest from the ability to undergo a solid-liquid transition, and the microstructural causes underlying this have been intensively researched using various rheological and structural characterization methods in the past. The propensity to gel or break up depends both on the suspending media properties and primary particle features such as shape, size, surface roughness and surface functionalization. In the present work, we developed a synthesis approach where we can independently tune these different particle features, with particle topography as an additional non trivial complexity. Silica particles are synthesized using a standard Stöber method, with an option to add surface roughness by electrostatic hetero-aggregation of smaller particles. To arrive at a reproducible and scalable functionalization, these cores are first functionalized with secondary-amines through silane chemistry. The click-like (amine -yne) chemistry enables the grafting of different kinds of functional molecules to the surface of the particles, such as hydrocarbons, polymers or fluorophores. These functional molecules have been modified beforehand with an alkynoate group, using the Fischer esterification process of an -OH group with propiolic acid. The amount of grafting agent to the particle surface can be tuned by the reaction conditions. This synthesis approach was used to fabricate both smooth and rough particles, where the thermoreversibility of the steric repulsion can be used to build aggregate networks to investigate their influence on the gels mechanical properties. Rheological measurements show how surface roughness delays the structural yielding due to interlocking of the particles, in addition to influencing the thixotropy as roughness counteracts flow induced cluster densification.