INFLUENCE OF THE HYDROGEL ABSORPTION PHENOMENON ON THE CONCENTRATION OF A DISSOLVED SOLUTE

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

PARANA

Workshop; FLUIDOS 2021; 2021

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