Influence of interaction between confined hydrogel beads on their growth swelling dynamics

SEBASTIÁN FALCIONI; YANINA L. ROHT; LEONARDO BINDA; GERMÁN DRAZER; IRENE IPPOLITO

Edinburgo

Conferencia; InterPore2023; 2023

Hydrogels are polymeric materials that can absorb large amounts of water, swelling and increasing considerably in size.They are used in a wide range of applications, including some in which the hydrogel is required to absorb liquid underpressure. For example, for soil remediation and water storage in agriculture, hydrogels maybe located deepunderground and must withstand the mechanical stress from the soil while swelling the water and at the same timeabsorbing any heavy metal ions present in the soil1.In this work we study the influence of confinement and interaction between hydrogels beads during their swelling. Alarge cylindrical vessel was used, where a single hydrogel can swell freely without interaction with the side walls. Ainitially dry hydrogel bead, diameter (2.8 ± 0.2) mm, is submerged in an aqueous solution containing a small amount ofdissolved fluorescein, which allows UV light visualization but does not affect the swelling. A top piston is placed incontact with the hydrogel. The piston can move vertically with negligible friction until it reaches a force sensor at a fixedand controllable height H. H determines the vertical confinement and is varied between 4 and 12 mm. The force exertedby the hydrogel on the piston is measured during swelling. Three different kinetic regimes were identified in the swellingof a single hydrogel bead, independent of the confinement H: 1) "flower like" swelling, in which the hydrogel beadpresents a dry core surrounded by a wet shell of wavy geometry due to a surface instability; 2) isotropic andhomogeneous swelling and 3) confined swelling, after the hydrogel bead reaches a size equal to H and swells undercompression in the vertical direction. The force exerted by the hydrogel bead on the piston was found to increase withconfinement (as H decreases). The pressure exerted by the hydrogel bead on the piston agrees with Maxwell'sviscoelastic model at constant strain. The measured pressure and deformation at long times show an elastic behaviorfor all the values of H studied. Finally, the influence of interactions between hydrogels in confined media is studiedvarying the total number of hydrogels beads between 5 and 30. It is observed that, for a given H, the force exerted onthe piston increases with the number of hydrogel beads present in the cell. However, the total force depends linearly onthe number of hydrogel beads until NH=20.