Characterization of Inter-Particle Friction in Suspensions Using Enhanced Hydrodynamic Resistance Approach

Natural and industrial suspensions consists of particles with variety of surface characteristics. Suspensions of latex particles in paint industry, for example, can be modeled as smooth particle suspensions. Whereas, coffee and suspensions of fumed silica and cornstarch consists of particles with rough surfaces. Closely interacting rough particles produce significantly different dynamics compared to the smooth particle case under the same creeping flow conditions. In this work, we studied the dynamics of a closely interacting pair of rough particles subjected to linear shear flow using Stokesian dynamics simulations. To account for the additional resistance due to frictional interactions, a near field pair-wise enhanced hydrodynamic resistance model based on the work of Wang et. al. [1] was used. In this model, the tangential components of the near-field resistance tensor were strengthened with O(1/h) form instead of the weak form O(log(1/h)) for the smooth particle case, where h is the average surface separation between the particles. Here, the parameters of the model, friction strength and friction range, relate to the density and height of asperities on the particle surface respectively. In this talk, we will present the relations describing the relative strengths of various tangential resistance modes for rough particles. The pair dynamics of rough particles as a function of the model parameters will be discussed. Since the rotation rate of the particle pair was found to be a good measure of hydrodynamic friction, a predictive model for the pair rotation rate as a function of particle orientation and the parameters of the friction model was constructed. Finally, we will propose an experimental protocol to measure the friction parameters of a given pair of rough particles by comparing the experimentally measured pair rotation rate with the rotation rate model.

[1] Wang, Mu, Safa Jamali, and John F. Brady. "A hydrodynamic model for discontinuous shear-thickening in dense suspensions." Journal of Rheology 64, no. 2 (2020): 379-394.