InterPore2026

Pattern Formation During Swelling in Aqueous Glycerin Solutions of Hydrogel Beads

22 May 2026, 10:20

1h 30m

Poster Presentation (MS02) Environmental Porous Media: Water, Agriculture, and Remediation Poster

Speaker

Mr Sebastián Ariel Falcioni (Universidad de Buenos Aires, Facultad de Ingeniería, Grupo de Medios Porosos, Buenos Aires, Argentina)

Description

Swelling is a fundamental process in natural systems and industrial applications, characterized by the volumetric expansion of materials due to the absorption of fluid. Swelling in polymeric gels, a classical problem in soft matter,$^{1,2}$ has received renewed attention in the case of hydrogels.$^{3,4}$ Hydrogels are three-dimensional (3D) networks of hydrophilic polymer chains that can absorb and retain a large amount of water or biological fluids while remaining insoluble and their swelling kinetics depend on both the mass transport of the absorbate as well as the deformation and elastic properties of the absorbent (gel network). The extremely large (but reversible) volume changes experienced by the hydrogel beads during swelling can result in complex shapes and the development of surface patterns.$^{5-8}$This is the result of the coexistence at early times of an inner dry core with high polymer volume fraction and an outer shell wetted by the penetrating solution. These surface instabilities could dramatically impact the interactions of the gel with the surrounding environment and, therefore their understanding is critical when tailoring gels for specific application fields. For example, instabilities could significantly impact the gel adhesive properties.$^{9,10}$
This study examines the swelling kinetics of polyacrylamide hydrogel beads in aqueous glycerin solutions of different concentrations. The total absorbed mass of the hydrogel beads remains nearly constant, independent of glycerin concentration, but the swelling process is markedly slower with increasing glycerin in the aqueous solutions. Absorption capacity curves exhibit universal kinetics when time proportional to the viscosity of the solutions. Additionally, using a simple laser imaging technique, we tracked the evolution of a dry core and a hydrated shell, along with the transient formation of surface patterns.
The evolution of the core-shell structure indicates a constant front velocity. By making the time non-dimensional with a characteristic swelling time that considers material properties of the gels and the viscosity of the solution, results in the collapse of the swelling curves into a universal behavior. This suggests that the leading effect of changing the concentration of glycerin in solution is to slow down the swelling kinetics due to an increase in the viscosity of the solution and the corresponding decrease in Darcy’s velocity inside the gels.
Simultaneously, we investigated the onset of surface the instabilities that appears during swelling. Our observations show a consistent transition from wrinkles to a labyrinthlike morphology, characterized by both a decrease in the number of lobules and an increase in their characteristic wavelength. Notably, we find that the instability wavelength scales with the geometry of the hydrated shell, independent of glycerin concentration. When time is rescaled with a characteristic poroelastic time, both number of lobules and wavelength from all concentrations collapse onto a universal curve, highlighting that solution viscosity primarily delays the onset of instability without altering its geometric nature.