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Rheology and 4D imaging of designer colloidal gels and their applications

English title Rheology and 4D imaging of designer colloidal gels and their applications
Applicant Vermant Jan
Number 192336
Funding scheme Project funding (Div. I-III)
Research institution Departement Materialwissenschaft ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Material Sciences
Start/End 01.04.2020 - 31.03.2024
Approved amount 868'170.00
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All Disciplines (2)

Discipline
Material Sciences
Other disciplines of Physics

Keywords (5)

confocal microscopy; soft matter; 3D printing; rheology; colloidal gels

Lay Summary (German)

Lead
Rheologie und 4D-Bildgebung von kolloidalen Designergelen und deren Anwendungen
Lay summary
Die vorgeschlagene Forschung befasst sich mit kolloidalen Gelen, die wichtige und allgegenwärtige weiche Materialien sind, die insbesondere von erheblicher industrieller Relevanz sind.  Relativ schwache attraktive Wechselwirkungen zwischen den Partikeln führen zu einer thermodynamischen Instabilität, die eine Aggregation induziert und bei ausreichend hohen Volumenanteilen zu  Netzwerkstrukturen mit einzigartigen rheologischen Eigenschaften führt (zeitabhängige Viskosität und Fliessgrenze), deren Eigenschaften ausgenutzt werden, sei es direkt in vielen Anwenderprodukten oder bei der Verarbeitung von Materialien als Zwischenprodukt.

In der vorliegenden Arbeit wollen wir das Verständnis und die Verbesserung der rheologischen Eigenschaften von ausgeflockten Suspensionen vorantreiben und dabei die jüngsten Entwicklungen von Modellsystemen, neue fortschrittliche rheometrische Techniken und schnelle 3D Mikroskopie Bildgebung nutzen. Das Ziel ist es, speziell auch die Leistung von Materialien in mindestens einer Anwendung im Zusammenhang mit dem direkten Tintenschreiben und dem eingebetteten 3D-Druck im Detail zu untersuchen und zu optimieren.   Insgesamt sollte das verbesserte Know-how zu besser gestalteten kolloidalen Gelen im Hinblick auf ihre rheologische Leistung führen. Dies könnte zu einer Vereinfachung der industriellen Dispersionen führen, was im Hinblick auf die Ressourceneffizienz und die wirtschaftlichen Auswirkungen vorteilhaft wäre, oder zu einer Verbesserung der Leistungen. 
Direct link to Lay Summary Last update: 07.04.2020

Responsible applicant and co-applicants

Employees

Name Institute

Associated projects

Number Title Start Funding scheme
157147 Exploiting particle shape and connectivity to interrogate flocculated suspension mechanics. 01.12.2014 Project funding (Div. I-III)

Abstract

The proposed research deals with colloidal gels which are important and ubiquitous soft materials, in particular being of significant industrial relevance. Relatively weak attractive interactions between particles lead to a thermodynamic instability which induces aggregation, and at sufficiently high volume fractions leads to percolating network structures possessing unique rheological properties whose properties which are exploited, be it directly in many user products or when processing materials as an intermediate. However, the complex rheology leads to challenges in a wide range of manufacturing processes, as for example in direct ink writing and embedded 3D printing. At the same time it is a topic of profound academic interest as they represent complex multi-scale materials for which rationalizing or predicting the structure property relations remains very difficult. The microstructure of such materials varies over multiple length scales, from the local packing in aggregates to structures at the level of up to tens of particle diameters. Moreover, this microstructure is inherently a metastable one and the effects of flow or processing history underpin the nonlinear and time-dependent responses. At low volume fractions and for relatively strong interparticle interactions, fractal concepts have been successful in describing flocs as the essential load bearing units. For weaker interacting systems, recent work suggest that the rheology of such materials is governed by dense, minimally interconnected clusters. However, how to use these concepts in the design of colloidal gels based on their interaction forces, particle topography and geometry and flow history effects is as yet an open question. In the present work we aim to advance the understanding and improve the rheological properties of flocculated suspensions, taking advantage of recent developments in the development of model systems, novel advanced rheometrical techniques and fast rheo-confocal imaging. The goal is to specifically also investigate in detail and optimize materials performance in at least one application related to direct ink writing and embedded 3D printing. The overall objective is to come to an integrated view on the design of colloidal gels, which takes into account the attractive interactions, the particle topography and the use of non-central interaction forces in addition to particle shape and processing history as handles in controlling colloidal gel rheology and its role in processing. The specific aims are (i) to obtain a direct visualization and understanding of the yielding phenomena in colloidal gels, as a function of the inter-particle interactions, with as a particular focus to elucidate the effect of bond rigidity by comparing gels created by a depletion interaction, a thermo-reversible gel and the effect of particle roughness ; (ii) to obtain data sets of the three dimensional structure as a function of time (4D imaging) to connect the microstructure to the time dependent rheology, to provide a micro-structural basis for improved thixotropy modeling, also connecting the micro-structural and micro-mechanical anisotropy in such systems; (iii) to use the knowledge and approaches to investigate the role of rheology in embedded 3D printing of colloidal gels, in order to improve the spatial and temporal resolution of these techniques by investigated both the rheology-structure relations of the embedding medium and the printing ink. Overall, the improved know-how should lead to better designed colloidal gels, in view of their rheological performance. This could lead to the simplification of industrial dispersions, beneficial in light of resource efficiency and economic impact, or to enhance the performances.
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