Paper Number
PO116 

Session
Poster Session

Title
Engineering flow mechanics in dense suspensions of surface-anisotropic colloids

Presentation Date and Time
October 12, 2022 (Wednesday) 6:30

Track / Room
Poster Session / Riverwalk A

Authors (Click on name to view author profile)

1. Pradeep, Shravan (University of Pennsylvania, Earth and Environmental Sciences)
2. Hsiao, Lilian (North Carolina State University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Shravan Pradeep¹ and Lilian Hsiao^2
1Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, PA 19104; ²Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27606

Speaker / Presenter 
Pradeep, Shravan

Keywords
colloids; glasses; jammed systems; suspensions

Text of Abstract
Dense suspensions are ubiquitous in our everyday life. These real-life suspensions are complex in nature, with its constituent particles exhibiting size polydispersity, surface roughness, diverse interactions, and softness. Here, we focus on decoupling the effect of one complexity – the surface roughness - on the flow properties of dense suspensions. Towards the goal, we synthesized smooth and rough poly(hydroxystearic acid)-grafted-poly(methylmethacrylate) colloids (PHSA-g-PMMA), with particle diameters (2a) ranging from 1.49 - 1.82 µm, and dispersed them in index-matched solvent, squalene, to generate colloidal suspensions with near hard-sphere interactions. Oscillatory and steady-shear rheological experiments were performed in the “near-equilibrium” low shear and “far-from-equilibrium” medium-to-high shear rates, respectively, to understand the flow properties of smooth and rough dense suspensions in the desired processing range. In the linear regime, close to the suspension jamming point, the viscoelastic moduli of rough suspensions were thousand fold higher compared to the smooth suspensions. Using arguments from high-frequency moduli, mode-coupling theory, and kinetic hopping model, we proposed that the increase in moduli in rough suspensions are due to the enhanced hydrodynamic lubrication interactions between the surface asperities in close contact. At high shear rates, dense suspensions shear thicken, where the suspension viscosity increases dramatically with increasing suspension stress. Using confocal rheometry, we characterize one of the first experimental 3D contact networks and estimated that the rough suspensions require, on average, two contacts less than smooth suspensions to generate the same shear thickening effect. Our work provides a fundamental framework to design smooth and rough dense suspensions for desired processing applications.