Paper Number
SC20 

Session
Suspensions and Colloids

Title
Viscoelastic creep and recovery in dense suspensions of rough colloids

Presentation Date and Time
October 11, 2022 (Tuesday) 9:50

Track / Room
Track 1 / Sheraton 4

Authors (Click on name to view author profile)

1. Saraswat, Yug Chandra (North Carolina State University, Chemical and Biomolecular Engineering)
2. Hsiao, Lilian (North Carolina State University, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Yug Chandra Saraswat¹ and Lilian Hsiao^2
1Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27607; ²Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC 27606

Speaker / Presenter 
Saraswat, Yug Chandra

Keywords
experimental methods; colloids; glasses; jammed systems; microscopy; suspensions

Text of Abstract
Creep and yielding in dense colloidal suspensions are considered to arise from the slow relaxation of cage dynamics and interparticle friction. The objective of this study is to elucidate the mechanism through which interparticle friction affects the slow recovery and rate-dependent creep rheology of dense suspensions. We use dense suspensions composed of fluorescent colloids with tunable roughness suspended at high volume fractions (0.6 = ? = 0.63) in a refractive index-matching squalene. The hard sphere-like poly (methyl methacrylate) colloids are synthesized with a grafted layer of poly (12-hydroxystearic acid), and roughness is induced by adding a crosslinking molecule during the nucleation step of the synthesis. Confocal laser scanning microscopy is used to determine the particle shape and volume fraction in the solvent to account for swelling. Dense suspensions are loaded onto a stress-controlled rheometer equipped with a parallel plate geometry, which applies constant shear stresses above and below the yield stress of the bulk material.In the suspensions, 2% below the maximum packing fraction, rough colloids exhibit lower strain deformation and enhanced viscoelastic recovery. Suspensions of rough colloids are more solid-like in nature, exhibiting 70 – 90% less strain deformation compared to smooth colloids suspended at the same jamming distance, for applied stresses that are within the linear regime (0.0075 Pa – 0.01 Pa). In the nonlinear stress regime (2 – 5 Pa), suspensions of rough colloids exhibit 20 – 30% lower strain than the smooth colloids. The suspensions of rough colloids display twice as much strain recovery as the suspensions composed of smooth colloids during creep recovery. These results suggest that the geometric frustration caused by surface roughness generates long-lived contacts between nearest neighbor colloids, and that the slow relaxation of these contacts is responsible for enhanced elasticity, solid-like minimal deformation, and higher viscoelastic recovery at a given applied stress.