Improving the mechanical performance of P(N-hydroxymethyl acrylamide/acrylic acid/2-acrylamido-2-methylpropanesulfonic acid) hydrogel via hydrophobic modified nanosilica

Hydrogels with high mechanical strength are essential for its most industrial applications. In this work, the hydrophobic SiO 2 nanoparticles (M-SiO 2 NPs) modified with octadecyltrimethoxysilane were used as physical crosslinker to toughen the mechanical properties of hydrogels. The solution of monomers containing M-SiO 2 NPs, N-hydroxymethyl acrylamide (NHAM), acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS), was polymerized to prepare a P(NHAM/AA/AMPS)-based composite hydrogel without any chemical cross-linker. The composition and microstructure of the hydrogel were carefully studied with Fourier transform infrared spectroscopy and scanning electron microscopy. The mechanical properties of the hydrogel were investigated through compressive and tensile tests. Dynamic swelling tests were carried out at different pH values (1.0–12.0) and salinity (2000–20,000 mg/L) to study the acid resistance, alkali resistance, and salt resistance of the hydrogel. The obtained results showed that the hydrogel exhibited excellent mechanical performance, which was attributed to the unique 3D network formed by the hydrogen bond between M-SiO 2 NPs and polymer as well as the hydrophobic association effect between the hydrophobic chains of M-SiO 2 NPs. Furthermore, the hydrophobic association effect was enhanced when contacting with salt, acid, and alkali solutions, thus endowing the hydrogel with intensified salt resistance and wider acid–base adaptability range.