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Contact and macroscopic ageing in colloidal suspensions.
Francesco Bonacci1, Xavier Chateau2, Eric M Furst3
1Navier, Ecole des Ponts, Univ Gustave Eiffel, CNRS, Marne-la-vallée, France.
Nature Materials
|March 4, 2020
Summary
Ageing in dense suspensions is driven by contact-controlled stiffening, not just structure. This finding impacts understanding of materials like cements and soils.
Area of Science:
- Colloid and Surface Science
- Materials Science
- Rheology
Background:
- Ageing in dense suspensions and pastes is typically attributed to structural rearrangements.
- A deeper understanding of the mechanisms governing material ageing is crucial for various industrial applications.
Purpose of the Study:
- To identify and characterize an alternative ageing mechanism in dense colloidal suspensions.
- To investigate the role of solid-solid contact stiffening in the shear-modulus ageing of suspensions.
Main Methods:
- Rheometry to measure bulk material properties.
- Confocal microscopy for visualizing microstructure.
- Particle-scale mechanical tests using laser tweezers for direct contact analysis.
Main Results:
- Identified 'contact-controlled ageing' as a significant ageing process.
- Demonstrated that this process governs shear-modulus ageing in silica and polymer latex suspensions.
- Established that contact-controlled ageing becomes dominant when electrostatic interactions are screened.
Conclusions:
- Contact-controlled ageing is a key mechanism in dense suspensions, distinct from structural dynamics.
- This mechanism is relevant under moderate ionic strengths, suggesting broad applicability.
- The findings necessitate a re-evaluation of ageing dynamics in diverse materials like cements, soils, and 3D printing inks.
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