Effects of particle roughness on the rheology and structure of capillary suspensions

• Published in: Colloids and surfaces. A, Physicochemical and engineering aspects Vol. 648; p. 129224
• Main Authors: Allard, Jens, Burgers, Sanne, Rodríguez González, Miriam Candelaria, Zhu, Yanshen, De Feyter, Steven, Koos, Erin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 05-09-2022
• Subjects: Capillary force; Capillary suspensions; Dynamic wetting; Graph theory; Particle networks; Rheology; Capillary suspensions; Graph theory; Capillary force; Particle networks; Rheology; Dynamic wetting
• ISSN: 0927-7757; 1873-4359
• DOI: 10.1016/j.colsurfa.2022.129224

We show that particle roughness leads to changes in the number, shape and resulting capillary force of liquid bridges in capillary suspensions. We created fluorescently labeled, raspberry-like particles with varying roughness by electrostatically adsorbing silica nanoparticles with sizes between 40 nm and 250 nm on silica microparticles. Rougher particles require more liquid to fill the surface asperities before they form pendular bridges, resulting in smaller and weaker bridges. In a system where the effective bridge volume is adjusted, higher particle roughness leads to less clustered networks, which show a higher yield strain for a matching storage modulus compared to the smooth particle networks. This finding suggests that the particle-particle frictional contacts also affects the strength of capillary suspensions. Using asymptotically nonlinear oscillatory rheology, we corroborate the non-cubical power law scaling of the third harmonic in the shear stress response that results from both Hertzian contacts and friction between particles connected by capillary bridges. We demonstrate that the repulsive Hertzian contact parameter A is sensitive to the liquid bridge strength and that roughness appears to shift the relative scaling of the power law exponents from adhesive-controlled friction to load-controlled friction.
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•Both the structure and rheology of capillary suspensions with smooth and rough particles are investigated.•With increasing particle roughness, weaker and less clustered networks are obtained for constant secondary liquid volume.•For a matching bridge size, the rough particle networks are less clustered with an extended linear viscoelastic region.•Asymptotically nonlinear oscillatory shear showed the particle contacts to be sensitive to the liquid bridge strength.•The nonlinear oscillatory data indicates a possible transition from adhesive-controlled to load-controlled friction.