Influence of the hydrogel absorption phenomenon on the concentration of a dissolved solute

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

Virtual

Congreso; XVI Meeting on Recent Advances in Physics of Fluids and its Applications; 2021

Hydrogels are polymeric structures that when incontact with water have the property of absorbing a large amount of it,swelling, and considerably increasing their size. The main objective of thiswork is to study the exchange properties (of water and solutes) with thesurrounding medium during the absorption and growth process of hydrogelsimmersed in an aqueous solution with a dissolved solute (water blue dye).To do this, in the first instance, the growth kineticsof hydrogels immersed in aqueous solutions with and without dissolved solutewere studied, without imposing any confinement that limits their growth.Then, an experimental device was designed consistingof a vertical fixed cell with transparent walls that allows us to visualize thegrowth of the hydrogels and to know the concentration of solute in differentplaces in it.Experiments were carried out varying the amount ofhydrogels present, the initial solute concentration at constant fluid volume.During them, the variations in intensity of light transmitted through theopening of the cell were recorded with a high-resolution video camera atconstant time intervals.With the information of the average concentration ofthe dye for each position of the cell and for every instant of time, it wasobserved that hydrogels have greater selectivity to water than to dissolved solute,generating an increase in the local concentration of the dye in different areasof the cell. This phenomenon is more pronounced by increasing the number ofhydrogels in the cell. The temporal variation of the concentration of solutepresent in different areas of the cell was analyzed: away from the hydrogels(above and below them) and in the interstices formed by the hydrogels betweenthem, distinguishing the dynamics corresponding to the first hours dominated byvolumetric growth by absorption and a second stage when the hydrogels reach aconstant volume. During the first stage, it is observed that the soluteconcentration in aqueous solution increases as the hydrogels grow, reaching amaximum concentration, particularly in the lower zone of the cell. Finally,when the hydrogels reach their maximum size, a mixture of the dye is visualizeduntil the solution is homogenized within the cell.