(262g) Contact Forces between Colloids in Particulate Gels

The structure and rheology of colloidal gels depend intimately on the strong attractive interactions between their constituent particles. Such attractions may arise from depletants, dispersion forces, or grafted polymers. Often these interactions are characterized solely by their strength and range. But other features of the particle contacts that arise in gels--their aging behavior and presence (or absence) of a critical bending moment, manifest in ways that make the single characteristic of strength of attraction insufficient for describing the wide range of gel elastic responses, yielding, and thixotropic behaviors. In this talk, I will discuss contact-controlled aging [1], consisting of the progressive stiffening of solid–solid contacts of an arrested colloidal suspension at high ionic strength and contrast this with the central-acting interactions of a depletion gel [2, 3]. Contact aging governs the shear-modulus aging of dense aqueous silica and polymer latex suspensions at moderate ionic strengths, and can be measured directly with laser tweezers. The interfacial nature of the contact forces provides new opportunities to control the structure and rheology of particle gels, and especially to control their time-dependent elasticity and yielding.

[1] Francesco Bonacci, Xavier Chateau, Eric M. Furst, Jennifer Fusier, Julie Goyon and Anaël Lemaître., Nat. Mater., 1–8 (2020).

[2] Kathryn A. Whitaker, Eric M. Furst,. J. Rheol. 60, 517–529 (2016).

[3] Kathryn A. Whitaker, Zsigmond Varga, Lilian C. Hsiao, Michael J. Solomon, James W. Swan, Eric M. Furst, Nat. Commun. 10, 2237 (2019).