Paper Number
SC22 

Session
Suspensions and Colloids

Title
Pinching dynamics of dense colloidal suspensions with depletion attractions

Presentation Date and Time
October 11, 2022 (Tuesday) 10:30

Track / Room
Track 1 / Sheraton 4

Authors (Click on name to view author profile)

1. Soetrisno, Diego D. (University of Houston, Department of Chemical and Biomolecular Engineering)
2. Gallegos, Mariah J. (University of Houston, Chemical and Biomolecular Engineering)
3. Martinez Narvaez, Carina (University of Illinois Chicago, Department of Chemical Engineering)
4. Sharma, Vivek (University of Illinois Chicago, Department of Chemical Engineering)
5. Conrad, Jacinta C. (University of Houston)

Author and Affiliation Lines (in printed abstract book)
Diego D. Soetrisno¹, Mariah J. Gallegos¹, Carina Martinez Narvaez², Vivek Sharma² and Jacinta C. Conrad^1
1Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204; ²Department of Chemical Engineering, University of Illinois Chicago, Chicago, IL

Speaker / Presenter 
Soetrisno, Diego D.

Keywords
colloids; gels; polymer solutions; suspensions

Text of Abstract
Macromolecular properties of polymers have a significant effect on their rheological response under extensional flow. Coil-stretch hysteresis, for instance, occurs only when the ratio of the drag coefficients of stretched ς_s and coiled chain ς_c exceeds 4.5, which affects the concentration dependence of the exponent of the polymer relaxation time λ_E. Polymer additives are often used in dense suspensions to enhance their rheological properties under both shear and extensional flow. In a mixture of colloids and non-adsorbing polymer, a recent study [Park et al., Phys. Rev. Lett. 122, 228003 (2019)] proposed that the size of stretched polymers controlled the shear response. Here, we study the extensional flow properties via the pinch-off dynamics of dense colloidal suspensions (volume fraction φ=0.40) with induced depletion interactions using a dripping-onto-substrate (DoS) protocol. We use a model colloidal system of methacrylate copolymer particles with dimethylacrylamide copolymer brushes suspended in refractive index and density matched 80 (w/w)% glycerol in water with NaCl added to screen electrostatics. Depletion attractions between the colloids are introduced by adding polyacrylamide polymers of various molecular weight and dispersity. We characterize the extensional properties by calculating the extensional viscosity η_E and relaxation time λ_E from the filament-thinning dynamics. The addition of polymer delays and modifies the pinch-off dynamics of the dense suspensions depending on the size and dispersity of the polymer. The concentration dependence of λ_E follows the ς_s/ς_c of the polymer, and the presence of particles did not affect λ_E when scaled with polymer free volume concentration normalized with the overlap concentration c/c*. These results provide insight into the role of polymer size in the extensional rheology of colloid-polymer mixtures.