Paper Number
PO73                         My Program 

Session
Poster Session

Title
Evolution of nonmonotonic viscous moduli during the formation of polymer hydrogels

Presentation Date and Time
October 22, 2025 (Wednesday) 6:30

Track / Room
Poster Session / Sweeney Ballroom E+F

Authors (Click on name to view author profile)

  1. Quirk, Eleanor L. (Stanford University, Chemical Engineering)
  2. Shi, Jiachun (University of Illinois Urbana-Champaign, Department of Chemical and Biological Engineering)
  3. Rogers, Simon A. (University of Illinois Urbana-Champaign, Chemical and Biomolecular Engineering)
  4. Mai, Danielle J. (Stanford University, Chemical Engineering)

Author and Affiliation Lines (in printed abstract book)
Eleanor L. Quirk1, Jiachun Shi2, Simon A. Rogers2 and Danielle J. Mai1
1Chemical Engineering, Stanford University, Stanford, CA 94305; 2Chemical and Biomolecular Engineering, University of Illinois Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Quirk, Eleanor L.

Keywords
experimental methods; gels; polymer solutions; rheometry; techniques

Text of Abstract
Hydrogels, defined as polymer networks swollen with water, are versatile materials used in consumer products, biomedical materials, and sustainable agriculture. Hydrogels are formed through gelation, which occurs when polymers in solution form chemical or physical crosslinks, resulting in a polymer network. This transition is monitored using in situ small-amplitude oscillatory shear rheology, which measures the dynamic elastic (G') and viscous (G") moduli. Typically, both moduli increase monotonically during gelation: G" initially exceeds G', then a crossover leads to G' surpassing G", and both moduli reach a final plateau as the system approaches maximum crosslinking. In some gelation processes, the viscous modulus overshoots its final plateau value shortly after the crossover, before decreasing to its plateau value. We hypothesize that the G" overshoot signals simultaneous polymer cluster growth and percolated network formation, followed by cluster incorporation into the network. Using star polymers terminated with photo-crosslinking functional groups, we observe that more polymer arms and higher polymer concentrations enhance the G" overshoot. During in situ photo-rheology, frequency sweeps collected between periodic irradiation reveal the G" overshoot is enhanced at high frequencies, consistent with faster relaxation of clusters in the sol than the overall polymer gel. Recoverable strain analysis provides additional insight into hydrogel microstructure during gelation. This work improves understanding of polymer network formation, providing valuable insights to guide material development for numerous applications.