Nanosilica-induced high mechanical strength of nanocomposite hydrogel for killing fluids

Nano-silica was introduced to enhance the mechanical strength of polymer hydrogels obtained via the crosslinking of polyacrylamide (PAM) and chromium acetate. Rheological properties, compression strength and compressive stress-strain of both nanocomposite and normal hydrogels without nano-silica were investigated by HAKKE rheometer, compression strength test device and electronic universal material testing machine. Moreover, environmental scanning electronic microscopic (ESEM) was adopted to observe the three-dimension network structure of nanocomposite and normal hydrogel, as well as the distribution of nano-silica. The results demonstrated that elastic moduli (G') and viscous moduli (G″) of nanocomposite hydrogel were both improved with increasing nano-silica concentration. Especially when silica content reached 10wt%, G' and G″ of nanocomposite hydrogel increased over one hundred times higher than those of normal hydrogel. The original compression strength of hydrogel was 70.8kPam(-1), while the resulting strength of nanocomposite was enhanced to be 196.64kPam(-1). When the hydrogel were sheared, the normal hydrogel was fractured under low strain, whereas nanocomposite hydrogel was not broken under high strain, and it quickly recovered its original shape after the release of load. In addition, the ESEM images indicated that a large quantity of silica particles aggregated and attached around the polymer chains, and others aggregated to fill into the three-dimension network of hydrogel, which induced the compaction of the space between the network layers and reduced the flowing of free water wrapped in the network, therefore the mechanical strength of hydrogel was enhanced.