Hydrogel fragmentation in a porous environment

Abstract

In order to feed a rapidly growing population in an already resource-strained world, the agricultural industry must find a way to increase production without necessitating the environmentally destructive practices of land conversion and freshwater withdrawal. Superabsorbent polymers, or hydrogels, were developed by the United States Department of Agriculture in the 1970s in anticipation of this reality, but have proven inconsistently effective in the field. Decades of research have shed little light on why this is the case, indicating only that the applied load and granularity of the soil matrix may be involved in some way. This study aims to advance this basic understanding through a fundamental analysis of hydrogel swelling behavior when subjected to a soil-mimicking porous environment and exposed to water. A series of quasi-two-dimensional confinement chambers with pore throats of a designated size were constructed, implanted with a single hydrogel sphere, submerged in water, and subjected to periodic observation. In all cases, the hydrogel sphere fragmented into numerous smaller pieces, a phenomenon never before observed in this context. Patterns of fragmentation varied by pore size, with tighter constrictions prolonging the swelling process and typically producing fragments of smaller size. Given the strong correlations between surface area and water retention time, as well as those between swelling dynamics and ultimate absorption capacity, these results could carry tremendous consequence for the functionality of this technology in the field. Further investigation is necessary to identify the precise environmental conditions that correspond to certain trends in fracture, but this study could begin to inform an adaptable redesign of these polymers to optimize their utility around the world.