Paper Number
GN4   Keynote                         My Program 

Session
Self-assemblies, Gels and Networks

Title
Surface brush density as a structural and rheological tuning parameter in a colloidal gel

Presentation Date and Time
October 20, 2025 (Monday) 10:50

Track / Room
Track 2 / Sweeney Ballroom B

Authors (Click on name to view author profile)

1. Zhuang, Calvin (University of California, Irvine, Chemical and Biomolecular Engineering)
2. Campbell, Robert (Northeastern University, Mechanical and Industrial Engineering)
3. Haghighi, Paniz (Northeastern University, Mechanical and Industrial Engineering)
4. Jamali, Safa (Northeastern University, Mechanical and Industrial Engineering)
5. Mohraz, Ali (University of California, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Calvin Zhuang¹, Robert Campbell², Paniz Haghighi², Safa Jamali² and Ali Mohraz^1
1Chemical and Biomolecular Engineering, University of California, Irvine, CA 92697; ²Mechanical and Industrial Engineering, Northeastern University, Boston, MA 02115

Speaker / Presenter 
Mohraz, Ali

Keywords
colloids; gels; microscopy; particualte systems; selft-assemblies; suspensions

Text of Abstract
The surface properties of colloidal particles play a critical role in their interparticle interactions and self-assembly, particularly in attractive systems that undergo gelation. In this work, we investigate how varying the density of grafted polymer brushes on colloidal particles may influence brush-mediated noncentral interparticle forces, which in turn control the microstructure and rheology of a particular class of aqueous depletion-induced gels. Our experimental system consisted of 2,2,2-trifluoroethyl methacrylate-co-tert-butyl methacrylate copolymer particles suspended in an index-matching mixed solvent of water and glycerin, and gelation is induced by the addition of a non-adsorbing polymer, polyacrylamide. Confocal microscopy and particle tracking were used to characterize the gel microstructure and dynamics across a range of depletant and salt concentrations. These experiments were complemented by Dissipative Particle Dynamics simulations. Our results suggest that high brush density suppresses brush interpenetration and favors the formation of dense, compact clusters. In contrast, reduced brush density allows for smaller interparticle distances and greater brush overlap, leading to potential entanglements that introduce local resistance to angular displacements between neighboring particles. This additional constraint promotes the formation of extended, string-like gel networks with distinct mechanical characteristics, and can shift the gelation boundaries in this system. Our findings suggest that brush entanglements may offer a mechanism for kinetic arrest beyond classical depletion and electrostatic interactions. By modulating surface brush density, it becomes possible to tailor both the microstructure and mechanical response of colloidal gels. This work lays the foundation for future studies on more complex systems, including bimodal attractive suspensions, where the combined effects of size disparity and mixed brush densities are expected to further enrich the structural and rheological landscape.