Influence of interaction between confined hydrogel beads on their growth dynamics

FALCIONI, S.; ROHT, Y. L.; BINDA, L.; DRAZER, G.; IPPOLITO, I.

Edimburgo

Congreso; InterPore 2023; 2023

Interpore

Hydrogels are polymeric structures that havethe property of absorbing a large amount of water, swelling and increasingconsiderably in size. They are used in a wide range of applications, inparticular, in certain applications the hydrogel is required to absorb liquid underpressure. For example, for soil remediation and water storage in agriculture,hydrogels are at depth and must withstand the mechanical stress from the soilwhile swelling water and at the same time absorbing the heavy metal ionspresent in the soil1. The main objective of this work is to studythe influence of confinement and interaction between hydrogels during theirgrowth. For this purpose, a cylindrical vessel of diameter D=23 cm was constructed where a single hydrogel can freely growwithout interaction with the side walls. The hydrogel, initially dry (diameter di=(2.8 ± 0.2) mm), issubmerged in an aqueous solution containing 5 mg/L of dissolved fluorescein,which does not affect the swelling and allows us to use UV light visualization.A piston is placed in the vessel, in contact with the hydrogel which canvertically displace without friction until reaching a force sensor at a fixed andcontrollable height H. H characterizes the vertical confinementand is varied between 4 and 12 mm. In the perpendicular plane (horizontal) tothis confinement the hydrogel is free to grow and its projection is visualizedwith a high resolution camera. Simultaneously, the force exerted by thehydrogel during swelling was measured for each H as a function of time. In the study of the growth of a singlehydrogel it was found that, independently of H, there are three stages with different kinetics: 1) "flowerlike" growth, in which the hydrogel presents a dry core surrounded by awet shell of wavy geometry corresponding to a surface instability; 2) isotropicand homogeneous growth and 3) confined growth, which begins when the hydrogelreaches a size equal to H and then itgrows under compression in the vertical direction. The force exerted by thehydrogel was found to increase with confinement (as H decreases). The pressure exerted by the hydrogel was observed to agreewith Maxwell´s viscoelastic model at constant strain. Then, the values ofpressure and deformation at long times show an elastic behavior for the wholerange of H studied. In addition, the influence of interactionsbetween hydrogels in confined media was studied. For this purpose, the size ofthe cylindrical vessel used was increased (D=54cm) and the number of hydrogels (NH)was varied between 5 and 30. It could be observed that, at constant H, the force exerted by the hydrogelarray increases with the amount of hydrogels present in the cell. Moreover, thevalue of the force found does not correspond to the sum of the individual forceexerted by NH hydrogels.