(518i) Modeling Sheared Gels of Rough Colloids

Colloidal gels are ubiquitous in nature and industry with applications in energy storage, consumer care, agrochemical and pharmaceutical industries, to name a few. These gels form when attractive particles suspended in solvent get arrested in nonequilibrium states. Depending on the properties of the solid and liquid phases, these materials display a range of rheological properties including yield stress, elasticity, shear rate dependent viscosity and thixotropy. These macroscopic properties emerge from the response of colloidal microstructure to various applied conditions^[1,2].

Gel microstructure depends on interparticle interactions via conservative potentials (such as electrostatic or depletion interactions) and hydrodynamic interactions. Many colloids encountered in nature and industry, such as carbon black, fumed silica, corn starch, and engineered raspberry-like particles, have rough or jagged surfaces. It is not well understood how surface morphology of colloids impacts the hydrodynamic interactions of closely interacting particles, which ultimately affect the microstructure and rheological properties of the gel.

In this work, Fast Stokesian Dynamics (FSD) simulations are employed to investigate the microstructural evolution of depletion gels made of rough colloids subjected to steady, linear deformation. The additional resistance due to roughness between closely interacting colloids is modeled using a thermodynamically consistent, pair-wise hydrodynamic model³. The dependence of sheared gel microstructure on colloid roughness is investigated at different applied shear rates. As colloid roughness increases, we found that closely interacting colloids get more strongly coupled, packing density of clusters reduces, and a more homogeneous gel microstructure emerges. We will present the underlying mechanism explaining these observations. Finally, we will discuss the rheology of these rough colloidal gels. The results indicate that colloidal roughness is another tunable parameter in the engineering and design of colloidal gels.

Acknowledgements

This work is funded by NSF #1735968 CREST Center for Complex Materials Design for Multidimensional Additive Processing (CoManD).

References:

1. Whitaker, Kathryn A., Zsigmond Varga, Lilian C. Hsiao, Michael J. Solomon, James W. Swan, and Eric M. Furst. "Colloidal gel elasticity arises from the packing of locally glassy clusters." Nature communications 10, no. 1 (2019): 1-8
2. Nabizadeh, Mohammad, and Safa Jamali. "Life and death of colloidal bonds control the rate-dependent rheology of gels." Nature Communications 12, no. 1 (2021): 1-9.
3. Madhu V. Majji and James W. Swan, “Parameterization of hydrodynamic friction in a model for sheared suspensions of rough particles”, Physical review fluids (2022).