Paper Number
GN24 My Program
Session
Self-assemblies, Gels and Networks
Title
Effect of microgel elasticity on tracer dynamics in microgels
Presentation Date and Time
October 21, 2025 (Tuesday) 1:30
Track / Room
Track 2 / Sweeney Ballroom B
Authors
- Edimeh, Peter (University of Houston, Chemical and Biomolecular Engineering)
- Conrad, Jacinta C. (University of Houston, Chemical and Biomolecular Engineering)
Author and Affiliation Lines
Peter Edimeh and Jacinta C. Conrad
Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204
Speaker / Presenter
Edimeh, Peter
Keywords
experimental methods; colloids; field-responsive; future of rheology; gels; industrial applications; microscopy; networks
Text of Abstract
The elasticity of polymer microgels governs both their bulk rheological response and the transport of embedded tracer particles. How elasticity and microgel concentration affect the tracer dynamics across different concentration regimes, however, remains incompletely understood. Here, we synthesize dual-stimuli-responsive poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM-co-PAA) microgels with tunable softness by varying the crosslink density. The microgels undergo a swelling transition near 32℃ as they are cooled, and we exploit this transition to modulate microgel concentration in situ. We characterize the dynamics of 100nm fluorescent polystyrene tracers in microgel matrices as they are cooled from the collapsed to swollen state and reach final volume fractions of ζ ≈ 0.4 (dispersed), ζ ≈ 0.6 (contacting), and ζ ≈ 1.0 (jammed or compressed). Using differential dynamic microscopy and single-particle tracking, we determine relaxation times τ and diffusivities D for the tracer particles as functions of temperature and the final (swollen) ζ. At low ζ ≈ 0.4, τ and D of the tracers monotonically increase and decrease upon cooling, respectively, for both soft and stiff matrices. At intermediate ζ ≈ 0.6, however, τ and D exhibit non-monotonic dependences on temperature, with local extrema near ~34℃, in stiff but not soft matrices. At high ζ ≈ 1.0, this non-monotonic behavior occurs in both soft and stiff matrices. Our results show how elastic compression modulates penetrant transport in microgel networks, which can inform the design of theranostics and biological scaffolds.