Physical behavior of superabsorbent hydrogels in sand.

摘要

Swelling equilibrium and kinetics of two commercial superabsorbent gel particles—sodium polyacrylate spheres and polyacrylamide-co-potassium acrylate grains—were studied in water and in sand at room temperature. Equilibrium experiments involved swelling gel particles at different depths in saturated sand columns packed with different sand sizes. Kinetic experiments were performed in a two-dimensional cell; both gel particle size and sand particle size were varied. Water flow in gel-conditioned sand was also investigated in columns and the two-dimensional cells for different gel dosages.; The equilibrium swelling degree of gels in saturated sand was less than in water; decreasing sharply with depth in the first few centimeters, independent of sand particle size, then decreasing gradually with depth. A model was developed to describe equilibrium swelling in sand using the Flory model for polymer gels and a Cavity-Expansion model for frictional sand.; For individual gel particles the kinetic relationship between the fractional approach to equilibrium and the square root of time was sigmoidal for swelling in water and in saturated sand. This relationship was described by a model based on Fick's first law which accounted for the movement of the boundary of the gel and the time variation of the polymer volume fraction at the surface.; When water was distributed from the top of a uniform gel-conditioned bed, a gel layer formed on the surface. The gel particles, initially in the sand, were set free by the impact of the water. The released gel particles settled less rapidly than the denser sand particles. One minute after the initial disturbance of the dry sand-gel mixture, the water-borne particles settled on the surface to form a swelling gel layer.; In the water flow experiments the advance of the wetting front was impeded, while surface movement increased, with increasing gel dosages. Two models were developed to describe flow in gel-conditioned sand: Swelling Soil model and Instantaneous Equilibrium model. Both models were based on Darcy's law and accounted for the movement of solids.