Contact and macroscopic ageing in colloidal suspensions

Abstract

The aging behaviour of dense suspensions or pastes at rest is almost exclusively attributed to structural dynamics. Here, we identify another aging process, contactcontrolled aging, consisting in the progressive stiffening of solid-solid contacts, after their initial formation rapidly arrests the microstructure. By combining rheometry, confocal microscopy, and particle-scale mechanical tests using laser tweezers, we demonstrate that this process governs the shear modulus aging of dense aqueous silica and polymer latex suspensions at moderate ionic strengths. We further show that contact-controlled aging becomes relevant as soon as Coulombic interactions are sufficiently screened out that the formation of solid-solid contacts is not limited by activation barriers. Given that this condition only requires moderate ion concentrations, contact-controlled aging should be generic in a wide class of materials, such as cements, soils, or 3D inks, thus questioning our understanding of aging dynamics in these systems.

Contact Aging Enhances Adhesion of Micropatterned Silicone Adhesives to Glass Substrates

“…Therefore, variations over time on the adhesive contact are of crucial significance for their design and application. So far, alterations of solid‐state contacts over time have been studied in other areas such as frictional contacts, [ 30,31 ] the stabilization of colloidal suspensions or granular matter, [ 32,33 ] incorporation of inorganic fillers into polymeric matrices, [ 34 ] and geophysical research on the origin of earthquakes. [ 35,36 ] In general, the phenomena observed are commonly based on the aging of atomic or molecular contacts that, in turn, influence macroscopic properties.…”

Yielding, thixotropy, and strain stiffening of aqueous carbon black suspensions

“…Such a structure evolving in time might result from progressive collective rearrangements between particles thanks to attractive interactions [56]. It might also result from the progressive strengthening of contact interactions of the particles with negligible spatial rearrangements, as discovered recently [46]. The strong and continuous increase of the elastic modulus over long time is more in favour of the latter option, i.e.…”

“…A similar result was recently obtained with silica suspensions in water with salt. In that case it was demonstrated that the elastic modulus finds it origin in direct contacts between particles which evolve in time, rather than in an increase of the interaction number thanks to geometrical rearrangements [46]. This suggests a similar origin of the strength of the CB suspensions.…”

Shear driven vorticity aligned flocs in a suspension of attractive rigid rods

“…However, at higher j's, due to the dense nature of the suspension, the initial re-percolation process is much quicker and is followed by a slower strengthening of the structure as a result of more local rearrangements and contact-driven ageing that was observed in systems with similar interactions. 90 Frequency sweep measurements show that both G 0 and G 00 are nearly independent of frequency, o. The frequency of the measurement was rescaled with t R (as oÁt R ) indicating we are accessing time scales below the single rod rotational relaxation time (Fig.…”