Contact and macroscopic ageing in colloidal suspensions
| Quand ? |
Le 28/03/2023, de 11:00 à 12:00 |
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| Où ? | Salle des thèses |
| Participants |
Julie Goyon |
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While the ageing behavior of dense suspensions or pastes at rest is almost exclusively attributed to structural dynamics, a set of experiments conducted on dense aqueous silica suspensions allowed us to identify another ageing process: contact-controlled ageing. We have investigated the origin of shear modulus and yield strength ageing in dense aqueous silica suspensions at moderate ionic forces.
We first showed by combining rheometry and confocal microscopy that the elastic modulus and yield stress of these suspensions at rest grow logarithmically with time while their structural evolution is rapidly arrested by the formation of thermally irreversible roll-resistant interparticle contacts [1]. These suspensions age in the absence of structural rearrangement.
By performing three-point with optical tweezer on particle rods made of silica particles (Fig. 1), we showed that both the rolling stiffness and rolling threshold grow logarithmically in time. By comparing the results of the measurements on the particle contact properties with the results of the rheometry tests, we were able to show that ageing of interparticle contacts governs both shear modulus ageing and yield stress ageing of these dense aqueous silica suspensions [2-3]. We also identified simple constitutive relationships between contact-scale bending stiffness and rolling threshold, which transfer to the macroscopic scale.
We then study the influence of the physico-chemistry of our dense silica suspensions at both macroscopic and macroscopic scales and show that the constitutive identified previously can be extended.
[1] Fusier, J., Goyon, J., Chateau, X., & Toussaint, F. (2018). Rheology signature of flocculated silica suspensions. Journal of Rheology, 62(3), 753-771
[2] Bonacci, F., Chateau, X., Furst, E. M., Fusier, J., Goyon, J., & Lemaître, A. (2020). Contact and macroscopic ageing in colloidal suspensions. Nature Materials, 19(7), 775-780
[3] Bonacci, F., Chateau, X., Furst, E. M., J., Goyon, J., & Lemaître, A (2021). Yield Stress Aging in Attractive Colloidal Suspensions. Phys. Rev. Lett. 128, 018003