Synthesis and dual response of ionic nanocomposite hydrogels with ultrahigh tensibility and transparence

Ionic nanocomposite hydrogels cross-linked by hectorite Laponite XLS with high tensile strength and ultrahigh tensibility were successfully synthesized for the first time via in situ copolymerization of N-isopropylacrylamide (NIPAm) and sodium methacrylate (SMA). The pH and temperature response, transparency, and mechanical properties of the ionic hydrogels were investigated. The results showed that the addition of only 2 mol% of SMA endowed the nanocomposite hydrogels with pH response, while the temperature response remained in the whole pH range. All the as-prepared hydrogels, even with 10 mol% of SMA, demonstrated transparency higher than 75%. The tensile strength evidently decreased from 60 kPa to 45 kPa when the SMA content was higher than 6 mol%. The elongation at break increased with increasing SMA content and 2800% was achieved for the sample containing 10 mol% of SMA. The effective network chain density was estimated from the tensile stress at elongation of 200% and the equilibrium storage modulus. The low chain density was the intrinsic origin of the ultrahigh tensibility for these ionic NC gels. This work provides a new way to prepare dual responsive hydrogels with ultrahigh tensibility and high transparency.